In numerous studies, it was emphasised that only a few of patented shape memory alloy applications are commercially successful due to material limitations combined with a lack of material and design knowledge and associated tools. This work further emphasises that these limitations may be improved or even resolved with proper design approaches and techniques; thus, the functionality and the reliability of shape memory alloy actuators could be realised and optimised. A brief review of the recent progress and development in optimising shape memory alloy linear actuator with different design methods, techniques and/or approaches are presented and discussed in this review.
The present work explores the generation of two-dimensional steady-state flexural waves that are non-reflective on a thin rectangular plate with free boundary conditions when excited by two macro-fiber composites (MFCs). The voltage signals to the MFCs have a frequency lying halfway between two adjacent resonant frequencies with a phase difference of
Hair cells are specialized sensory cells found in the auditory and vestibular systems of many vertebrates. Many of these cells display an active hair bundle motility that amplifies the hair cell’s response to small stimuli, increases frequency sensitivity, and produces an amplitude compression that allows the cell to transduce a large range of input amplitudes. These features are important in an animal’s ability to detect and understand complex stimuli in its environment. The hair bundle’s nonlinear amplification results from combination of a nonlinear stiffness produced by opening and closing ion channels and an adaptation motor that brings the hair bundle close to a dynamic instability. This article presents the models and designs for a bio-inspired, artificial hair cell inspired by active hair bundle motility. These sensors are based on cantilevered beams with a nonlinear stiffness and a piezoelectric actuator to mimic the adaptation motor. Artificial hair cells can serve as bio-inspired microphones hydrophones, accelerometers, or other dynamic sensors. By mimicking hair bundle motility, these sensors could detect smaller stimuli, have enhanced frequency resolution, and transduce a wider range of input levels compared to traditional sensors.
This article deals with the geometric nonlinear static and dynamic analyses of thin functionally graded structure sandwiched between functionally graded piezoelectric materials. The properties of functionally graded material are graded in thickness direction according to power law distribution, and the variation in electric potential is assumed to be quadratic across the thickness of functionally graded piezoelectric material layers. The functionally graded material structure is modeled using finite element modeling considering complete Green–Lagrangian strains. The finite element formulation is derived using Hamilton’s principle based on first-order shear deformation theory. The ensued nonlinear algebraic equations are then solved using the modified Newton–Raphson method. Shape and vibration control of functionally graded plate is presented using functionally graded piezoelectric material. Fuzzy logic controller is used to control the vibrations. The numerical results predict that functionally graded piezoelectric material can control the shape and vibration of functionally graded plate.
This article contributes to the definition of an unconventional actuation system coupled with an adaptive control algorithm, it is intended specifically for slender/highly flexible wings flutter suppression. The design and validation process of the novel actuation architecture is presented together with the performance analysis of the post-flutter dynamics control. Robustness of the overall control architecture is verified with respect to the uncertainties deriving from the unpredictable degradation of the structural properties. The proposed actuation system is based on a row of multiple mini-spoilers, located in proximity of the leading edge and coordinated by a modified model reference adaptive control algorithm. The spoiler configuration is optimized by computational fluid dynamics numerical simulation, whereas the aerodynamic database is derived by wind tunnel tests on the prototype by means of a six-axes force balance. The resulting aeroelastic mathematical model is then used to implement and validate the adaptive control algorithm for a wide range of conditions, from on-design flutter speed and nominal structural stiffness to post-flutter speed and reduced structural stiffness. The two degree of freedom aeroelastic model is successfully controlled in all conditions. This article aims at defining a robust procedure for aeroelastic phenomena control system design, which employs a synergy of modeling, simulation, and experimental approaches. Pertinent conclusions are discussed in the final section of the article.
The development and accelerated use of optimization frameworks in aircraft design is a testament to their ability to identify optimal and often non-intuitive shapes as a result of multi-disciplinary design objectives. Airfoil design is a continuously revised multi-disciplinary problem, and is pivotal to illustrate the performance of optimization frameworks involving numerical simulation, flexible shape parametrization, and intelligent evolutionary algorithms. An often overlooked component of this classic problem is to consider the dynamic aeroelastic behavior under trim conditions, which can generate explicit boundaries to the flight envelope. Trim introduces a significantly strong coupling with objectives governing static performance, e.g. aerodynamic and/or structural, thereby resulting in a highly nonlinear and discontinuous design space. In this paper, a multi-objective particle swarm optimization framework for multi-disciplinary performance improvement is presented, pertaining to aerodynamic, structural and aeroelastic design criteria at trim conditions. The framework is assisted by the construction of adaptive Kriging surrogates, which is cooperatively used with the numerical solver to identify optimal solutions within a computational constraint. Designer preferences are introduced to reflect the optimal compromise between the objectives. Results of the optimization process indicate a large spread in design variable influence and interaction, and a subtle yet clear distinction between all objectives is illustrated through the catalog of final airfoil candidates obtained.
In this article, a penny-shaped crack in the isotropic plane of three-dimensional transversely isotropic piezoelectric semiconductors is analyzed via the displacement discontinuity boundary element method. The general solutions are derived based on the generalized Almansi’s theorem and the operator theory. Green’s functions are derived using the Hankel transformation under uniformly distributed extended displacement discontinuities (including displacement discontinuities, potential discontinuity, and electron density discontinuity) on a penny-shaped crack in the isotropic plane of three-dimensional transversely isotropic piezoelectric semiconductors. Using the extended displacement discontinuity boundary element method, penny-shaped cracks in transversely isotropic plane of three-dimensional piezoelectric semiconductors are studied, and the stress, electric displacement, and electric current intensity factors under uniform mechanical-electric-current loads applied on the penny-shaped crack surface are calculated. The fracture behaviors of piezoelectric semiconductors are studied.
This article presents an unprecedented concept for resilient bridge columns comprising precast modules designed for disassembly. Resiliency is provided by superelastic shape memory alloys that minimize permanent drift and engineered cementitious composite that minimizes damage, while keeping the rest of the column elastic. The precast modules consist of prefabricated plastic hinges and prefabricated concrete-filled fiber–reinforced polymer tubes. The columns are very desirable candidates for accelerated bridge construction. Two 1/4-scale column models with engineered cementitious composite plastic hinges incorporating two types of shape memory alloy bars, one made of nickel–titanium and the other of copper–aluminum–manganese, were designed and tested under simulated earthquakes. To assess the influence of reusing column components, each of the models was first tested under a series of ground motions, and then the models were disassembled, inspected, reassembled, and subsequently retested. The reassembled models reached the same capacity as the original models but were more flexible. A simple modeling method was able to match the global measured response of the models with a reasonable accuracy.
Due to low tensile strength of concrete, seasonal temperature, shrinkage of concrete, and so on, many of hydraulic concrete structures experience cracking. An optical fiber–based approach is introduced to implement the crack detection in hydraulic concrete structures. The experimental and theoretical investigations on bending loss and time-domain reflection behaviors of optical fiber are performed. According to the bending loss mechanism of optical fiber, the monitoring method of hydraulic concrete crack is presented. First, the effect of optical fiber bending radius on optical loss is analyzed. The mathematical model between bending radius and optical loss is established. Then, the identification principle of concrete crack using bending loss data of optical fiber is studied. Considering the crack characteristics of hydraulic concrete structure, the arrangement forms of optical fiber, which are used to monitor the tension crack and hybrid crack in hydraulic concrete structure, are proposed. Finally, the relationship between crack development and optical loss is investigated using laboratory experiments with optical fiber.
Hydrogels are categorized as soft materials that undergo large deformation when they are subjected to even minor external forces. In this work, the performance of a variety of micro-valves, based on pH-sensitive hydrogel jackets coated on rigid pillars, is studied considering the gel deformation under fluid flow, employing fluid–structure interaction simulations. In this regard, an analytical solution to plane-strain inhomogeneous swelling of a cylindrical jacket is proposed. This is used as a tool to validate the finite element model. Then, a micro-valve consisting of one hydrogel jacket is studied in various inlet pressure and pH values performing fluid–structure interaction simulations. Thereafter, a variety of jacket patterns are investigated in order to identify the effects of the pattern on the micro-valve performance for various fluid stream pressures and pH values. The leakage pressure of the valves is also computed for each of the patterns. Fluid–structure interaction simulation is found to be essential to accurate design of the hydrogel-based microfluidic devices.
An innovative concept for a multifunctional structural battery using lithium-ion battery materials as load bearing elements in a sandwich panel construction has been demonstrated. The structural battery prototype has exhibited an initial capacity of 17.85 Ah, an energy density of 248 Wh L–1, a specific energy of 102 Wh kg–1, and a capacity retention of 85.8% after 190 charge–discharge cycles at ~C/3 rate and eight mechanical loading cycles (upto 1060 N). The mechanical stiffness in three-point bend tests follows expectations based on sandwich beam theory, proving that the battery materials are sharing in the load-carrying function of the sandwich panel. While areas for improvement of the fabrication and performance of the prototype still exist, the results of the current investigation demonstrate the promising potential of the proposed structural battery concept for the efficient use of space and mass in an electric vehicle.
The aim of this work is to investigate the effect of the small magnetorheological fluid gap on the braking performance of the magnetorheological brake. In this article, theoretical analyses of the output torque are given first, and then the operating principle and design details of the magnetorheological brake whose magnetorheological fluid gap can be altered are presented and discussed. Next, the magnetic circuit of the proposed magnetorheological brake is conducted and further followed by a magnetostatic simulation of the magnetorheological brakes with different sizes of fluid gap. A prototype of the magnetorheological brake is fabricated and a series of tests are carried out to evaluate the braking performance and torque stability, as well as the verification of the simulation results. Experimental results show that the braking torque increases with the increase in the current, and the difference for the impact of the fluid gap on braking performance is huge under different currents. The rules, which the experimental results show, have an important significance on both the improvement of structure design for magnetorheological brake and the investigation of the wear property under different fluid gaps.
Conventionally modeled as spring–damper system, the end-stops in vibration energy harvesters set a limit to the displacement of the proof mass at sufficiently high excitation levels. In some studies, it is seen that the end-stop parameters needed adjustment to fit the simulations to the measurements at particular operating condition. In this article, the discrepancy between the simulation and measurement results on varying the operating condition is investigated in detail. A check on sensitivity of an electrostatic in-plane gap closing energy harvester to the parameters end-stop stiffness, end-stop damping, and end-stop position at various biases and excitation levels is performed. The simulations at 3-V bias and root mean square (RMS) acceleration amplitude 0.6g show a remarkable variation of 30 Hz in up-sweep jump-down frequency on varying end-stop position by 0.12 µm. The simulation results also show a significant increase in sensitivity of up-sweep jump-down frequency to end-stop damping on increasing excitation level at fixed bias. The article also discusses the sensitivity in jump frequencies to perturbations in the excitation signal due to the presence of noise, where the jump-down frequency becomes smaller as the noise level increases. The trajectories studied at 8-V bias and RMS acceleration amplitude 0.6g with different end-stop parameters show a strong influence of the end-stop model parameters on the motion of the proof mass. A lumped model of the device is fitted to the measurements for a whole range of operating conditions with one fixed set of model parameter, where asymmetric end-stop positions and their effect on the device behavior are shown to be crucial. The results presented in this article show that in order to reproduce and analyze the measured behavior of the harvester over a range of operating conditions, very fine details in the model are significant.
As a main component of space deployable structure, shape memory polymer composites are exposed to long-term periodic sharp temperature changes. It is necessary to investigate the influence of temperature on strength property of shape memory polymer composites. In this article, a micromechanical strength predication model was developed based on composite bridging model, which was used to define the stiffness matrix and relate the stress increment to the fiber and matrix. Furthermore, the progressive failure strength of shape memory polymer composites was simulated simply based on the properties of the material and the geometric parameters of the laminates. Comparison of the predictions with the experimental measurements was carried out. In general, the overall correlation between the theory and the experiments was reasonable. Furthermore, the model has been applied to predict the transverse strength, axial strength, and in-plane shear strength of different composite laminates (fiber content and ply angle) at different temperatures.
Green’s functions of infinite and semi-infinite plane problems of one-dimensional quasicrystals with piezoelectric effect are obtained in a closed form by Stroh formalism. Some numerical examples under different loading conditions, such as line forces, line dislocations, and a line charge, are given to explain the mechanical and electric behaviors of the quasicrystals. Various elastic–electric constants of quasicrystals are analyzed and the coupling effects between the phonon and phason fields are studied. The presented solutions will be useful for many boundary value problems of one-dimensional quasicrystals with piezoelectric effect. Moreover, the numerical results can be used to verify the accuracy of the solutions by some numerical methods, such as the finite element and boundary element methods. Furthermore, the Stroh formalism can be generalized to the researches on more complex problems of quasicrystals.
This article presents a spatial impact source identification based on a one-dimensional fiber Bragg grating sensor array for application in tubular structures. The effective number of sensors and the sensor arrangement method were investigated for the plumbing pipe structure as the application subject. The fiber Bragg grating sensors were used to determine the impact location via the signal processing of the measured acoustic emission signals with a sampling frequency of 100 kHz. The root mean squared value–based algorithm, which was newly verified for a stiffened composite structure, was employed to identify the impact source in this article. Impact source identification was implemented according to the sensor arrangement and number of sensors, which were selectively used on the pipe structure among six multiplexed fiber Bragg grating sensors in one optical fiber line. This process shows that impact location detection is possible with only a one-dimensional sensor array compared to the results of a two-dimensional sensor array. The impact location could be predicted within a maximum error range of 31.12 mm, even if only one sensor was used to identify the impact source.
Gossamer space structures technology have gained widely applications in space missions. However, the vibration problem is a great challenge which makes the technology complicated. The overall motivation of this work is to develop a vibration control system for gossamer space structures. In this study, a space membrane structure with piezoelectric stack actuators bracketed on its support frame is considered. First, the description of the smart space membrane structure and its dynamic model are presented. Then, a decentralized adaptive fuzzy control method is developed to control the structure vibration. Finally, experimental system is built up, and two vibration control experiment cases are carried out to verify the proposed control method. Experimental results demonstrate that the proposed control method is more effective than the fuzzy control method.
A piezoelectric vibration energy harvester aiming at collecting energy from the operation of an electromagnetic digital actuator is presented. It is based on the frequency up-conversion and can simultaneously obtain the information of discrete position location. The objective is an improved reliability of such digital actuators ensuring sample controls of the actuator positions. The considered electromagnetic digital actuator is capable of achieving two-dimensional in-plane movements by switching a mobile permanent magnet among four discrete positions. The demonstration of a first step toward integrated additional autonomous functions scavenging a part of the mechanical energy of the mobile permanent magnet is achieved. The vibration energy harvester consists of a piezoelectric cantilever beam magnetically attached to the mobile permanent magnet. The limited magnetic interaction force allows a frequency up-conversion strategy to be set. The frequency up-conversion technique that is used here consists of a "low frequency" excitation that drives a much higher natural frequency oscillator. Indeed, once the energy harvester separates from the mobile permanent magnet, a free oscillation occurs and the induced mechanical energy is harvested. This design concept is numerically analyzed and experimentally validated. Harvested energy of 4.7 µJ is obtained from preliminary experiments using a simple out-of-plane cantilever beam with 9 N/m stiffness and 16 mN magnetic attraction between the vibration energy harvester and the mobile permanent magnet when they contact each other. This energy is in accordance with the requirements for wireless communication of simple information. Finally, an L-shaped cantilever beam optimized design is proposed for future in-plane integration.
The full field distributions in loaded electromagnetoelastic composites with semi-infinite cracks and other localized defects are predicted by employing micro-to-macroscale analyses. At the micro level, the effective properties of the electromagnetoelastic composite, which consists of piezoelectric and piezomagnetic constituents, are determined by employing a micromechanical analysis which takes into account the detailed interaction between the phases. The subsequent macroscale analysis employs the jumps of the K-field of a crack embedded within a homogeneous electromagnetoelastic medium, computed at the boundaries of a rectangular domain that is sufficiently far away from the localized effects. Then, the double finite Fourier transform is applied and the solution of the problem in the transform domain is derived. Inversion of the Fourier transform provides, in conjunction with an iterative procedure, the resulting electromagnetoelastic field distributions. Both crack fronts perpendicular and parallel to the poling (the axis of symmetry of the composite) are considered. After the verification of the offered approach, results are presented for piezoelectric/piezomagnetic composites with a semi-infinite crack which is interacting with a cavity. In addition, the field distributions in cracked porous electromagnetoelastic materials are presented. A particular emphasis is given to the induced magnetic field caused by the application of electromechanical loading, and to the induced electric field caused by the application of magnetomechanical loading.
Vertical component of seismic excitations tremendously affects the performance of bridges during the earthquakes. Several conducted studies identified the lack of engineering attention to the vertical seismic excitation as the main reason of various considerable bridge damages during the past earthquakes. Thus, in this article, an innovative system with superelastic properties is proposed for retrofitting and also new design of the bridges which can simultaneously mitigate the effects of vertical and horizontal seismic excitations. In order to investigate the efficiency of the new system, an evaluation is performed through many nonlinear time history analyses on a three-dimensional model of a detailed multi-span simply supported bridge using a suite of representative ground motions of the bridge region. The analyses are conducted separately on the pertinent issues that affect the performance of the new proposed system. As a part of the study, to identify the sensitivity of the new system and evaluate the overall seismic performance, several assessment parameters are utilized. The results show that the proposed system is efficient for reducing bridge responses as well as improving nonlinear performance of the columns during vertical and horizontal seismic excitations.
Piezoelectric laminated curved beams or laminated curved smart beams, one of the most popular elements, are widely used in nano- or micro-electromechanical systems due to their excellent properties such as small volume, lightweight, and quick response. In this article, the finite deformation of piezoelectric laminated curved beams is analyzed based on Lagrangian and Eulerian description. The piezoelectric actuating character for the deflection in the curved beams bonded with piezoelectric film (polyvinylidene fluoride) driving layers is investigated. Choosing the deformed radius of curvature and tangent slope angle as fundamental parameters, the governing equations of laminated curved smart beams under static mechanical and electrical loadings are derived. First, the equilibrium equations are deduced and decoupled using the deformed angle of tangent slope as the only variant. And then the analytical solutions of laminated curved smart beams are presented using harmonic functions. Finally, the static deformations of the laminated curved smart beams are calculated by this method and the finite element method. The results exhibit good consistency and show the validation of the present method. Circular and spiral beams covered with piezoelectric layers are researched further. Effects of radius, thickness ratios, and stacking sequence on deflections of the piezoelectric laminated beams are explored as well.
This article focuses on the development of a shape morphing composite skin representing a wing extrados. The objective is to design and manufacture a skin capable of changing its geometry in order to improve its aerodynamic efficiency. One geometry is considered to be the nominal geometry and a deformed geometry is identified. It is obtained upon application of a displacement at the aftmost boundary of the active portion of the wing profile. The displacement is imposed on the skin by shape memory alloy wires. These actuators are combined with a self-locking transmission mechanism that maintains the deformed geometry without any further energy consumption. The lay-up of the composite skin is optimised such that the deformed profile approaches the desired geometry as closely as possible. This lay-up selection routine is done through an ANSYS Parametric Design Language sub-routine. The finite element model is validated experimentally by conducting mechanical testing on the composite skin.
A systematic development of a continuum model is presented, which is capable of describing the magneto-mechanical behavior of magnetic polymer gels commonly referred to as "ferrogels". In the present research, ferrogels are treated as multicomponent, multiphase materials. They consist of a polymer network (P), fixed magnetic particles (f), mobile magnetic particles (m), and liquid (L). By considering ferrogels as multicomponent materials, interaction among constituents of ferrogels can be captured. This helps in understanding the process occurring inside ferrogels under the influence of external stimuli, such as magnetic fields. In our modeling approach, the field equations of ferrogels are derived within the framework of the theory of mixtures. The basic equations include Maxwell’s equations, balance of mass, linear momentum, angular momentum, energy, and entropy. In the framework of the theory of mixtures, balance relations are first presented at the constituent level also referred to as partial balance relations. By summing partial balance relations over all constituents and imposing the restrictions of theory of mixtures, balance relations of mixture (for the ferrogel) are obtained. In the current work the specific magnetization (magnetization per density) is considered as an evolving variable. It is demonstrated that balance of angular momentum is satisfied using the evolution equation of specific magnetization and constitutive laws. In the process of modeling, a suitable free energy function is introduced and thermodynamically consistent constitutive laws are formulated. Introducing certain assumptions, a reduced model of the ferrogel, a coupled magneto-mechanical formulation, is subsequently presented. The reduced model consists only of a polymer network (P) and fixed magnetic particles (f). It is concluded that the reduced model compares well to the existing ones in the literature. The magneto-mechanical problem based on the reduced model is solved in 2D using the finite element method. The only unknowns for the finite element method implementation are mechanical displacement and magnetic potential. Deformation of a ferrogel in a magnetic field is subsequently investigated. Elongation and contraction of a ferrogel are observed when a magnetic field is applied in the x- and y-directions, respectively. The numerical results were compared with existing experimental work in the literature. A good qualitative agreement was found between numerical and experimental results.
This article outlines a compact annular-radial-orifice flow magnetorheological valve through theoretical calculation, simulation analysis and experiment verification. The fluid flow paths of this proposed magnetorheological valve consist of a single annular flow channel, a single radial flow channel and an orifice flow channel through structural design. The finite element modelling and analysis of the magnetorheological valve was carried out using ANSYS/Emag software, including achieving optimal magnetic field distribution and yield stress in the annular flow path and radial flow path, respectively. Moreover, this proposed magnetorheological valve was prototyped and evaluated experimentally, showing that the magnetorheological valve has significantly improved its efficiency, especially the pressure drop at the 1.0 mm width of annular resistance gap and 0.5 mm width of radial resistance gap.
Static stability analysis of a size-dependent magneto-electro-elastic functionally graded nanoplate has an immense contribution in identification and improvement of the performance of nano-electro-mechanical systems. A refined trigonometric plate theory is employed to formulate the magneto-electro-elastic functionally graded nanoplate for the first time. Magneto-electro-elastic properties of nanoplate change in spatial coordinate based on power-law form. Regarding the small-scale effects at nanoscales, the size-dependent nonlocal continuum theory is employed to derive governing equations of the nonclassical magneto-electro-elastic functionally graded nanoplate. Analytical solution possessing functions which satisfy different boundary conditions is adopted to solve the equations. The results illustrate the size-dependent buckling behavior of magneto-electro-elastic functionally graded nanoplate affected by magnetic potential, electric voltage, various boundary conditions, small-scale parameter, material composition, plate side-to-thickness ratio, and aspect ratio.
Graphene nanosheets were exfoliated from graphite using liquid exfoliation method. Smart sensing layer was prepared by dispersing graphene nanosheets in thermoplastic polyurethane. The smart sensing layers thus obtained were pasted on to the glass fiber laminated composite specimens. The sensing layer due to its piezoresistivity was employed for detecting strains in the composite specimens. The results show that the smart sensing layer can be employed for strain sensing in the composite structures. The results hold promise for various applications of these sensors for structural health monitoring in composite parts.
An exact closed-form solution for the three-dimensional free vibrational response of a simply-supported and multilayered magneto-electro-elastic plate considering the nonlocal effect is presented. The solution is derived using the pseudo-Stroh formulation and propagator matrix method. Various numerical examples are presented for a homogeneous elastic plate, piezoelectric plate, magnetostrictive plate, and sandwich plates made of piezoelectric and magnetostrictive materials. The natural frequencies and the corresponding mode shapes of the multilayered plates show the influence of stacking sequence and the important role that the nonlocal effect plays in dynamic analysis of nanostructures. This exact solution is useful for it provides benchmark results to assess the accuracy of nonlocal thin plate models and finite element formulations.
The need for broad-band vibration isolation performance of the structures is fulfilled by magnetorheological elastomer–based smart vibration isolation system. The smart isolation capabilities of magnetorheological elastomer isolator vary with the input dynamic deformation levels. In this study, force transmissibility measurement approach is adapted to evaluate the influence of dynamic deformation on the field-induced isolation capabilities of magnetorheological elastomer. The variation in isolation capabilities of magnetorheological elastomer is assessed in terms of isolation effect. Isolation performance of magnetorheological elastomer is enhanced with the increase in the magnetic field. Under increased dynamic deformation levels, the isolation characteristics of magnetorheological elastomer are influenced by the Payne effect. Dominance of the Payne effect under non-magnetized state of magnetorheological elastomer has enhanced the isolation effect at larger strain levels. The influence of strain on isolation characteristics of magnetorheological elastomer is verified from the magnetic force simulation between a pair of dipoles performed in ANSYS (version 14).
This article proposes and validates the principle of a new magnetorheological elastomer (MRE) dynamic vibration absorber (DVA) for powertrain mount systems of automobiles. The MRE DVA consists of a vibration absorption unit and a passive vibration isolation unit. The vibration absorption unit composed of a magnetic conductor, a shearing sleeve, a bobbin core, an electromagnetic coil, and a circular cylindrical MRE is utilized to absorb the vibration energy, and the passive vibration isolation unit is used to support the powertrain. The finite element method is employed to validate the electromagnetic circuit of the MRE DVA and obtain the electromagnetic characteristics. The theoretical frequency-shift principle is analyzed via the established constitutive equations of the circular cylindrical MRE In order to demonstrate how the parameters of the MRE influence the vibration attenuation performance, the MRE DVA is applied to a powertrain mount system to replace the conventional passive mount. The frequency-shift property of the vibration absorption unit and the vibration attenuation performance of the MRE DVA on the powertrain mount system are experimentally tested. To validate and improve the vibration attenuation performance for the semi-active powertrain mount systems, an optimal variable step algorithm is proposed for the MRE DVA and numerical experiments are carried out.
Piezoelectric structures have been used in a variety of applications ranging from vibration control and sensing to morphing and energy harvesting. In order to employ the effective 33-mode of piezoelectricity, interdigitated electrodes have been used in the design of macro-fiber composites which employ piezoelectric fibers with rectangular cross section. In this article, we present an investigation of the two-way electroelastic coupling (in the sense of direct and converse piezoelectric effects) in bimorph cantilevers that employ interdigitated electrodes for 33-mode operation. A distributed-parameter electroelastic modeling framework is developed for the elastodynamic scenarios of piezoelectric power generation and dynamic actuation. Mixing rules (i.e. rule of mixtures) formulation is employed to evaluate the equivalent and homogenized properties of macro-fiber composite structures. The electroelastic and dielectric properties of a representative volume element (piezoelectric fiber and epoxy matrix) between two neighboring interdigitated electrodes are then coupled with the global electro-elastodynamics based on the Euler–Bernoulli kinematics accounting for two-way electromechanical coupling. Various macro-fiber composite bimorph cantilevers with different widths are tested for resonant dynamic actuation and power generation with resistive shunt damping. Excellent agreement is reported between the measured electroelastic frequency response and predictions of the analytical framework that bridges the continuum electro-elastodynamics and mixing rules formulation.
Unwanted accretions on structures, such as aircraft and wind turbine icing or deposits in pipes, are a common problem, which can pose a serious safety threat if not treated effectively and punctually. In this article we investigate the capability of piezo-excited structural waves to delaminate accreted material. The core of the concept is to utilise the stress distribution associated with waves propagating through the structure to detach unwanted build-up. We apply a wave-based technique for modelling piezoelectric excitation based on semi-analytical finite elements to calculate the shear stress at the interface between the host structure and the accretion generated by piezo-actuated waves. Our analyses include the effects of the actuator’s dynamics and allow for comparing different types of actuators, identifying the most effective frequency of excitation and formulating realistic power requirements. For the dual purposes of proof of concept and validation of the model, we present a demonstration experiment in which patches of accreted material are removed from a beam-like waveguide with emulated anechoic terminations using ultrasonic excitation.
This work demonstrates the ability of a torsion-based shear-mode energy harvester to power a sensor module by integrating a temperature sensor circuit with a purpose developed piezoelectric energy harvester. A 10-cm3 energy harvester was developed for this application and was found to produce over 200 µW of maximum power through an optimal load resistance under 0.25 gpk acceleration excitation at its resonant frequency of 237 Hz. This harvester was then tested with two interface circuits: a standard interface diode bridge rectifier and a nonlinear synchronous electrical charge extraction circuit that were compared for their suitability in powering the sensor module. Through this, the synchronous electrical charge extraction nonlinear conditioning circuit was found to have superior performance when charging a capacitor and with DC loads at low voltages and was capable of providing a maximum power output of 37 µW under 0.25 gpk acceleration at 237 Hz. This output power was then used to successfully power a temperature sensor module consisting of a temperature sensor, a microcontroller, and a radio-frequency identification memory chip at a sensing frequency of 0.5 Hz.
A new multi-piezoelectric microcantilever sensor is introduced in this article for replacing laser sensors in atomic force microscopes. This microcantilever consists of multiple piezoelectric layers over its surface, and a consensus algorithm is designed to provide a robust and accurate estimation of the deflections at the tip of the microcantilever. The dynamic equation set of the microcantilever is developed first and then the consensus observer is designed. A set of Riccati equations is used to obtain the optimal gains for the observer, and the robustness of the microcantilever is considered by designing a H norm constraint. A set of numerical simulations is conducted to evaluate the performance of the microcantilever. Results show that the consensus-based multi-piezoelectric microcantilever can successfully provide an accurate estimation of the deflections at the tip of the microcantilever. It is also shown that the robustness of the design can positively improve the estimation performance in the presence of noise. Additionally, a comparison with a single-layered design shows the advantages of the new sensor.
This article proposes new methods for enhancing the active harvest of piezoelectric energy using the synchronized switch harvesting on inductor (SSHI) technique. It was experimentally confirmed that the energy harvested by the original synchronized switch harvesting on inductor technique was decreased by the suppression of the vibration amplitude, and this critical problem was solved by developing new control strategies, namely, switch harvesting considering vibration suppression (SCVS) and adaptive SCVS (ASCVS). The SCVS technique was designed to intentionally skip some of the switching actions of the original synchronized switch harvesting on inductor technique, while the ASCVS technique enables more flexible variation of the number of skipped switching actions. The skipping of the switching actions facilitates the recovery of the vibration amplitude produced by the excitation force, and the developed strategies thus maintain the vibration amplitude at the highest possible level, resulting in increased energy harvest. The results of the experimental implementation of the proposed strategies showed that they enabled the harvesting of as much as 10.5 times the energy harvested by the original synchronized switch harvesting on inductor technique. The ASCVS technique particularly enables flexible enhancement of the harvested energy under various vibration conditions.
Shape memory alloys are attractive engineering materials due to their potential application as actuators using the ability to memorize shapes through a thermomechanical loading. This article develops a numerical investigation of different shape memory alloy actuator configurations considering bias and antagonistic arrangements. Numerical simulations are carried out using the finite element method together with a constitutive model for shape memory alloys. Parametric analysis is carried out evaluating the performance of each actuator configuration based on stress and strain. Basically, four representative configurations of general actuators are treated: shape memory alloy wire, linear spring connected to a shape memory alloy wire, two elastic springs connected by a shape memory alloy wire, and two shape memory alloy wires connected by a spring.
This article presents numerical analyses of functionally graded piezoelectric beam with piezoelectric semiconducting material properties using meshless method. Unlike piezoelectric dielectric materials, electron density and electric current are additionally considered in constitutive equations for piezoelectric semiconductors. Mutual coupling of elastic displacements, electric potentials, and electron density increases the complexity of the analyzed problem. For the solution of the set of partial differential equations with non-constant coefficients, the local radial basis function collocation method is proposed in this work. Approximating the spatial variations of all physical fields in the partial differential equations by the multiquadric radial basis function entails an ensuing system for time-dependent problems solved by the Houbolt finite-difference scheme as a time-stepping method. The presented local radial basis function collocation method is verified using the corresponding results obtained using the finite element method. The influence of material parameter gradation and initial electron density is then investigated, along with transient analyses.
Electrorheological finishing method is a promising method for small parts fabrication. The small footprint of the tool can provide material removal by virtue of numerical control machine. The characteristics of electrorheological polishing fluid is tested by Haake CV20 rheometer. The dependence of shear stress and viscosity of the electrorheological polishing fluid under different supply voltage, as well as the field dependence of shear stress of ER polishing fluid at different shear rate, was obtained. Hydrodynamic pressure model in working area was studied based on the phenomenon of hydrodynamic lubrication theory of Bingham fluid, and it is proved that the pressure distribution is the dominant factor on the footprint shape. The experiments further showed that the efficiency of material removal is a combined action of hydrodynamic pressure and wheel speed.
Active repairs using piezoelectric actuators can play a significant role in reducing the crack damage propagation in thin plate structures. Mode-I crack opening displacement is the most predominant one in tension, and it is responsible for the failure which in turn affects the load carrying capability of the cracked structure. In addition, there are limited studies that investigated the effect of the piezoelectric actuator over mode-I active repair. In this study, the mode-I stress intensity factor for a plate with a center crack, and a bonded piezoelectric actuator was modeled using the linear elastic fracture mechanics. For this, an analytical closed-form solution is developed using the virtual crack closure technique taking into account mode-I as the only effective mode, coupling effects of the piezoelectric patch, and the singular stress at the crack tip. In addition, the total stress intensity factor was obtained by the superposition of the stress intensity factor obtained from the stresses produced by the piezoelectric actuators on the crack surfaces as the only external loads on the cracked plate and the stress intensity factor due to the far-field tension load. The proposed analytical model for mode-I stress intensity factor was verified by a finite element–based approach using ANSYS finite element software. The results demonstrated a good agreement between the analytical and finite element models with a relative error of less than 4% in all the cases studied. The results illustrated that the piezoelectric patch is efficient in reducing stress intensity factor when an extension mode of the actuator is applied. However, applying a contraction mode of the piezoelectric actuators produced negative strain which increased the stress intensity factor and thus the severity of the cracked structure and could lead to damage propagation.
We investigate the effect of including the second mode of natural vibration on the computed response of a forced non-linear gravity-loaded beam–mass structure used for non-linear piezoelectric energy harvesting. Using the method of assumed-modes and Lagrange’s equations, we develop the discretized equations of generalized coordinates of the system including the electro-mechanical equation. The equation of motion is further simplified to find the single-mode approximation. The phase-portraits, time-histories, Poincaré sections, and frequency–response curves of the system are computed. It is shown that the number of mode shapes affects the response, and it is required to include higher modes to improve the analytical–computational results. The system shows distinct behavior varying from a linear single-frequency response to a multi-frequency chaotic response. The average power across the load resistor consequently shows a noticeable variation depending on the characteristics of the overall system response.
A study on iron-gallium (Galfenol) unimorph harvesters is presented which is focused on extending the power density and frequency bandwidth of these devices. A thickness ratio of 2 (ratio of substrate to Galfenol thickness) has been shown to achieve maximum power density under base excitation, but the effect of electrical load capacitance on performance has not been investigated. This article experimentally analyzes the influence of capacitive electrical loads and extends the excitation type to tip impulse. For resistive-capacitive electrical loads, the maximum energy conversion efficiency achieved under impulsive excitation is 5.93%, while the maximum output power and output power density observed for a 139.5 Hz, 3
Harnessing of ultrasonic guided waves confined in local features such as bends and welds, known as feature-guided waves, has emerged as a promising technique for non-destructive testing and structural health monitoring of industrial and aerospace structures. This article introduces a fiber Bragg grating based technique which uses feature-guided waves to detect anomalies or defects in plate structures with transverse bends. We are able to obtain good consistency between simulation and experimental results, both in the case of defect-free bent plates and those with transverse defects. Such results establish fiber Bragg gratings as a viable alternative to conventional techniques for structural health monitoring of bent plates.
The objective of this paper is to derive an approximate closed-form solution to the
To predict dispersion curves it is common to use different solution approaches depending on the material type, isotropic or composite, of the medium in which the wave propagates. The two different solution methods are defined in different domains, frequency–wavespeed domain for isotropic materials, and wavenumber–wavespeed domain for composites which can lead to difficulties, and unsatisfying results when predicting the dispersion curves for hybrid laminates which contain both isotropic and composite materials. This article, therefore, proposes a unified formulation defined in the wavenumber–wavespeed domain for both isotropic and composite materials. The unified formulation, simple, and mathematically straightforward formulation, utilizes Christoffel’s equation for a lamina to obtain the eigenvalues and eigenvectors. The eigenvalues and eigenvectors are then used to set up the field matrix from which the dispersion curves could be retrieved. Once the dispersion curves were obtained the waves are grouped using a modeshape analysis. A spline algorithm is applied to obtain a continuous solution from a rough domain which was used to reduce computational time. In addition, this article highlights the challenges faced in the numerical process, and provides a discussions of the methods used to overcome these obstacles.
This paper deals with piezoelectric shunt damping enhanced with negative capacitances. A novel electrical circuit layout is addressed, based on the use of two negative capacitances. It is shown that the shunt performances, in terms of vibration reduction and stability margins, are increased as compared with the classical single negative capacitance layouts. Then, the article focuses on the comparison of a simple resistive shunt, enhanced by a pair of negative capacitances, with a classical resonant shunt. It is shown that the newly proposed enhanced resistive shunt can show equivalent performances in terms of vibration attenuation than the resonant shunt, with at the same time an increased robustness to frequency detuning, in the case of mono-modal damping. The broadband control capability of the resistive shunt coupled to the new negative capacitance layout is also evidenced. The main part of the work is analytical, and then the model is validated by an extensive experimental campaign at the end of the paper.
This article presents an adaptive maximum power point tracking technique for broadband vibration energy harvesting. The presented technique employs a discontinuous conduction mode buck–boost converter to emulate a matched resistor for a vibration energy harvester. Instead of traversal search, the optimal duty cycle can be tuned in one step based on direct calculation of source impedance, which is realized by active pulse width modulation perturbation strategy; based on it, the circuit can work well in impedance match adaptively without any prior knowledge of a harvester. The prototype circuit is implemented by an ultra-low-power consumption MSP430 microcontroller with a stable external power supply. It produces 1.32 mW (0.4 g and 88.2 Hz acceleration) from a piezoelectric vibration energy harvester and 1.16 mW (0.12 g and 19.3 Hz acceleration) from an electromagnetic vibration energy harvester. According to the definition of power–bandwidth product, the experimental results achieve 75.2% and 39.9% of the theoretical optimal capacity of the piezoelectric vibration energy harvester and electromagnetic vibration energy harvester, respectively. The detailed experimental data indicate that the proposed approach achieves a large improvement than employing a fixed load resistance in a wide frequency band. Furthermore, the possibility of self-powered is confirmed based on a brief estimation of power losses on the proposed circuit.
High noise levels in the helicopter cabin adversely affect aircrew communication and reduce comfort in the short-term and may lead to hearing loss in the long-term if flight helmets cannot provide sufficient protection to the aircrew. A cabin noise exposure survey has been performed on a Royal Canadian Air Force CH-147F Chinook heavy lift helicopter to evaluate the noise environment and noise protection performance of the flight helmet. Investigation results showed that the low-frequency noise attenuation provided by the Royal Canadian Air Force flight helmet was marginal in high-speed flight conditions that generate loud cabin noise. Therefore, in-canal earphone integrated with active noise cancellation capability was investigated to provide enhanced noise protection and improve clarity in voice communication. Simulation and proof-of-concept test results verified that active noise cancellation in-canal earphones can serve as a feasible technical solution to provide enhanced noise attenuation to mitigate the low-frequency N/rev tonal noise generated by the aerodynamic pressure from the helicopter rotor blades.
The present article addresses the study of an adaptive-passive beam structure with a shape-memory alloy based actuator. In order to mitigate adverse dynamic effects resulting from externally induced vibrations, the structure is able to automatically tune its natural frequency to avoid resonance. The adaptive-passive beam configuration is based on an underslung cable-stayed girder concept. Its frequency tuning is achieved by temperature modulation of the shape-memory alloy elements through a closed-loop control process based on a proportional-integral-derivative algorithm. The effectiveness of the proposed control solution is substantiated by numerical simulations and experimental tests on a small-scale prototype. The validated numerical model enables the simulation of the proposed control approach in a real-scale footbridge, subjected to a prescribed pedestrian loading. The results are very encouraging and show that, by activating the shape-memory alloy elements, the system is able to successfully shift its natural frequency and to mitigate the effects of induced vibrations.
Piezoelectric energy harvesting has attracted extensive research in the advancement of new designs and techniques over the last decade. The cantilever shaped piezoelectric energy harvesting beam is one of the most employed designs, due to its simplicity and flexibility for further performance enhancement. The strain distribution along the cantilever piezoelectric energy harvesting beam is nonuniform, which would induce fatigue damage at the root of the cantilever on the long run. This particular issue has seldom been addressed in the literature. This article presents an experimental investigation on the fatigue behavior of a cantilever piezoelectric energy harvesting beam at different base excitation levels. The experimental study is augmented with analytical formulation to examine the strain levels and with finite element analysis formulation to model the piezoelectric energy harvesting beam with a macro fiber composite piezoelectric transducer. A two-dimensional model is developed based on the three-dimensional model to investigate crack propagation in the piezoelectric energy harvesting beam. Furthermore, the electromechanical impedance technique is employed to monitor the progression of damage in the experimental specimens. The root mean square deviation and relative root mean square deviation of the impedance values and voltage obtained from the macro fiber composite transducer provide a profound introspection into the damage propagation in the piezoelectric energy harvesting beam. This study provides an insight into the behavior of the piezoelectric energy harvesting beam undergoing fatigue loading due to a uniform sinusoidal base excitation by analyzing the output voltage, resonant frequency, tip displacement, tip velocity, and impedance variations. It will pave the way for future studies on the fatigue-based design guides for piezoelectric energy harvesting beams.
This article analyses the Rolamite architecture exploiting shape-memory alloys as power element to obtain a solid-state actuator. The Rolamite mechanism was discovered in the late 1960s, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so-called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works, the force was provided, thanks to cut-outs of various shapes in the strip, although this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this article, we developed the idea of exploiting the shape-memory alloy as Rolamite power element, and therefore, to use the shape-memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analysis, where the martensite–austenite transition is modelled in a simplified way, shows that this application is feasible, mainly thanks to the initial precurvature of the shape-memory alloy strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.
This research explored a new linear hybrid actuator, which consists of a pneumatic cylinder with a magnetorheological brake embedded in its piston. Magnetorheological brakes are promising actuators since they can apply large forces in a small actuator size, but they can only oppose motion, as they are passive actuators. Pneumatic cylinders are desirable actuators due to their high force-to-weight ratio and ability to apply active forces. However, they require expensive servo valves for precise position control. The new hybrid actuator benefits from the advantages of magnetorheological brakes and pneumatic cylinders. It can apply forces using compressed air and can resist external forces using the magnetorheological brake. The embedded brake also eliminates the undesirable side effects of using compressed air and allows precise positioning of the piston anywhere in its stroke with simple solenoid valves. Fields such as haptics and robotics might benefit greatly from the use of the hybrid actuator where a high force-to-weight ratio could be employed. The study contributes (1) a triple helix flux guide for the linear magnetorheological brake, (2) serpentine flux path to enable larger braking forces, (3) shear mode activation, and (4) control algorithms that enable use of simple solenoid valves and improved power efficiency. When compared to an existing purely pneumatic control algorithm, the hybrid actuator exceeded the performance in position tracking and force disturbance rejection. A power management algorithm demonstrated that disabling the brake when the piston was in position vastly decreases the power consumption.
This article analytically formulates and investigates the evolution of electromechanical admittance of piezoelectric transducers collocated on a finite beam from wave propagation perspective. First, the analytic wave solutions are obtained based on the linear piezoelectricity and the Timoshenko beam theory. Then, the evolution of wave propagation to vibration on a finite beam has been formulated in terms of a wave unit which appears periodically due to the multiple reflections at beam supports. The formulation has been extended to describe the underlying mechanism how electromechanical signatures evolve from wave units. The support conditions and material damping of a beam have been considered explicitly for both wave units and electromechanical signatures. The validity of the proposed formulation has been demonstrated through proof-of-concept numerical examples providing valuable physical insights into the relevance between wave units and electromechanical signatures.
Piezoelectric shunt damping is investigated as one possible solution for improving the vibroacoustic behavior of noise-prone lightweight structures. The negative capacitance shunt circuit appears to be the best choice due to its broadband damping effect. Usually it is built from analog electronic components, such as operational amplifiers, resistors and capacitors. Laboratory tests are possible with this setup, but it is limited to low vibrational excitation levels, because the known circuits are not capable of accessing a sufficient voltage amplitude at the piezoelectric transducers, which is required for high vibration amplitudes. Therefore an improved approach is presented in this paper, which addresses the specific voltage requirements of a common piezoelectric transducer. It comprises a tailored power source and an appropriate concept for the negative capacitance shunt hardware. There only standard operational amplifiers together with an external high-voltage power amplifier circuit are used to cover the whole operating range of a piezoelectric transducer. A demonstrator board is developed and experimentally investigated at a test structure. Finally, the results are compared with a conventional setup. It can be shown that using the full voltage range of the piezoelectric transducer allows higher damping of structures without any saturation effects.
To adjust the contact force of piezoelectric friction dampers for a benchmark base-isolated structure, a self-tuning fuzzy proportional–derivative controller and an adaptive fuzzy proportional–derivative controller are developed. Considering three candidate signals, namely, the isolation displacement, isolation velocity, and roof acceleration, the best feedback signal for the self-tuning fuzzy proportional–derivative controller is selected based on the Pareto-optimal front. The performance of the self-tuning fuzzy proportional–derivative controller during both near-field and far-field earthquakes is enhanced using an adaptive fuzzy proportional–derivative controller, in which the output gain of the self-tuning fuzzy proportional–derivative controller is adaptively tuned according to the kind of entering earthquake. The control objective is to reduce the isolation system deformations without significant increase in superstructure accelerations during far-field and near-field earthquake excitations. Membership functions and fuzzy control rules are simultaneously tuned using a multi-objective cuckoo search algorithm. Considering 14 real-data earthquakes, simulation results show that the proposed controllers perform better than other reported control strategies in terms of simultaneous reduction of the maximum base displacement and superstructure accelerations. Also, they provide acceptable responses in terms of the inter-story drifts, root mean squared of base displacement, and the floor acceleration. Opposite to other reported control strategies, piezoelectric friction dampers controlled by the self-tuning fuzzy proportional–derivative controller and adaptive fuzzy proportional–derivative controller never enter the saturation area.
On the basis of shear working mode of magnetorheological fluid, in this article, a novel temperature controllable yield stress measurement device is designed, and the double magnetic circuit structure and the heating structure are proposed. And then, the magnetic field and temperature field of the measurement device are simulated, respectively, by the finite element method. Furthermore, several experiments are carried out to evaluate the magnetic field, measurement precision, and repeatability of the self-designed device. The results indicate that the proposed measurement device has uniform magnetic field distribution and controllable temperature and also has high yield stress testing accuracy and repeatability.
When the flight of an unmanned aerial vehicle is controlled by a ground pilot, a wing deflection monitoring is required to avoid overload wing structural failures. Therefore, integrated structural health monitoring technologies are being developed to transfer such information to the pilot. In general, this information can be monitored visually by the ground pilot. In this study, a haptic interface enables human–machine communication through tactile sense and provides synchronized information exchange between a pilot and an unmanned aerial vehicle. In other words, we propose not a vision interface but a haptic interface to transfer the wing deflection information to the ground pilot; this interface is named "Fly-by-haptic," which is beneficial because the vision of the ground pilot is already performing multiple tasks. For a proof of concept, four integrated fiber Bragg grating sensors were installed on a half wing specimen to measure dynamic strains. The wing deflection information was estimated by the displacement–strain transformation matrix. The wing deflection information was wirelessly transferred to actuate vibro-haptic motors installed in a pilot arm–wearable haptic interface. Finally, a human test was performed using the developed haptic interface; the test results determined that the 15 participants, who are novices, showed 100% accuracy for wing deflection.
Recent studies have demonstrated that it is feasible to harvest energy from raindrop. A challenge in designing a raindrop energy harvester is the rain droplet would accumulate on the surface of the harvester and affect its performance. In a previous work, we have modelled the dynamics of a piezoelectric beam subjected to water droplet impacts with a water layer formed on the surface. This work presents a theoretical model to describe the transient dynamics during the formation of water layer on the beam. The average water droplet impact force is described by a partially inelastic impact coefficient that varies during the formation of water layer. The maximum root mean square voltage measured experimentally is 0.05 V with an average percentage error of 6.94% compared to the theoretical model. Experimental result revealed that the optimal performance of the harvester occurs before the water layer spreads to the width end of the beam.
Hysteresis nonlinearity widely exists in piezoelectric actuated nano-positioning applications, which degrades their tracking accuracy and limits their precision positioning applications. This paper presents a novel hysteresis modeling and compensation approach to alleviate the adverse effect of the asymmetric and rate-dependent hysteresis nonlinearity for a piezoelectric transducer actuated servo stage. By integrating a generalized input function with the play operator of the classical Prandtl–Ishlinskii model, a novel polynomial-based rate-dependent Prandtl–Ishlinskii (PRPI) model is proposed to capture the hysteresis behavior of the piezoelectric positioning stage, where a polynomial function of input and a time rate function of input are introduced to formulate the generalized input function. Meanwhile, a new adaptive differential evolution optimization algorithm is developed to identify the parameters of the proposed PRPI hysteresis model. Based on the PRPI hysteresis model with the identified parameters, an inverse feedforward controller is constructed to achieve the accurate tracking motion. Furthermore, the hysteresis compensation error of the proposed PRPI model is theoretically analyzed. Finally, comparative experiments are conducted, and the experimental results provided in this paper demonstrate the effectiveness and superiority of the proposed inverse PRPI model compensation approach.
This article describes the optimal configuration and combination of piezoelectric transducers and inductors for the synchronized-switch-damping-on-an-inductor technique. The technique suppresses structural vibrations by inverting the polarity of the electric voltage in a piezoelectric transducer using a switched inductive shunt circuit at each displacement extremum. The energy dissipation rate of synchronized switch damping on an inductor depends on the impedances of the transducer and the inductor in the circuit, especially the resistive component, in this inversion. For this study, mathematical models of the equivalent resistances of transducers and inductors for this inversion phenomenon were formulated based on experiments with various transducers and inductors. Using these models, the optimal ratio of the thickness–area of patch-type piezoelectric transducers and that of the length–cross-sectional area of the lead of the inductors were analytically obtained. The optimization of series–parallel connections of multiple transducers and inductors was also shown to be equivalent to this one. The optimal mass budget allocation for the transducers and inductors was also formulated. Two examples of optimization, involving an increase in energy dissipation rates by a factor of 4, were presented. The examples showed that the time taken to suppress free vibrations in a clamped beam was reduced to half through the optimization.
Creep and relaxation phenomena are being observed in shape memory alloys, not only at high temperatures but also at room temperature, due to their martensitic transformation. Transformation-induced creep and stress relaxation in shape memory alloys occur due to temperature variations during loading and unloading cycles. In this work, a one-dimensional fully coupled thermomechanical model was employed to develop a continuum framework for studying these behaviors in shape memory alloy wires. A decrease or increase in stress was observed during forward or reverse transformation at a constant amount of strain, showing the stress relaxation and stress recovery, respectively. Similarly, the model predicts that strain increases or decreases when stress is held fixed in the course of forward or reverse transformation, meaning the phenomena of creep and creep recovery, respectively. This model provides the ability of investigating the effects of different ambient temperatures, strain rates, applied stresses and strains, and wire radii on the creep and relaxation responses of shape memory alloys. Relaxation and creep experiments at different ambient temperatures and loading or unloading rates were also done on NiTi wires, and the theoretical predictions were shown to be in a good agreement with the empirical observations.
The traditional delay-and-sum imaging algorithm usually requires sending an excitation pulse at each piezoceramic transducer and obtains a damage image by drawing only ellipses. A multi-delay-and-sum imaging algorithm is proposed for damage detection of thin-plate-like structures using sparse piezoceramic transducers. Compared with the traditional delay-and-sum imaging algorithm, the proposed algorithm sends only one excitation pulse for each detection. A reflection coefficient is employed in the proposed method to cancel the artifacts caused by the boundary reflection signals, and the reflection coefficient is determined by the distribution of piezoceramic transducers and strength of the reflection signals. An additional time compensation due to the excitation pulse is also made to reduce the error of damage locating. To increase the image pixel value of a damage, the damage image is obtained by drawing both ellipses and hyperbolas with transmitter–sensor pair signals. The experimental results obtained on an aluminum alloy plate demonstrate that the proposed multi-delay-and-sum imaging algorithm can identify a bonded mass damage efficiently and accurately.
This article presents a novel approach for damage detection applied to structural health monitoring systems exploring the residues obtained from singular spectrum analysis. In this technique, a lead zirconate titanate patch acting as actuator excites the structure, and three other patches are used as sensors to receive the structural responses. This method is based on a high-frequency excitation range in order to overcome the problem caused when the low-vibration modes are excited. In this method, a wideband chirp signal, with low amplitude and variable frequency, is used to excite the structure. The response signals are acquired in the time domain, and the singular spectrum analysis procedure is performed. The residues obtained between the reconstructed and original time series are used to compute statistical metrics. The residues calculated from singular spectrum analysis are used to compute the root mean square deviation and correlation coefficient deviation metric indices, rendering the damage detection approach more reliable. Tests were carried out on an aluminum plate, and the results have demonstrated the effectiveness of the proposed method making it an excellent approach for structural health monitoring applications. The results exploring different numbers of components used during the reconstruction process of time series are obtained, and the highlights are presented.
Based on an extended linear theory for dielectrics, this work presents exact solutions for the electromechanical responses of a dielectric nano-ring subjected to mechanical and electrical loads. By incorporating terms involving the strain gradient and the electric field gradient into the electric Gibbs free energy, both the direct and converse flexoelectric effects can be captured. The general solution to the differential governing equation is a linear combination of modified Bessel functions and the electromechanical fields are obtained by solving boundary value problems. The influences of the material surfaces and the electric circuit conditions on the electromechanical coupling behavior of the dielectric nano-ring have also been considered. It is found that the flexoelectricity and the surface effect on the electromechanical fields are substantial, and they are affected by the size of the ring structure. Moreover, the flexoelectric effect is sensitive to the material length scales introduced by the new theory and the electric circuit conditions. From simulation results, it is also suggested that nano-scaled electromechanical coupling devices could be built based on dielectric materials through flexoelectricity, which thereby opens up new perspectives for nano-technology.
Piezoelectric transducers have applications from ultrasonic structural health monitoring to micro-electromechanical systems. Small physical size coupled with large actuation is desirable in many applications, requiring unique transducer designs to take advantage of the material properties. Screen-printed piezoceramics were developed as a means of mass producing mezzo-scale transducers that are geometrically small and light weight, but large enough to generate significant actuation. Screen-printed piezoceramic transducers display significantly different properties than chemically identical bulk ceramic elements, largely attributed to high void fraction of screen-printed piezoceramic materials and detrimental to the functionality of traditional transducer designs. This article presents analysis, simulation, and initial testing of new designs for screen-printed piezoceramic transducers with concentric through-thickness electrodes. Analytical models were developed enabling analysis across material properties and design parameters. Analytical results were verified against finite element models for some designs. Prototypes were created and underwent initial testing to assess the properties of the design.
"Functional integration" is to integrate two or multiple systems or mechanisms that are independent with each other and to realize the two or multiple functions using only one actuation system. Maximization of engineering applications of actuation systems could be achieved through the use of the "functional integration" concept-based structural design. In this article, an integrated semi-active seat suspension, mainly composed of a switching mechanism, a transmission amplification mechanism, and a damping force- or torque-controllable rotary magnetorheological (MR) damper working in pure shear mode, for both longitudinal and vertical vibration attenuation, is proposed, designed, and fabricated. The switching mechanism employs the parallelogram frames as a motion guide which keeps the seat moving longitudinally and vertically. Both longitudinal and vertical motions are transformed into a reciprocating rotary motion that is transmitted to the rotary MR damper after an amplification by a gear mechanism. The torque generated by the MR damper can be tuned by adapting the applied current in real time, and hence, effective two-dimensional vibration control of the seat could be realized. The mathematical model of the semi-active seat suspension system is established, and vibration isolation performance of the system is simulated and analyzed. Based on the established experimental test rig, the prototype of the semi-active seat suspension system is tested, and the results of the mathematical model and the experimental test are compared.
This article proposes a new technique that advances long-gauge carbon fiber line sensor technology, with and without post-tensioning of the sensor, to measure changes in strain levels in structural areas. Carbon fiber line sensors were fabricated to produce a slim high-strength sensor with a diameter of less than 1.4 mm using a carbon fiber tow with a width of 6 mm. A theoretical analysis of these sensors as well as several series of experiments was conducted to investigate the effect of fiber arrangement on the error compensation of the carbon fiber line sensors. The results revealed that using two sets of carbon fiber line sensors, one as an active sensor and the other to compensate the errors of the first, is an effective method when both sensors have a convergent fiber arrangement and change in resistance. A post-tensioning method was implemented to enhance the overall behavior of the sensor. The results showed that the post-tensioning method yields significant improvement in the linearity and cyclic ability up to 6000 microstrains and reduces the fluctuation errors in the change in resistance from ±0.031% to ±0.007%. Finally, the possibility of repairing damaged carbon fiber line sensors is also discussed.
This paper develops an analytical model for predicting the performance of simply-supported multi-layered piezoelectric vibrating energy harvesters. The model includes the effects of material and geometric non-linearities, as well as axial pre-tension/compression, and is validated against experimental devices for a large range of base accelerations. Numerical and experimental investigations are performed to understand the benefits of using simply-supported devices compared to cantilevered devices. Comparisons are made in an unbiased manner by tuning the resonant frequency to the same value by modifying the geometry, and the results obtained indicate that simply-supported devices are capable of generating higher voltage levels than cantilever devices. The model is also used to investigate the benefits of using multi-layered devices to improve power density. Depending on harvester composition, power-per-unit-volume of piezoelectric material for a device is increased through the stacking of layers.
In this article, a method for addressing temperature effects using Lamb waves is developed with application to baseline comparison damage detection. The proposed method is based on baseline signal stretch with an improved minimum residual allowing correction over a larger temperature range. The effectiveness of the proposed approach in detecting (artificial) damages is demonstrated experimentally over a large temperature. The method is also shown to accurately detect and localise a crack in an aluminium panel and actual impact damage on a carbon fibre reinforced polymer panel.
Neural networks are commonly recognized tools for the classification of multidimensional data obtained in structural health monitoring (SHM) systems. Their configuration for a given scenario is, however, a challenging task, which limits the possibilities of their practical applications. In this article the authors propose using the neural network ensemble approach for the classification of SHM data generated by guided wave sensor networks. The overproduce and choose strategy is used for designing ensembles containing different types and sizes of neural networks. The proposed method allows for a significant increase of the state assessment reliability, which is illustrated by the results obtained from the practical industrial case of a full-scale aircraft test. The method is verified in the process of detecting fatigue cracks propagating in the aircraft load-carrying structure. The long-term experiments are performed in variable environmental conditions with a net of structure-embedded piezoelectric sensors.
This article presents a phase-based fuzzy logic controller for magnetorheological elastomer vibration absorber to trace the excitation frequency rapidly. The phase difference between the relative acceleration of the vibration absorber mass and the absolute acceleration of the primary system is used as the input signal of the fuzzy logic controller to calculate the desired magnetic current. Compared with the traditional stiffness control strategy, the proposed controller does not rely on the accurate relationship between the magnetic current and the resonant frequency of the magnetorheological elastomer vibration absorber. Simulation and experiment results demonstrate that the proposed stiffness controller is efficient to make the magnetorheological elastomer vibration absorber trace the excitation frequency rapidly. When the excitation frequency varies, the magnetorheological elastomer vibration absorber can be tuned properly within several seconds.
This work addresses the multi-fidelity analysis-driven design of a thermal transport system based on the flow of liquid metal through a structural laminate as induced by a solid-state magneto-hydro-dynamic (MHD) pump. A full three-dimensional model of the thermal transport system is both simplified to a reduced-order algebraic model, which correctly captures trends in the global system response, and alternatively implemented in an finite element framework, which captures essential global and local aspects of the system response not attainable via reduced-order modeling. The predictions of each model are validated against previously published experimental data. It is shown in detail for the first time in the context of MHD systems that a multi-fidelity approach to the multi-objective design optimization problem can leverage both the speed of the algebraic model and the accuracy of the finite element model, leading to effective predictions of optimal system designs in a reasonable amount of time. A relatively new algorithm for multi-objective and parameterized Pareto optimization is employed, and a clear path of continued development is identified.
This article deals with damage detection process under varying temperature. Carbon fibre–reinforced polymer samples are investigated using electromechanical impedance method. In the article, influence of changing temperature on resistance in electromechanical impedance is investigated. Authors propose new approach for compensation of temperature influence on damage detection. Damage detection is based on root mean square deviation index. Due to strong damping of utilized composite material, low-frequency range is utilized in this research. Real part of electromechanical impedance is measured for frequency band 1–20 kHz. Damage is in the form of artificially made delamination with different sizes. Authors also discuss the problem of influence of structure’s boundary condition on low-frequency measurements. In the research, scanning laser vibrometry for guided wave propagation method is utilized for visualization of the introduced delamination.
Electronic devices are high-demand commodities in today’s world, and such devices will continue increasing in popularity. Currently, batteries are implemented to provide power to these devices; however, the need for battery replacement, their cost, and the waste associated with battery disposal present a need for advances in self-powered technology. Energy harvesting technology has great potential to alleviate the drawbacks of batteries. In this work, a novel piezoelectret foam material is investigated for low-level vibration energy harvesting. Specifically, piezoelectret foam assembled in a multilayer stack configuration is explored. Modeling and experimentation of the stack when excited in compression at low frequencies are performed to investigate piezoelectret foam for multilayer energy harvesting. An equivalent circuit model derived from the literature is used to model the piezoelectret stack. Two 20-layer prototype devices and one 40-layer prototype device are fabricated and experimentally tested via harmonic base excitation. Electromechanical frequency response functions between input acceleration and output voltage are measured experimentally. Modeling results are compared to experimental measurements to assess the fidelity of the model near resonance. Finally, energy harvesting experimentation in which the device is subject to harmonic base excitation at the fundamental natural frequency is conducted to determine the ability of the stack to successfully charge a capacitor. For a 20-layer stack excited at 0.5 g, a 100-µF capacitor is charged to 1.45 V in 15 min, and produces a peak power of 0.45 µW. A 40-layer stack is found to charge a 100-µF capacitor to 1.7 V in 15 min when excited at 0.5 g, and produce a peak power of 0.89 µW.
We investigate experimentally five different designs of an energy harvester based on mechanical vibration and highly nonlinear solitary waves. The harvester consists of a metamaterial formed by granular chains, an oscillator that taps the metamaterial, a solid in contact with the metamaterial, and a piezoelectric element glued to the solid. The overall principle is that the oscillator taps the metamaterial and creates a train of solitary waves along each chain. At the interface between the chains and the solid, part of the acoustic energy refracts into the solid where it coalesces at a point and triggers the vibration of the solid. Here, a transducer converts the focalized stress wave and the waves generated by the reverberation with the edges into electric potential. In the study presented in this article, we evaluate the effect of certain harvester parameters on the amount of energy that can be extracted. We considered five different designs by changing the oscillator, the dimension of the array, the solid material, and the transducer boundary condition. For each design we computed the power density, and we found that the density obtained with the best design is four orders of magnitude higher than the worst design.
Identification of location and magnitude of impact forces on a rectangular carbon fibre–epoxy honeycomb composite panel has been experimentally investigated through an inverse approach. The dynamic signals captured by a single piezoelectric (PZT) sensor installed on the panel remotely from the impact locations are utilized to identify the impact forces generated by an instrumented hammer. A number of potential impact locations on the panel are assumed to be known a priori. An actual impact is then occurred at one or two of these locations. The objective is to simultaneously identify the location and magnitude of the impact forces using the PZT sensor. The problem is solved through minimization of an extended matrix form of the convolution integral incorporating linear superposition of the responses due to impact at different locations. The under-determined problem is ill-posed and is regularized by Tikhonov and generalized cross validation methods. It is revealed that impact forces occurred at any location among four possible locations can be well identified.
Piezoelectric sensor diagnosis and validity assessment as a prior component of structural health monitoring system are necessary in the practical application of electromechanical impedance technique. This article proposed an innovative sensor self-diagnosis process based on extracting the characterization of the real admittance (inverse of impedance) signature within a high-frequency range, which covered both diagnosis on damaged sensor after its installation and discrimination of sensor and structural damages during structural health monitoring process. Theoretical analysis was derived from the impedance model of piezoelectric-bonding layer-structure dynamic interaction system. Experimental investigations on piezoelectric sensor-bonded steel beam involved with structural damages of mass addition and notch damage were conducted to verify the process. It was found that the real admittance was reliable and critical in sensor diagnosis, and sensor faults of debonding, scratch, and breakage can be identified and differentiated from structural damage. Validity assessment of the diagnosed damaged sensor was addressed through resonant frequency shift method. The results showed that the validity of damaged sensor for structural health monitoring was inordinately depreciated by sensor damage. This article is expected to be useful for structural health monitoring application especially when damaged piezoelectric sensors existed.
A fan-structure piezoelectric energy harvester was proposed and tested in order to collect wind energy. Polyvinylidene fluoride was chosen due to its flexibility and longevity when compared to lead zirconate titanate. The impact-induced piezoelectric energy harvester consists of a stator and a rotor and a circular array of four cantilevers, utilize the rotor blades’ periodic impact on the free end of the cantilevers to generate oscillatory motion of cantilevers. A circular array of polyvinylidene fluoride cantilevers was fixed around the rotor in order to increase output power, save space at the same time. Static and transient characteristics of different cantilevers were investigated using finite element method and the result showed that polyvinylidene fluoride triangular cantilever performs the best in output voltage and power. Under the condition of optimal impedance and optimal overlap distance, a sum AC output power of four cantilevers without connection to each other approach to 0.75 mW was measured at the wind speed of 7 m/s when the blade number of rotor is 7 or 9. Two branches 0.27 mW DC output power was obtained when each two cantilevers in parallel connection in the case of full-wave rectification of each cantilever at the wind speed of 7 m/s.
In this article, the saturation kinetics model that describes chronoamperometric response of PPy(DBS) in our recently published work is extended to study the effect of mass and charge density on the step response of PPy(DBS). The saturation kinetics model is based on a mechanistic approach for charge storage in conducting polymers and leads to the development of structure-dependent input-output relationships to develop a cation concentration sensor. In this article, we demonstrate the use of poles and residues in the saturation kinetics model to deconstruct the chronoamperometric and chronocoulometric response by seperating the contributions from double layer charge accumulation and faradaic ion transport. We show that: (i) the number of redox sites, and therefore the number of ingressing ions at saturation, is directly proportional to the mass of the conducting polymer, (ii) the accessibility of these redox sites associated with ion ingress is inversely proportional to the conducting polymer charge density, (iii) the rate of ion ingress is found to be inversely proportional to mass and charge density, due to the decrease in the driving force per unit redox site and redox site accessibility, respectively. For lower charge densities, the mass has a dominant effect on saturation and rate of ion ingress, with charge density effects becoming apparent as it increases. The saturation charges obtained are consistent with the peak charges during cyclic voltammetry, thus validating the mechanistic interpretations. The findings of this article highlight the trade-offs between charge storage and transport properties for conducting polymer devices.
The cochlea displays an important, nonlinear amplification of sound-induced oscillations. In mammals, this amplification is largely powered by the somatic motility of the outer hair cells. The resulting cochlear amplifier has three important characteristics useful for hearing: an amplification of responses from low sound pressures, an improvement in frequency selectivity, and an ability to transduce a broad range of sound pressure levels. These useful features can be incorporated into designs for active artificial hair cells, bio-inspired sensors for use as microphones, accelerometers, or other dynamic sensors. The sensor consists of a cantilever beam with piezoelectric actuators. A feedback controller applies a voltage to the actuators to mimic the outer hair cells’ somatic motility. This article describes three control laws for an active artificial hair cell inspired by models of the outer hair cells’ somatic motility. The first control law is based on a phenomenological model of the cochlea while the second and third models incorporate physiological aspects of the biological cochlea to further improve sensor performance. Simulations show that these models qualitatively reproduce the key aspects of the mammalian cochlea, namely, amplification of oscillations from weak stimuli, higher quality factors, and a wider input dynamic range.
Polymers such as polyvinylidene difluoride, polypropylene and polyamide-11 show great promise for providing light-weight, flexible and fibrous piezoelectric materials that can be integrated into technical textile fabric structures for energy harvesting applications. Durability is an important parameter for the textiles and especially for functional and smart materials. This research work provides an insight on the piezoelectric behaviour of polypropylene, polyamide-11 and polyvinylidene difluoride in terms of peak-to-peak voltage generation capabilities after washing at 40°C with the addition of detergent as described in test method BS EN ISO 105-C06:2010. It was observed that the peak-to-peak voltage generated by polypropylene monofilaments retained similar values with only slight differences, while the monofilaments of polyvinylidene difluoride and polyamide-11 showed higher peak-to-peak voltage generation after washing. These changes have been explained using the changes in the crystallinity and phase, as determined by Fourier transform infrared spectroscopy analysis.
The equi-biaxial fatigue behaviour of silicone-based magnetorheological elastomers in external magnetic fields was studied. Wöhler curves relating fatigue life to stress amplitude and dynamic stored energy for magnetorheological elastomers with a range of magnetic particle contents were derived. It was found that the fatigue life of magnetorheological elastomers in magnetic fields was higher than that without magnetic fields. Under constant stress amplitude conditions, the presence of magnetic fields resulted in longer times for the samples to undergo large deformations and thus complex modulus (E*) decreased at a slower rate during the fatigue process, especially for low stress amplitudes. Magnetorheological elastomer samples tested in the presence of magnetic fields reached limiting values of E* at failure ranging from 1.28 to 1.44 MPa. The application of magnetic fields was found to have negligible influence on the damping loss factor of magnetorheological elastomers containing various volume fractions of carbonyl iron particles.
The use of shape memory alloys as a rebar in concrete structures has been receiving increasing attention among researchers. In this study, it is intended to evaluate the application of superelastic Nitinol in reducing the damage to the coupling beams and opening corners within a concrete shear wall. Abaqus finite element software was utilized to develop three verified coupled shear wall models. First, a model without diagonal and shape memory alloy rebars is developed to assess conventional shear walls with openings. Steel diagonal rebars are embedded in the coupling beams of the second model, and shape memory alloy diagonal rebars are embedded in the coupling beams of the third model. Shape memory alloy is also implemented in the opening corners of the third model. All models are subjected to cyclic loading to evaluate the concrete damage. Results indicated that the diagonal rebars reduced damage to the coupling beam and opening corners. The damages were the least when shape memory alloy diagonal rebars are utilized in the model. The superelastic behavior of the shape memory alloy also reduced permanent displacement of the shear wall subjected to substantial lateral loadings.
Bistable oscillator has been recognized as an effective means by which to improve the linear resonant energy harvesting performance for its unique double-well restoring force potential. As oscillating in a high-energy orbit, the oscillator should be located at a distance from one stable to the other with a much higher velocity or acceleration. However, the vibration level in environment would be too low to provide the oscillator with a larger velocity to overcome the potential well barrier. This article is focused on the enhancement of a bistable piezoelectric oscillator with an elastic magnifier for high-energy orbit harvesting. The elastic magnifier positioned between the bistable piezoelectric oscillator and the base is to amplify the base vibration level in order to provide the bistable piezoelectric harvester with large movement. A 2-degree-of-freedom nonlinear lumped-parameter model of the bistable piezoelectric harvester with an elastic magnifier (bistable piezoelectric harvester + elastic magnifier) is derived to exhibit the large-amplitude periodic oscillation behaviors. With the comparison of the electromechanical responses obtained from theory and experiment, the results show that the output displacement, tip velocity, and harvesting voltage under open-circuit condition of the bistable piezoelectric harvester + elastic magnifier configuration are 15 mm, 1500 mm s–1, and 13 V, respectively, while those of the only bistable piezoelectric harvester configuration are 1 mm, 120 mm s–1, and 2 V under the excitation level of 8.69 m s–2 and frequency of 16 Hz. It is verified that the bistable piezoelectric harvester with an elastic magnifier can generate larger output performance than that of the bistable piezoelectric harvester without elastic magnifier at several excitation frequencies and levels.
The botryoid hybrid nano-carbon materials were incorporated into cementitious materials to develop a new type of self-sensing cementitious composites, and then the mechanical, electrically conductive, and piezoresistive behaviors of the developed self-sensing cementitious composites with botryoid hybrid nano-carbon materials were comprehensively investigated. Moreover, the modification mechanisms of botryoid hybrid nano-carbon materials to cementitious materials were also explored. The experimental results show that the compressive strength and the elasticity modulus of the self-sensing cementitious composites botryoid hybrid nano-carbon materials decrease with the increase in the botryoid hybrid nano-carbon material content, while the Poisson’s ratio does the opposite. The percolation threshold zone of the self-sensing cementitious composites botryoid hybrid nano-carbon materials is from 2.28 to 3.85 vol.%. The optimal content of botryoid hybrid nano-carbon materials is 3.38 vol.% for piezoresistivity of the self-sensing cementitious composites botryoid hybrid nano-carbon materials. The amplitude of fractional change in resistivity goes up to 70.4% and 28.9%, respectively, under the monotonic compressive loading to failure and under the repeated compressive loading within elastic regime. The piezoresistive stress/strain sensitivity reaches (3.04%/MPa)/354.28 within elastic regime. The effective modification of botryoid hybrid nano-carbon materials to electrically conductive and piezoresistive properties of cementitious materials at such low content is attributed to their botryoid structures, which are beneficial for the dispersion of botryoid hybrid nano-carbon materials and the formation of conductive network in cementitious materials. The use of botryoid hybrid nano-carbon materials provides a new bottom–up design and fabrication approach for nano-engineering multifunctional cementitious composites.
Bistable generator for vibration energy harvesting is one of the most promising solutions to reach practically enhanced performance. Due to the buckled–spring–mass–specific behavior, the deformation of the piezoelectric transducer is nonlinearly dependent on the displacement, especially in the inter-well motion case. An analytical model is developed using harmonic balance analysis for the buckled–spring–mass generator architecture. Contrary to the usual method, a special doubled frequency voltage solution in the inter-well motion case is assumed in harmonic balance analysis to obtain an accurate predictive model, which is validated by experimental results. The influence of five critical parameters on the performance is thoroughly discussed. Design rules are then deduced: low damping ratio, properly high coupling level, matched load, optimal buckling level, and low characteristic frequency are required to get optimal performance in the inter-well motion case. Besides, we show some interesting results about the parameter optimization study.
This article presents a nonlinear parametric model of force amplification ratio and an electromechanical model to couple the deformable frame with the piezoelectric stack in order to promote high-efficiency energy harvesting from human walking locomotion. Two improved frames (Frames I and II) are developed based on the modeling and simulation results. The experiments verified these modeling and simulation results that improved frames demonstrate a higher amplification ratio (8.4 for Frame II and 8.0 for Frame I), in comparison to the original frame (3.5). The experiments also verified these results that under the simulated walking excitation (100 N, ~1.4 Hz), the piezoelectric stack coupled with Frame II produces 4.1 mJ energy during each step, higher than the stand-alone stack (0.16 mJ) and the stack with the original frame (0.64 mJ). Note that the energy conversion efficiency of Frame II (9.1%) is even lower than that of Frame I (10.7%) and the stand-alone stack (25.8%). As such, this article concludes that the energy output of the piezoelectric stack depends largely on the frame deformations in terms of seven coupled frame parameters, instead of only one frame parameter (tilt angle), as commonly used in the referenced literature.
This article identifies and studies key parameters that characterize a horizontal diamagnetic levitation mechanism–based low frequency vibration energy harvester with the aim of enhancing performance metrics such as efficiency and volume figure of merit. The horizontal diamagnetic levitation mechanism comprises three permanent magnets and two diamagnetic plates. Two of the magnets, lifting magnets, are placed co-axially at a distance such that each attracts a centrally located magnet, floating magnet, to balance its weight. This floating magnet is flanked closely by two diamagnetic plates which stabilize the levitation in the axial direction. The influence of the geometry of the floating magnet, the lifting magnet, and the diamagnetic plate is parametrically studied to quantify their effects on the size, stability of the levitation mechanism, and the resonant frequency of the floating magnet. For vibration energy harvesting using the horizontal diamagnetic levitation mechanism, a coil geometry and eddy current damping are critically discussed. Based on the analysis, an efficient experimental system is setup which showed a softening frequency response with an average system efficiency of 25.8% and a volume figure of merit of 0.23% when excited at a root mean square acceleration of 0.0546 m/s2 and at a frequency of 1.9 Hz.
This work reports an input-dependent performance study of a nonlinear piezoelectric energy harvester with introduced magnetic interaction. The performances of the novel harvester with two external magnet arrays (I and II) are compared. Array II that has symmetric magnetic force yields better voltage output under frequency sweep test. As such, the energy harvesting capacity with Array II is performed under two vibration inputs (I and II). Under excitation Input I with periodic varying frequency, experimental results show that the nonlinear piezoelectric harvester outperforms its linear counterpart (no magnetic interaction) at alternating input bandwidths. A 104.5% improvement of root mean square voltage output (318.2% of power output) is obtained under excitation of 0.334g (root mean square) and bandwidth of 7 Hz. No advantage is observed under Input II consisting of one principal and finite non-principal components. However, detailed study indicates that the amplitude of the principal component and the amplitude ratio of the non-principal components to the principal component in Input II are essential to maintain large-amplitude periodic motion. Our work provides useful insights into the design, characterization, and application of nonlinear energy harvesters with external magnetic forces based on a priori knowledge of input.
Multi-layer piezoelectric stack is a transducer stacked by numerous thin piezo layers which can convert an electrical energy into a mechanical energy in transmitter mode (actuators or vibrators) and can also convert a mechanical energy into an electrical energy in receiver mode (sensors and energy harvesters). Modelling vibrations of multi-layer piezoelectric stack plays a key role in design, fabrication and optimization of many multi-layer piezoelectric stack–based applications. In this article, a simplified transfer matrix of multi-layer piezoelectric stack, which considers the whole multi-layer piezoelectric stack to be an equivalent homogenous bulk, is proposed and formulated to model multi-layer piezoelectric stack–based vibration. When compared with a direct analytical method, the proposed transfer matrix greatly facilitates derivation of analytical solutions or direct calculations when multi-layer piezoelectric stack is stacked with other structures. Compared with using the transfer matrix proposed in the literature, which is subjected to individual piezo layer in multi-layer piezoelectric stack, the proposed simplified transfer matrix contributes to a much simpler form of analytical solution and greatly reduces the computational effort. Case studies have been carried out, which validate the effectiveness of the proposed simplified transfer matrix of multi-layer piezoelectric stack in both transmitter mode and receiver mode.
A layer-wise finite element approach is adopted to analyse the hollow cylindrical shell made of functionally graded material with piezoelectric rings as sensor/actuator, under dynamic load. The mechanical properties of the substrate are regulated by volume fraction as a function of radial coordinate. The thickness of functionally graded material shell and piezo-rings is divided into mathematical sub-layers and then the general layer-wise laminate theory is formulated through introducing piecewise continuous approximations across the thickness, accounting for any discontinuity in derivatives of the displacement at the interface between the ring and cylinder. The virtual work statement including structural and electrical potential energies yields the three-dimensional governing equations which are reduced to two-dimensional differential equations, using layer-wise method. For axisymmetric case, the resulted equations are solved with one-dimensional finite element method in the axial direction. By assembling stiffness and mass matrices, the required stress and displacement continuities at each interface and between the two adjacent elements are forced. The results for free vibration and static loading are applied to study the convergence and verified by comparing them to solutions of similar existing problems. The induced deformation by piezoelectric actuators as well as the effect of rings on functionally graded material shell is investigated.
This article aims at investigating the filtering abilities of periodic structures with nonlinear interconnected synchronized switch damping on inductor electrical networks. Periodic structures without electrical networks themselves naturally have the function of filtering since the structure response breaks into pass bands and stop bands when the structure is excited by an external force with multiple or varying frequencies. Introduction of linear electrical networks in the periodic structure makes stop bands of the structure wider than that of the structure without electrical networks. However, nonlinear piezoelectric electrical networks may have better effect on the mechanical wave attenuation than linear piezoelectric electrical networks in terms of frequency band. Therefore, this article proposes a piezoelectric periodic structure with nonlinear interconnected synchronized switch damping on short-circuit/synchronized switch damping on inductor electrical network. A transfer matrix formulation including the interconnected electrical network is also proposed for deriving the characteristics of elastic wave propagation. The results show that the proposed technique permits enhancing the damping abilities in particular frequency bands compared to electrically independent periodic cells, which, combined with structural tailoring, would allow achieving high damping performance.
Dielectric elastomers belong to a larger group of materials, the so-called electroactive polymers, which have the capability of transforming electric energy to mechanical energy through deformation. VHB 4910 is one of the most popular materials for applications of dielectric elastomers and therefore one of the most investigated. This paper includes a new micromechanically motivated constitutive model for dielectric elastomers that incorporates the nearly incompressible and viscous time-dependent behaviour often found in this type of material. A non-affine microsphere framework is used to transform the microscopic constitutive model to a macroscopic continuum counterpart. Furthermore the model is calibrated, through both homogeneous deformation examples and more complex finite element analysis, to VHB 4910. The model is able to capture both the purely elastic, the viscoelastic and the electro-viscoelastic properties of the elastomer and demonstrates the power and applicability of the electromechanically coupled microsphere framework.
Embedded and surface bonded piezoelectric wafers have been widely used for control and monitoring purposes. Several nondestructive evaluation and structural health monitoring techniques, such as electromechanical impedance and wave propagation–based techniques, utilize piezoelectric wafers in either active or passive manner to interrogate the host structure. The basis of all these techniques is the energy transfer between the piezoelectric wafer and the host structure which takes place through an adhesive bonding layer. In this article, the high-frequency dynamic response of a coupled piezoelectric-beam system is modeled including the adhesive bonding layer in between. A new three-layer spectral element is developed for this purpose. The formulation of this new element takes into account axial and shear deformations, in addition to rotary inertia effects in all three layers. The capabilities of the proposed model are demonstrated through several numerical examples, where the effects of bonding layer geometric and material characteristics on dispersion relations and damage detection capabilities are discussed. The results highlight the importance of accounting for the adhesive bonding layer in piezoelectric-structure interaction models, especially when the high-frequency dynamic response is of interest.
The optimal number and location of control devices not only play a major role in an effective structural control system but also lead to a cost-effective design. This article presents a multi-objective optimization method based on a new genetic algorithm for simultaneous finding of the optimal number and placement of actuators and magnetorheological dampers, in active and semi-active vibration control of structures. The proposed strategy considers three objective functions to be minimized through optimization, including peak inter-storey drift ratio, peak acceleration and peak base shear force to make sure both human comfort and safety of the structure are guaranteed. Also, by choosing a pre-defined level of performance on dynamic responses of a structure, the designer can decide on decreasing or increasing the number of control devices in a systematic way and minimize the control cost. The approach is then validated through a nonlinear 20-storey benchmark problem. The results from active control system show how a problem that was initially solved with 25 actuators can be solved with less than a quarter of those actuators, having similar results in terms of aforementioned indices. The optimal distribution of different numbers of magnetorheological dampers in the same benchmark building is also studied in this article and compared to those obtained from actuators. Due to highly nonlinear behaviour of these devices, and also the complexity of the under-study benchmark structure, few reported researches have been conducted in this area. Also, the comparison between optimal places of active and semi-active control devices in the same structure has hitherto not been reported in the open literature.
The work in this study explores the excitation of high-frequency dynamic instabilities to enhance the performance of a strongly nonlinear vibration-based energy harvesting system subject to repeated impulsive excitations. These high-fraequency instabilities arise from transient resonance captures (TRCs) in the damped dynamics of the system, leading to large-amplitude oscillations in the mechanical system. Under proper forcing conditions, these high-frequency instabilities can be sustained. The primary system is composed of a grounded, weakly damped linear oscillator, which is directly subjected to impulsive forcing. A light-weight, damped nonlinear oscillator (nonlinear energy sink, NES) is coupled to the primary system using electromechanical coupling elements and strongly nonlinear stiffness elements. The essential (nonlinearizable) stiffness nonlinearity arises from geometric and kinematic effects resulting from the traverse deflection of a piano wire coupling the two oscillators. The electromechanical coupling is composed of a neodymium magnet and inductance coil, which harvests the energy in the mechanical system and transfers it to the electrical system which, in this present case, is composed of a simple resistive element. The energy dissipated in the circuit is inferred as a measure of energy harvesting capability. The large-amplitude TRCs result in strong, nearly irreversible energy transfer from the primary system to the NES, where the harvesting elements work to convert the mechanical energy to electrical energy. The primary goal of this work is to numerically and experimentally demonstrate the efficacy of inducing sustained high-frequency dynamic instability in a system of mechanical oscillators to achieve enhanced vibration energy harvesting performance. This work is a continuation of a companion paper (Remick K, Quinn D, McFarland D, et al. (2015) Journal of Sound and Vibration Final Publication) where vibration energy harvesting of the same system subject to single impulsive excitation is studied.
Nonlinear characterizations of an autoparametric vibration-based energy harvester are investigated. The harvester consists of a base structure subjected to an external excitation and a cantilever beam with a tip mass. Two piezoelectric sheets bounded to both sides of the cantilever beam are used to harvest the energy. The governing equations accounting for the coupled effects of the base vibration, the response of the cantilever beam and the generated power are derived. Approximate analysis of the simplified governing equations is then performed by the method of multiple scales. The usefulness of this approach is demonstrated by deriving analytical expressions for the global frequency and damping ratio of the cantilever beam. Their dependence on the electrical load resistance is quantified. Analytical expressions for the amplitudes of the base displacement and the displacement of the tip mass are derived. An expression that relates the output power to the load resistance, global damping, and displacement of the tip mass is derived. The effects of the external force and electric load resistance on the nonlinear responses of the system are determined. The results show different responses for different operational electric loads. The broadening of the excitation regime over which energy can be harvested is analyzed. The effects of the load resistance on the types of bifurcations near resonance are determined.
In the modelling of thin-sheet piezoelectric actuators the effect of bending of the actuator itself is usually ignored. The current paper presents a model of a surface bonded piezoelectric actuator subjected to electric loading, which contains both the axial and bending deformations. The static electromechanical response of the actuator is studied under different mechanical and geometrical conditions to evaluate the effect of bending. An imperfectly bonded interface is proposed to simulate debonding and to study its effect on the actuation process. The problem is formulated as integral equations in terms of the interfacial shear and normal stresses, which are solved by using Chebyshev polynomials. Based on the solution, the effect of bending of the actuator upon load transfer is analysed. Illustrative examples are presented to show the effect of the material property, the geometry and the interfacial debonding on the response of the integrated structure.
Analysis of the load versus separation concerning electrorheological fluids between electrodes with application of a constant potential difference in squeeze mode was performed. From the result of the simulation, it was found that there are three forms as follows: an approaching state in which an upper electrode approaches its adjacent particle, compressive deformation of the particles, and buckling deformation and rupture of chain formation while the electrode approaches the outermost particle. From a comparison of the simulation result with the experimental result, the experimental result and simulation result are similar in form to each other. The array of the chain between the electrodes, just after the electric field is applied, although the load is not applied on the electrode, is composed of a group of strung-close particles and the electrodes that are out of contact with respect to the neighboring particles; after the load is applied, the spacing between the electrode and the particle becomes narrow, and the chain collapses due to buckling without each touching the other.
Nonlinear forced vibration of a magneto-electro-elastic rectangular plate is studied based on the first-order shear deformation theory. The excitation force is harmonic, the boundary condition is considered to be immovable simply supported, and the plate rests on a viscoelastic foundation. The electric and magnetic fields are assumed to be applied along the thickness direction, and different magneto-electric boundary conditions are considered. Magneto-electric behavior of the plate is modeled using Gauss’ laws for electrostatics and magnetostatics. The system is discretized using Galerkin method and then multiple time scale method is used to solve the obtained equation analytically. As a result, closed-form solutions are obtained for the frequency responses of the plate in the primary and subharmonic resonances. Time history and phase portraits of the plate are also obtained numerically. Some examples are carried out to validate the proposed model and to investigate the effects of electric and magnetic potentials, material properties, and plate size on the frequency responses of these smart multiphase plates.
A new explicit, two-dimensional plane strain, time domain spectral finite element is developed to enhance the simulation of guided waves generated by active piezoelectric sensors in laminated composite strips. A new multi-field layerwise theory is formulated for composite laminates with piezoelectric actuators and sensors which captures straight-crested symmetric and anti-symmetric Lamb waves. Third-order Hermite polynomial splines are employed for the approximation of displacements and electric potential through the thickness, and the piezoelectric actuators and sensors are physically modeled through coupled electromechanical governing equations. A multi-node finite element formulation is presented entailing displacement and electric degrees of freedom at nodes collocated with Gauss–Lobatto–Legendre integration points. Stiffness, diagonal mass, piezoelectric, and electric permittivity matrices are described, and the coupled transient electromechanical response is predicted by a properly formulated explicit time integration scheme. The numerical results of a nine-node time domain spectral finite element are correlated with the reported numerical results and with measured Lamb wave data generated by piezoceramic active sensor pairs in carbon/epoxy plate strips. Important effects introduced by the stiffness and mass of the active actuator/sensor system on Lamb wave propagation are captured by the developed finite element and quantified.
Random response of dielectric elastomer balloon disturbed by electrical or mechanical fluctuation is analytically investigated in this article. The stochastic differential equation governing the oscillating behavior around the stable equilibrium position is first derived by introducing the translation transformation. The stationary joint probability density about the disturbing stretch ratio and its rate of change is analytically established by adopting the stochastic averaging of energy envelope; the statistics quantities, such as the mean value and the standard deviation of the disturbing stretch ratio, are then subsequently calculated. Two special cases, the first case with only voltage fluctuation and the second one with only pressure variation, are discussed in detail, and the random response properties are summarized. The accuracy of the analytical solution is verified by comparing with the Monte Carlo simulation for the perturbation with weak intensity, and the valid ranges for the mean voltage and pressure are illustrated. This work provides an effective technique to evaluate the detection precision of new type of sensors based on the dielectric elastomer.
A novel configuration of an energy harvester for local actuation and sensing devices using limit cycle oscillations has been modeled, designed and tested. A wing section has been designed with two trailing-edge free-floating flaps. A free-floating flap is a flap that can freely rotate around a hinge axis and is driven by trailing edge tabs. In the rotational axis of each flap a generator is mounted that converts the vibrational energy into electricity. It has been demonstrated numerically how a simple electronic system can be used to keep such a system at stable limit cycle oscillations by varying the resistance in the electric circuit. Additionally, it was shown that the stability of the system is coupled to the charge level of the battery, with increasing charge level leading to a less stable system. The system has been manufactured and tested in the Open Jet Wind Tunnel Facility of the Technical University Delft. The numerical results could be validated successfully and voltage generation could be demonstrated at cost of a decrease in lift of 2%.
In this article, a new hybrid rotary-translational vibration energy harvester design is investigated. The design employs two coils which increase the peak output power by ~34% compared with a previous single-coil design. Peak power is shown to increase from 167 to 223 mW under a root-mean-square host acceleration of 5.4 Hz and 500 milli-g (where g = 9.81 m/s2). The measured peak power density of the double-coil device is 7 mW/cm3, compared to 5.5 mW/cm3 for the original single-coil variant. The average power increased from 35 to 39.7 mW. Further to this, the device is made more robust through the inclusion of low loss wear resistant elastomer, and the effects of the wear-mitigation measures are examined.
A method is offered for the prediction of the electromechanical field in periodic piezoelectric composites with embedded semi-infinite cracks. It is based on the knowledge of the K-field in piezoelectric materials in which the material constants are replaced by the effective moduli of the piezoelectric composite. In addition to the existing semi-infinite crack, the proposed method can analyze localized inhomogeneities near the crack tip. The established effective K-field is applied at the boundaries of a rectangular domain that should be sufficiently far away from the crack tip and the other inhomogeneities. The proposed approach is based on the combined utilization of a micromechanical analysis, the representative cell method and the higher-order theory. The micromechanical analysis establishes the effective electromechanical constants of the piezoelectric composite, and the representative cell method reduces the periodic composite that is discretized into numerous identical cells to a single cell problem in the Fourier transform domain. The governing equations and constitutive relations that are formulated in this single cell are solved by employing the higher-order theory where discretization into subcells is employed. The inverse of the Fourier transform provides the electromechanical field at any point in the composite. The proposed approach is verified for crack fronts that are parallel and perpendicular to the poling direction (axis of symmetry). Applications are given for a cracked porous piezoelectric material, cracks that have been arrested by cavities and for a periodically bilayered composite with a semi-infinite crack.
Predictive design to control the geometric configurations of a novel sub-wavelength scale energy scavenger to harvest energy at lower sonic frequencies (<~1 kHz) is presented. In this work, defying the conventional physics of structural resonance at lower frequencies, the traditional solution of large size harvesters is argued by adopting the physics of local resonance in designing the energy harvesters with sub-wavelength scale foot print. It is reported that during the local resonance, the wave energy passing through the acoustoelastic sonic crystals remains trapped within the soft matrix as the dynamic strain energy; hence, it is proposed to harvest that same trapped energy by strategically embedding the smart materials inside the matrix, capable of electromechanical transduction (e.g. lead zirconate titanate). The proposed acoustoelastic sonic crystal model was able to harvest energies at four different frequencies within <~1 kHz with possible loading conditions and respective lead zirconate titanate placements. Through experimental validation, a particular acoustoelastic sonic crystal model with sub-wavelength geometry (~3.65 cm) was investigated. Against 10 k resistive load, a maximum power density of ~92.4 µW/cm2 was achieved. It is further reported that the geometrical model of the proposed harvesters can be predictively altered while filtering the acoustic waves and harvest the energy, simultaneously.
In this article, freely vibrating multilayered piezoelectric plates are analyzed through a set of adaptive global piecewise-smooth functions along with governing differential equations and associated boundary conditions, which are consistently derived from the classical theorem of virtual displacements. The analysis demonstrates the capability of the adaptive global piecewise-smooth functions to treat any multilayered plate as if it were made up of a single layer even in the presence of multiphysics analyses such as piezoelectric layers. The relevant model is essentially two-dimensional because it is based on an expansion through the thickness of the plate aimed at modeling a three-dimensional dynamical behavior. In order to demonstrate the effectiveness of the model, all the results are compared to exact three-dimensional results; these latter are extracted through a three-dimensional model based on a transfer matrix technique whose numerical stability is achieved using scaled electric potentials. The exact graphical results are herein illustrated, thus showing both the effectiveness of using weighted electric potentials and the capability of adaptive global piecewise-smooth functions to converge at exact results through a minimum computational effort.
In recent years, the aerospace and automotive industries experienced a growing interest in the implementation of structural members’ bonding using adhesive films. Adhesive joints contribute to manufacturing savings and are advantageous from a structural prospective as they provide a relatively uniform stress distribution at the bonded region, hence reducing local stress concentration. Regretfully, the adhesive bonds’ strength is vulnerable to the presence of defects which limits their use for structural purposes. A particularly dangerous class of defects—generically referred to as "kissing bond"—consists of localized imperfections that do not provide adequate bonding between the adherent and the adhesive yet maintaining the two surfaces in contact. Past attempts at detecting kissing bonds using ultrasonics were only marginally successful stressing the need to search for more reliable methods. This article describes a novel, in situ, impedance-based method for bond-line degradation detection during the service life of a structure. The method relies on piezoelectric transducers embedded within the adhesive bond-line and actuated by a low-voltage harmonic signal. The article focuses on deriving an approximate analytical model describing the dynamic behavior of the actuator embedded in the homogeneous bond-line. A study describing the sensitivity of the electro-mechanical response of the transducer to the changes in various bond-line properties and adhesion conditions is also presented.
Elastic metamaterials, which have huge potential in wave guiding and attenuation applications, can be built from structures with periodic piezoelectric patch arrays. Passive shunts offer the benefits of simplicity and low cost. In this paper, the effects of the magnitude and phase angle of the shunt impedance on the attenuation constant of a beam with periodic piezoelectric patch arrays were studied in order to determine the optimal shunt that produces the widest and most effective band gaps. The attenuation constants were found to be large when the phase angle is
The finite element method is proposed to analyze coated fiber composites with piezoelectric and piezomagnetic phases. The computational homogenization technique is applied for fiber composites with magnetoelectroelastic properties to determine effective material parameters. The evolution of the magnetoelectroelastic fields at the macroscopic level is resolved through the incorporation of the microstructural response. The microstructural analyses are performed on the representative volume element, where essential physical geometrical information about the microstructural components is included. Circular cross section of fibers is considered in numerical analyses. A thin coating layer is considered on the surface of the piezoelectric fiber which is embedded in the piezomagnetic matrix. Influence of the coating layer on the effective material properties is analyzed.
The work gives a theoretical and experimental contribution to the problem of smart materials connected to double curved flexible shells. In the theoretical part the finite element modeling of a double curved flexible shell with a piezoelectric fiber patch with interdigitated electrodes (IDEs) is presented. The developed element is based on a purely mechanical eight-node isoparametric layered element for a double curved shell, utilizing first-order shear deformation theory. The electromechanical coupling of piezoelectric material is added to all elements, but can also be excluded by setting the piezoelectric material properties to zero. The electrical field applied via the IDEs is aligned with the piezoelectric fibers, and hence the direct d33 piezoelectric constant is utilized for the electromechanical coupling. The dynamic performance of a shell with a microfiber composite (MFC) patch is investigated using frequency response functions (FRFs) obtained via external impact test as well as internal random signal excitation using the MCF patch as an actuator. The experiments are used to validate the numerical results. Good agreement between theory and experiments is obtained in a large frequency range. Discrepancies and insights into optimal modeling frequency range and non-linear behavior are discussed.
In electromechanical measurement techniques, passive transducers and passive electrical networks often interact. In some applications, continua are considered as part of the system, where fields are formed and waves are propagated. In this article, networks, continua, and electromechanical transducers feature sufficient amplitude linear behavior in their environment (e.g. for operation around a bias) and are reciprocal. In addition, all elements of the system have constant parameters during the measurement. Then, the skillful application of the inherent reciprocity of these systems can lead to surprisingly useful benefits. This is shown by actual examples from metrology. The examples include the precise determination of transduction coefficients. It is also shown how the linearity of a system is checked by utilizing reciprocity relations. Although the facts of the matter are well known, its potential is often overlooked or disregarded in measurement techniques.
The purpose of this work is to demonstrate a new simple stand-alone method of characterizing the impedance of a pyroelectric cell. This method utilizes a pyroelectric single pole low-pass filter technique. Utilizing the properties of a pyroelectric single pole low-pass filter technique, a known input voltage is applied and using simple equations, capacitance Cp and resistance Rp at a frequency range of 1 mHz to 1 Hz can be calculated. For verification purposes, an LCR meter and an impedance analyzer were exploited at 10 and 100 Hz, respectively. Results showed that Rp values for two materials, lead zirconate titanate-5A and polyvinylidene difluoride, were within 8%, and Cp values were within 7.5%. In addition, to verify the importance of the impedance values in energy harvesting applications, output power was measured with varying impedance values. The optimal load resistances for polyvinylidene difluoride and lead zirconate titanate-5A were consistent with the measured pyroelectric impedance at the particular heat range with 10.9% and 1.4%, respectively. The pyroelectric single pole low-pass filter method presented here demonstrates that for pyroelectric materials the impedance depends on two major factors: (1) average working temperature and (2) the heating rate. Neglecting these two factors can result in inefficient and unpredictable behavior of pyroelectric materials when used in energy harvesting applications.
The use of piezoelectric materials for vibration energy harvesting at low frequencies is challenging and requires innovative structural design. Here, a flexible longitudinal zigzag structure is developed to enhance energy harvesting at low-frequency ambient vibrations. The proposed structure is composed of orthogonal beams which enable vibration energy harvesting in two directions. A theoretical model based on Euler–Bernoulli beam theory is formulated to study the dynamic response of the structure under free vibrations. The free vibration analysis demonstrates that low operating frequencies can be obtained by increasing the number of, and/or the length of, beams in the proposed structure. To validate the accuracy of the developed theoretical model, finite element analysis is performed using ANSYS. On verification of the model’s accuracy, the piezoelectric effect of the active beams is considered in the model to evaluate the energy harvesting performance of the proposed flexible longitudinal zigzag structure. Numerical results demonstrate that the output voltage and the working frequency of these energy harvesting structures can be tailored through simply altering the number of beams. Overall, the results indicate that the proposed structure is capable of efficient energy conversion at low frequencies, which makes them suitable for a wide range of working conditions.
This article presents a novel piezoelectric energy-harvesting device. Different from the existing designs in the literature, the proposed device is based on the principle of nonlinear energy sink in order to achieve simultaneous broadband energy harvesting from the nonlinear energy sink and vibration suppression for the primary structure. First, the concept of the proposed design is described. Subsequently, system modeling and parameter identification are addressed. The performance of the apparatus under transient responses is examined through both numerical simulation and experimental study. The results show that the proposed apparatus behaves similarly as the nonlinear energy sink with the following features: 1:1 resonance, targeted energy transfer, initial energy dependence, and so on. Broadband voltage output is achieved when the nonlinear energy sink is activated.
Throughout the ages, ensuring structural safety has always been a vital task as civil infrastructures deteriorate due to the surrounding environment with time. Although various non-destructive techniques exist nowadays for maintaining the structural integrity, most of the techniques require expensive equipment with highly trained experts. In addition, onsite techniques may require a downtime period of the structure, causing inconvenience for the public. The purpose of this study is to introduce a cost-effective, impedance-based health monitoring approach using the electromechanical impedance technique. Since one device with a piezoelectric material is used to monitor a single area, this can be extremely costly when covering large areas such as bridges and buildings. To overcome this problem, a technique is introduced in this study for one device to monitor multiple areas, significantly reducing the equipment cost when covering large areas.
The high-frequency nature of impedance-based structural health monitoring makes the utilization of impedance signature for model-based damage characterization a challenging problem. In this study, a novel damage characterization approach that utilizes impedance signature measured with a single piezoelectric wafer is developed. Length-varying spectral elements are introduced to minimize the total number of elements required to describe the system, along with the number of damage characterization parameters. Several objective function definitions are studied and their behaviour with respect to each damage parameter is investigated. It has been found that an objective function definition based on the frequency shift in impedance peaks is the most effective definition compared to root mean square deviation and correlation-based objective functions. A novel damage localization method, referred to as sine-fit localization method, is developed based on the underlying periodic behaviour of impedance peak shifts as a function of damage location. The sine-fit localization method is integrated with gradient descend method in a two-stage optimization algorithm for damage characterization. The developed algorithm is capable of solving the ill-posed problem of damage characterization with few iterations and small number of objective function evaluations, which makes it computationally very efficient.
Recent technological advancements in the efficiency of microprocessors, sensors, and other digital logic systems have increased research effort in vibration energy harvesting, where trace amounts of energy are scavenged from the ambient environment to provide power. Due to the complexity and nonlinearity of most vibration energy harvesting systems, existing research has relied primarily on numerical and finite element methods for harvester design and validation. Although these methods are useful, a vetted analytical model provides intuitive understanding of the governing dynamics and is useful for obtaining rough calculations when designing vibration energy harvesting systems. In this article, an analytical framework for linear electromechanical transducer modeling is developed into the coupled electromechanical model; a transfer function characterizing the dynamics of second-order VEH systems, which includes inputs for mechanical and electrical domain lumped parameters as complex impedances. The coupled electromechanical model transfer function is validated against frequency sweep data from a linear vibration energy harvesting experimental setup. The experimental setup demonstrated good correlation with the coupled electromechanical model, with not more than 0.9% error in natural frequency overall, 6% error in damping ratio for purely resistive loads, and 11% for reactive loads.
Piezoelectric cantilevers are widely used in vibration energy harvesting. Simple cantilever-based harvesters are mostly unidirectional. In this article, we develop a cantilever-pendulum system that can harvest vibratory energy of excitations from an arbitrary direction. The new design consists of a traditional piezoelectric cantilever with a pendulum attached to the tip. It is shown analytically and experimentally that with proper parametric combination this system can induce modal energy interchange between beam vibration and pendulum motions due to 1:2 internal resonance, which ultimately yields multi-directional energy harvesting by a single cantilever. The underlying mechanisms of this design are analyzed in detail.
An experimental and computational comparison of the structural and electromechanical coupling properties of composite beams with surface-mounted and embedded piezoelectric disks shows that the embedded sensors tend to have higher electromechanical coupling coefficients due to improved strain transfer between the transducer and host material. Experimental testing of fiber–epoxy composite beams with embedded and surface-mounted piezoelectric disks under quasi-static three-point bending tests shows that bending elastic moduli and ultimate stresses are not significantly different between these two cases, while ultimate strains are greater for the surface-mounted cases compared with the embedded cases. Electromechanical coupling decreases with increasing bending loads due to either debonding between the sensor and host structure or due to damage of the brittle piezoelectric material. Embedded sensors tend to show a smaller degradation in electromechanical coupling with increasing stress level.
Axisymmetric indentation problem of a rigid perfect electrical insulator indenter on a functionally graded piezoelectric coating bonded to a piezoelectric substrate is investigated. The electromechanical properties of the functionally graded piezoelectric coating are assumed to vary as an exponential function along the thickness direction. The technique of the Hankel integral transform is applied to reduce the indentation problem to a singular integral equation. The numerical methods are developed and applied to compute the contact pressure for a cylindrical indenter and a spherical indenter. The effects of the material property gradient on the contact pressure, contact region, indentation depth, and electrical potential are analyzed. The numerical results are also obtained for the indentation responses of three different piezoelectric substrates.
This article evaluates the amount of energy that can be extracted from a gust using an aeroelastic energy harvester composed of a flexible wing with attached piezoelectric elements. The harvester operates in a subcritical flow region. It is modeled as a linear Euler–Bernoulli beam sandwiched between two piezoceramics. The extended Hamilton’s principle is used to derive the harvester’s equations of motion and an eigenfunction expansion is used to form a three-degree-of-freedom reduced-order model. The degrees of freedom retained in the model are two flexural degrees for the in-plane and out-of-plane displacements, and a torsional degree for the rotational displacement. Wagner and Küssner functions are used to represent the unsteady aerodynamic and gust loading, respectively. The amount of energy extracted from the system is then compared for two different deterministic gust profiles, 1-COSINE and two sharp-edged gusts forming a square gust, for various magnitudes and durations. The results show that the harvester is able to extract more energy from the square gust profile, although for both profiles the harvester extracts more power after the gust has subsided.
Piezoelectric energy harvesting (PEH) systems, as a kind of electromechanically coupled system, are composed of two essential parts: the piezoelectric structure and the power conditioning interface circuit. Previous studies have shown that the energy harvesting capability of a piezoelectric generator can be greatly enhanced by up to several hundred percent by using synchronized switch harvesting on inductor (SSHI) interface circuits, the most extensively investigated family of synchronized bias-flip interface circuits. After SSHI, some other bias-flip circuit topologies, which utilize active approaches for PEH enhancement, have been proposed sporadically. Yet, how active is active enough for harvesting as much energy as possible was not clear. This paper answers this question through the generalization and derivation of existing bias-flip solutions. The study starts by analyzing the energy flow in existing featured interface circuits, including the standard energy harvesting (bridge rectifier) circuit, parallel-SSHI, series-SSHI, pre-biasing/energy injection/energy investment scheme, etc. A synchronized multiple bias-flip (SMBF) model, which generalizes the bias-flip control and summarizes the energy details in these circuits, is then proposed. Based on the topological and mathematical abstraction, the optimal bias-flip (OBF) strategy towards maximum harvesting capability is derived. A case study on the series synchronized double bias-flip (S-S2BF) circuit shows that the potential of the PEH interface circuits can be fully released by using the OBF strategy. The proposed SMBF model and OBF strategy set the theoretical foundation and provide a new insight for future circuit innovations towards more powerful PEH systems.
Piezoelectric energy harvesters have great potential for achieving inexhaustible power supply for small-scale electronic devices. However, the insufficient power-generation capability and the narrow working bandwidth of traditional energy harvesters have significantly hindered their adoption. To address these issues, we propose a nonlinear compressive-mode piezoelectric energy harvester. We embedded a multi-stage force amplification mechanism into the energy harvester, which greatly improved its power-generation capability. In this article, we describe how we first established an analytical model to study the force amplification effect. A lumped-parameter model was then built to simulate the strong nonlinear responses of the proposed energy harvester. A prototype was fabricated which demonstrated a superior power output of 30 mW under an excitation of 0.3g (
In this article, a shape memory alloy rod element is derived based on the co-rotational formulation. In the co-rotational approach, the rigid body modes are removed from the total deformations by employing a local coordinate system at element level, and hence, the major part of geometric nonlinearity is isolated. The linear shape memory alloy rod element is developed using a shape memory alloy constitutive model together with the small strain framework employed by the co-rotational approach. The one-dimensional shape memory alloy model is adopted to calculate both the pseudo-elastic response and the shape memory effects. The new formulation is exploited to perform static analysis of tensegrity structures in order to study the accuracy and robustness of the proposed element and its capability to describe the structural response of shape memory alloy devices.
For improved flexibility and conformability of piezoelectric fiber–reinforced composite actuator, it is reconstructed in a recent study by the use of short piezoelectric fibers (short piezoelectric fiber–reinforced composite) instead of continuous fibers (continuous piezoelectric fiber–reinforced composite). This modification facilitates its application in short piezoelectric fiber–reinforced composite layer form instead of continuous piezoelectric fiber–reinforced composite patch form particularly in case of host structures with highly curved boundary surfaces. But the corresponding change in actuation capability is a major issue for potential application of short piezoelectric fiber–reinforced composite that is studied in this work through the control of vibration of a functionally graded circular cylindrical shell under thermal environment. First, an arrangement of continuous piezoelectric fiber–reinforced composite actuator patches over the host shell surface is presented with an objective of controlling all modes of vibration. Next, the use of short piezoelectric fiber–reinforced composite actuator layer for similar control activity is demonstrated through an arrangement of electrode patches over its surfaces. Subsequently, an electric potential function is assumed for the consideration of electrode patches and a geometrically nonlinear coupled thermo-electro-mechanical incremental finite element model of the harmonically excited overall functionally graded shell is developed. The numerical results reveal actuation capability of short piezoelectric fiber–reinforced composite actuator layer with reference to that of the existing continuous piezoelectric fiber–reinforced composite/monolithic piezoelectric actuator patches. The effects of temperature, size of electrode patches, properties of piezoelectric fiber–reinforced composite, and functionally graded properties on the control activity of short piezoelectric fiber–reinforced composite/continuous piezoelectric fiber–reinforced composite actuator are also presented.
This article presents an analytical solution for power output from a doubly curved piezoelectric energy harvester. The energy harvester is made of an elastic core layer coupled with one or two surface-bonded piezoelectric layers. Five mechanical equations of motion together with Gauss’s equation are derived on the basis of first-order shell theory and solved simultaneously for simply supported mechanical boundary conditions. The influence of structural damping is taken into account using Rayleigh damping. The electromechanical frequency response functions that relate the power output and circuit load resistance are identified from the exact solutions. Finally, the performance of the system is analyzed extensively for different parameters such as type of energy harvester including unimorph and bimorph panel in series or parallel connections of piezoelectric layers, circuit load resistance, geometrical parameters, and material properties of core and piezoelectric layers.
This article describes the development of variable camber morphing wing, which is mainly composed of corrugated structures. The morphing wing with both leading edge and trailing edge morphing sections is proposed and the prototype model is designed by consideration of finite element structural analysis with actuation mechanisms and aerodynamic analysis. Through wind tunnel experiment with the manufactured prototype model, smooth actuation without harmful deformation under 20 m/s airflow is demonstrated. The observed deformation shape is well correlated with simulated shape by analysis. Thereby, the feasibility of the present morphing wing mechanism and design process are verified.
Vibration energy harvesting extracts energy from the environment and can mitigate reliance on battery technology in wireless sensor networks. This article presents the nonlinear responses of two multi-mass vibration energy harvesters that employ a velocity amplification effect. This amplification is achieved by momentum transfer from larger to smaller masses following impact between masses. Two systems are presented that show the evolution of multi-mass vibration energy harvester designs: (1) a simplified prototype that effectively demonstrates the basic principles of the approach and (2) an enhanced design that achieves higher power densities and a wider frequency response. Various configurations are investigated to better understand the nonlinear dynamics and how best to realise future velocity-amplified vibration energy harvesters. The frequency responses of the multi-mass harvesters show that these devices have the potential to reduce risks associated with deploying vibration energy harvester devices in wireless sensor network applications; the wide frequency response reduces the need to re-tune the harvesters following frequency variations of the source vibrations.
This work proposes a new adaptive sliding mode controller to enhance ride comfort and steering stability of automobile associated with a semi-active magneto-rheological damper. In this study, a Macpherson strut type suspension system which is widely used in light vehicles is considered. The dynamic model of the Macpherson strut with magneto-rheological damper is obtained and the governing equations are then formulated using kinematic properties of the suspension system following Lagrange’s formulation. In the formulation of the model, both the rotation of the wheel assembly and the lateral stiffness of the tire are considered to represent the nonlinear characteristic of Macpherson type suspension system. Subsequently, in order to effectively reduce unwanted vibrations, a new adaptive sliding mode controller is designed by adopting moving sliding surface instead of conventional fixed sliding surface. In order to demonstrate the effectiveness of the proposed controller, a cylindrical magneto-rheological damper is designed and manufactured on the basis of practical application conditions such as required damping force. Then, ride comfort, suspension travel, and road handling are evaluated and some benefits of the proposed controller such as enhanced ride comfort are evaluated.
During the past decades, research in self-healing materials has focused on the improvement in the mechanical properties, making stronger materials, able to bear increasing solicitations. This strategy proved to be costly and in some cases inefficient, since materials continue to fail, and maintenance costs remained high. Instead of preparing stronger materials, it is more efficient to prepare them to heal themselves, reducing repairing costs and prolonging their lifetime. Several different self-healing strategies, applied to different material classes, have been comprehensively studied. When new materials are subject of research, the attention is directed into the formulations, product processing and scale-up possibilities. Efforts to measure self-healing properties have been conducted considering the specific characteristics of each material class. The development of comprehensive service conditions allowing a unified discussion across different materials classes and the standardization of the underlying quantification methods has not been a priority so far. Until recently, the quantification of self-healing ability or efficiency was focused mostly on the macroscale evaluation, while micro and nanoscale events, responsible for the first stage in material failure, received minor attention. This work reviews the main evaluation methods developed to assess self-healing and intends to establish a route for fundamental understanding of the healing phenomena.
The investigation focuses on simultaneously optimizing the locations and thicknesses of piezoelectric curved actuators as well as transient control voltages to achieve the best performance index. A curved shell element is deduced and the nodal displacement constraint equations are used to couple the piezoelectric curved shell element and the base shell element. Then the dynamic finite element equations of the piezoelectric shell structure are formulated. Based on the optimal vibration control theory, an integrated design optimization model is proposed. The linear quadratic performance index is taken as the objective function, and the control voltages as well as the number and volume of the actuators are considered as the constraints. The design variables include not only the locations and control voltages but also the thicknesses of the piezoelectric actuators. A two-layer optimization scheme is proposed to address this optimization problem with discrete and continuous variables coexisting. Because the control voltage is transient and time-varying, the linear quadratic optimal controller is used for the optimal control voltages in the inner layer. A simulated annealing algorithm is employed to optimize the locations and thicknesses of actuators in the outside layer. Numerical examples are implemented to demonstrate the accuracy of the curved shell element, the validity of the theoretical model, and the feasibility and effectiveness of the proposed optimization scheme.
Even though it is omnipresent in nature, there has not been much research in the literature involving turbulence as an energy source for piezoelectric fluidic harvesters. In the present work, a grid-generated turbulence forcing function model which we derived previously is employed in the single degree-of-freedom electromechanical equations to find the power output and tip displacement of piezoelectric cantilever beams. Additionally, we utilize simplified, deterministic models of the turbulence forcing function to obtain closed-form expressions for the power output. These theoretical models are studied using experiments that involve separately placing a hot-wire anemometer probe and a short PVDF beam in flows where turbulence is generated by means of passive and semi-passive grids. From a parametric study of the deterministic models, we show that a white noise forcing function best mimics the experimental data. Furthermore, our parametric study of the response spectrum of a generic fluidic harvester in grid-generated turbulent flow shows that optimum power output is attained for beams placed closer to the grid with a low natural frequency and damping ratio and a large electromechanical coupling coefficient.
A space curved surface shape reconstruction algorithm is proposed for shape perception and reconstruction of flexible plate structure. First, biorthogonal strain data measured by optimal distributed Fiber Bragg grating sensor network are converted to discrete curvature data. Second, interpolation is done to achieve curvature continuity for structural deformation. Third, moving coordinate systems are established in two orthogonal directions of the orthogonal curved network on the plate surface. Then, all nodal coordinates are computed using the given boundary conditions and nodal curvature. Coordinate transformation is done for two orthogonal coordinates according to the coupling relationship. Finally, a square flexible smart Fiber Bragg grating plate is constructed by implanting fiber grating sensor network, and a visualization experimental platform is constructed. Experimental analysis and verification were done. The experimental results show that the proposed shape reconstruction algorithm has good reconstruction performance for pure bending deformation, torsional deformation, and low-frequency dynamic vibration shape.
The stability and nonlinear vibration of a NiTi shape memory alloy hybrid laminated composite panel under aerodynamic and thermal loads are investigated. The partial differential dynamic equations of the shape memory alloy hybrid laminated composite panel are derived based on the large deformation theory, the first-order piston theory of aerodynamic pressure and a simple constitutive model of shape memory alloy. Then, the general expressions of multimode discrete equations of the shape memory alloy hybrid laminated composite panel are obtained for the first time using Galerkin method. The stability of the shape memory alloy hybrid laminated composite panel is analyzed first based on the Routh–Hurwitz criteria, and the results show that the temperature and aerodynamic pressure parameter plane can be divided into a flat and stable region, a flutter region, and a buckling region, and the flat and stable region can be greatly enlarged as the shape memory alloy volume fraction increases. Meanwhile, numerical results of the dynamic equations show that the shape memory alloy hybrid laminated composite panel can produce various dynamic motions, and the bifurcation characteristics of the responses with temperature obtained by numerical method coincide well with the stability boundaries determined by analytical method.
This work presents a vibration-based electromagnetic energy harvester that relies on a mechanical motion amplification mechanism. The aim is to convert a small persistent base motion into larger oscillations in order to generate greater amounts of electric power. The device can be used in situations where a small cyclic relative motion occurs between two surfaces, and where a device can be fitted to generate energy from within. Unlike conventional amplification mechanisms that rely heavily on gears, we employ a compliant mechanism of the flextensional type for energy harvesting. Such a mechanism contains few mechanical parts and attains its mobility from the elasticity of the material, thereby reducing excessive clearance, friction, and power losses. To convert the amplified mechanical motion into electrical energy, a permanent magnet is attached to the output end of the mechanism and is designed to oscillate past a stationary coil. A quasi-static model is formulated in conjunction with a finite element model of the mechanism in order to evaluate the amplification ratio, internal stresses in the flexure joints, output voltage, and power in terms of the design parameters of the flextensional mechanism. The results are supported experimentally on a cam-driven polymer flextensional mechanism across a range of operating speeds and load resistance. A parametric study is conducted to investigate the effect of the various design parameters on the system performance. An effort is made to optimize the design parameters to achieve higher output power levels while minimizing the internal stresses generated in the mechanism.
This article focuses on developing a pneumatic artificial muscle as a variable elastic device and a magnetorheological fluid brake as a variable viscosity device and a variable friction device. We executed a throwing motion using a 2-degree-of-freedom manipulator as a case study of the control of dynamic motion. To investigate the throwing motion, we proposed the spring model of the manipulator, which includes a variable viscoelastic joint. Next, the manipulator and the spring model were extended to 2 degrees of freedom. In addition, the spring model was verified by comparing the simulation and experimental results. The simulation results reproduced the experimental results. Furthermore, we maximized the velocity of the end effector during the throwing motion by searching for adequate drive timing of the second joint in the simulation. In the simulation, hand speed was improved by releasing the second joint on the basis of the angular acceleration of the first joint. Finally, the simulation results were reproduced experimentally under the same conditions.
In this article, the design and analysis of a hybrid trailing edge control surface of an unmanned aerial vehicle are presented. The structural design was performed to increase and decrease the camber of the control surface to match selected airfoil profiles. The design was first analyzed with the help of finite element method to assess the morphing capability. The morphed control surface was then analyzed aerodynamically and comparisons with the original target profiles were made. According to the aerodynamic analyses, it was concluded that the control surface can successfully morph into target profiles with very minor changes in the target aerodynamic values while still ensuring the structural integrity and the safety of the control surface.
This article seeks to reduce the stiffness of NiTi parts from a nonporous state to that of human bone by introducing porosity. Compact bone stiffness is between 12 and 20 GPa while the currently used bone implant materials are several times stiffer. While very stiff implants and/or fixation hardware can temporarily immobilize healing bone, it also causes stress shielding of the surrounding bone and commonly results in stress concentrations at the implant or immobilization hardware’s fixation site(s). Together these processes can lead to implant or fixation hardware and/or the surrounding bone’s failure. Porous NiTi can be used to reduce the stiffness of metallic implants while also providing necessary stabilization or immobilization of the patient’s reconstructed anatomy. In this work, mechanical behavior of porous NiTi with different levels of porosity is simulated to show the relation between the stiffness and porosity level. Then porous structures are fabricated through additive manufacturing to validate the simulation results. The results indicate that stiffness can be reduced from the bulk value of 69 GPa to as low as 20.5 GPa for 58% porosity. The simulation shows that it is possible to achieve a wide range of desired stiffness by adjusting the level of porosity.
The thermo-mechanical behaviour of pseudoelastic shape memory alloy helical springs is of concern discussing stabilised and cyclic responses. Constitutive description of the shape memory alloy is based on the framework developed by Lagoudas and co-workers incorporating two modifications related to hardening and sub-loop functions designated by Bézier curves. The spring model takes into account both bending and torsion of the spring wire, thus representing geometrical non-linearities. Simplified models are explored showing that a single point in the wire cross section is enough to represent the global spring behaviour in spite of complex stress–strain distributions. The experiments are carried out considering different deflection amplitudes, frequencies and ambient temperatures, which influence the spring behaviour to different extents. The model is fitted against a calibration data set resulting in 1.3% residual standard deviation relative to the full range force. Compared to the validation data set, the errors are below 10% relative to the full range of the complex modulus. Uncertainty analysis of the model parameters using a Markov chain Monte Carlo technique shows low to high parameter correlation, and the relative uncertainties are less than ±12%. Both the heat capacity and the convection coefficient are clearly identifiable from the performed experiments.
Additive manufacturing of nickel–titanium has two distinct advantages over conventional methods. It circumvents the difficulties associated with machining of nickel–titanium and it provides a freedom-of-design that conventional processing cannot match. In this article, we analyze the effects of processing parameters on the structural and functional outcomes of selective laser melted nickel–titanium parts. Notably, we expand the parametric envelope compared to the previous studies by utilizing a higher power 300 W laser. Optimal process parameters are identified for additively manufacturing of nickel–titanium parts with verified shape memory behavior and complex structures with accurate features are fabricated.
Vibrational energy harvesting using piezoelectric cantilever beams has received significant attention over the past decade. When compared to piezoelectric cantilever-based harvesters, piezopatch energy harvesters integrated on plate-like thin structures can be a more efficient and compact option to supply electrical power for wireless structural health and condition monitoring systems. In this article, electroelastic modeling, analytical and numerical solutions, and experimental validations of piezopatch-based energy harvesting from stationary random vibrations of thin plates are presented. Electroelastic models for the series and parallel connected multiple piezopatches are given based on a distributed-parameter modeling approach for a thin host plate excited by a transverse point force. The analytical and numerical solutions for the mean power output and the mean-square shunted vibration response are then derived. The experimental measurements are carried out by employing a fully clamped thin plate with three piezopatches connected in series. It is shown that the analytical and numerical model predictions for the mean power output and the mean-square velocity response are in very good agreement with the experimental measurements. The electroelastic modeling framework and solution methods presented in this work can be used for design, performance analysis, and optimization of piezoelectric energy harvesting from stationary random vibration of thin plates.
The use of piezoelectric materials in vibration control problems has been widely investigated over the last years. The main control techniques using piezoelectric materials are the active and passive ones. In the particular case of aeroelastic control, passive piezoelectric networks have a weak capability of improving the flutter envelope. Although active systems can achieve good control performance, the potential large amount of power required for actuation is an important issue. The synchronized switch damping techniques were developed to overcome the drawbacks of passive and active control. These nonlinear techniques increase the electromechanical conversion and enhance the shunt damping. In this article, an energy flow analysis is employed to investigate the effects of two switch damping techniques on the aeroelastic behavior of a plate-like wing in two case studies. In the first one, the energy flow analysis is presented for the base excitation condition without aerodynamic influence. The working principle of switch damping techniques and the energy return phenomenon are discussed. In the second case, the energy flow analysis is employed to discuss the aeroelastic evolution and semi-passive control effects over a range of airflow speeds.
The coupling of magnetic and mechanical fields due to the constitutive behavior of a material is commonly denoted as magnetostrictive effect. The latter is only observed with large coupling coefficients in ferromagnetic materials, where coupling is caused by the rotation of the domains as a result of magnetic (Joule effect) or mechanical (Villari effect) loads. However, only a few elements (e.g. Fe, Ni, Co, and Mn) and their compositions exhibit such a behavior. In this article, the constitutive modeling of nonlinear ferromagnetic behavior under combined magnetomechanical loading as well as the finite element implementation is presented. Both physically and phenomenologically motivated constitutive models have been developed for the numerical calculation of principally different nonlinear magnetostrictive behaviors. On this basis, magnetization, strain, and stress are predicted, and the resulting effects are analyzed. The phenomenological approach covers reversible nonlinear behavior as it is observed, for example, in cobalt ferrite. Numerical simulations based on the physically motivated model focus on the calculation of hysteresis loops and the prediction of local domain orientations and residual stress going along with the magnetization process. Finally, a model for ferroelectric materials is applied in connection with the physically based ferromagnetic approach, in order to predict magnetoelectric coupling coefficients in multifunctional composite.
Nonlinearity can be used to enhance broadband rotating piezoelectric vibration energy harvesting, but how to construct a proper nonlinear rotating harvester is a challenging problem in engineering applications. This article presents a Melnikov-theory-based method to explore broadband mechanism and necessary conditions of nonlinear rotating piezoelectric vibration energy harvesting system. First, a perturbed state-space representation of nonlinear rotating energy harvesting system is built based on its dynamic model. It can be seen that bi-stability of the unperturbed nonlinear system is the physical basis of achieving broadband and low-frequency rotating energy harvesting. Second, the Melnikov function is defined to derive two necessary conditions of homoclinic bifurcation and chaotic motions. Then simulations are performed to identify the key parameters and their effects on the Melnikov conditions, including distance, rotating frequency, and excitations. It can be seen that homoclinic bifurcation and chaotic motions can occur in nonlinear rotating energy harvesting systems under single-frequency and broadband excitations. Finally, the experiments are carried out to validate the two necessary conditions. The results demonstrate that the proposed method can provide important guidelines for optimally designing nonlinear rotating piezoelectric energy harvesters in practice.
This study delves into the propagation of Love-type wave in a corrugated piezoelectric layer overlying an isotropic elastic half-space. The expression of dispersion relation has been established in a closed form for both the cases of electrically open condition and electrically short condition. The pronounced effect of various affecting parameters, namely wave number, corrugation parameter of upper boundary surface, corrugation parameter of common interface between the layer and the half-space, piezoelectric constant and dielectric constant of corrugated piezoelectric layer, undulation parameter and position parameter on the phase velocity of Love-type wave, has been remarkably traced out. In order to observe the prominent effect of these affecting parameters on the phase velocity of Love-type wave, numerical computation and graphical demonstration have been accomplished for specific type of corrugated boundary surfaces present in the layer. Moreover, comparative study has been wrapped up to reveal the latent characteristics of the problem by means of graphical illustrations for both the cases of electrically open and electrically short conditions. As a special case of the problem, it is observed that procured dispersion relation for both the cases of electrically open condition and electrically short condition is in well agreement with the classical Love wave equation.
In this work, new advances concerning the feasibility of extruded cementitious hollow tubes as containing/releasing devices for healing agents and their potential scaling up are presented. Specifically, sodium silicate and potassium silicate were evaluated as healing agents in terms of their ability to diffuse through cracks and of their ability to restore the initial mechanical properties of mortars. Their effect was investigated also in combination with the use of a hydrophobic coating applied to the inner surface of some of the hollow tubes to enhance the release of the healing agents along the crack path. A colorant was added to the sodium/potassium silicate solutions to help highlighting the fracture area covered by the healing agents, thus allowing a qualitative evaluation of the effect of the hydrophobic coating. Finally, image analysis was performed to correlate the mechanical strength/stiffness recovery to the area covered by the healing agent, as well as to the position of the tubes within the samples. On the whole, satisfactory results were obtained as far as restoration of the mechanical properties is concerned: the best performance was displayed when using cementitious hollow tube containing sodium silicate, with maximum values of bending load and stiffness recovery for the system of more than 70% and 50%, respectively.
A new type of intelligent composite structure is proposed, consisting of reinforced concrete and prestressed hybrid fiber-reinforced polymer sheets. The hybrid fiber-reinforced polymer consists of basalt and carbon fibers. The carbon fibers function as both sensitive and structural materials to improve stiffness of the hybrid fiber-reinforced polymer sheets and provide a self-monitoring function, whereas basalt fibers function only as structural materials to improve their ductility and decrease the cost. A series of experiments were performed to study the mechanical and monitoring performances of the hybrid fiber-reinforced polymer–concrete composite structures. The results show that their mechanical and self-monitoring performances are markedly upgraded through prestressing the hybrid fiber-reinforced polymer sheets. The prestress improves both the strengthening and monitoring performances. Compared with the control beams, the cracking, steel yielding, and peak loads are improved by 44%, 26%, and 36%, respectively. Results reveal that the prestress also upgrades the monitoring sensitivity and stability of the hybrid fiber-reinforced polymer sheets. Since the electrical behavior is closely related to the mechanical behavior of the hybrid fiber-reinforced polymer–concrete composite beams, the strain, cracking, steel yielding, and the debonding and rupture of the hybrid fiber-reinforced polymer sheets can be well identified through the resistance measurement. A built-in health monitoring function is, thus, demonstrated for the intelligent hybrid fiber-reinforced polymer–concrete composite structures.
This article deals with the equivalent elastic and piezoelectric constants of macro-fiber composite patches. Two types of macro-fiber composite patches, macro-fiber composite-d31 and macro-fiber composite-d33, are considered. The former one is dominated by the d31 effect, while the latter one mainly uses the d33 effect. First, based on the representative volume element technique, homogenized elastic and piezoelectric constants of those fiber-based substrate layers in macro-fiber composite patches are obtained through linear mixing rules. Second, using the obtained homogenized constants for fiber-based substrate layers, the overall elastic and piezoelectric constants of macro-fiber composite patches are obtained by modeling of multi-layer laminated macro-fiber composites based on the Reissner–Mindlin hypothesis. Finally, the homogenized overall material constants of macro-fiber composite patches are used to evaluate the structural behavior of macro-fiber composite bonded smart structures. The results calculated by homogenized constants are compared with those obtained by multi-substrate-layer modeling approach, as well as with those reported in the literature.
The use of shape memory alloy actuators has steadily increased within the fields of aerospace, robotics, and biomedical engineering due to their superior properties compared to other actuation systems. Position control of shape memory alloy actuators is difficult due to the highly non-linear behavior but has been well studied using numerous approaches. Electrical resistance can be used to estimate strain in shape memory alloy actuator wire due to a correlation between the two parameters. Previous models of this correlation are subject to one or more drawbacks such as being limited to a single applied load, not accounting for hysteresis effects, or applying only to a specific actuator size. This article presents a stress–strain–resistance model that accounts for varying applied load, major and minor hysteresis effects and is normalized in terms of actuator geometry. Results of simulation and a simple position control experiment are demonstrated, validating the performance of the model. Furthermore, a correlation between the model and an augmented version of the Liang and Rogers model is also presented.
The B19-phase transition and the related tensile properties of Ti50Ni30Cu20 shape memory alloys were investigated after hydrogen doping. The results revealed that the presence of hydrogen suppressed the B2–B19 transition by decreasing transformation enthalpies. Aging at room temperature lowered martensitic transformation temperature, which might have been associated with the variation of hydrogen contents and states. Ti50Ni30Cu20 shape memory alloys manifested high thermal cycling stability after the aging treatment. In addition, the increase in the hydrogen content was accompanied by an increment in detwinning stress of B19 phase, whereas the elongation of Ti50Ni30Cu20 alloys decreased. Based on our analysis, these effects were caused by the combined activities of different hydrogen states, including those of hydrides and solid-solution hydrogen.
A novel technique is presented to maintain closed-loop performance of a smart piezo structure at an elevated temperature. Square cantilevered plate instrumented with a piezoelectric sensor and a piezoelectric actuator is taken as a test structure. Finite element model of the smart plate is developed using Hamilton’s principle. Finite element model is reduced to first three modes using modal truncation and subsequently a model in state space is derived. First three modal displacements and velocities are observed by a Kalman observer. Negative first modal velocity feedback is employed to control structural vibrations. Performance of the smart structure in open loop as well as in closed-loop changes appreciably at elevated temperature because piezoelectric strain coefficient as well as permittivity increases with increase in temperature. This change in performance is successfully suppressed by application of suitable DC bias on piezoelectric patches. DC bias applied on sensor is blocked from entering signal conditioner by a DC blocker circuit. DC blocker circuit is simulated in LTspice® software to verify its performance.
In recent years, increased interest in broadband vibration energy harvesting schemes has been a main topic of interest among researchers. One of the most successful approaches toward broadband vibration energy capture has been with bistable inertial generators. These devices leverage a nonlinear restoring force to exploit the hardening spring response to increase the resonant frequency bandwidth beyond the characteristically narrowband resonant frequency associated with conventional linear inertial generators. However, one issue with bistable energy harvesters is the presence of low-amplitude oscillations whose energy is insufficient to overcome the potential energy separatrix barrier between the competing potential wells. This article presents the effects of controlling the magnitude of the potential energy separatrix by means of a high-permeability electromagnet in order to increase the resonant response bandwidth for low-amplitude harmonic excitations. An analytical model of the bifurcation space resulting from two control parameters is presented along with an experimental validation study. Finally, an open-loop control law is developed and tested to validate the resonant frequency bandwidth augmentation for harmonic chirp excitations.
McKibben artificial muscles are one of the most pragmatic contractile actuators, offering performances similar to skeletal muscles. The McKibben muscles operate by pumping pressurized fluid into a bladder constrained by a stiff braid so that tensile force generated is amplified in comparison to a conventional hydraulic ram. The need for heavy and bulky compressors/pumps makes pneumatic or hydraulic McKibben muscles unsuitable for microactuators, where a highly compact design is required. In an alternative approach, this article describes a new type of McKibben muscle using an expandable guest fill material, such as temperature-sensitive paraffin, to achieve a more compact and lightweight actuation system. Two different types of paraffin-filled McKibben muscles are introduced and compared. In the first system, the paraffin-filled McKibben muscle is simply immersed in a hot water bath and generates isometric forces up to 850 mN and a free contraction strain of 8.3% at 95°C. In the second system, paraffin is heated directly by embedded heating elements and exhibits the maximum isometric force of 2 N and 9% contraction strain. A quantitative model is also developed to predict the actuation performance of these temperature sensitive McKibben muscles as a function of temperature.
This article reviews the main progress in the development of typical thermoset shape memory polymers. Thermoset polymers are usually stronger in their microstructure than thermoplastic polymers due to their covalently crosslinked three-dimensional networks. The virtues of thermoset polymers make them great source materials for shape memory polymers. However, their three-dimensional networks endow thermoset shape memory polymers with not only high shape fixity rates and shape recovery rates but also low deformation abilities and brittleness. In the past decade, many breakthroughs have been made regarding thermoset shape memory polymers. Typical thermoset materials, such as epoxy resin, cyanate resin, thermoset polyurethane, polyimide, and polystyrene, have been studied as raw materials for shape memory polymers. Studies on thermoset shape memory polymers have been carried out to not only improve their fundamental properties (i.e. broadening of their operating temperatures and service environments and enhancing their thermal stabilities and mechanical properties) but also introduce functional performance properties (e.g. responsiveness to light, electricity, magnetism, and chemical stimuli). This article aims to present a brief review of the development of thermoset shape memory polymers, including the selection and preparation of materials, the improvement of properties, the functionalization of their composites, and their potential applications.
In this article, energy harvesting from a beam with traveling mass is studied. Harvesting was carried out by attaching a thin piezoelectric patch directly on the beam. A theoretical formulation was presented for the problem of energy harvesting from moving mass on a simply supported beam. To validate the results, an experimental setup was designed and fabricated to measure the beam response and voltage induced in the piezoelectric patch during the mass traveling on the beam. The results indicate that the analytical and experimental values for the beam midpoint deflection and the piezoelectric voltage are in good agreement. Finally, the effect of resistive load on the harvested power was considered and the optimum resistive load for maximizing the power was calculated.
This article presents the conceptual design, modelling, prototyping and testing of a novel rotary motor featuring shape memory alloy wires and overrunning clutches. The device comprises a shape memory alloy wire wound around a low-friction cylindrical drum contrasted by a backup beam spring and fitted to the output shaft through an overrunning clutch. Electrical heating produces a contraction of the wire, hence a rotation of the drum which is transferred to the shaft. Thanks to the overrunning clutch, during the recoiling phase, the drum rotates backward while the shaft does not move. Spurious backward movements of the shaft are contrasted by a second overrunning clutch linking the shaft to the frame. This article develops a model for the quasi-static simulation of the motor and the experimental characterization of a prototype device featuring three active drums, a rotary sensor and an angular brake to apply the external load. Despite the low degree of optimization, the tested motor performs well in terms of specific stroke, specific output torque and specific output work per cycle. Winding of the wire on the drum impairs somewhat the fatigue life with respect to publish data on straight wires, a drawback which calls for further design refinements.
Real-time monitoring of structural integrity is an important challenge. This article presents the results of damage detection in real time for two materials: Al 6061-T6 and twill weave carbon fibre-reinforced epoxy composite. The natural frequency as a global dynamic technique was adopted and the structure was evaluated based on the change in the natural frequency. A square thin plate with simply supported edges was investigated under the effect of sinusoidal signal which was generated via mechanical vibration exciter to carry out the natural frequency of the panel. A smart sensor (piezoelectric ceramic lead zirconate titanate) bonded to the surface of the composite panel was used to capture the signals. Experiments demonstrate the effect of change in crack depth and the response of these panels. The results were measured via monitoring technique and evaluated using root mean square deviation index as statistical analysis.
A traditional aircraft is optimized for only one or two flight conditions, not for the entire flight envelope. In contrast, the wings of a bird can be reshaped to provide optimal performance at all flight conditions. Any change in an aircraft’s configuration, in particular the wings, affects the aerodynamic performance, and optimal configurations can be obtained for each flight condition. Morphing technologies offer aerodynamic benefits for an aircraft over a wide range of flight conditions. The advantages of a morphing aircraft are based on an assumption that the additional weight of the morphing components is acceptable. Traditional mechanical and hydraulic systems are not considered good choices for morphing aircraft. "Smart" materials and structures have the advantages of high energy density, ease of control, variable stiffness, and the ability to tolerate large amounts of strain. These characteristics offer researchers and designers new possibilities for designing morphing aircraft. In this article, recent developments in the application of smart materials and structures to morphing aircraft are reviewed. Specifically, four categories of applications are discussed: actuators, sensors, controllers, and structures.
In this article, a new method to identify damage and assess the bearing capacity of a bridge is put forward, and the long-gauge strain influence line coefficient is chosen as the damage index. First, the relationship between the local element bending stiffness and long-gauge strain was studied according to the theory of the strain influence line under moving vehicle loads. Then, the static strain response is extracted from the long-gauge strain history using empirical mode decomposition method, and the maximum value is used to construct the strain envelope coefficient curve. A series of studies on damage identification and bearing capacity assessment based on the long-gauge strain envelope coefficient index are conducted, and a real bridge test is carried out on a continuous box girder bridge. The numerical analysis and practical bridge test results show that the method exhibits good performance in locating and quantifying damage, and that it has engineering significance in bearing capacity evaluation and post-bridge structure reinforcement design.
Mechanical waves can be broadly categorized into traveling waves and standing waves. In this study, the nature of the waves in a finite solid medium is investigated to reveal the excitation parameters that influence their behavior. Theoretical and experimental analysis is conducted to find the conditions for generating traveling waves using piezoelectric ceramics as the actuation agent in piezo-structural-coupled systems. A continuous electromechanical model is developed in order to predict the structural dynamics and is validated through experiments. The results from this study provide the fundamental physics behind the generation of mechanical waves and their propagation through finite mediums.
This article describes the development and validation of a new thermomechanically coupled multi-layered shape memory alloy beam finite element. The finite element is formulated, assuming coupled equilibrium equations for the mechanical and thermal problems. The constitutive shape memory alloy model of Lagoudas and coworkers is implemented in the formulation. Multi-field kinematic hypotheses are proposed, combining a first-order shear displacement field with a sixth-order polynomial temperature field through the thickness of the beam, enabling adequate representation of the temperature and phase transformation profiles due to rapid thermal loading, uneven thermal loading, and boundary conditions and multi-layered configurations with variable thermal properties. The non-linear transient discretized equations of motion of the shape memory alloy beam are synthesized and solved using the Newton–Raphson method with an implicit time integration scheme. Numerical results illustrate the time response of uniform and bi-layered NiTi beams under various thermomechanical loads predicted by the developed finite element. Correlations of the beam element predictions with those of plane stress two-dimensional finite element shape memory alloy models demonstrate excellent agreement in the calculated displacement, temperature, and phase transformation fields. Additionally, the developed beam finite element yields computationally fast simulations providing an effective tool for the design and simulation of rod, beam, and strip shape memory alloy actuators and active structures.
In this article, the effective properties of new active–passive multifunctional viscomagnetoelectroelastic composite materials are modeled and numerically predicted. The correspondence principle, extended to linear viscomagnetoelectroelasticity, and the Carson transform are coupled to the Mori–Tanaka micromechanical mean field approach. Based on the viscomagnetoelectroelastic convolution integral equations and the interfacial operators, the concentration tensors are derived for multi-phase and multi-coated viscomagnetoelectroelastic composites. The effective properties are derived in the frequency domain and then inverted numerically to the time domain using the inverse transform. The effective properties are thus obtained in both frequency and time domains. The obtained hybrid multifunctional coefficients can be used for their active and passive properties. The resulting visco-magneto-electro-elastic effects can be enhanced by a proper choice of the shape and volume fraction of reinforcements as well as by coating thickness.
This article presents the modeling and experimental validation of a piezoelectric stack energy harvester with a flexure-free convex force amplification frame to convert walking force into electricity. Compared to a stand-alone piezoelectric stack, experiments show an 8 times greater voltage output and a 112 times greater power output of such an energy harvester. A finite element method is used to provide a more accurate electromechanical model using Hamilton’s principle and the piezoelectric constitutive equations. Simulation results from such a finite element method agree with the single-degree-of-freedom model. Experimental measurement shows the percentage errors of the output power are of 3.53% for the finite element method and 8.04% for the single-degree-of-freedom model of the piezoelectric stack energy harvester.
A finite element–based code was developed to capture the effect of particle shape on the electromechanical properties of three typical piezoelectric polymer composites. The electrical energy density and electric displacement distribution patterns were modeled by putting particles with different shapes into the model. To evaluate the reliability of investigations, differential equations were solved using Mori–Tanaka and finite element methodologies, where model predictions were appropriately consistent with each other regardless of particle shape and volume fraction of minor phase. Polymer composites filled with continuous fiber revealed similar electromechanical features irrespective of the piezoelectric nature of polymers. On the other hand, strain- and stress-induced electrical displacement distributions were sensitive to particle shape. The results suggest that densities corresponding to relative strain energy and relative electrical energy of composites containing continuous fiber inclusions are both higher than the analogous values obtained for the systems filled with short fiber and spherical particles. Likewise, the polymer composite with continuous fiber revealed improved electric displacement distribution compared to those filled with the other two types of filler. The truthfulness of the developed model was further ensured by placing multifarious particles into the host polymers, which is of vital importance from application point of view.
Wireless sensors have emerged as a reliable method for structural health monitoring. Wireless sensors should ideally have their own power supply, which is a conventional battery in most cases. However, sensors are often retrieved, and batteries must be replaced because of their finite lifespan. In many applications, wireless sensors must be operated in locations that are difficult to access, and these systems often have a desired operational lifespan that exceeds that of conventional batteries. Given this limitation, research devoted to alternative methods, such as energy harvesting or wireless power transmission of batteries, has rapidly increased. In this article, we investigated potential solutions to this challenge by collecting energy from a laser beam to power a wireless sensor. The proposed laser power transmission system features the capabilities of transmitting power to and rapid switching direction to sensor nodes using a laser mirror positioner. The delivered light is captured by a photovoltaic cell and collected in a storage medium to supply the required power to a wireless strain gauge device. Validation of the proposed technology was performed by static and dynamic strain measurements, and the obtained signals from the wireless strain gauge device were compared with those of the wired data acquisition.
This article describes self-similar patterns for capacitors used in electrostatic energy harvesting. The fractal geometry used in this approach allows increasing the active surface of the electrodes when the overlap is small, while featuring similar active surfaces when the electrodes are far away from each other. This therefore significantly increases the capacitance variation and hence magnifies the energy harvesting abilities. In particular, this article explores Cantor-inspired fractal capacitors for electrostatic energy harvesting. It is shown that such an approach can increase the capacitance variation by a factor of two and the harvested energy by a minimum factor of four (considering a charge-constrained cycle with constant charging voltage). However, it is also demonstrated that under some configurations, an optimal fractal order appears and is tightly related to the displacement magnitude.
The principle and structural configuration of an active controlled microfluidic valve with annular boundary driven by a circular piezoelectric unimorph actuator is presented in this article. Its active controlled flowrate is modeled using the classical laminated plate theory and the extended Bernoulli equation in fluid mechanics. According to the established mathematical model, we simulate and analyze the influence of the voltage applied to the circular piezoelectric unimorph actuator and the structural parameters on the flow characteristics. The prototypes of the active controlled microfluidic valves with annular boundaries of three different combinations of the inner and outer radii are fabricated and tested. The experimental results show that the active controlled microfluidic valves with annular boundaries possess the on/off switching capability and the continuous control capability of the fluid with simple structure and easy fabrication processing; the maximum flowrate of the active controlled microfluidic valve with the annular boundary with the inner and outer radii of 1.5 and 3.5 mm, respectively, is 0.14 mL/s when the differential pressure of the inlet and outlet of the active controlled microfluidic valve is 1000 Pa and the voltage applied to circular piezoelectric unimorph actuator is 100 V; and the established flowrate model can accurately predict the controlled flowrate of the active controlled microfluidic valves with the maximum relative error of 6.7%.
The piezoelectric laminated curved beams are currently one of the most popular elements used in nano- or micro-electromechanical systems because of the fact that the piezoelectric driving parts are small, lightweight, and quick response. This article presents an analytical model of the piezoelectric laminated curved beams with variant curvature. And the influence of secondary converse piezoelectric effect on the deflection of the curved beams fully covered with piezoelectric actuators is investigated. Using the radius of curvature and the tangent slope angle of the laminated curved beam as the basic parameters, the quantities of rotation angle, radial, and tangential displacements are decoupled and expressed as harmonic functions. The results of the isotropic curved beams are compared with the existing solutions and the data show the validation of the present method. The presented method can be used to analyze the curved piezoelectric beams being any curve. Some closed-form solutions of circular beams fully covered with piezoelectric layers are presented. Two kinds of ply angle (0/) and (/–) are investigated in this article. The effects of aspect ratio, thickness ratio, and stacking sequence on the characters of the piezoelectric laminated circular beams with and without secondary converse piezoelectric effect are explored.
Distributed compliance systems with integrated variable stiffness elements show great promise for reconciling the conflicting requirements of morphing. The distinct structural properties of each equilibrium configuration allow bi-stable laminates to provide stiffness variability in a purely elastic, energy-efficient manner. This article presents a novel morphing concept based on a distributed arrangement of embeddable variable stiffness bi-stable composites inside a 500 mm chord NACA 0012 profile (where ‘NACA’ is the National Advisory Committee for Aeronautics). The structural response of the aerofoil is assessed numerically and experimentally, with a particular focus on the global stiffness modification potential via the snap-through of the component laminates. Extending the validated finite element models to include a weak static aeroelastic coupling permits evaluation of the aerodynamic adequacy of the final, passively morphed shapes. This concurrent aero-structural methodology is finally employed to develop an improved design. The results allow for assessing the feasibility and potential of the innovative morphing approach exploiting selective compliance provided by the stiffness variability of the integrated bi-stable elements.
Shear horizontal guided waves are attractive for structural health monitoring applications in view of the non-dispersive behaviour of the fundamental mode, possibly higher frequencies of operation and a less complex multi-modal structure. One of the key issues with the deployment of shear horizontal guided waves of modes for structural health monitoring applications is the general non-availability of techniques to sense this family of modes effectively. This article demonstrates the detection of fundamental shear horizontal waves in an aluminium plate by placing a fibre Bragg grating along a direction perpendicular to that of propagating guided elastic waves. In order to uniquely identify the three fundamental plate-guided modes, we map the experimentally measured group velocities as detected by the fibre Bragg grating to theoretically obtained group velocity dispersion curves. We find that the experimentally measured group velocity values using time-of-flight measurements from a perpendicularly placed fibre Bragg grating are in agreement with the theoretical curve for the
We report a finite element method study on the effect of surface roughness on the field-induced magnetization of micrometric iron particles and on the interparticle magnetostatic forces between them. Calculations were carried out for two-dimensional geometries in which particles were modelled as discs. Roughness was introduced as semicircular protrusions or as triangular- or square-wave profiles. Interestingly, we found that increasing amplitudes of the triangular- or square-wave profiles facilitated the magnetization of the particles, resulting in larger interparticle forces at fields below saturation. The effect of the semicircular protrusions and of the spatial frequency of the wave profiles was comparatively small, suggesting that in real systems the effect of particle roughness on magnetic properties may depend on the specific surface morphology. The permeability of the particles also influenced the extent to which roughness facilitated the magnetization process: a larger permeability resulted in larger differences between the magnetization curves of the smooth and the rough particles. Results are relevant to magnetorheological fluids, since we show that surface roughness can affect the magnetic interactions between particles.
In this article, a novel brake for application in wind turbines developed with the focus on long-term stability is proposed. The brake, whose transmission of power is based on magnetorheological fluids, is designed for fail-safe operation under industrial standards. The long-term stability performance over a lifetime of up to 20 years can be ensured by the use of a Taylor-vortex flow in idle mode that causes a mixing effect for preventing particle separation. Beside a detailed description of the design, long-term measurements with requirements for use in wind turbines emulating a timely reduced aging of the magnetorheological fluid will be presented by applying Hardware-in-the-Loop simulations. The results show an outstanding torque performance over an emulated lifetime of 20 years of use in wind turbines that outpaces the capability of conventional brakes whose power transmission is based on dry friction.
This article presents analysis and model validation of a single cantilever frequency up-conversion mechanism under stochastic excitation when configured as an electromagnetic energy harvester. The results show that the mechanism is able to achieve an increase in the root mean square velocity of the cantilever end when excited at frequencies below the natural frequency of the beam in the range of 3–7 Hz, as compared to a simple cantilever. The maximum observed gains in root mean square velocity from the experiment varied from 69% at a fundamental excitation frequency of 7 Hz to 153% at 3 Hz for cantilevers with natural frequencies in the range of 8.5–13.3 Hz as compared to a simple cantilever device with the same range of natural frequency. Comparison between the experimental and simulation results demonstrates that the mathematical model of the mechanical system is able to predict the response under such excitation conditions with 99% of the points in the parameter space being fitted at the 95% confidence level. Configured as an electromagnetic harvester based on low-frequency vibration, the device has been shown in the experiment to have a potential gain in average power delivery of 91.5% compared to a simple cantilever structure.
In this article, by applying the Euler–Bernoulli model and using the consistent size-dependent theory, the nonlinear formulation of functionally graded piezoelectric material nanobeam is developed. In this formulation, the nonlinear geometric effect resulting from mid-plane stretching for the nanobeam behavior is taken into account, and the nonlinear governing equations of the functionally graded piezoelectric material nanobeam are derived using Hamilton’s principle and the variational method. The power-law distribution rule is assumed for the mechanical properties in beam thickness. Afterwards, in the special case, analysis of nanobeam under mechanical and electrical loading for the clamped–clamped and cantilever functionally graded piezoelectric material nanobeams are investigated, and the effects of electrical force, mechanical force, and material properties of functionally graded piezoelectric material beam on the static responses, buckling, and free vibrations are discussed and some significant results are obtained.
Harvesting ambient vibration energy using piezoelectric elements is a popular energy harvesting technique. Energy harvesting efficiency is the research focus. Using synchronous electric charge extraction technology in piezoelectric energy harvesting systems can greatly improve the energy harvesting efficiency. This article presents a self-powered efficient synchronous electric charge extraction circuit for piezoelectric energy harvesting systems, in which four self-powered switch circuits are used to optimize the time sequence of charge extraction so that the rectifier bridge circuit used in traditional synchronous electric charge extraction can be saved. The effect of phase lag on extraction efficiency, system energy, and loss of overall circuit is analyzed. A piezoelectric vibration experimental platform is built for testing the power generation performance of the self-powered efficient synchronous electric charge extraction and those published energy harvesting circuits. The experimental results accord with the theoretical analysis. Moreover, the harvesting energy of the proposed self-powered efficient synchronous electric charge extraction is about three times more than those of the standard energy harvesting circuit under its maximum power point and the self-powered synchronized switch harvesting on inductor in most cases. The energy harvesting efficiency of self-powered efficient synchronous electric charge extraction remains at a high level (>80%) in most cases, and the maximum energy harvesting efficiency is up to 85.1%.
In this study, nonlinear vibration of a clamped–clamped beam containing magnetic shape memory alloy is investigated through combining the constitutive relations of magnetic shape memory alloy and the large deformation response of Euler–Bernoulli beam. Due to the presence of moderately large strains, the effect of mid-plane stretching is taken into consideration. The magnetic shape memory alloy elements are bounded on the top surfaces in the clamped roots of the beam. Since magnetic shape memory alloy units should be always under compressive stress during the vibration, an appropriate compressive pre-strain is applied in magnetic shape memory alloy elements. In order to derive the governing equation of motion, Hamilton’s principle is utilized, and Galerkin’s method is applied in order to numerically solve the set of nonlinear equations. Variation of the strain in magnetic shape memory alloy elements during the beam vibrations makes it necessary to consider the influence of magnetic shape memory alloy on the beam response as well as the damping effects. Vibration-induced deformation in the beam is transferred to the magnetic shape memory alloys causing reorientation in them. It is shown that as a result of hysteresis behavior of magnetic shape memory alloys, the total energy of the beam dissipates until the amplitude of deformation is low enough that reorientation may no longer be induced in the magnetic shape memory alloys. A detailed study is carried out to investigate the effects of magnetic shape memory alloy elements on the damping as well as the natural frequencies of the beam. The influence of the initial conditions, magnetic field, number of magnetic shape memory alloy elements, and also the pre-strain in magnetic shape memory alloy is numerically investigated.
In this article, the static bending response of the functionally graded piezoelectric material plate is investigated based on the first-order shear deformation plate theory (FSDT) under mechanical, electrical, and thermal loads using finite element method. All mechanical, thermal, and piezoelectric properties, except Poisson’s ratio, obey the power law distribution through the thickness. The effects of different volume fraction index, thickness, and various loading conditions are studied on the deflection of functionally graded piezoelectric material plate. The deflection of functionally graded piezoelectric material plate under thermal and electrical loadings versus power law index has been obtained. It is inferred that the correlations between the deflection and the power law index are completely different in the mechanical and thermal loadings, which can be used to design structures in actuator or sensor state. By considering the variation of deflection versus power law index, the proper operation point of the structure can be selected based on the sensor or actuator behavior of the plate.
Tubular dielectric elastomer actuators have been utilized for a number applications where bi-directional positioning is required, for example, positioning of loads and haptic interfaces. Previous model validation and control design research carried out by the authors on extendable metal electrode–based actuators (which need no internal stressing) has concentrated on the design of open-loop type model-based controllers to reject both measurable and unmeasurable vibration disturbances on a prototype tubular actuator developed by Danfoss A/S. A developed electromechanical model and its linearized form were important components in the control design work carried out previously. This work examines the design and implementation of a closed-loop controller on a second-generation extendable metal electrode dielectric elastomer tubular actuator. This actuator has the same strain characteristics as the original prototype but contains more rolled material leading to greater push–pull force capability. Electromechanical model validation of the larger actuator is initially carried out for a range of different operating conditions both with and without loading. Additionally, the increased capacitance of this actuator, due to a greater amount of dielectric elastomer material, could have implications for the accuracy of the gain scheduling term (which is used to linearize the model), when there is dynamic input voltage stimuli. The overall popularity of the proportional, integral and derivative controller, due to its transparency and simple structure, made it the obvious choice for the feedback controller to be considered here. Model-based design of the proportional, integral and derivative controller, via the internal model control design procedure, is then achieved using a reduced-order linear representation of the linearized electromechanical model. The real-time performance of the designed controller is examined to changes in desired position of the payload (servo performance) and its ability to reject periodic vibratory base disturbances to try and maintain the payload in a fixed position.
During past four decades, applications of magnetorheological and electrorheological fluids in adaptive sandwich structures have been widely studied, primarily for the purpose of vibration control. The rapid response time of controllable magnetorheological/electrorheological fluids to an applied magnetic/electric field and reversible variations in their stiffness and damping properties have been the key motivations for adaptive structures applications. This article presents a comprehensive review of the reported studies on applications of magnetorheological/electrorheological fluids for realizing active and semi-active vibration suppression in sandwich structures. The review focuses on methods of characterizing the magnetorheological/electrorheological fluids in the pre-yield region, magnetic/electric field-dependent phenomenological models describing the storage and loss moduli of fluids, experimental and analytical methods developed for vibration analysis of sandwich structures with magnetorheological/electrorheological fluid treatments, analysis of structures with partial magnetorheological/electrorheological fluid treatments and optimal treatment locations, and developments in control strategies for vibration suppression of magnetorheological/electrorheological sandwich structures. The studies on dynamic responses of fully and partially treated magnetorheological/electrorheological-based sandwich beams, plates, shells, and panels are also discussed, including the mathematical modeling methods and associated assumptions, methods of solutions, and experimental methods.
A new shape memory alloy of Ferrous origin (Fe-Ni-Co-Al-Ta-B, referred to as FNCATB) is reported recently that shows huge Superelasticity in comparison with its earlier variants, such as Nitinol and Cu-Al-Be alloy, commonly employed in vibration damping applications. The performance of the FNCATB alloy based Superelastic damper is explored herein and compared with its conventional alternative. The optimal performance of the dampers is ensured by maximizing the equivalent damping, a closed form expression of which is derived based on the force–deformation behavior of the combined structure–damper system. The formulation closely follows that of conventional yield damper but with an additional term
One of the challenges in the emerging field of origami engineering is achieving large deformations to enable significant shape transformations. Bistable compliant mechanisms provide a means to achieve this, and the goal of this research is to investigate the feasibility and design of a compliant bistable mechanism that is actuated by magneto active elastomer material. When exposed to an external field, magneto active elastomer material deforms to align embedded magnetic particles with the field. We investigate a case study using magneto active elastomer actuation through the development of finite element analysis models to predict the magnetic field required to snap the device from its first stable position to its second for various geometries and field strengths. The finite element analysis model also predicts the displacement of the mechanism as it moves from one position to the other to determine whether the device is in fact bistable. These results can be used to understand the relationship between the substrate properties and the bistability of the device. The experimental results validate the finite element analysis models and demonstrate the functionality of active magneto active elastomer materials to be used as actuators for such devices and applications of origami engineering.
In this study, healing of conventional non-shape memory syntactic foam embedded with shape memory polyurethane fibers was investigated per the biomimetic close-then-heal strategy. The syntactic foam was made of epoxy matrix dispersed with 30% by volume of glass microballoons, 5% by volume of shape memory polyurethane fibers, and three levels of thermoplastic healing agent (5%, 10%, and 15% by volume). Notched beam specimens were prepared and fractured by tension to create macroscopic cracks. Three levels of tensile stresses (26.5, 24.5, and 22.5 kPa) were applied to the fractured beam specimens during healing, in order to evaluate the healing capability of the composite under in-service conditions. It is found that the tensile stress level and healing agent content have a significant effect on the healing efficiency. Subjected to 22.5 kPa of tensile stress, the healing efficiency determined by peak tensile load is as high as 90%.
This article presents a smart composite that shows a reversible bending deformation from an initial flat configuration into a 90° angle controlled by local thermal activation. The novelty lies within the structural fixation of the deformation at room temperature without continuous energy input. The new structural architecture of antagonistic performing shape memory alloy actuators embedded in a shape memory polymer matrix is presented. The shape memory polymer is locally heated from the rigid glassy state to the easily deformable rubbery state by integrated heating wires. By subsequent activation of the different shape memory alloy actuators by resistive heating, the reversible performance can be realized. By deactivation of the heating wires in the shape memory polymer, the shape memory polymer fixates the deformation in its rigid condition. The actuation characteristics of the smart composite are investigated by thermo-mechanical experiments. The performance of the smart composite was investigated by thermo-mechanical experimentation of the individual components. The results show that a 90° bending deformation is feasible with the current material dimensions, but repeated deformation is restricted due to fatigue of the alloy. By superposition of the bending forces of the individual components, it is possible to estimate the bending angle of the composite material.
A one-dimensional approach to simulate the mechanical properties of multifunctional pseudoelastic NiTi shape memory alloy has been developed. A novel laser processing technique was applied to a NiTi wire to locally alter the pseudoelastic properties, giving the wire different regions with unique material properties. An innovative analytical expression was developed and validated experimentally. The simulated material responses closely predicted the experimentally measured laser-processed shape memory wires.
This study presents a miniature haptic actuator (10 mm (L) x 10 mm (W) x 6.5 mm (H)) based on magnetorheological fluids, which is designed to provide realistic touch sensations to users. Its primary goals are to evaluate mechanical or actuation performances of the prototype magnetorheological actuator and to assess its effectiveness in conveying haptic sensations to users by conducting the psychophysical experiments. The mechanical performance study evaluated the prototype’s output forces from haptic perspectives using a dynamic test frame. The psychophysical experiments studied human subjects’ perceptions on haptic sensations produced by the prototype. The mechanical test results show that the magnetorheological actuator is capable of generating a wide range of frequency-dependent output forces (from 1.5 N to nearly 9 N). The psychophysical experiments show that the actuator offers various kinesthetic and vibrotactile sensations to human operators. Overall, the results suggest a feasibility of using the magnetorheological haptic actuator in real-world applications, such as a haptic keypad and functional buttons in small consumer electronics and hand-held devices.
"Use of piezoelectric actuators as elements of intelligent structures" is a classic article authored by Crawley and De Luis originally published in the AIAA Journal in 1987. The article provides an elegant one-dimensional model describing the behavior of piezoelectric transducers bonded to a structure, including the effect of the adhesive film. The use of the Crawley’s solution is widespread and up-to-date the model accounts for thousands of citations. This article discusses some of the limitations of the Crawley model and offers a simple, yet more generic solution to the problem by considering the inertia term in the piezoelectric transducer. Although omitted in the original work, this article shows that near the transducer’s resonance, the shear stress distribution at the interface between the adhesive and the substrate might be substantially dissimilar from the one described by Crawley and De Luis. In particular, for either relatively high frequencies or for soft adhesive films, the Crawley equation does not provide an accurate model to the transducer/substrate coupling. Finally, in this work we present an analytical solution for the dynamic electro-mechanical admittance of the transducer bonded to the substrate. A simple finite element method validation study is also offered to support the findings of the proposed model.
A simple method is introduced for the detection of damage in the cables of cable-stayed bridges. The approach presented herein utilizes the change in support reactions to localize and quantify the damage in the cables. Determination of support reactions was achieved by detection of the deck element shear forces adjacent to the supports. The analytical approach is formulated as a recursive optimization damage detection technique, in which model updating is employed to account for the changes in the cable stiffness as a result of damage. The efficiency of this approach was evaluated on a reduced-scale cable-stayed bridge in the laboratory. In addition to the laboratory experiments, the proposed approach was also evaluated by simulating damage in an actual cable-stayed bridge through numerical studies. Several different damage scenarios with various levels of damage were considered in the experiments, as well as in the numerical simulations. The results indicate that the proposed method is capable of identifying the location of the damaged cables in the bridge for cases involving up to two damaged cables.
The object of this work is the conceptual design and modelling of a transducer based on fibre optic sensor and conceived to measure rotations of rigid components around a pivot. The device, namely, post-buckling-fibre Bragg grating, is constituted of a flexible metal plate hosting a fibre Bragg grating strain sensor; the edges of the plates are hinged onto the rotating rigid bodies, eccentrically with respect to the pivot. In this way, any increase in rotation produces a further bending of the plate corresponding to a fibre Bragg grating wavelength shift. Among the different applications, an aileron morphing architecture is considered. This architecture is composed of a rib made of three rigid parts, hinged each other and moved through a dedicated kinematic chain. Two post-buckling-fibre Bragg grating devices are installed between the adjacent rib blocks giving a measure of their current angular rotation. A peculiarity of the proposed device is its ability in working in post-buckling configuration, with two main advantages: (1) easy, plug-and-play, installation (the device supporting plate can be manually bent and plugged within the connection hinges) and (2) tuning of the sensitivity or range of measure, on the basis of the fibre Bragg grating location onto the plate and of the initial post-buckling level. At first, the conceptual design was dealt with a theoretical model describing the post-buckling behaviour of beams, highlighting the effect of the main design parameters; then, the plate displacement field was related to rotation angle of the rib; a dedicated numerical (finite element) model was thus realized to prove the concept feasibility and simulate in detail its functionality. Finally, experimental set-up was provided in order to validate the design.
Vibration band gaps and elastic wave propagation are examined in the metamaterial plates manufactured with periodic locally resonant membranes arranged in a square array. Periodic metamaterials exhibit unique dynamic characteristics stemming from their ability to act as mechanical filters for wave propagation. As a result, waves propagate along the periodic cells only within specific frequency bands called the pass bands, while being blocked within other frequency bands called the stop bands. The proposed metamaterial plates are equipped with sources of local resonances which act as local absorbers of mechanical vibrations. The macroscopic dynamical properties of the resulting periodic structures depend on the resonant properties of substructures which contribute to the rise of interesting effects such as broad stop band characteristics that extend to lower frequencies. Externally excited piezoelectric polyvinylidene difluoride membranes are used to support the local resonators. The stiffness of the piezo-membranes is tunable by means of an external voltage allowing us to control the location and bandwidth of the local resonance frequencies. The predicted band structures are validated by investigating the frequency response of the plate to external mechanical excitations using a comprehensive finite element model of the entire structure. By examining the proposed metamaterial plate, it is shown that it would be possible to actively control the wave propagation both in the spectral and spatial domains in an attempt to steer, stop, and/or confine the propagation of undesirable external disturbances.
Piezoelectric sensors have been widely used for structural health monitoring. However, a single piezoelectric sensor has limited coverage, and multi-channel piezoelectric sensors require massive cabling and channeling devices. This article presents a serial-connected piezoelectric sensor array equipped with conductive fabric tape for damage diagnosis on a wide area, structure using an ultrasonic propagation imaging system. The sensor array was developed as a single channel sensing technique with multiple sensors. Using conductive fabric tape for installation provided convenient and compact installation, light weight, and comparatively low attenuation, compared with the lead wire for the easy smartilization of structures. An aluminum plate with various artificial damages was tested with the proposed sensor array combined with the ultrasonic propagation imaging system. The ultrasonic propagation imaging system stimulated the sensitive areas of the serially connected piezoelectrics and generated multi-wave sources covering a wide area. The multi-source wave propagation video visualized the damages in the form of anomalous waves. Consequently, multi-cabling and multi-channeling are not required because multiple piezoelectrics can be deployed by serial connections using conductive fabric tapes because of the multi-source wavefield generating capability of the ultrasonic propagation imaging system. Therefore, light-weight, compact, and easy installation of the sensor network and inspection for full-scale structures become possible.
In this study, the dynamic response and the active vibration control behavior of cantilever-type structure over wide temperature range (–70°C to 70°C) are investigated experimentally and numerically. A cantilever structure of titanium alloy integrated with the collocated piezoelectric ceramic (PZT-5H) was studied for effective vibration amplitude reduction. The experimental results are verified with the numerical results which show good agreement among them. For the numerical simulations, finite element formulation using first-order shear deformation theory is implemented. The nonlinear fuzzy logic controller is designed as multi-input single-output system using 49 rules and implemented both experimentally and numerically to perform active vibration control. The results show that even moderate fluctuations in the temperature under study can considerably influence the performance of the piezoelectric ceramics used as sensors and actuators resulting in degraded performance for active vibration control.
Hysteresis behavior of piezoelectric actuators degrades the accuracy and performance of the micro or nano positioning stage. As a remedy to this problem, a hysteresis model and a compensator based on time series similarity are proposed in this article. To generate this dynamic hysteresis model, geometric and time scale similarity of output displacement time series of piezoelectric actuators are studied. Furthermore, to compensate for hysteresis behavior, an inverse model based on time series similarity and an inverse model–based feedforward compensator are proposed. This novel model–based compensator is validated against the Prandtl–Ishlinskii model–based one and is assessed for effectiveness and practicality.
Inspired by the hair cells of vertebrates and aquatics, we proposed a hair sensor design that mimics the directionality and linearity of hair cells. The sensor promotes a novel use of piezoelectric microfiber with unique helical electrodes. The sensing mechanism was modeled both analytically and numerically. The analytical model explicitly illustrates the effects of the various design parameters on the performance of the sensor; the numerical model took into account the complex geometry of the sensor and elucidated the importance of the orientation of piezoelectric polarization on the piezoelectric effects. Both models provide valuable insight to optimize the sensor performance. Hair sensor prototypes were fabricated and characterized in the laboratory. The sensor output was found to be linearly dependent on the magnitude of applied displacements. Besides, at the same magnitude of deflection, the sensor responses followed a cosine function with the loading direction, which is similar to what is observed on the directionality of biological hair cells. These experimental observations were consistent with the results of model simulations. An algorithm was proposed to determine the magnitude and direction of acoustic stimuli by utilizing just a pair of orthogonally polarized and closely spaced hair cell sensors.
Textured polycrystals of NiTi-based shape memory alloys (SMA) exhibit pronounced anisotropic properties which significantly influence their response to mechanical and thermal loading. In this work, a constitutive model tailored for non-proportional multi-axial loading of NiTi SMA exhibiting two-stage phase transformation via R-phase is enhanced so that the anisotropy of martensitic structure is captured. Numerical simulations of the mechanical response of a NiTi SMA helical spring subjected to thermal cycling at a constant applied force are performed and compared with experimental data. Quantitative correspondence between experiments and simulations demonstrates the predictive potential of the model. Simulations also provide detailed information on the evolution of distributions of phase fractions and stress within a cross-section of the wire forming the spring. Because the loading is non-proportional, the evolution is rather complex and intriguing.
A coordinated theoretical, numerical, and experimental study is carried out in an effort to understand ultrasonic guided wave propagation and interaction with disbond, as well as, to identify disbond in a honeycomb composite sandwich structure using surface-bonded piezoelectric wafer transducers. In contrast to most of the work done previously, a fast and efficient two-dimensional semi-analytical model based on global matrix method is used to study dispersion characteristics as well as transient response of the healthy honeycomb composite sandwich structure subjected to relatively high-frequency piezoelectric wafer transducer excitations. Numerical simulations are then conducted using commercially available finite element package, ABAQUS, in order to explore guided wave propagation mechanisms due to the presence of disbond. Numerical simulations are further broadened to investigate the effect of disbond size on the amplitudes and group velocities of propagating guided wave modes. A good agreement is observed between the theoretical, numerical and experimental results in all cases studied. It is noticed that the presence of disbond, in particular, amplifies the first anti-symmetric (A0) mode and increases its group velocity. Finally, based on these modal behaviors, the location of an unknown disbond, within the piezoelectric wafer transducer array is experimentally determined by applying a probability-based damage detection algorithm.
Piezoelectric cantilever actuators are widely used in micro/nano-positioning applications due to their relatively accurate response and large operating bandwidth. One of the main obstacles in the way of implementing high-accuracy position tracking in high frequencies is the piezoelectric hysteresis phenomenon. It is known from previous research that piezoelectric materials exhibit a rate-dependent hysteresis loop. The purpose of this article is to obtain a novel hysteresis model that can accurately describe the output of the piezoelectric actuator. This is done by introducing a hysteresis model in the form of an actuated linear dynamic system. This model provides the ability to capture both rate-dependence and magnitude characteristics of the system, and it is simple and easy to implement in real-time. As a result, the proposed method accurately predicts the position of the piezo-actuated beam in a wide range of input frequencies and amplitudes. To demonstrate its effectiveness, the proposed hysteresis model is used along with a robust control loop to track the position of a piezo-actuated beam plant. It is shown using experimental results that utilizing this model leads to accurate position control in a wide range of frequencies.
In this article, an analytical investigation of the stability behavior (i.e. buckling and post-buckling) of rectangular cross-ply piezo-laminate through the width delamination is performed. The piezo-layers act as an actuator in this study. The Rayleigh–Ritz method is used, and the displacement fields are obtained by incorporating polynomial series. The minimum potential energy principle is applied to achieve the equations analytically which are subsequently solved by using the Newton–Raphson iterative procedure. Comparison is made between the obtained results with those gathered by finite element analysis, and good agreement is observed. This method is demonstrated to be quite capable of predicting buckling and post-buckling analysis of delaminated piezo-composite materials.
Shape memory polymers show high promise in the area of morphing structures. Thermally activated shape memory polymers will exhibit shape memory effect under appropriate loading and thermal configurations. In this article, the steps in which a one-dimensional thermo-mechanical viscoelastic model is expanded into three-dimensional form are fully described. For the one-dimensional constitutive model, the standard linear viscoelastic arm is in series with a thermal and storage element. The three-dimensional translation is initiated by transforming Young’s modulus into bulk and shear modulus. Also, the compliance and stiffness matrix for correlating elements are defined and applied into the model. A binding factor is defined by the authors in the one-dimensional model in order to account for the storage strain energy within the polymer. To program the three-dimensional model into finite element analysis software, it was rendered into a time discrete form. The time discrete form was used to develop a UMAT subroutine code within ABAQUS to generate a numerical simulation. Finally, the results of this model are compared to available experiment data and previous model developed by the authors. Numerical simulation results clearly exhibit the thermo-mechanical properties of the polymer which include shape fixity, shape recovery, and recovery stress.
Piezoelectric materials possess nonlinear behavior when actuated in a large electric field and show a large deflection when embedded inside a composite laminate such as a LIghtweight Piezoelectric Composite Actuator. Linear and nonlinear COMSOL multi-physics finite element models were developed and validated using the actuation response of three different layups of LIghtweight Piezoelectric Composite Actuators under a cantilever beam configuration. The linear model incorporated the linear piezoelectric coefficient given from the manufacturer, while the nonlinear model incorporated the nonlinear piezoelectric coefficient plus permanent strain offset in the piezoelectric material as a result of a high applied electric field. The linear model significantly underestimated the experimental values of the actuator response and it showed that taking nonlinearity and permanent strain offset into account is an essential practice when an actuator is operated in high electric fields and accurate prediction is required.
The main aim of this article is to present the usage of type-2 fuzzy logic controller to control a shape memory actuator. One of the main advantages of the fuzzy systems is that they do not require creating any mathematical model of the controlled plant which simplifies the control task. However, a dynamic system model was created to adjust the proportional–integral–derivative controller parameters. Different types of controllers were tested experimentally by controlling the position of the commercially available shape memory alloy actuator NM70 made by Miga Motor company. Despite its small size, it distinguishes itself by its strength. To enhance real-time performance, simplified interval fuzzy sets were used. The algorithm was implemented in the ATmega32 microcontroller. The dedicated PC application was also built. The obtained results confirmed that type-2 fuzzy controller performed efficiently with a nonlinear plant which is difficult to control. The research also proved that interval type-2 controllers, which are a simplified version of the general type-2 controllers, are very efficient. They can handle uncertainties without increasing drastically the computational complexity. Experimental data comparison of the proportional–integral–derivative reference with the fuzzy logic controller type-2 and type-1 clearly indicates the superiority of the former, especially in reducing overshooting.
Polyelectrolyte hydrogels are viscoelastic electroactive polymers which respond to external physical or chemical stimuli by a reversible volume phase transition. Novel fabrication methods allow the creation of hydrogel layer composites in which each layer shows a different sensitivity (e.g. to a different stimulus). This offers new opportunities, for example, in the design of new microsensors, microactuators and microfluidic devices as well as for high-selective membranes and target-specific drug delivery systems. Since only few research groups numerically investigated the transport mechanisms in hydrogel layer composites, a gap remains to describe the movement and transient distribution of ions inside the layer system.
In this article, the multifield formulation is adopted to describe the transient distribution of ions in salt-sensitive hydrogel layer composites on the basis of a numerical simulation. For this, the Nernst-Planck and the Poisson equation are solved using one-dimensional finite elements for both anionic-anionic and anionic-cationic gel layer composites under chemical stimulation. Between adjacent gels, an additional interlayer is introduced to account for the physical and chemical bonding region between the gels. Adaptive mesh refinement provides a good resolution close to the interface between the adjacent gel layers. The obtained results are used to predict the osmotic pressure inside the gels and the dependent swelling of the gel layer composite. The excellent agreement of the obtained results with the Donnan equilibrium demonstrates the high potential of the method applied to predict the behavior of hydrogel layer composites.
This article deals with the squeeze strengthening effect which causes an enhancement in the shear stress of magnetorheological fluids. To obtain a boost of the shear stress, the magnetorheological fluid has to be normally compressed while it is exposed to a magnetic field in order to create stronger particle structures. First, experimental investigations are presented using a magnetorheological fluid test-actuator with a conical shear gap to compress the magnetorheological fluid. A modeling approach is then proposed which combines the rheological behavior with tribological effects to describe the squeeze strengthening effect. Although an enhancement in shear stress of more than factor two is achieved, the applied compression can only be sustained during a certain range of shearing because the magnetorheological fluid is displaced which breaks the created stronger particle structures. As shown by an extended test setup a control of the compression force by adjusting the shear gap height is only possible within a small range of operation due to mechanical limitations. Thus, a self-induced continuous compression is indispensable to utilize the squeeze strengthening effect in rotating devices. A concept for a new magnetorheological fluid test-actuator enabling a self-induced squeeze strengthening effect through an eccentric shear gap design by two independent rotations is presented and theoretically investigated.
This article presents a novel technique to quantify the kinetics of faradaic response in polypyrrole (doped with dodecylbenzenesulfonate) (PPy(DBS)) and its application in developing a cation sensor. This technique is based on the analysis of the impedance/admittance transfer function of PPy(DBS) and the representation of its reduction chronoameprometric response using system poles and residues. The results presented in this paper demonstrate that the pole of the transfer function is an intrinsic quantity and the residue corresponding to the system pole is an extrinsic quantity. The residue of the system pole for a redox-step potential is dependent on the concentration of cations and is observed to have linear dependence on electrolyte concentration (R 2 > 0.9). Thus, the residues can be used to accurately estimate the concentration of cations in an electrolyte solution and enables the use of PPy(DBS) as a high-precision cation sensor. The experimental investigation supporting this analysis demonstrates that the sensitivity of residue to concentration can be varied by equilibrating PPy(DBS) a priori in the cation containing solution of known concentration and by varying the morphology of PPy(DBS).
The demand for lightweight devices attracts attention toward porous materials. Among them, porous shape memory alloys are of interest due to superior mechanical and biological properties. High cost related to fabrication and characterization of such materials makes it necessary to model their mechanical properties before fabrication. Experimental observations of dense shape memory alloys show tension–compression asymmetry which in turn can affect the mechanical response of porous ones. In this article, the effects of this asymmetric response on the mechanical response of porous shape memory alloys are investigated by comparing three models: asymmetric, symmetric with tensile, and symmetric with compressive material parameters. To this end, a constitutive model considering asymmetric material response is proposed based on microplane theory. Then, this model is used to simulate the stress–strain response of porous shape memory alloys. The results are compared with available experimental and numerical data, and a good agreement is observed. It is concluded that in comparison with the asymmetric model, the symmetric model with tensile material parameters under-predicts the stress level while the model with compressive one over-predicts the stress level. In addition, the effects of porosity on the asymmetric response as well as hysteresis of stress–strain curve in tension and compression are assessed.
Hysteretic phenomena have been observed in different branches of engineering sciences. Although each of them has its own characteristics, Madelung’s rules are common among most of them. Based on Madelung’s rules, we propose a general approach to the simulation of both the rate-independent and rate-dependent hystereses with either congruent or non-congruent loops. In this approach, a static function accommodates different properties of the hystereses. Using the learning capability of the neural networks, an adaptive general model for hysteresis is introduced according to the proposed approach and it is called the neuro-Madelung model. Using various hystereses from different areas of engineering with different properties, the proposed model has been evaluated and the results show that the model is successful in the simulation of the considered hystereses. Comparison of the performance of the proposed model with different hysteresis models on experimental data indicates that the neuro-Madelung model has much better performance than them and its results are in excellent agreement with experimental data. In addition, an implicit inverse of the neuro-Madelung model is introduced. Its application in an open-loop control of a rate-dependent hysteresis is assessed and the results show its success.
In this article, analytical and semi-analytical models of upper and lower bounds for the effective moduli of transversely isotropic piezoelectric heterogeneous materials based on the generalized Hashin–Shtrikman variational principle are presented. Compact matrix formulations are used to derive closed-form bound expressions for coupled and uncoupled effective moduli. Analytical models are given for some uncoupled coefficients and simplified formulations for the others. For more narrow bounds, downstream and upstream bounds are developed based on an incremental procedure. Numerical predictions are performed based on the developed methodological approaches, and the obtained results showed the applicability and effectiveness of the proposed models for transversely isotropic elastic and piezoelectric composite materials with ellipsoidal reinforcements of different types and shapes.
In this article, two piezo-based rotating inertial actuators are considered for the suppression of the structure-borne noise radiated from rotating machinery. Each inertial actuator comprises a piezoelectric stack element shunted with the Antoniou’s gyrator circuit. This type of electrical circuit can be used to emulate a variable inductance. By varying the shunt inductance it is possible to realise two tuneable vibration neutralisers to suppress tonal frequency vibrations of a slowly rotating machine. Also, reductions in the noise radiated from the machine housing can be achieved. First, a theoretical study is performed using a simplified lumped parameter model of the system at hand. The simplified model consists of a rotating shaft and two perpendicularly mounted shunted piezo-based rotating inertial actuators. Second, the shunted piezo-based rotating inertial actuators are tested on an experimental test bed comprising a rotating shaft mounted in a frame. The noise is radiated by a plate that is attached to the frame. The experimental results show that a reduction of 11 dB on the disturbance force transmitted from the rotating shaft through the bearing to the housing can be achieved. This also generates a reduction of 9 dB for the plate vibration and the radiated noise.
This article discusses the development, analysis, and testing of a mechanism designed to passively balance the energy requirements of mechanical systems and smart structures in order to reduce the size and weight of their actuation systems and to minimize the associated energy consumption. This passive energy balance is achieved by coupling a negative stiffness mechanism to the positive stiffness of the mechanical system being driven, thereby creating a net zero stiffness system which can be actuated with minimal energy requirements. The negative stiffness mechanism proposed here uses a cable spooling around a spiral-shaped pulley to convert decreasing forces in a pre-stretched linear extension spring into increasing torque output, thereby creating a torsional spring with negative output stiffness. An analytical model of the system was developed, and the geometry of the spiral pulley was optimized for a representative design case. An experimental demonstrator was then built and tested, confirming the ability of the concept to drastically reduce torque and energy required to actuate a representative load.
In this article, we demonstrate the potential of encapsulated unsaturated polyester resin toward introduction of temperature-triggered healing functionality in a representative cycloaliphatic epoxy matrix. Unsaturated polyester resin was encapsulated in poly(urea–formaldehyde) shell by dispersion polymerization technique which resulted in the formation of free-flowing microcapsules (diameter ~130 ± 49 µm) with a core content 58 ± 4%. Calorimetric studies confirmed the chemical activity of the encapsulated unsaturated polyester resin, which spontaneously polymerized in the presence of a free radical initiator, 2,2'-azobis(2-methylpropionitrile), at temperature as low as 80°C. Temperature-triggered healing of epoxy-microcapsule composites was performed at 110°C and the healing efficiency was quantified as the ratio of impact strength of healed and virgin specimens. The healing efficiency was found to increase with the increasing amount of microcapsule in the formulation and reached a maximum (100 ± 2%) at 20% (w/w) loading. Fractographic analysis of the surface revealed the flow pattern of chemically active resin from the ruptured microcapsules, which subsequently cured in the presence of 2,2'-azobis(2-methylpropionitrile) pre-dispersed in the matrix.
A novel cement–sand-based piezoelectric smart composite was developed for conducting structural health monitoring for civil structures. To overcome the incompatibility between piezoelectric materials and reinforced concrete containing cement and sand, for the first time, sand was used to fabricate the new composite in this study. Two sets of specimens containing 30 and 50 vol% lead zirconate titanate were prepared using normal mixing and spread methods, followed by the characterization of the properties of the composites. The composite exhibited desirable piezoelectric strain and voltage coefficients. Furthermore, the dielectric constant and loss of the composite were also determined. The results indicated that the piezoelectric effect and dielectric constant were enhanced with increasing lead zirconate titanate content. Compressive tests were conducted to study the sensing effect of the composite. The investigation demonstrated the feasibility of using the new composite as sensors in structural health monitoring systems to prevent possible failure of civil structures.
The aim of this article is to model and analyze reversible shape adaptive panels integrated with one-way shape memory alloy actuators and to examine the effects of martensite variants reorientation. A robust three-dimensional macroscopic model is implemented to simulate shape memory effect, pseudo-elasticity, and ferro-elasticity features of shape memory alloys. The shape memory alloy constitutive model provides analytical closed-form solutions for self-accommodation and martensite reorientation mechanisms while proposing an iterative solution scheme for martensite transformation or orientation assuming an exponential form for transformation kinetics. The finite element formulations are derived based on the first-order shear deformation theory considering the modified Sanders shell assumptions and including geometrical nonlinearity in the von Kármán sense. An iterative incremental procedure on the basis of the elastic-predictor inelastic-corrector return mapping algorithm is introduced to solve the coupled governing equations of equilibrium with both material and geometrical nonlinearities. The numerical illustrations emphasize the feasibility of reversible shape adaptive panels integrated with thermally activated pre-strained one-way shape memory alloy ribbons or layers. Effects of martensite reorientation, pre-strain, temperature, arrangement, and dimension of shape memory alloys as well as of thermal cycles are investigated, and their implications on the performances of reversible shape adaptive spherical panels are highlighted, and pertinent conclusions are outlined.
In this study, novel modular shape memory alloy wire–based torsional actuators were designed and fabricated. These shape memory alloy–based actuators provide rotational displacements. The mechanical and thermal properties of a single module shape memory alloy torsional actuator were characterized. Next, a modular shape memory alloy torsional actuator was configured by connecting single actuator modules in series. This modular actuator can be used directly as a soft or biologically inspired robot. Finally, the rolling motion and shape transformation of the modular shape memory alloy torsional actuator (soft robot) were demonstrated with a simple open-loop-based control scheme experimentally validating the novel mobility and actuation of the proposed actuator. For a control input, sequentially coordinated square waves of electric current were supplied to the shape memory alloy actuating units.
This paper describes the development and testing of a variable-span wing (VSW) concept. An aerodynamic shape optimisation code, which uses a viscous two-dimensional panel method formulation coupled with a non-linear vortex lattice algorithm and a sequential quadratic programming optimisation routine, is used to solve a drag minimisation problem to determine the optimal values of wing span for various speeds of the vehicle’s flight envelope while subject to geometric constraints. Structural design is performed using the finite element method for static analysis where the particular interface between wing parts is conveniently modelled. A full-scale prototype is built for ground testing the wing/actuator system. The wing is built in composite materials and an electro-mechanical actuation mechanism is developed using an aluminium rack and pinion system driven by two servomotors. Bench tests, performed to evaluate wing under load, showed that the system is capable of performing the required extension/retraction cycles and is suitable to be installed on a UAV airframe fully instrumented for evaluating the VSW concept prototype in flight. The data collected from the performed flights showed full functionality of the VSW and its aerodynamic improvements over a conventional fixed wing for the higher speed end of the flight envelope.
Ferromagnetic shape memory alloys are a type of shape memory alloys that exhibit inelastic strains when subjected to magnetic fields. So far, several constitutive models have been proposed to predict ferromagnetic shape memory alloys’ behaviors under the application of a magnetic field and a compressive stress. In this article, an available constitutive model in a continuum framework is used to investigate the behaviors of Ni–Mn–Ga under biaxial compressive stresses. Since the required model parameters in the original approach are not unique for all loading conditions, the model is modified so that a unique set of model parameters suffices to study different loading conditions. Loading history is also considered in an improved way, and two-dimensional phase diagram is generalized to three-dimensional phase diagram, called reorientation surface in this work, to directly enter the effects of loading history on reorientation start conditions. The orthogonality property of a surface and its gradient vector are used to obtain the general conditions which must be satisfied to ensure continuation of reorientations.
This paper presents a compact motor (6 mm in diameter) with a single piezoelectric stack actuator and a frame structured stator, which works under the principle of natural inchworms. Preliminary motion analysis and dynamic modeling are conducted based on the assumption of structural rigidity. The prototype can generate output torque of about 279 nNm and speed up to 200 rpm with a power input of 60 Vpp at the frequency of 12.7 kHz. In addition, rotational concentricity of the motor is discussed via analyzing captured video of the operating motor. Compared with the previous prototype that is 17 mm in diameter, the simplicity of the motor structure provides an effective miniaturization solution, which is important to many applications such as medical instruments and consumer electronics.
The interactions between low-Reynolds-number fluid flow and an electroactive membrane wing is characterized to illustrate changes in harmonic and transient behavior from electric field excitation of the membrane wing. The wing is constructed of a dielectric elastomer material that changes its tension as a function of the applied field. The field excitation leads to changes in the shape of the wing under aerodynamic loads and subsequently, increased lift and delay of stall. Prior work in time-averaged lift and drag characterization is extended to better understand dynamic characteristics. Benchtop membrane structural dynamics are compared with visual image correlation, hotwire measurements, and particle image velocimetry within a low-Reynolds-number wind tunnel. An applied electric field leads to a 13.7% reduction in structural resonance of the membrane under ambient conditions while wind tunnel measurements illustrate a 5.1% reduction in resonance under the same applied field. Despite these differences, the structural and fluid dynamic harmonics are closely correlated for low-Reynolds-number flow at 10 m/s.
Reciprocal time reversal (inverse filtering) of acousto-ultrasonic fields is a very efficient technique to focus elastic waves through reverberant isotropic and anisotropic media. Such a methodology relies on the correlation of the experimental Green’s function that is acquired by a set of receiver sensors from a limited number of impact sources. However, although heterogeneities and discontinuities within the structural response can be compensated by the inverse filtering process, environmental effects such as temperature variations as well as incoherent noise measurements and the finite number of excitation sources may degrade the quality of time reversal focusing. The scope of this article was to study the factors affecting the impact location imaging using the reciprocal time reversal method in the presence of complex diffuse wave fields. Particularly, a signal-stretch strategy was developed to compensate the temperature changes before remitting the back-propagated wave field at the focus point. Then, in order to investigate the imaging performance and the sensitivity of the proposed methodology, different sets of libraries with reduced input signals were created and tested. Finally, different configurations of the receiver piezoelectric sensors were used to perform the reciprocal time reversal method. To validate this research work, two geometrically complex composite structures, that is, a composite tail rotor blade and a stiffened composite panel, were used. Results showed that both the temperature compensation and the signal processing with the reduced time traced signals and receiver sensors allowed obtaining an accurate identification of the impact events.
In this article, polyacrylonitrile–kraton–graphene (PAN-KR-GR) ionomeric polymer membrane sandwiched between Pt electrode-based ionic polymer–metal composite (IPMC) actuator is developed. The aim of this study is to design and prepare multifunctional ionic polymer–metal composite membrane for robotic application. The water uptake capacity and ion exchange capacity of polyacrylonitrile–kraton–graphene ionomeric membrane is 133.33% at 45 °C for 8 h of immersion and 1.4 meq g–1 of dry membrane, respectively. Proton conductivity and maximum water loss of ionic polymer–metal composite membrane is 5.26 mS cm–1 and 38% after applying 7 V for 12 min, respectively. Scanning electron micrographs shows the smooth and uniform coating of platinum (Pt). Cyclic voltammetry, linear sweep voltammetry, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and tip displacement of PAN-KR-GR-Pt IPMC membrane are also examined. A multifinger-based gripping system for dexterous handling is developed for robotic application.
Polymer composites subjected to cyclic loading would exhibit damage precursors, such as crazes and microcracks, during the first few load cycles. However, damage precursors are not readily detectable with existing sensing techniques, and as such current service life prediction methods depend on macroscopic damage measures. For critical airframe structures, information on macroscopic damage does not provide adequate warning time for corrective actions. This article explores the feasibility of embedding particulate magnetostrictive particles for sensing damage precursors during the early stage of fatigue damage. The sensing is based on the notion that magnetostrictive particles undergo irreversible changes in magnetization intensity when subjected to cyclic loading, and that this change can be captured with an induction coil sensor. In the sequel, Terfenol-D particles are embedded between layers of pre-preg AS4/3501-6 material system. The specimen is then subjected to fatigue loading while monitoring the change in the strength of the magnetic flux density using pickup coil. Results show that the embedded system exhibits a change in magnetic state, in tens to hundreds of millivolts of pickup coil, starting from the first few load cycles. Scanning electron microscopy and acoustic emission data were used to validate the observed results.
This article presents a fatigue crack characterization technique using a nonlinear instantaneous baseline not only to identify but also to locate fatigue damage in an aluminum plate. In conventional ultrasonic structural health monitoring approaches, damage is identified by comparing the newly measured signal with the baseline signal prerecorded when the structure is in its pristine state. The need to compare the current signals with prerecorded signals makes these methods unattractive, since the measured signals are also affected by the changing environment and load conditions of the structure. To overcome this deficiency, the technique proposed here replaces the prerecorded baseline with an instantaneous baseline which can be obtained when the structure is inspected. The measurement of instantaneous baseline utilizes the nonlinear properties of fatigue cracks when subjected to different amplitudes of excitations. Then damage is characterized in terms of a damage index value which is defined as the spectral changes in each path. The short-time Fourier transform is adopted to obtain the spectrogram. The experimental tests are presented to validate the effectiveness of this damage detection technique. A fatigue crack on an aluminum plate was located accurately with a set of surface-bounded piezoceramic (lead zirconate titanate) transducers by adopting the instantaneous baseline.
Shape memory alloys are a class of smart materials that can recover their original shape by heating above a temperature called austenite transformation temperature when subjected to deformation at low temperature. This property enables the shape memory alloy to be used as a unique actuator. Also, the material’s resistance changes during transformation. Thus, the change in resistance and other electrical properties can be used to sense the deformation, which eliminates the requirement of additional sensors. An artificial neural network, described in our earlier study, was able to accurately model the relationship between the electrical properties and manipulator position. This study aims to develop a control methodology of a shape memory alloy–actuated rotary manipulator using the feedback signal from the previously developed artificial neural network model, thus eliminating the need of any external position sensor. The control methodology using variable structure control technique is experimentally tested under different conditions. Also, the effect of environmental temperature on the ability of artificial neural network to predict manipulator position is analyzed using phenomenological model simulations. It is concluded that this system gives a robust performance with a small tolerance (less than 5°) and can operate well even when the ambient temperature changes considerably.
A multilayer piezoelectric actuator is a promising linear vibrator. In this article, a simple distributed-parameter analytical model of piezoelectric actuator, which can model vibration characteristics of piezoelectric actuator–based applications, is formulated. Based on the physical analysis of piezoelectric actuator, a simplification is proposed, justified and applied to fundamentals of thickness-extension-mode piezoelectricity. This simplification subtly enables piezoelectric actuator to be effectively modelled as a whole and allows for a formulation of a simple analytical model. Compared with other modelling methods in the literature, the proposed model with a small number of easily accessible parameters is easy to handle and extend with little compromised accuracy. The effectiveness of the proposed model has been validated by a three-dimensional finite element analysis model of piezoelectric actuator developed in commercial software ANSYS.
This article presents a novel approach to model the mechanical response of smart polymeric materials. A cyclobutane-based mechanophore, named "smart particle" in this article, is embedded in an epoxy polymer matrix to form the self-sensing smart material. A spring–bead model is developed based on the results from molecular dynamics simulation at the nanoscale to represent bond clusters of a smart polymer. The spring–bead network model is developed through parametric studies and mechanical equivalence optimization to represent the microstructure of the material. A statistical network model is introduced, which is capable of bridging the high-accuracy molecular dynamics model at the nanoscale and the computationally efficient finite element model at the macroscale. A comparison between experimental and simulation results shows that the multiscale model can capture global mechanical response and local material properties.
The incorporation of active materials into composites is an active area of research. However, the design and optimization of such composites is challenging because detailed analysis using finite element analysis (FEA) is computationally intensive. This work presents a new reduced-order model for laminates containing shape memory alloy (SMA) wire meshes that significantly reduces the computational burden on design analysis while maintaining good accuracy. The approach is based on a foundation of classical laminated plate theory (CLPT). It considers fully non-linear stress distributions and incorporates a detailed phenomenological model of the hysteretic SMA constitutive behavior. The reduced-order CLPT-based model and its numerical implementation are fully described and unique laminate responses are presented. The model is validated against a corresponding high-fidelity FEA model of an SMA-based laminate. The reduced-order model produces accurate predictions at significantly less expense than the high-fidelity FEA approach, with normalized root-mean-squared error below 10% for most design cases.
In this work the mechanical and viscoelastic properties of magnetic Silly Putty are investigated. Silly Putty is a non-Newtonian material whose response depends on the rate at which it is deformed. For a rapid deformation, it behaves as an elastic solid, while over a relatively long time scale, the polymer molecules can be untangled and it flows as a fluid. The purpose of this article is to study the behaviour of this material firstly under a quasi-static compression and shear loading, and secondly under dynamic shear loading. The Silly Putty under study has a volume fraction of ferromagnetic particles. Hence, both quasi-static and dynamic stress are coupled with several strengths of magnetic field in order to assess the influence of the magnetisation on the mechanical and viscoelastic properties of the material. The approach adopted in this work followed the Design of Experiment method so that evaluating the influence of the variables and their interactions on the system response is possible. The results highlight a strong dependence on the deformation rate, while the influence of the magnetic field is weak, especially under dynamic shear tests in which the viscous components are predominant.
A one-dimensional finite element method for generally layered smart beams is presented in this paper. The model implements the first-order shear deformation beam theory and is based on the preliminary analytical condensation of the electric state to the mechanical state. This allows us to establish an effective mechanical beam kinematically equivalent to the original smart beam including the effects of electro-elastic couplings. The contributions of the external electric loads are included in both the equivalent stiffness properties and the equivalent mechanical boundary conditions. Hermite shape functions, which depend on parameters representative of the staking sequence through the equivalent electro-elastic stiffness coefficients, are used to formulate the finite element method. The state space representation is then invoked for the assembled smart beam finite element model to favor its implementation in a block diagram environment for multi-domain simulation. Validation results and solutions for passive and active vibrations damping system are presented last.
Recent research has shown that estimations of the transformation temperatures of superelastic Nitinol using differential scanning calorimetry can be inaccurate, in part, due to the residual stress in the material. Superelastic Nitinol is selected as the end-cap material in a tunable cymbal transducer. The differential scanning calorimetry accuracy is initially probed by comparing transformation temperature measurements of cold-worked superelastic Nitinol with the same material after an annealing heat treatment, administered to relieve stresses from fabrication. The accuracy is further investigated through a study of the vibration response of the cymbal transducer, using electrical impedance measurements and laser Doppler vibrometry to demonstrate that the change in resonant frequencies can be correlated with the transformation temperatures of the Nitinol measured using differential scanning calorimetry. The results demonstrate that differential scanning calorimetry must be used with caution for superelastic Nitinol, and that an annealing heat treatment can allow subsequent use of differential scanning calorimetry to provide accurate transformation temperature data.
This article presents a new field-deployable algorithm harnessing the metal-wire-based variant of the electro-mechanical impedance technique, warranting drastically lesser number of piezo sensors, for damage detection and localization on large two-dimensional structures such as plates. The metal-wire-based approach is a new variant of the electro-mechanical impedance technique. Although less sensitive than the conventional electro-mechanical impedance technique, it is a panacea in situations where direct bonding of lead zirconate titanate (PZT) patches on the host structure is not possible, such as inaccessible structural locations, parts under continuous impact from external loads, brittle materials (triggering signatures without any peaks) or high-temperature locations. This article first reports detailed experimental investigations into the practical aspects of the metal-wire-based electro-mechanical impedance technique. These cover the effect of various associated parameters, such as the wire cross-section, shape, discontinuity and other related issues. Repeatability of signature is also investigated along with the effect of possible breakage in the wire and inadvertent bending. The technique is further adapted by replacing the wire by a thin foil, which is found to improve the damage sensitivity substantially. The proposed algorithm for damage localization on two-dimensional structures uses the PZT patches in the metal-wire-based orthogonal twin-array configuration. The metal-wire-based electro-mechanical impedance technique is first simulated through finite element method, coupled with the basic impedance model, to test the algorithm on the numerical model of a mild steel plate, 1200 mmx970 mmx8 mm in size. The algorithm is then validated through full-scale test on the actual plate, covering damage at various locations. The developments of this article shall pave way for practical application of the metal-wire-based electro-mechanical impedance technique on large two-dimensional structures with minimum number of sensors, especially in situations where the direct electro-mechanical impedance technique is not feasible to be used.
In this article, the concept of constraint factor is proposed, and a new hysteretic operator consisting of a constraint factor and a polynomial is presented. Based on the constructed hysteretic operator, the one-to-multiple mapping of hysteresis is transformed into one-to-one mapping by expanding the input space, so that the mapping between the expanded input space and the output space comprises one-to-one and multiple-to-one mappings. Finally, a neural network is employed to approximate hysteresis for piezoelectric actuators. The validation performance of experimental tests suggests that the proposed approach is effective.
The wind-induced vibration of a high-rise chemical tower controlled by pseudo-elastic shape memory alloy cables was studied in this work. Based on taking into account phase transformations of shape memory alloy, the motion equation of the shape memory alloy–controlled chemical tower was established by the finite element method, which was coupled with phase transformation equations of shape memory alloy. The incremental finite-element-based Newmark integration method and the iterative method were utilized to solve this motion equation, and the dynamic response of the shape memory alloy–controlled chemical tower was analyzed. The results were compared with those of the chemical tower without any cables and under the control of common cables. It is found that pseudo-elastic shape memory alloy cables have good vibration suppression effect on the chemical tower. In addition, the vibration suppression effect of shape memory alloy cables is affected by the operating temperature, initial pre-strain of shape memory alloy, cross-sectional size of shape memory alloy, and the angle between each shape memory alloy cable and the ground.
The ability to control flexural wave propagation is of fundamental interest in many areas of structural engineering and physics. Metamaterials have shown a great potential in subwavelength wave propagation control due to their inherent local resonance mechanism. In this study, we propose a transformation method to derive the material properties of a flexural waveguide and implement the functionality based on a design of active elastic metamaterials. The numerically demonstrated flexural waveguide can not only steer an elastic wave beam as predicted from the transformation method but also exhibit various unique properties including extraordinary wave beam deflection and tunabilities over a broad frequency range and various steering directions. The waveguide is equipped with an array of active elastic metamaterials composed of the electrorheological elastomer subjected to adjustable electric fields. Such metamaterial-based waveguides provide a new design methodology for guided wave signal modulation devices and could be useful for applications such as tunable beam steering, high signal-to-noise sensors, and structural health monitoring.
In this work, the field-dependent rheological properties of the magnetorheological fluid system, featuring plate-like iron particles, at different magnetic fields in quasi-static mode are investigated using MCR 301 magnetorheometer at ambient temperature. At an intermediate field strength, static yield stress exhibits H1.5 dependency, eventually becoming field independent at higher field. Later on, the temperature-dependent properties are analysed at the different magnetic field intensities. Observational data are obtained from magnetic field ranging from 0.0 to 1.1 T and in the temperature range 30°C–120°C. It is noted that at low field strength, the static yield stress increases initially with temperature and decreases with further increase in temperature. A yield stress model is suggested based on the average normalized sensitivity and magnetic field to describe the measured variation in the magnetorheological fluid response at higher temperature. This information will be useful for predicting thermal sensitivity of device performance.
The two-way shape memory behaviour of semicrystalline networks was investigated on systems based on poly(-caprolactone) featuring significantly different network architecture. Crosslinked poly(-caprolactone)s were prepared by thermal curing from methacrylic end-capped linear chains having various methacrylation degrees. By conveniently reducing the methacrylation degree, the crosslink density of cured materials was varied over a range of one order of magnitude, leading to comparable changes in the material compliance in the rubbery region, but only to moderate variations in melting and crystallization temperatures (Tm and Tc) and in the crystallinity content. When subjected to constant non-zero stress and to cooling–heating cycles from above Tm to below Tc, the materials undergo a reversible two-way elongation–contraction effect, whose extent depends on material structure and applied stress. The structural changes in the crystalline phase accompanying the cooling-induced elongation were studied through differential scanning calorimetry and X-ray diffraction analyses. The elongation process involves different contributions of entropy- and crystallization-driven processes, whose amounts were investigated as a function of the loading conditions and the molecular architecture. The role of the network density towards a controlled two-way response is evidenced, showing that a proper value of the crosslink density has to be identified to maximize the two-way elongation capabilities.
Buckling control of space structures using piezoelectric actuators is an emerging area of research. In particular, cylindrical shells present several challenges as they exhibit multiple buckling modes. This work focuses on placement of ring actuators on cylindrical shells exhibiting axisymmetric buckling. A new method based on the characteristic wavelength of the cylindrical shell is proposed for actuator placement. It is shown by means of numerical studies that passive control of these shells shows a distinct advantage over the conventional actuator placement. It is possible to obtain a stiffer load–axial shortening response as well as a peak load enhancement of the shell using the present approach. The results obtained give important insights into the actuator placement problem for cylindrical shells undergoing axisymmetric buckling.
In this work, we critically examine the effectiveness of the time-reversed Lamb wave based baseline-free damage detection technique for notch-type damage in isotropic plates, through finite element (FE) simulation of an integrated actuator–plate–sensor system. The FE simulation has been verified with experiments. We show that the single-mode tuning, hitherto recommended for improving performance of the time-reversal process (TRP) based technique, does not generally lead to the best reconstruction of the original input signal. The results of the TRP in the presence of notch-type damage show that the damage indices (DIs) computed using the conventional main wave packet of the reconstructed signal do not show any significant change with an increase in damage size, which is consistent with some recently reported experimental results by other groups. A new method of computing the DIs with extended signal length is proposed, which shows excellent sensitivity to damage, and also ensures a low threshold for the undamaged case, when used at the best reconstruction frequency. The same refined DIs, however, are not effective, when used at the so called sweet spot frequency exciting a single mode. Refined DIs based on correlation and similarity of the reconstructed signal reflect the true severity of damage.
Recently, the increasing need for performing intricate operations in small dimensions has motivated many researchers and industrialists to focus on minirobots. Different types of minirobots with diverse locomotive mechanisms have been designed for various applications. Modular design is a new method which is employed to fabricate small robots with more flexibility and capability. In many works, each module of modular minirobots has rotational displacement. In this article, a flexible minirobot module is developed and manufactured which can produce controlled rotational displacement. Shape memory alloy springs are applied as the actuators to provide impressively large strokes. The final fabricated flexible minirobot module is verified by the open-loop experimental tests. In order to achieve the desired maneuvers and have a perfect tracking of reference input, a nonlinear fuzzy controller is developed and implemented to control the maneuvers of flexible minirobot module. Finally, the results are discussed which show good agreement between the simulations and experimental tests.
By embedding actuators within a compliant structure (compliant mechanism), it is possible to develop adaptive system, that is, a shape morphing structure that is capable of producing many different shapes of its output surface. Such structures are of interest for a number of applications. This article presents the new solution of adaptive shape morphing compliant structure with embedded actuators that is capable of changing its shape on demand to meet various performance requirements; the physical prototype of this structure is manufactured. Upgraded approach to the synthesis of compliant mechanisms with embedded actuators is also presented. The existing design methodology for simultaneous synthesis of compliant mechanism and actuator placement often produces compliant system with intersecting structural elements as well as actuators which is very difficult to manufacture. Thus, the design methodology is improved so that compliant systems are obtained without intersecting elements. The scalability of the shape morphing compliant structure is investigated as well. Two possible applications of the novel developed shape morphing structure are presented, for adaptive compliant gripper and shape morphing wing that resembles the profile of a bird wing.
This article deals with the sampling surfaces method developed recently by the authors and its implementation for the three-dimensional coupled steady-state thermoelectroelastic analysis of functionally graded piezoelectric laminated plates subjected to thermal loading. The sampling surfaces formulation is based on choosing inside the nth layer
Among smart and functional materials, the shape memory alloys are enabling the development of a new class of devices for the automotive, aerospace, biomedical, and mechanical applications based on the shape memory and superelastic effects. In this work, a study on the mechanical response of NiTi shape memory micro-elements, in the so-called "snake-like" configuration, is reported. These elements were patterned by means of laser micro-processing from thin NiTi sheets and then chemically etched. Different micro-elements, as function of the number of the curvatures replicated, were fabricated and tested. The functional performances of the micro-elements were characterized through calorimetric analysis for the definition of the operating temperatures and through thermo-mechanical testing for the evaluation of their actuating response. Mechanical tests were carried out to assess the tensile behavior of martensite and austenite phases separately, and for evaluating the thermal hysteresis under different constant loads during cooling/heating loops. Moreover, finite element modeling was also accomplished to analyze the stress distribution in both the martensitic and austenitic phases as loading.
Pneumatic artificial muscles are actuators known for their low weight, high specific force, and natural compliance. Employed in antagonistic schemes, these actuators closely mimic biological muscle pairs, resulting in applications for humanoid and other bio-inspired robotic systems. Such systems require precise actuator modeling and control in order to achieve high performance. In the present study, refinements are introduced to an existing model of pneumatic artificial muscle force-contraction behavior. The force-balance modeling approach is modified to include the effects of non-constant bladder thickness and up to a fourth-order polynomial stress–strain relationship is adopted in order to accurately capture nonlinear pneumatic artificial muscle force behavior in contraction and extension. Moreover, the polynomial coefficients of the stress–strain relationship are constrained to vary linearly with pressure, improving the ability to predict behavior at untested pressure levels while preserving model accuracy at tested pressure levels. Lastly, a detailed geometric model is applied to improve force predictions, particularly during pneumatic artificial muscle extension. By modeling the deformation shape of the actuator ends as sections of an elliptic toroid, pneumatic artificial muscle force predictions as a function of strain are improved. These modeling improvements combine to enable enhanced model-based control in pneumatic artificial muscle actuator applications.
This study presents a comparison of the energy harvesting capacity of monolithic and composite piezoelectric materials, especially in the same energy harvesting configuration. The energy harvesting device was composed of a cantilever beam with active piezoelectric materials, a full-bridge rectifier circuit and an electrical load (resistance). Two energy harvesting devices were fabricated, both of which had piezoelectric patches mounted on top and bottom of the cantilever vibrating element. The first energy harvesting device utilized PZT-5H patches as a monolithic piezoelectric material, and the second energy harvesting device used macro-fiber composite patches as a composite piezoelectric material. The vibrating element used in this study was a stainless steel cantilevered beam with the same dimension as the patch. Characteristics of the energy harvesting devices, including generated power, current, and voltage, were compared in frequency domain and evaluated with respect to the electrical load under different excitation levels. In addition, the effects of the natural frequencies of the energy harvesting devices to the harvesting performance were evaluated. The power density (i.e. power over volume) and specific power (i.e. power over mass) of the energy harvesting devices were compared. In addition, the current density (i.e. current over volume) and specific current (i.e. current over mass) were also presented. Finally, the charging and discharging performances of the energy harvesting devices were also evaluated using a polymer Li-ion battery as the electrical load.
This work was carried out in the framework of a funded project aimed at evaluating the feasibility of an ad hoc clutch for the disengagement an auxiliary device, i.e. the vacuum pump used with the powerbrake in diesel engine vehicles, when its operation is not required. In this way it is possible to improve the overall vehicle efficiency. Strict design specifications were defined with reference to available room, torque transmission, absence of axial loads and fail-safe operation. A magnetorheological clutch with permanent magnets was conceived to fulfil the technical requirements. Different clutch geometries were compared with particular reference to the fail-safe operation and torque capabilities. After an iterative procedure, in which both mechanical design and magnetic field analyses were considered, the most promising solution was defined and a prototype was built and tested. A four-pole sliding permanent magnet was adopted to generate the magnetic field. The experimental results validated the developed models and demonstrated the feasibility developed models and demonstrate the feasibility of the proposed solution. A principle for the automatic clutch actuation is also presented.
A nonlinear frequency response analysis of a smart functionally graded plate operating under a heated substrate plate surface is presented. The analysis is mainly for investigating the effect of temperature on the harmonically exited nonlinear vibration characteristics of smart functionally graded plates and also on the corresponding control authority of piezoelectric fiber–reinforced composite actuator bonded to the substrate plate surface. A negative velocity feedback control strategy is utilized so as to achieve smart damping. The temperature-dependent material properties of the ceramic metal–based functionally graded plate are graded in the thickness direction. Based on the von Karman nonlinear strain–displacement relations and assuming periodic motion, a nonlinear dynamic incremental finite element model of the overall smart functionally graded plate is developed. An arc-length extrapolation technique with a new strategy for determining the arc length is used for numerical solutions. The analysis reveals significant effects of temperature and metal volume fraction in substrate on the structural dynamic behavior of the overall plate. The analysis also reveals the effects of temperature, metal volume fraction in substrate, fiber volume fraction in piezoelectric fiber–reinforced composite, and fiber orientation in piezoelectric fiber–reinforced composite on the smart damping. For using the piezoelectric fiber–reinforced composite actuator in the form of a patch, its optimal location and size are numerically determined.
This article introduces a novel design for a soft morphing actuator capable of pure twisting motion through a pair of shape memory alloy wires embedded in a polydimethylsiloxane matrix at constant and opposite eccentricity across the cross section in opposite directions. This report introduces the design of the actuator, the manufacturing method, and experimental results for the twisting angle and twisting force when varying the dimensions of the matrix of the actuator. Afterward, a simple model is applied to verify the effect of matrix dimensions on the twisting angle of the actuator. The results show that there is an optimal actuator thickness for both the twisting angle and the twisting force of the actuator, that there is a trade-off between the twisting angle and the twisting force for the actuator’s thickness, and that a longer length is better for both metrics within the tested dimensions.
Lead zirconate titanate actuators and sensors have been the widely used in Lamb wave–based damage detection applications. The excitation frequency, waveform, and wave propagation characteristics should be comprehensively considered to effectively conduct diagnosis of incipient forms of damage. In this article, we investigate Lamb wave propagation in a beam under lead zirconate titanate actuation/sensing, in which the lead zirconate titanate effects are included. First, mathematical models are developed to account for both unimorph (i.e. sensor mode) and bimorph (i.e. actuator mode) configurations. The Timoshenko beam theory is adopted for both base beam and lead zirconate titanate layers to accommodate high-frequency responses. Second, the fully coupled electromechanical governing equations are determined and solved in an analytical form to formulate the spectral finite element model. Finally, parametric studies are carried out to determine the optimal actuation frequency, sensor size, actuator, and sensor placement. Our spectral finite element model predictions are validated by the experimental data and results in the literature. The application of spectral finite element model in the Lamb wave–based damage detection is demonstrated as well. In summary, the newly developed spectral finite element model provides an analytical framework in which to predict Lamb wave propagation under lead zirconate titanate actuation and sensing, as well as to develop new interrogation schemes.
This article demonstrates the ability of surface-coated triboluminescent materials to detect damage in carbon fiber–reinforced polymer specimens. An experimental protocol was developed to test the efficiency of the triboluminescent-based diagnostic method using carbon fiber–reinforced polymer coupons under combined bending–compression conditions. Luminescence, emitted from the triboluminescent coatings under quasi-static loading, was detected by capturing digital images. We employed image processing software to quantify change in luminescence as a function of triboluminescent concentration. We observed that 10%, 20%, and 30% triboluminescent coating resulted in 25.3, 27.9, and 40.4 (arbitrary units) total luminescence, respectively, which shows a positive correlation of triboluminescent concentration with luminescence. Finite element simulation was also performed to understand the stress and strain distribution and to aid in understanding and correlating light emission regions on the carbon fiber–reinforced polymer coupons under bending deformation. This work represents a step toward the development of a robust technology that employs triboluminescent materials for early damage detection, consistent with theoretical predictions of damage occurrence.
A deterministic model is presented for predicting the passive and stimuli-responsive characteristics of biomolecular networks. These biomolecular networks consist of multiple bilayer interfaces that can incorporate stimuli-responsive molecules such as peptides and proteins. A model is presented and a lumped parameter method is used to obtain the network equations for several case studies. The model is then utilized to predict the response of a biomolecular network that exhibits rectification behavior due to the presence of voltage-responsive protein incorporated into the interfacial bilayer. This article demonstrates the electric response of systems of biomolecular networks and prompts further research into their use for engineering applications.
This article presents a novel design of a miniature haptic actuator based on magnetorheological fluids for mobile applications with the aim of providing various haptic sensations to users in mobile devices. The primary design goal for a haptic actuator for mobile applications is to miniaturize its size while achieving large forces and low power consumption. To this end, this study proposes to design the actuator’s piston head (or plunger) in cone shape and activate multiple modes of magnetorheological fluids. A prototype actuator was designed and fabricated based on a simulation model. Using a dynamic test frame, the performance of the prototype actuator was evaluated in terms of the force (resistive force) produced by the prototype. The results show that the small actuator (10 mm x 10 mm x 6.5 mm) produced a maximum resistive force of about 5 N and the force rate of nearly 80% at 0.3 W. This change in resistive force or the force rate is sufficient to provide several steps of force variation that is explicitly perceivable for operators, depending on the input power. The results demonstrate a feasibility of using the proposed actuator’s applications in mobile devices, conveying realistic haptic sensations to users.
The dielectric relaxation effect on the flow behavior of electrorheological fluids under dynamic shear was studied. The flow curves of electrorheological fluids in the dynamic state were simulated with shear rates from 0.1 to 1000 s–1 under different relaxation times. When the magnitude of the relaxation time is smaller than 10–2 s, the break shear rate changes little at different relaxation times. But the break shear rate changes obviously when the magnitude of the relaxation time is larger than 10–2 s. To further understand the influence of the relaxation time, Sr/Ba-doped TiO2 electrorheological fluids were prepared and their dielectric properties and flow curves under shear flow were tested. The relaxation time of the electrorheological fluid is influenced by the Sr/Ti mole ratio but not the Ba/Ti mole ratio, and the electrorheological effects of the fluids were highly influenced by varying the Sr/Ti mole ratios. The experimental results agreed well with the above computer simulation. Finally, a possible mechanism was proposed to explain the effect of dielectric relaxation on flow behavior of electrorheological fluids.
This study presents an experimental investigation of the application of a periodic array of shunted piezoelectric patches with negative capacitance for the broadband control of waves propagating on a flexible plate. A 15 x 5 array of piezoelectric patches is bonded onto the top surface of a freely supported rectangular plate. The patch array is intended to serve as an active interface between two regions of the plate, where one region has an input disturbance force and the other does not. Each patch is shunted through a single circuit, reproducing a resistance in series with a negative capacitance. The magnitude of the reactive part of the negative shunting impedance is tuned close to the intrinsic capacitance of the piezoelectric patch. The real part is adjusted for either light damping so as to induce a reactive (reflective) response, or with heavy damping to induce greater absorption. The experimental responses of the system equipped with this active interface display a strong attenuation or reflection of vibrations, depending on the shunt resistance, over a large frequency range, including the mid-frequency regime. In an effort to control vibroacoustic phenomena, this study represents the first attempt to implement an integrated smart metacomposite active interface on a plate structure.
Sandwich structures with polyurethane foam core and glass fiber–reinforced polymer facesheets with three orientations were investigated experimentally and numerically under three-point bending tests at 80 °C, at a relatively low load level associated with a linear viscoelastic response. Off-the-shelf piezoelectric transducers were inserted inside one of the facesheets and were interrogated in pitch-catch at low ultrasonic frequencies during testing. The objective of this article is to investigate ability and sensitivity of the embedded transducers to detect creep deformation. The denoised received waveforms were analyzed in the time domain, where guided wave speeds were found to exhibit a drop due to temperature changes (most significant in the sandwich samples with off-axis orientation), followed by an increase, eventually reaching an asymptotic value. The waveforms were also processed in the joint frequency–time domain, with a novel signal processing technique built upon Gabor wavelet transforms and their contour lines. It is shown that this wavelet contour technique indirectly captures the trend of physically measured displacements and can differentiate among the three different fiber orientations in the facesheets, and among room temperature and 80 °C. This technique has the potential to effectively track creep time-dependent response and life performance in smart sandwich composites.
In this article, active flutter and aerothermal postbuckling control of the nonlinear composite laminated panel with large deformation in supersonic airflow using the piezoelectric material are investigated. The distributed piezoelectric actuator and sensor pairs are bonded on the top and bottom surfaces of the laminated panel. The von Karman strain–displacement relation is used in the structural modeling. Unsteady aerodynamic pressure is evaluated by the supersonic piston theory. Hamilton’s principle and the assumed mode method are applied to formulate the equation of motion of the structural system. A discrete linear-quadratic-Gaussian controller is designed in this study to conduct the active flutter and postbuckling control. The proportional feedback control method is also applied in designing the controller. Time domain responses of the structural system are computed using the Runge–Kutta method. The control effects of the two control methods are compared. The influences of the placements of the piezoelectric actuator and sensor pairs on the control effects are also investigated. This study is helpful for the active aeroelastic design of the nonlinear structural system.
A novel ducted turbine, referred to as a Wind Tower, as a smart architectural integrated design for capturing wind power in residential or commercial applications is theoretically and experimentally studied. A mathematical model is developed to predict the flow behavior inside the tower, and a velocity coefficient is defined to correct the results at different test conditions. A 1/8-scale wind tower prototype, including a four-quadrant-peak windcatcher rooftop, a tower, a nozzle, and a turbine, is designed and fabricated. The results from the mathematical model provide a good estimation of the output power obtained from experimental tests. Significant changes in the output wind speed due to pressure differences created by the surrounding environment and the Wind Tower components configuration are observed. The advantages of requiring low maintenance, and being reliable and sustainable, together with its special design that eliminates bird/bat mortality, make the Wind Tower a promising solution for residential, commercial, and off-grid applications.
Multi-layered two- and three-component magnetorheological elastomer (MRE) isolators were designed using a one-dimensional phononic crystal (PC) model. The elastic wave propagation properties of the two kinds of structures were studied using the transfer matrix method. Results show that the elastic band gap (EBG) position can be regulated by an external magnetic field and that the width of EBGs can be adjusted by varying component thickness. The three-component structure, which includes lead, can better tune the EBGs of MRE vibration isolators.
In this article, we report a novel linear-to-rotary motion converter that employs a single-crystal 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-29PT) (PMN-29PT ) stack actuator and asymmetric compliant mechanics for flexural hinges. This unique motion converter is compact, economical to fabricate and has the capacity to be utilized in small-scale applications. The linear-to-rotary motion converter prototype was designed and fabricated using a seven-bar linkage kinematic model. Additionally, compliant mechanics at flexural hinges were used in place of conventional revolute joints. The converter consists of a stack actuator and a structural mechanism, including flexural hinges and a pivot hinge to convert linear motion to rotary motion. To determine the feasibility of the mechanism design and to estimate the accurate rotational motion of the designed converter, numerical simulations utilizing COMSOL Multiphysics 4.3 and experimental validation were performed by evaluating the displacement of the stack actuator and the rotational angle of the linear-to-rotary motion converter according to the changes of driving voltages. The experimental results show that the linear-to-rotary motion converter can produce a rotation angle of 1.52° at an input voltage of 900 V. The unique linear-to-rotary motion converter design proposed here can be applied to various engineering fields, instead of existing mechanical linear-to-rotary mechanisms, due to the advantages in compact size and precise control.
In this study, ongoing investigations to apply piezoelectric materials as an energy harvester are extended. In doing so, effectiveness of single unit impact dampers is increased using piezoelectric materials. For this reason, barriers of the impact damper are replaced with cantilever beams, which are equipped with the piezoelectric patches. For convenience, this kind of impact dampers is named as "piezo-impact dampers." The piezo-impact damper is not only a vibration suppressor but also it is an energy harvester. An analytical approach is presented to formulate the voltage and power generation in the barriers of the piezo-impact dampers. Variation in output voltage is studied with changing the main parameters of the piezo-impact damper. Furthermore, damping inclination, which presents the ability of vibration suppressing in impact dampers, is calculated with varying the main parameters of the impact damper. Regarding calculated output voltage and damping inclination in the piezo-impact dampers, two "energy-based" and "vibratory-based" design methods are presented. Finally, using several user-oriented charts, the discussed design methods are combined to provide a powerful piezo-impact damper.
This work studies the synergistic effect of self-assembled carbon nanofiber nanopaper and hexagonal boron nitrides on the electrical and thermal properties and the electro-activated shape recovery behavior of shape memory polymer nanocomposites. The combination of the carbon nanofiber nanopaper and hexagonal boron nitrides results in improved electrical and thermal conductivities of the shape memory polymer nanocomposites. The carbon nanofiber nanopaper was coated on the surface of the shape memory polymer nanocomposite in order to achieve the shape recovery induced by electrical Joule heating. The hexagonal boron nitrides were blended into the shape memory polymer resin to improve the thermal conductivity and decrease their thermal dissimilarity with carbon nanofiber nanopaper, which enhanced the heat transfer from the nanopaper to the underlying shape memory polymer nanocomposite to accelerate the actuation.
Without employing ad hoc stress or deformation assumptions, various equations and solutions for circular cylinders are deduced systematically and directly from axisymmetric problem of transversely isotropic electro-magneto-thermo-elastic media. These equations and solutions can be used to construct the exact theory of cylinders. A method for the solutions of two-dimensional equations is presented, and with the method, the exact theory can now be explicitly established from the general solution and Lur’e method. The exact solutions for cylinders with nonhomogeneous boundary conditions are derived directly from the exact theory. Not taking into account the coupling effect, the result reduces to the corresponding solution of the elastic counterpart. Furthermore, an illustrative example studied also indicates that the exact or accurate solutions can be obtained in use of the exact theory. Hence, the results obtained here are considered reliable as a basis for more general applications.
Fluctuating heat radiating from the environment is an unused and unknown source. This study investigates pyroelectric energy harvesting as a way to tap a fluctuating radiation heat source. Appropriate circuitry coupling and the frequency of the radiation source play a key role in the ability to harvest this energy. Hence, a design of experiment approach that limits factors to temperature change frequency, electrical resistance, and capacitance is utilized to develop a full-factorial model at three levels for each factor. In order to quantify and maximize the harvested energy, a response surface model was developed. The optimum values for temperature change frequency, resistance, and capacitance were predicted to be 0.05 Hz, 7330 k, and 100 µF, respectively, for a PZT-5A sample with a volume of 0.684 cm3. The maximum response of 62.89 µJ was predicted for the optimum values.
Interdigitated electrode configurations produce nonuniform electric field and stress in the vicinity of the electrodes, creating a volume where the material is not uniformly polarized. This results in enhanced hysteresis in interdigitated electrode configurations relative to the hysteresis in the bulk material. The dielectric loss in a macro-fiber composite with interdigitated electrodes was characterized and is compared to the dielectric loss of the same material under a uniform field. The dielectric loss in the interdigitated electrode arrangement was found to be significantly larger and had a strong dependence on electric field amplitude. The dielectric loss is expressed in terms of an effective loss tangent (tan ) and a more general damping model. A mechanism that contributes to the hysteresis is that the local stress in the ferroelectric material beneath the interdigitated electrodes induces ferroelastic polarization reorientation during each electric field cycle. The interactions between polarization gradients and residual stress are assessed using a finite element model with a micromechanical-based constitutive law.
Pneumatic artificial muscles are a class of pneumatically driven actuators that are remarkable for their simplicity, lightweight, high stroke, and high force. The McKibben artificial muscle, which is a type of pneumatic artificial muscle, is composed of an elastomeric bladder, a braided mesh sleeve, and two end fittings. Gaylord first developed an analysis of the McKibben artificial muscle based on the conservation of energy principle. The Gaylord model predicts block force but fails to accurately capture actuation force versus contraction ratio behavior. To address this lack, a non-linear quasi-static model is developed based on finite strain theory. The internal stresses in the bladder are determined by treating it as a cylinder subjected to applied internal pressure and a prescribed kinematic constraint of the outer surface. Subsequently, the force balance approach is applied to derive the equilibrium equations in both the axial and circumferential directions. Finally, the closed-form pneumatic artificial muscle quasi-static actuator force is obtained. The analysis was experimentally validated using actuation force versus contraction ratio test data at a series of discrete inflation pressures for two different pneumatic artificial muscles: a large pneumatic artificial muscle (L = 128.5 mm, B = 7.85 mm, with a latex bladder) and a miniature pneumatic artificial muscle (L = 43.9 mm, B = 2.3 mm, with a V330 elastomeric bladder).
In this work, the thermal and mechanical responses of shape memory alloys are studied under different loading and boundary conditions. To this end, a common one-dimensional constitutive model for shape memory alloys capturing both pseudoelasticity and shape memory effect is implemented into ABAQUS commercial finite element package via a user material subroutine. The main benefit of this one-dimensional user material is its capability to simulate any mechanical as well as thermal loading path. Hence, it can be utilized in finite element simulation of any complicated smart structure consisting of shape memory alloy wires. To validate the proposed numerical approach, its predictions are shown to be in a good agreement with those obtained by analytical and other approved numerical solutions under different thermal and mechanical loading and boundary conditions. Since shape memory alloys are integrated into many applications as actuation elements, the actuation response of an axial shape memory alloy actuator heated from one end is studied using finite element method. Finally, the developed user material is employed in finite element simulation of a smart landing gear as a real-world smart structure.
This article presents the development of a novel magnetorheological damper which has a self-sensing ability. In this study, a linear variable differential sensor, which was based on the electromagnetic induction mechanism, was integrated with a conventional magnetorheological damper. The working principle, configuration, and prototype of the displacement differential self-induced magnetorheological damper based on the integrated linear variable differential sensor technology were presented. A mathematical model of the proposed displacement differential self-induced magnetorheological damper was established. The finite element model was built with two-dimensional Maxwell software and the magnetic simulations were presented. With this approach, the influence of the flux leakage, the winding cylinder in different basic values of structure parameters, and materials were determined to obtain an optimal displacement differential self-induced magnetorheological damper. Finally, the dynamic performance of the displacement differential self-induced magnetorheological damper was evaluated with a fatigue test machine. The experimental results indicated that the developed displacement differential self-induced magnetorheological damper based on the integrated linear variable differential sensor technology can output controllable damping force and displacement relative self-induced voltages simultaneously.
The work summarized here explores the application of various substrate materials to macro-fiber composites for the purpose of generating curvature. This research experimentally determines the free strain of the macro-fiber composite through its full range of actuation and then examines the resulting deflections when bonded to various substrates. In addition, loads are applied to the resulting unimorph while in a cantilever configuration and the deflections recorded. These results are used to validate finite element models, which are used to explore further design possibilities, including a bimorph configuration. The goal of this work is to determine the substrates that maximize curvature in both unloaded and loaded configurations. The results show that using thin and high modulus substrates results in the largest deflection under loading.
Piezoelectric-hydraulic actuator is a hybrid device that consists of a hydraulic pump driven by piezoelectric stacks coupled with a conventional hydraulic cylinder and a set of fast-acting valves. Nowadays, such hybrid actuators are being researched and developed actively in many developed countries by requirement of high performance and compact flight system. In this research, operation principle and performance testing of the hybrid actuator were introduced. Two types of piezo-stacks are selected for experimental performance testing to identify the factors of piezo-stack which affect the performance of the hybrid actuator. The performance of piezo-stacks due to electrical power supply and self-heating was considered. Output no-load velocities and blocked force were measured on performance testing. The results showed that the maximum blocked force was 346 N and no-load velocity was 101 mm/s, resulting in maximum output power of 8.74 W at 1000 V applied voltage and 250 Hz pumping frequency.
Ferroelectric fibers based on a commercial lead zirconium titanate powder were investigated by a new characterization method to measure single fiber properties, such as large signal polarization and longitudinal free strain, and small signal properties, such as piezoelectric constant. To verify the measurements, the free strain data were compared with dynamic mechanical analyzer measurements. For this investigation, lead zirconate titanate fibers were sintered in lead-rich atmosphere at different temperatures. Microstructure and phase composition were analyzed by scanning electron microscope and X-ray diffraction. By increasing the temperature from 1150°C to 1200°C, the electromechanical behavior of the fibers could be improved: an increase in remnant and saturation polarization occurred. A d33 as of ~430 and ~400 pm/V could be measured for 1150°C and 1200°C, respectively. These d33 values are very close to the one reported on the data sheet of the material.
This article presents a sensorless resistive-based control method to control shape memory alloy wire actuators to be used in the development of a laparoscopic surgical locking system. Shape memory alloy wire electrical resistance is measured to control the martensite phase fraction of shape memory alloy wire. The martensite phase fraction is calculated based on mathematical heating model, resistance models, and the measured resistance. Experiments are conducted to evaluate the validity and performance of the method in the control of the locking system angle. The results show that the sensorless resistive-based control method accurately controls the wire without using any position sensors, resulting in the lower cost, size, and weight of the system. The results show very small steady-state errors, verifying the practicability of this method. The sensorless resistive-based control method has the potential to be used in many applications in which cost and space are limited and the use of an external sensor is impossible or costly.
The purpose of this study was to explore the properties of sintered hydroxyapatite specimens for developing a suitable hydroxyapatite target and a fabrication process for the radio frequency sputtering of implants. Using a compound surface treatment of sand blasting and acid etching followed by hydroxyapatite radio frequency sputtering, this work planned to develop a commercial dental implant system in the near future. First, in addition to producing hydroxyapatite parts using hot isostatic pressing, this study examined the properties of hydroxyapatite parts produced through cold pressing followed by sintering in vacuum and air. The experimental results showed that the index of crystallization, density, and Vickers hardness of the parts sintered in air were more favorable than those of parts sintered in vacuum, and that the parts sintered in vacuum could crack or break. Second, hydroxyapatite sputtering was performed on the hot isostatic pressing–produced and cold pressing–produced targets on titanium dental implant surfaces at power levels of 50 and 90 W. The results showed no cracks in the cold pressing–produced hydroxyapatite targets when the sintering condition was at 1050 °C. By contrast, cracks occurred in the hot isostatic pressing hydroxyapatite targets at a relative density in excess of 93.35%. Observing scanning electron microscopy cross-sectional images revealed that the sputtering deposition rate was approximately 0.456 nm/min at the sputtering power level of 50 W and 1.139 nm/min at 90 W.
Conductive asphalt concrete can be used to help pavement snow melting/deicing by an asphalt pavement electrical heater. It is an emerging technology to ensure safety driving during winter time. Based on the Joule heating law, an electric current passing through the conductive asphalt concrete (a conductor) could generate enough heat to prevent snow accumulation and icing on the asphalt pavement surface. This article provides a review on the material design, construction technique, performance evaluation, and engineering applications of conductive asphalt concrete. The literature shows that the conductivity and mechanical properties of conductive asphalt concrete are strongly dependent on the material compositions and mixing programs. Meanwhile, the mechanism of conductivity improvement is identified according to the characteristics of conductive additives. In addition, the effects of service conditions on the resistivity are evaluated. Asphalt pavement electrical heater technique shows some appreciable advantages in environment protection and traffic safety aspects, although it has few applications in the highway industry. It therefore recommends that further investigations on asphalt pavement electrical heater are indispensable and should focus on some covered issues besides the existing research, such as proper material selection, resistivity stability, desirable high operational efficiency, and suitable construction technique.
Structural health monitoring is an important problem of interest in many civil infrastructure and aerospace applications. In the last few decades, many techniques have been investigated to address the detection, estimation, and classification of damage in structural components. One of the key challenges in the development of real-world damage identification systems, however, is variability due to changing environmental and operational conditions. Conventional statistical methods based on static modeling frameworks can prove to be inadequate in a dynamic and fast changing environment, especially when a sufficient amount of data is not available. In this paper, a novel adaptive learning structural damage estimation method is proposed in which the stochastic models are allowed to perpetually change with the time-varying conditions. The adaptive learning framework is based on the use of Dirichlet process (DP) mixture models, which provide the capability of automatically adjusting to structure within the data. Specifically, time–frequency features are extracted from periodically collected structural data (measured sensor signals), that are responses to ultrasonic excitation of the material. These are then modeled using a DP mixture model that allows for a growing, possibly infinite, number of mixture components or latent clusters. Combined with input from physically based damage growth models, the adaptively identified clusters are used in a state-space setting to effectively estimate damage states within the structure under varying external conditions. Additionally, a data selection methodology is implemented to enable judicious selection of informative measurements for maximum performance. The utility of the proposed algorithm is demonstrated by application to the estimation of fatigue-induced damage in an aluminum compact tension sample subjected to variable-amplitude cyclic loading.
A new approach for monitoring the weight of trucks in motion using the bridge response is introduced in this article. The proposed technique is based on the use of strain rosettes for acquisition of shear strains near bridge supports. Bridge weigh-in-motion monitoring using shear force is a new approach that differs from the prevailing techniques based on the measurement of flexural strains. Formulations are introduced using the shear force response of the bridge in the computation of gross vehicle weights. The method requires truck speeds, influence lines, and shear force responses for the computation of gross vehicle weight. All these are acquired by two sets of rosette sensors attached in series on the webs of bridge girders. An experimental program was designed to evaluate the response of the proposed approach in real-time monitoring of moving truck weights. This was accomplished by instrumentation and load testing of a two-span prestressed concrete box girder bridge by a calibrated truck. Field test results are presented and compared with the actual weight of the calibrated truck.
Shape memory polyurethanes are materials that can recover a finite pre-deformed shape in response to thermal stimuli due to the combined action of hard and soft segments in the molecular configuration. In this study, affine network models are used to describe the mechanical behaviors of the soft segment phases. Furthermore, a new four-element recovery model is constructed for the hard segment phase in consideration of the structure change during the recovery process. In addition, as shape memory polyurethanes are temperature-sensitive materials, the influence of temperature on the parameter viscosity is investigated. A phenomenological constitutive model is proposed, with which the thermomechanical behavior of shape memory polyurethanes is predicted and the simulation results agree well with the experimental results.
Piezoelectric energy harvesters can be used to convert ambient energy into electrical energy and power small autonomous devices. In recent years, massive effort has been made to improve the energy harvesting ability in piezoelectric materials. In this study, reduced graphene oxide was added into poly(vinylidene fluoride) to fabricate the piezoelectric nanocomposite films. Open-circuit voltage and electrical power harvesting experiments showed remarkable enhancement in the piezoelectricity of the fabricated poly(vinylidene fluoride)/reduced graphene oxide nanocomposite, especially at an optimal reduced graphene oxide content of 0.05 wt%. Compared to pristine poly(vinylidene fluoride) films, the open-circuit voltage, the density of harvested power of alternating current, and direct current of the poly(vinylidene fluoride)/reduced graphene oxide nanocomposite films increased by 105%, 153%, and 233%, respectively, indicating a great potential for a broad range of applications.
This article presents two models that have the aim of analysing three-dimensional freely vibrating plates made of an arbitrary combination of structural and/or piezoelectric layers. The first model is derived from a displacement-based variational statement, and it investigates the possibility of approaching exact three-dimensional results at any degree of accuracy. This model has been developed as if the plates were virtually made of a single layer, and it is herein referred to as the approximate analysis model. The second model is based on solving the set of three-dimensional linear equations coupling the relevant mechanical and electric quantities, and it therefore provides exact results. The latter model is derived from the transfer-matrix technique which, having shown numerical instability in the multiphysics problem being dealt with, was then successfully modified to provide exact and reliable results. Excellent agreement has been obtained between the models, and this shows how the exact approach here designed is stably able to overcome ill conditioning problems, while the first model, having been validated by the exact results, could be applied to effectively investigate multiphysics problems for general boundary conditions, and for cross- and/or angle-ply laminates, at any level of required accuracy.
Noise in a vehicle is generally caused by the vibration of various automotive components, such as the dashboard, door panels, and roof. For example, vibrations caused by the engine may cause a dash panel to vibrate leading to noise in the vehicle cabin. The control of such noise and vibration may be achieved by placing a viscoelastic or other suitable damping material on the automotive component; however, conventional damping materials usually have a high density, which can lead to significant increases in the overall mass of the sound insulation system. A lightweight alternative employs piezoceramic patches connected to a resistor–inductor circuit, where the mechanical vibration, converted into electrical energy by the piezoceramic, is dissipated in the form of thermal heat through the resistor. The presence of an inductive element allows the system to perform in the vicinity of a mode of the vibrating structure, in an effect similar to a resonant vibration absorber. In this work, the damping capacity of this resonant electrical circuit is demonstrated in a dash panel installed between coupled reverberant and anechoic rooms for assessments of sound transmission loss. Finite element simulation and theoretical analysis are used to support the choice of the electrical component values and the correct placement for piezoelectric patches. The resulting sound transmission control is compared to baseline measurements with conventional viscoelastic material thermally bonded to the panel surface. The work is concluded with a discussion on the achieved results and mass saving benefits of the proposed damping technique.
Steel moment-resisting frames are prone to extensive damage in seismically active zones. Large permanent deformations in structural members following strong earthquakes can be mitigated using smart materials such as shape memory alloys. In this article, three-dimensional finite element analyses are conducted to study the seismic performance of beam–column connections incorporating shape memory alloy plates. Eight beam–column connection subassemblies with shape memory alloy plates in the plastic hinge of beam were analyzed under cyclic loading. Based on the numerical results, the recentering properties of superelastic shape memory alloy plates were found to be effective in reducing the residual drifts of a flange plate beam–column connection, while displaying an excellent ductility. In addition, shape memory alloy plates could prevent the occurrence of local buckling and damage in structural members. The new self-centering connections could also exhibit a good energy dissipation capability.
This article is concerned with the electromechanically coupled multiscale behaviors of the heterogeneous piezoelectric materials, which consist of periodic or non-periodic distributed microstructures. A multiscale framework based on the extended multiscale finite element method is developed to capture the large-scale solutions on the coarse-scale mesh without resolving the entire small-scale features. In this method, the microscale fluctuations in the mechanical displacement and electrical potential are related to the macroscopic deformation and electrical fields through the multiscale base functions. To improve the accuracy of the multiscale method, the periodic boundary conditions are developed to calculate the multiscale base functions for those piezoelectric structures composed of periodic microstructures. Moreover, the oversampling techniques are introduced to derive the oscillatory boundary conditions to construct the base functions for those piezoelectric structures with non-periodic heterogeneous microscopic features. The efficiency and accuracy of the multiscale method proposed for the piezoelectric materials are validated through the examples where the structures consist of periodic or non-periodic heterogeneous microstructures. The results indicate that the multiscale method developed can effectively obtain the macroscale response of piezoelectric materials (displacement or electrical potential) as well as the response in the microscale (stress or electrical displacement).
The transmission interface deformation for a disk-type magnetorheological clutch appears unavoidably due to machining error, assembling error, and thermal stress. To study the transmittable torque variation due to interface deformation, the common deformation forms of a disk-type magnetorheological clutch are summarized. And then, an experimental test-bed is designed and established. After this, the experiments of transmittable torque due to deformed disks are carried out in the test-bed. The research results indicate that interface deformation has certain influence on the transmittable torque of magnetorheological clutch. For the skew deformation, the transmittable torque will increase approximately linearly with the increment of deformation value. For the warping deformation, when the deformation value is positive, the torque variation rule is the same as skew deformation. While the deformation value is negative, the torque decreases first as the absolute deformation value is smaller and then increases as the absolute deformation value becomes larger.
The susceptibility of composite materials to internal damage caused by low-velocity impact is well known and creates a major concern related to structural health monitoring. This research presents a near-field impact monitoring method based on the two-dimensional multiple signal classification method for the composite structure. Since elastic waves attenuate quickly in the complex aircraft composite structures and impacts may happen near the sensors, near-field impact monitoring method is important. However, most of the methods reported are based on the far-field assumption. When impacts occur not far enough from the sensors, this belongs to the near-field situation, where the elastic wave fronts are spherical and the direction estimation method with the plane wave hypothesis is no longer valid. Hence, this article focuses the research of a near-field multiple signal classification–based impact localization method. To verify the proposed method, two experiments are performed on composite structures. The localization results are in good agreement with the actual impact occurring positions in near-field area. Finally, the proposed method is applied to a real aircraft composite oil tank showing its successful performance on complex composite structure.
H- and T-shaped cross sections are known to be susceptible to rotational single-degree-of-freedom aerodynamic instabilities. Here, such self-excited aerodynamic response of a T-shaped cantilever structure is used to extract energy, which is then converted into electric power through an electromagnetic transducer. The complex fluid–structure interaction between the cantilever harvester and wind flow is analyzed numerically and experimentally. To study the dynamic response of the cantilever and estimate the power output from the harvester, numerical simulations based on the vortex particle method are performed to determine the aerodynamic damping of the harvester section and to analyze the stability behavior of the section. The estimated aerodynamic damping parameter together with the mechanical and electrical damping parameters in the harvester are used to find the critical wind speed of flutter onset as well as the optimum load resistance. Wind tunnel experiments are conducted to validate the simulation results.
The use of smart materials in vibration control problems, including aeroelastic response, has been investigated in several researches over the last years. Although different smart materials are available, the piezoelectric one has received great attention due to ease of use as sensors, actuators, or both. The main control techniques using piezoelectric materials are the active and passive ones. In the case of aeroelastic control, passive piezoelectric networks have a weak capability of improving the flutter stability margin. Although active systems can achieve good vibration control performance, the amount of external power and added hardware are important issues for active aeroelastic control. In this article, the self-powered semi-passive piezoelectric control of a wind tunnel model aeroelastic response is presented as an alternative to active and passive systems. Linear and nonlinear aeroelastic cases are examined using a test apparatus that allows for experiments of pitch and plunge degrees of freedom of a typical section. Piezoelectric coupling is introduced onto the plunge degree of freedom, and two different semi-passive control schemes are employed: the synchronized switch damping on short circuit and the synchronized switch damping on inductor. An autonomous and self-powered switching circuit is employed, providing a useful self-powered method of aeroelastic control.
When the temperature of asphalt concrete is above a certain threshold, bitumen may start flowing through any possible crack and healing it. Induction heating is a technique for increasing the temperature of asphalt mixture. It consists of adding electrically conductive and magnetically susceptible particles to the mixture. These particles can be heated thanks to the action of an induction heating apparatus. The objective of this article is to investigate the effect of different asphalt mixture porosities and different types of bitumen on the induction-healing rates of asphalt concrete. With this purpose, semi-circular test samples made of porous asphalt mixture, with bitumen pen 70/100, and dense asphalt mixture, with bitumen pen 40/50, both of them containing steel wool fibres, have been analysed through successive three-point bending and induction heating tests. It has been found that the minimum temperature above which healing of asphalt mixture starts depends on the capacity for flow of bitumen at the threshold temperature. Moreover, the maximum healing level reached by asphalt mixture after damage is related to the type of bitumen used. Finally, it has also been found that successive heating of asphalt mixture may damage the structure of the material, reducing its healing capacity.
A model of motion of an agonistic–antagonistic shape memory alloy actuator is developed in this article. The model shows that the dynamics of the actuator can be well described by a nonlinear motion model of human muscle with nonlinear damping. To complete the model, a method for the determination of the damping properties of the actuator system is suggested. To this end, an analytical expression for the damping coefficient of the system was developed. The experimental verification of the proposed model of motion was conducted through a comparison of the experimentally measured and numerically simulated step responses. The simulated step responses were in close agreement with their experimentally measured counterparts on the shape memory alloy actuator prototype.
This study is focused on developing a morphing skin that can perform ±30° pure shear morphing. Carbon fibre–reinforced plastic rods–reinforced and Kevlar-reinforced silicone rubber matrix composite skin is designed, fabricated, tested, and utilized on the demonstrator wing. This skin design has achieved satisfactory wrinkle onset angle (>50°) without applying pre-tension or pre-stretch, low in-plane shear stiffness that allows the skin of 1 m2 to perform 30° shear morphing under 30 kg actuating force, designable out-of-plane stiffness, considerable damage tolerance, and simplicity in fabrication. This article describes the designing process of the skin, where a carbon fiber–reinforced plastic rod–reinforced skin is tested and revised to the final design; the study on the mechanism of different types of wrinkles as well as the strategies of wrinkles reduction, where two complementary wrinkle characterization methods are used; analysis and testing on out-of-plane stiffness; and finally, the utilization of skin on a demonstrator morphing wing structure. The presented skin can also be used as morphing face sheet.
This study addresses the effects of frequency and load resistance on energy harvesting using a mechanically excited ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation in [011] cut Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystals. The crystals were mechanically driven through the phase transformation, and voltage across a resistive load was measured. The effects of frequency and resistive load on the electrical energy generated were measured. Over the range of frequencies and load impedances tested, the crystals behaved as a charge source. The current increased linearly with frequency, and the voltage increased linearly with load impedance. Impedance matching to maximize the energy harvested is discussed. The energy harvested using the phase transformation was on average 27 times, with a peak of 108 times, the energy harvested using the same crystals operating in the linear piezoelectric regime under the same stress excitation amplitude.
Piezoelectric materials, such as lead zirconate titanate, display high electromechanical coupling, low internal losses, and exceptional environmental durability making them the material of choice for acoustic imaging transducers. Traditionally, piezoelectric transducers are actuated in the thickness-extension mode and they often make use of "matching" films to improve the signal transmissibility into lower acoustic impedance targets. In this article, we propose the use of transducers coupled to a structure in a direction orthogonal to the resonating plane. An analytical solution for the electromechanical behavior of a piezoelectric plate coupled transversely is derived. The analytical model shows that when resonated transversely, a transducer could display significantly lower effective acoustic impedance compared to transducers actuated in the thickness-extension mode. This feature eliminates the need for the matching films, hence helping reducing manufacturing costs. General guidelines on how to optimize the design of the proposed transducer for impedance imaging are also given. Finally, this article shows one example of how using a lead zirconate titanate transducer resonated transversely can reliably detect matrix cracking in fiberglass composite plates.
In this study, we intend to introduce a nonlinear dynamic theory for analyzing dynamic behavior of plate-like polypyrrole-based trilayer actuators for the first time. Within the displacement field of a first-order shear deformation plate theory and contemplating the nonlinear strain–displacement relations, nonlinear equations of motion are derived using Hamilton’s principle. The nonlinear governing equations are solved using the generalized differential quadrature method together with Newmark’s time integration scheme and the Newton–Raphson iterative method. For the assessment of the accuracy of the present theory, experimental data available in the literature are utilized. Two types of boundary conditions for both steady-state and dynamic analyses are investigated. The present results indicate the importance of considering geometric nonlinearity in the system.
Textured surfaces, formed through wrinkling and folding, are observed abundantly in nature. We are especially motivated by the unique capabilities of some species of cuttlefish that camouflage themselves by rapidly switching from smooth to textured skin by expressing protuberances called papillae. Inspired by this, we developed a shape memory alloy–elastomer composite as a platform for reversible surface texture. A shape memory alloy wire embedded in an elastomer is forced to shrink due to Ohmic heating. This shrinkage is used to drive the reversible buckling of a thin stiff film attached to the elastomer surface. The platform is scalable, produces wrinkling patterns in the flip of a switch, operates at voltages under 10 V, and can be operated reversibly over multiple cycles. The amplitude and kinetics of the surface wrinkling are experimentally characterized. The wrinkle patterns appear and disappear in timescales ranging from tens of seconds to as little as a second depending on the voltage actuating the shape memory alloy wire. Finally, this platform can create reversible wrinkle patterns in a spatially reconfigurable fashion, that is, the location of the texture changes can be varied in real time. A two-dimensional shear lag model is developed to establish the important design parameters governing the formation of wrinkles.
In this article, simulation for PbZr0.516Ti0.484 (lead zirconate titanate)–Pt functionally graded piezoelectric material bimorph actuator is carried out. It consists of seven layers of lead zirconate titanate–Pt with a symmetric composition profile from the center (0% Pt, 10% Pt, 20% Pt, 30% Pt, 20% Pt, 10% Pt, and 0% Pt%). The structural parameters which include length, width, and thicknesses of piezoelectric layers and substrate layer (30% Pt) are optimized based on their first resonance frequency. The bimorph actuator based on optimized parameters shows the first resonance frequency at 960 Hz as compared to resonance frequency (7761 Hz) of original design of functionally graded piezoelectric materials. Large actuation is observed in functionally graded piezoelectric materials of proposed design. The proposed functionally graded piezoelectric material actuator can be effectively used at low frequency (960 Hz) with high tip displacement (35 µm) under 500 V. This work is helpful in fabricating functionally graded piezoelectric materials for specific applications.
Cracks in reinforced concrete provide preferential access for aggressive substances into the concrete. Therefore, the corrosion of reinforcement bars is accelerated. Besides, carbonation, sulfate attack, and alkali–silicate reaction take place deep inside the concrete. Fortunately, from previous experiments, it was found that cracks in concrete can be healed with water and Ca is a main chemical element of the reaction products of self-healing. However, the ion concentrations in water can be various depending on the sources of water. There is still a lack of information on the effect of ion concentrations on self-healing. In this article, the effect of Ca2+ ions on self-healing was investigated experimentally. Ca(OH)2 was added into water as a healing agent. Self-healing behavior of cracks with saturated Ca(OH)2 solution was explored and compared with that with distilled water. In order to gain deeper insight into the mechanism, the reaction products of self-healing were characterized by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. In addition, the filling fraction of cracks as a function of time was determined by means of backscattered electron image analysis. The efficiency of self-healing induced by saturated Ca(OH)2 solution was evaluated and compared with that with distilled water.
In order to design efficient low-frequency piezomagnetoelastic energy harvesters, an effective analytical model which considers the effects of the electromechanical coupling and the nonlinear magnetic force is required. In this paper, the harvester consists of a partially covered piezoelectric cantilever beam with a fixed magnet mass at the top of the magnet tip mass. A nonlinear distributed-parameter model based on Euler–Bernoulli beam theory and Galerkin discretization is developed. The used mode shapes in the Galerkin discretization take into account the fact that the magnetic force and the piezoelectric sheet do not cover the whole beam. In addition, we develop an approximated distributed-parameter model that is based on the classical mode shapes of a fully covered piezoelectric cantilever beam in the Galerkin discretization. These distributed-parameter models are compared with a lumped-parameter model and experimental measurements. The results show that the derived distributed-parameter model accurately predicts the experimental measurements and particularly the accompanying softening behavior. On the contrary, it is demonstrated that the approximated distributed-parameter and lumped-parameter models give erroneous predictions of the resonance region, the level of the harvested power, and the softening behavior. In order to investigate the effects of the load resistance and the softening behavior on the performance of the harvester, a parametric study based on the analytically validated model is then performed. The results show that the presence and importance of the softening behavior depends on the electrical load resistance. It is also demonstrated that the presence of the softening behavior plays an important role in the short- and open-circuit configurations.
The early-age hydration processes of concretes with mineral admixtures have been monitored and evaluated by a newly developed ultrasonic method based on embedded cement-based piezoelectric composite sensors. With the embedded ultrasonic (P-wave) measurement system, the waveform, wave velocity, attenuation coefficient index, and frequency-domain spectrum of detected ultrasonic waves during hydration can be recorded. The mineral admixtures examined include fly ash, slag, and silica fume, which replace part of the cement in concrete mixtures. It is found that the ultrasonic transmission parameters can be related to the microstructure changes of the concrete. Both the acceleration effects of silica fume and the retardation effects of fly ash and slag on the early hydration of concrete can be determined and explained through the analysis and comparison of the characteristics of the velocity curves. The attenuation coefficient index curve provides additional observation for the study of hydration kinetics. Moreover, the function of fresh concrete in filtering the high-frequency component of the wave varies with time, and concrete can be considered as low-pass frequency spectral filter. Frequency spectra analysis at different ages of fresh concrete provides useful information to reveal the early-age hydration process.
This paper focuses on the development of a 3D hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics®. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can describe minor loops which are essential for both Galfenol sensor and actuator design. A group of stress versus flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime. Through incorporating C code with MATLAB, the computational efficiency is improved by 78% relative to previous work.
This article reports the development of flexible arrays of soft membrane microelectromechanical system pressure sensors that are inspired by the functional implications of the lateral line organ present in the blind cavefish. Being blind, this fish relies on the lateral line of pressure gradient sensors present on its body to sense the surrounding obstacles. A flexible, low-powered, lightweight, sensitive yet robust microelectromechanical system sensor array is fabricated using liquid crystal polymer material. Such arrays can guide an autonomous underwater vehicle to navigate in unsteady and dirty-water environments. The object detection abilities of the blind cave characin fish are investigated through proof-of-concept experiments conducted on the live fish. Similarly, the abilities of the microelectromechanical system array in determining the velocity and distance of an underwater object are investigated by testing them in water tunnel. Experimental results demonstrate the array’s ability to detect the velocity of moving underwater objects with a high accuracy and an average error of only 2.5%.
The scavenging of electrical energy from normal human activity has a number of attractions, and footfall energy is seen as one of the most attractive sources. However, footfall motion is characterised by relatively large forces and low velocities, and this makes it inherently poorly matched to electromagnetic generators which operate most efficiently at high speeds. In order to achieve an efficient velocity amplification, a novel mechanism has been developed which makes use of a spring and flywheel as energy storage elements and a ‘striker’ mechanism which controls energy storage and release. This energy harvesting mechanism is capable of being used either in footwear or under a floor. In this article, the structure of the proposed mechanism is described; the optimisation of the system parameters, based on a dynamic model, is discussed; and experimental results for an under-floor system are presented.
This article presents a novel strategy for finite element model updating of flexural structures. The method is based on modal parameters extracted from dynamic distributed macro-strain responses. The objective function that comprised low-order modal macro-strain and frequency was established first, while local bending stiffness, density, and boundary conditions of structures can be selected as the design variables. Both numerical simulation and experiment were conducted to verify the effectiveness of the proposed method. The long-gauge macro-strain sensors chosen in this article are first addressed, and the fundamental sensing properties of the macro-strain sensors confirm great dynamic measurement capacity. Simulation and experimental results show that both the local parameter (bending stiffness) and the global parameters (mass density and rotational stiffness of support) can be well identified. Notably, the updated finite element model can predict local response modal macro-strain and global response (frequency and displacement mode) because the local information-sensitive index and global information-sensitive index are included in the objective function. Therefore, the proposed finite element model updating strategy constitutes a new alternative in performance assessment of flexural structures.
The exploitation of nonlinear behavior in vibration-based energy harvesters has received much attention over the last decade. One key motivation is that the presence of nonlinearities can potentially increase the bandwidth over which the excitation is amplified and therefore the efficiency of the device. In the literature, references to resonating energy harvesters featuring nonlinear oscillators are common. In the majority of the reported studies, the harvester powers purely resistive loads. Given the complex behavior of nonlinear energy harvesters, it is difficult to identify the optimum load for this kind of device. In this paper the aim is to find the optimal load for a nonlinear energy harvester in the case of purely resistive loads. This work considers the analysis of a nonlinear energy harvester with hardening compliance and electromagnetic transduction under the assumption of negligible inductance. It also introduces a methodology based on numerical continuation which can be used to find the optimum load for a fixed sinusoidal excitation.
A unified formulation of finite layer methods based on the Reissner’s mixed variational theorem is developed for the three-dimensional dynamic responses of simply supported, functionally graded carbon nanotube–reinforced composite plates with surface-bonded piezoelectric sensor and actuator layers and closed- and open-circuit surface conditions. In the formulation, the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations in the primary field variables of each individual layer, respectively, such as the elastic displacement, transverse shear and normal stress, electric potential, and normal electric displacement (flux) components. The relevant orders used for expansion of these variables in the thickness coordinate can be freely chosen, such as linear, quadratic, or cubic ones. Four different through-thickness distributions of carbon nanotubes in the carbon nanotube–reinforced composite layer are considered, and the effective material properties of the layer are estimated using the rule of mixtures. The accuracy and convergence rate of the frequency parameters of the sandwiched hybrid carbon nanotube–reinforced composite and piezoelectric plates obtained using assorted Reissner’s mixed variational theorem–based finite layer methods are assessed by comparing their solutions with the exact three-dimensional solutions available in the literature.
This article deals with the analysis of the power consumption in the piezoelectric ceramic patch of lead zirconate titanate and the losses arising from the adhesive bonding with the host structure. When a lead zirconate titanate patch is utilized as an impedance transducer in the electromechanical impedance technique, it acts both as a sensor and as an actuator (dual effect) for the range of frequency. Power consumption occurs in two forms. First part of the energy is used to actuate the lead zirconate titanate patch and produce deformations. The other part of the energy is dissipated within the piezo-mechanical system due to the internal mechanical loss and the associated heat generation. The determination of the power consumption characteristics for an active piezo-system is very important for designing an efficient intelligent structure with optimized mass and energy combination. Adhesive bond itself acts as an added stiffness, mass and damper and plays an important role in mechanical and electrical energy conversion. Hence, a detailed investigation is needed to characterize the power consumption and energy issues associated with bond layer driven by lead zirconate titanate patch, which is the main aim of this article.
Self-sensing actuation has been extensively used in vibration control of flexible structures over the last three decades. Positive position feedback controller has been commonly used in this field due to the robustness against spillover phenomena. Piezoelectric clamped capacitance is the most important parameter that affects the performance of this technique. In this study, the effect of capacitance change on performance and stability of a self-sensing system with positive position feedback controller is investigated. Based on this analysis, some modifications are suggested to increase the stability of the closed-loop system against capacitance change. An online Fourier transform–based capacitance measurement method is used, which guarantees good performance and stability of closed-loop system in the presence of capacitance change. Experimental results are also presented to show the effectiveness of this method in vibration control of cantilever beam.
This article focuses on the active vibration control of a kind of two-connected piezoelectric flexible plate. A finite element model of the connected plate integrated with distributed piezoelectric sensors and actuators is derived, including bending and torsional vibrations. In this model, two connected hinges are simplified as regular plate elements to facilitate the system. A modified optimization method based on the energy dissipation rate is used for the optimal placement of piezoelectric sensors and actuators. The bending and torsional vibrations of the two-connected plate can be decoupled on measurement and driving control, due to the appropriate placement of the lead zirconate titanate sensors and actuators. The proportional and derivative control, the proposed nonlinear controller, and T-S fuzzy control algorithms are applied to suppress the bending and torsional vibrations of the two-connected plate. The numerical simulation and experimental results demonstrate that the last two control algorithms can suppress the low-order bending and torsional vibration more effectively than that of the designed proportional and derivative control algorithm.
In this study, a three-dimensional thermomechanical constitutive model based on the microplane theory is proposed to simulate the behavior of shape memory alloy tubes. The three-dimensional model is implemented in ABAQUS by employing a user material subroutine. In order to validate the model, the numerical results of this approach are compared with new experimental findings for a NiTi superelastic torque tube under tension, pure torsion, and proportional tension–torsion performed in stress- and strain-controlled manners. The numerical and experimental results are in agreement indicating the capability of the proposed microplane model in capturing the behavior of shape memory alloy tubes. This model is capable of predicting both superelasticity and shape memory effect by providing closed-form relationships for calculating the strain components in terms of the stress components.
In the context of the theory of nonlinear magneto-elastic deformations, the problem of the extension (shortening) of a cylinder of finite length under the influence of a magnetic field applied far away in free space is studied. The boundary value problem is solved using the finite element method. There exist exact solutions for the problem, which are based on the assumption of working with infinitely long cylinders. In this communication, results are obtained for different relations between the radius of the cylinder and its length, comparing the results for the magnetic field between short and long cylinders. As well as this, the influence of applying such external traction through the direct contact with an external machine has been studied.
It is essential to have a robust sensor fault detection and isolation algorithm integrated with successful online continuous structural health monitoring scheme to avoid false alarms. In this work, a sensor fault detection and isolation technique based on null subspace method is presented. The robustness of the proposed sensor failure detection and isolation algorithm is demonstrated using the vibration data obtained from an experimental study of a scaled down bridge model. Studies presented in this article clearly indicate that the proposed method is robust in identification of exact time instant of sensor fault and also isolation of faulty sensor. The proposed algorithm is equally good for all possible types of sensor faults (both additive and multiplicative) and also capable of isolating multiple sensor faults in spatial location of the structure.
This study consists of the calculation of the effective properties for active fiber composites made of either circular or square cross-section fibers not only by using finite element analysis and representative volume elements, but also based on the asymptotic homogenization method. Thus, there is an investigation about different approaches, which have specific mathematical formulations and unique characteristics. The comparison between numerical and analytical approaches shows that the numerical results are in good agreement with investigations performed by both analytical and semi-analytical methods, mainly the predictions for loading applied in fiber direction. For active fiber composites made of circular cross-section fibers, the maximum difference between asymptotic homogenization method and finite element analysis is from 1.29% to 5.49% for mechanical and piezoelectric effective properties, respectively, considering representative volume element in square arrangement. However, for active fiber composites made of square cross-section fibers, the maximum difference between semi-analytical method and finite element analysis is from 2.15% to 17.09% for mechanical and piezoelectric effective properties, respectively, considering representative volume element in square arrangement.
While wireless sensor networks have been successfully deployed on a variety of civil infrastructure systems for structural monitoring, past studies have shown that there is room for improvement in terms of network robustness and overall resource consumption efficiency. The mechanisms employed by biological nervous systems (e.g. signal modulation, communication, and integration) can be used as inspiration for overcoming the performance bottlenecks seen in existing wireless sensor nodes and networks. The mammalian auditory system is of particular interest due to its unique signal decomposition techniques (performed by the cochlea) that enable real-time processing of complex sound signals. In this article, a novel wireless sensor architecture based on the operational principles of cochlea is described. The performance of the proposed sensor is validated on a single-degree-of-freedom structure that is excited by seismic ground motion signals, thus demonstrating its real-time monitoring capabilities while maintaining high data compression rates.
Energy harvesting is now an established field, and the linear equivalent circuit models for single- and multiple-degree-of-freedom systems are being routinely used to assess the energy harvesting efficiency of various interface and electronic circuits. However, as the field of energy harvesting moves toward more complex systems such as nonlinear energy harvesting and fluidic energy harvesting, modified equivalent circuits are required to effectively capture the behavior of these devices. This article presents two general methods (a system-level approach and a dependent source equivalent approach) that can adequately model the behavior of more advanced harvesters. These approaches can also be easily used to model single- and multiple-degree-of-freedom linear harvesters. Equivalent circuits for both piezoelectric and electromagnetic harvesters are discussed. Four case studies are presented to illustrate the application of these equivalent circuit approaches including the following: (1) a piezoelectric Duffing harvester, (2) an electromagnetic Duffing harvester, (3) a simplified aeroelastic harvester, and (4) a piezoelectric Duffing harvester with a rectifier circuit.
This article develops and proves the concept of morphing bi-stable glass fiber–reinforced polymer laminates using electrothermal alloys to trigger the snap-through from one stable configuration to another. The presented concept considers an alternative to existing morphing bi-stable concepts wherein actuators are used to elastically actuate bi-stable laminates to snap between stable configurations. These existing concepts are restricted to some bi-stable laminates with certain layups and sizes. For the concept discussed here, the electrothermal alloys are embedded in the laminates and are used as internal heating sources. Morphing can be achieved by heating and subsequently cooling the local region of the laminate, and no energy is needed to maintain the deformation. One-way and a two-way morphing bi-stable laminates are designed and manufactured. The finite element simulation is performed to predict the thermally induced morphing process. The experimental morphing process is compared with the simulated process, and good agreement between experiments and predictions is found. The basic principle of this morphing bi-stable structure is discussed. Based on the same principle, more different forms of morphing bi-stable structures can be designed and manufactured.
Human footfall is an attractive source of energy for harvesting for low-power applications. However, the nature of footfall is poorly matched to electromagnetic generators. Footfall motion is characterised by high forces and low speeds, while electromagnetic generators are normally most efficient at relatively high speed. This article proposes a novel mechanism for converting the low-speed motion of footfall to a higher speed oscillating motion suitable for electromagnetic power generation. The conversion is achieved using a cantilever beam which is deflected by the footfall motion using a special ‘striker’ mechanism which then allows the cantilever to oscillate freely at a relatively high speed. An arrangement of permanent magnets attached to the cantilever causes an alternating magnetic field, and a stationary coil converts this to a usable voltage. This article describes the mechanism and provides a mathematical model of its behaviour which allows the system parameters to be optimised and its performance predicted. The performance of a prototype device is presented, and it is shown that this is capable of generating up to 60 mJ/step and that the conversion efficiency is up to 55%.
A novel piezohydraulic vibration isolator consisting of a hydraulic cylinder and piezodiscs was presented for low-frequency and wide-bandwidth vibration energy harvesting. The analytical model for performance evaluation was established first based on the theory of vibration analysis and simulated to obtain the influence of backpressure and proof mass on equivalent bulk modulus and stiffness of fluid, and optimal frequency and generated voltage of the piezohydraulic vibration isolator. And then, a prototype was fabricated and tested. The research results show that, under other parameters given, the energy generation performance of a piezohydraulic vibration isolator can be tuned with changing backpressure and proof mass. And there are a series of optimal parameter combinations of backpressure and proof mass for a piezohydraulic vibration isolator to achieve the same optimal frequency and almost the same voltage. The minimal optimal tested frequency of 13 Hz and the relative voltage of 81.6 V were obtained at 0.2 MPa and 10 kg. For parameter combinations (0.4 MPa/10 kg, 0.4 MPa/5 kg and 0.8 MPa/5 kg), the optimal frequency and generated voltage are 19 Hz/98 V, 27 Hz/96.8 V and 39 Hz/94.8 V, respectively. Correspondingly, the bandwidths to generate voltage of 40 V are 28/35/30 Hz, respectively.
Ferromagnetic shape memory alloys are a class of shape memory alloys which can produce inelastic strains when exposed to magnetic fields. The existing constitutive models for these alloys are mostly accompanied by a phase diagram using which critical stresses and magnetic fields for start and finish of forward and reverse reorientations are determined. In this article, an available model is modified in a continuum framework, and explicit kinetic laws together with the corresponding phase diagram in stress–field space are obtained. The proposed phase diagram is unique for a specified ferromagnetic shape memory alloy although the original model predicts different phase diagrams for different conditions. The model is further improved through a phenomenological approach to be able to capture the reported experimental findings. Numerical predictions for several stress–strain responses at different constant applied magnetic fields are compared with available experimental results. Good agreements are seen between the theoretical and empirical findings, indicating validity of the proposed model and the corresponding phase diagram in studying the magneto-mechanical behaviors of ferromagnetic shape memory alloys.
Kapton membranes have received much attention in the fabrication of space inflatable antenna technology in the recent years. While prized for their light designs, their delicate nature makes them susceptible to various kinds of disturbances in space environments that result in structural vibrations or wrinkle formation. In this regard, macro-fiber composite actuators have been commonly used for vibration control of these membrane structures. However, wrinkle control remains one of the major challenges in their designs. Some of the research in the previous literature has attempted to quantify the wrinkle behavior of these membranes when subject to boundary forces. Yet, in all the previous study, the effects of macro-fiber composite patches, a major compartment of these structures, on their wrinkle formation have been ignored. The presented article studies the effects of these patches on localization of wrinkles and their patterns in Kapton membranes. The numerical results are validated experimentally using photogrammetry techniques. Two membrane configurations are studied: one considers rectangular membranes with clamped-sliding boundary conditions and the other pertains to square membranes with symmetric corner loadings.
Temperature variations have significant effects on guide wave propagation and therefore increase the detection uncertainty of the guided wave–based structural health monitoring system. A novel temperature compensation technique combining an adaptive filter and optimal baseline selection is developed to enhance the robustness and effectiveness of guided wave–based damage detection. The adaptive filter is the finite length unit impulse response digital filter based on adaptive linear neuron network. This article focuses on three main issues for practically implementing the proposed method: (a) establishment of temperature compensation standard, (b) parameter design of compensation filter, and (c) determination of temperature gradient to reduce the number of selected baselines. Experiments are conducted on two stiffened composite plates to verify the proposed method for effective and robust temperature compensation under a large temperature range from –40°C to 80°C. Results show that temperature interval for baselines of low-frequency signals, such as 50 kHz, can be up to 20°C to provide good temperature compensation with the proposed method, while temperature interval for baselines of high-frequency signals, such as 450 kHz, can be up to 12°C.
Energy harvesting from ambient vibration is an emerging and promising solution to the power supply problem associated with autonomous sensors. This article proposes a novel strategy of harvesting damping energy from vibration control devices. A novel system, termed electromagnetic damper cum energy harvester, is employed to fulfill both vibration damping and energy harvesting functions. Electromagnetic damper cum energy harvester is essentially an electromagnetic device connected to a specially designed energy harvesting circuit, which is a buck–boost converter operating in a discontinuous conduction mode. The energy harvesting circuit can achieve satisfactory efficiency without any feedback loop. The effectiveness of the dual-function electromagnetic damper cum energy harvester is demonstrated through a numerical case study of bridge stay cables under wind excitations, in which the major parameters of electromagnetic damper cum energy harvester are determined through a simple design approach. Simulation results project average output power ranging from 82.5 to 2396.8 mW at a wind speed of 9–15 m/s, corresponding to an overall efficiency of 42.3%. The dual-function electromagnetic damper cum energy harvester also exhibits vibration control performance comparable to an optimally designed viscous fluid damper.
A self-assembly method is developed for creating a thin shell of multiwall carbon nanotubes on aramid fibers. The fibers show resistive behavior and exhibit a gauge factor of approximately 1.6, which is competitive with existing foil strain gauges. The robust sensing package could be used in the development of embedded strain sensors in multifunctional composites.
The active vibration suppression of smart composite and sandwich shallow shells equipped with distributed monolithic piezoelectric and piezo-fiber reinforced composite (PFRC) sensors and actuators is studied using a four-node quadrilateral shallow shell element based on a fully coupled, accurate and efficient layerwise (zigzag) theory. The shell element uses the concept of electric nodes to satisfy the equipotential condition of electroded sensor surfaces without making any approximations or averaging. The effective electromechanical properties of the PFRC laminas are computed using a coupled three-dimensional iso-field micromechanical model. Both classical (constant gain velocity feedback (CGVF)) and optimal (linear quadratic Gaussian (LQG)) control strategies are studied. A truly collocated actuator–sensor arrangement is proposed and shown to remove the instability in CGVF control of shallow shells with conventionally collocated actuators and sensors. The effects of piezoelectric fiber orientation and volume fraction ratio of PFRC, and the radius of curvature and span to thickness ratio of the shell on the control performance, are studied. It is shown that the LQG control not only suppresses the transient vibration under step/impulse excitations, but also eliminates the beating phenomena under harmonic excitation when the forcing frequency is close to the natural frequency of the system.
The linear viscoelastic behaviour of magnetorheological elastomers is analysed in this work according to their formulation and working conditions. This study comprised both the synthesis of different magnetorheological elastomers and the strain and frequency sweep characterization under different magnetic fields and temperatures. The characterization was performed by a Physica MCR 501 rheometer from Anton Paar, equipped with a magnetorheologic cell 70/1T MRD. In the synthesis with a given elastomeric matrix, samples with different magnetic particle content are studied with two types of curing conditions: under the action of a magnetic field (anisotropic magnetorheological elastomers) and without a magnetic field (isotropic magnetorheological elastomers). The working conditions are excitation frequency, temperature and the applied external magnetic field. In this work, a new procedure to determine the linear viscoelastic behaviour is proposed; the loss factor is analysed in addition to analysing the storage modulus to determine the linear viscoelastic region of each sample. The results show that high temperatures and magnetorheological elastomers with higher volume fraction of magnetic particles restrict the linear viscoelastic behaviour of magnetorheological elastomers.
This article presents a method for localizing near-field acoustic emission sources in isotropic and homogeneous thick plate using coupled piezoelectric film strain sensors. This acoustic emission source localization method is based on the phase difference of the acoustic emission signals measured by two acoustic emission sensors spaced at a predetermined distance. This phase difference cancels out certain frequency contents of the measured acoustic emission signals, which can be related to the acoustic emission source direction. A theoretical formulation which predicts these trough frequency values and acoustic emission source direction angles for the coupled acoustic emission sensors is first presented. Rayleigh wave is employed since its wave speed does not change in homogeneous half space, and its amplitude is greater than other elastic wave modes. Both elastodynamic solution and experimental data are used to validate the acoustic emission source localization technique. It is seen that the theoretical predictions, elastodynamic solution, and the experimental results are in good agreement with each other. Experimental data from acoustic emission monitoring of a stiffened steel plate specimen under fatigue loading are also used to test this method. Results show that the coupled piezoelectric film strain sensors are effective in determining the acoustic emission source direction in thick steel plates.
In this study, a computational model is developed using finite-element techniques within a continuum micromechanics framework to capture the effect of electron-hopping-induced conductive paths at the nanoscale which contribute to the macroscale piezoresistive response of the nanocomposite. This is achieved by tracking the position of the nanotubes under applied deformations and modifying the conductivity of the intertube region depending on the relative proximity of individual pairs of nanotubes. The formation and disruption of the electron-hopping pathways are highly dependent on intertube distances and under deformations can result in microstructural rearrangements in terms of electrostatic properties leading to transitions in material symmetries and component magnitudes of the effective electrostatic properties. Thus, in order to capture the complexities of changing inhomogeneous nanoscale electrostatic behavior, where analytical Eshelby’s approaches cannot be used, a computational micromechanics model is needed. The effective conductivity and piezoresistive strain tensor coefficients are evaluated using volume-averaged energy equivalencies for aligned CNT–polymer nanocomposites in the transverse direction exploring different volume fractions of CNTs in the polymer and the maximum electron-hopping range. The impact of the electron-hopping mechanism on the effective piezoresistive response is studied through the macroscale effective gauge factors under different loading conditions. The effective piezoresistive strain coefficients and macroscale effective gauge factors are observed to be nonlinear with applied macroscale strain and are highly dependent on the type of boundary conditions. The effective macroscale gauge factors observed in the current study have magnitudes comparable to experimental observations reported in the literature with higher gauge factors observed closer to the percolation threshold.
This article presents a self-powered interface circuit for the optimized synchronous electric charge extraction technique applied to piezoelectric vibration energy harvesting. A peak detector circuit is developed to detect the maximum and minimum vibration displacements and drive the electronic switches synchronously. This approach does not require additional piezoelectric elements to power the electronic interface itself for which a detailed analysis and a simple model are proposed to give a better understanding on the working principle. Finally, the influence of the switching phase lag and the peak detector power consumption on the harvested power is studied. Experimental studies are conducted and successfully compared with the theoretical approach.
Powder metallurgy process was used in this work to produce NiTi specimens. Uniaxial compression, X-ray diffraction and differential scanning calorimetry were used for characterising the produced samples. L9 orthogonal arrays were chosen based on the Taguchi method for conducting the experiments. In order to optimise the processing parameters and also to determine the level of importance of each parameter, experiments were performed based on grey relational method. Our goal was to optimise recoverable strain () and the finishing temperature of austenitic transformation (A f ). Sintering time, compaction pressure, milling time and the atomic percentage of Cu were all selected as controllable parameters. Our results reveal that the sintering time and the atomic percentage of Cu are the most significant parameters. The findings were verified through a confirmatory test.
The governing equation of a nanotube-based mass sensor is derived with consideration of surface energy, transversem shear deformation, and rotary inertia. Dependencies of the frequency shift and the sensitivity of the sensor on the attached mass are obtained in closed form. The results show that the traditional model, which neglects the surface energy, predicts a higher attached mass and lower sensitivity of the sensor. On the other hand, neglecting the transverse shear deformation and rotary inertia of the sensor will result in a lower prediction of attached mass and a higher prediction of sensitivity of the sensor. It is also found that the surface energy has no effect on the mode shape of the sensor. However, the effect of the location of the attached mass on the mode shape is significant. In particular, if the attached mass is close to the midpoint of the sensor, the frequency shift and sensitivity become very significant.
Magnetorheological elastomers are a new kind of magnetorheological materials mainly composed of polymer rubber and micro-sized magnetizable iron particles. Dynamic vibration absorbers based on magnetorheological elastomers are widely used in vibration systems with small amplitude since they have the advantages of no sealing equipments, good stability, and rapid response. In this article, a shear-mode semi-active dynamic vibration absorber based on magnetorheological elastomers is proposed, and the dynamic design principle of an axial semi-active dynamic vibration absorber attached to ship shafting is studied. The material preparation of magnetorheological elastomers and their properties under different magnetic fields are discussed. The structure of a single semi-active dynamic vibration absorber is designed, and theoretical analysis of shift-frequency property of a single semi-active dynamic vibration absorber is also investigated. The magnetic flux density of magnetorheological elastomers in the semi-active dynamic vibration absorber is analyzed using ANSYS software. A compact and efficient semi-active dynamic vibration absorber for shafting axial vibration control is proposed. Furthermore, a linear relationship is found between the excitation current and the natural frequency of a single semi-active dynamic vibration absorber. The results show that the designed axial semi-active dynamic vibration absorbers have better performance than classic passive dynamic vibration absorbers in terms of frequency-shift property and vibration absorption capacity.
The goal of this study is to investigate the prestressing effect of shape memory alloy bars in reinforced concrete beams; bars are prestressed by external force or recovery stress due to shape memory effect. The shape memory alloy bars are heated by hydration heat of concrete during curing to induce the shape memory effect. To achieve this goal, this study conducts bending tests of concrete beams reinforced by shape memory alloy bars as well as those reinforced by steel bars. The beams with shape memory alloy bars with recovery stress show the same or slightly larger flexural strength than those with shape memory alloy bars prestressed with external force. Thus, this study indicates that the recovery stress of shape memory alloy bars plays the same role as the prestressing force, and that the shape memory effect can be induced by hydration heat of concrete instead of heating by electronic resistance.
This article presents a new setup and investigates neural control approaches developed to control a 1-degree-of-freedom shape memory alloy–actuated manipulator. Shape memory alloy–actuated manipulators have drawbacks such as hysteretic behavior and parameter uncertainty. The suggested control approaches should deal with these problems and make the manipulator to track the desired position. First, a mathematical model of the manipulator is presented. The control methods are then developed and applied to the experimental setup. The high performances of the proposed controllers are indicated by experimental results. A comparison between the applied control approaches is made based on the step response main factors and the control signal of each method. Finally, the frequency range for which the suggested methods are appropriate is confirmed.
In this study, a kind of morphing skin composed of silicon rubber and shape memory polymer composite tube is designed, manufactured, and investigated. Significant stiffness variation for the morphing skin can be obtained through changing its environment temperature. First, in order to investigate the basic elastic properties of the morphing skin, the Rule of Mixture is used to predict the effective engineering modulus and modulus ratio with different matrix volume fractions. The tensile test is conducted on the skin in two states (cold state and heated state) to validate the accuracy of the theoretical method. Second, the temperature distribution of shape memory polymer composite tube heated by the hot fluid is obtained through the finite element analysis. Moreover, a corresponding heating system is designed and manufactured to provide heat for the morphing skin. Based on the heating system, the deflection and recovery performances are also investigated through the stress-bearing capability and thermal cycling tests, respectively. Finally, the infrared test is carried on the morphing skin to show the temperature distribution during the heating process.
In this work, a design strategy is presented, addressed to adaptive structural systems, driven by shape memory alloy actuators. The peculiar behaviour of shape memory alloy materials, non-linear and fully dependent on three parameters (stress, strain and temperature), and the load path itself complicate the numerical simulation process. This is even more evident if those active elements are integrated within complex structures. Actuators generate forces. Integrated shape memory alloy–based structural actuator capability is strongly influenced by the hosting structure stiffness. It does in turn depend on the geometrical configuration. The structural architecture may be then said to modulate the performance of the aforementioned devices. The layout modifies in fact the structural resistance that opposes the action of a generic shape memory alloy actuator, even if the same topological point is referred to. This opposition affects the change of phase process (martensite austenite) regulating shape memory alloy peculiar phenomena and then impacts its performance. For simple, linear shape memory alloy actuators, the structure may be represented as an oriented spring where all the information of the parent structure is concentrated in its scalar stiffness property. This value is a function of the specific layout. A way to compute this equivalent structural stiffness comes directly by its definition: the ratio between the generated actuation force and the derived homologue structural displacement, that is, displacement occurring along the same force direction. Because such stiffness is what the shape memory alloy actuator feels, in this article it is referred as ‘perceived stiffness’. In this article, the structural layout effect on linear shape memory alloy actuator performance is initially evaluated for a simple spring. The approach is then extended to a complex active structural system, element of an aircraft wing morphing architecture. The referred device is capable of deforming wing regions while resisting the aerodynamic and the structural loads and recovering the original shape, once the actuation stops. Structural actuator geometry is optimised as a function of the attained structural displacement (figure of merit). The work is concluded with a discussion on the achieved results, namely, rotation, vertical displacement, internal stress (strain) levels and activation temperature.
Thermomechanical coupling in shape memory alloys causes temperature variations during cyclic loading, especially at high strain rates. This leads to dependence of response in each cycle to those in the previous ones until the stabilized response is attained. In this article, a fully coupled thermomechanical model is used to study either stress- or strain-controlled cyclic loadings on shape memory alloy wires. Experiments are carried out to verify the numerical results of this model. Instead of considering temperature changes, the material’s temperature is taken to be constant, but parameters in the shape memory alloy phase diagram are assumed to vary cycle by cycle. By introducing a cycle-dependent phase diagram, any specified cycle can be deemed as a quasi-static loading–unloading whose response is achieved independently from the previous cycles. Moreover, the number of cycles to reach stabilized hysteresis loops is achieved with no need to solve the transient cycles. Variations in the phase diagram parameters and the number of cycles to reach stabilization are studied at different conditions for two types of stress- and strain-controlled cyclic loadings.
It is difficult to make sure that the spliced polarization-maintaining fiber length is the same in every fabricating polarization-maintaining fiber loop mirror sensor, and it is also difficult to make sure that sensing length is the same in every experiment. To find out how these uncertain factors influence the axial strain sensitivity of polarization-maintaining fiber loop mirror, we perform the research on the influences of polarization-maintaining fiber length and sensing length on axial strain sensitivity. In this article, a theoretical model for axial strain sensitivity of polarization-maintaining fiber loop mirror is deduced first. By analyzing the theoretical model, we find that the axial strain sensitivity is unrelated to polarization-maintaining fiber length and sensing length. Then, we experimentally investigate the influences of polarization-maintaining fiber length and sensing length on axial strain sensitivity of polarization-maintaining fiber loop mirror. The axial strain sensitivities in the experiments are almost the same for different polarization-maintaining fiber lengths and different sensing lengths. The experimental results agree with the theoretical ones. The results can provide help for fabricating and applying polarization-maintaining fiber loop mirror sensor. The results can be applied in the temperature, displacement, and vibration sensors of polarization-maintaining fiber loop mirror and can also be applied in photonic crystal fiber loop mirror sensor.
This article presents an in situ structural health monitoring imaging system for the localization of impacts on a composite complex structure such as a tail rotor blade. Unlike conventional plate-like panels, this composite structure presents a strong anisotropy and inhomogeneous elastic nature due to the presence of both glass fibre and carbon fibre, a geometrically complex shape due to the curvature of the blade’s airfoil section and variations in the mechanical behaviour due to local changes in the thickness. The proposed imaging technique is based on the inverse filtering or reciprocal time reversal approach applied to the waveforms originated from a point of the structure of unknown location (impact source) and a number of signals stored in a database containing the experimental Green’s function of the medium. Unlike other ultrasonic impact localization methods, the present technique allows achieving the optimal focalization of the impact point in the spatial and time domain, by taking advantage of multiple linear scattering and a small number of receiver sensors.
Nowadays, ionic polymer metal composite actuators are widely used in many fields such as biometric, biomedical, and micro-manipulator devices. Although extensive research exists on control of the ionic polymer metal composite actuators, not much research has been done on robust control considering the nonlinear dynamics of the ionic polymer metal composite. In this study, for the first time, a closed-loop robust controller based on quantitative feedback theory is designed to overcome the actuation performance degradation of the ionic polymer metal composite actuators. First, an analytical electromechanical model is developed to fully describe dynamics of the flexible ionic polymer metal composite actuator. The model is based on the Euler–Bernoulli beam theory and includes structural damping to model viscoelastic behavior of the ionic polymer metal composite actuator. Considering the highly nonlinear and uncertain dynamics of the ionic polymer metal composite actuator, a feedback controller based on quantitative feedback theory is designed to suppress the arbitrary external disturbances and consistently track desired input. Results indicate that the robust quantitative feedback theory control techniques can significantly improve the ionic polymer metal composite performance against nonlinearity and parametric uncertainties.
A strong integration between different design tools is desirable to improve the work of engineers, reducing the number of errors and speeding up the design process. In this article, the authors present a strong integration between three-dimensional computer-aided design models and multidomain simulation applied to the design of a magnetomechanical energy harvester. A MATLAB framework controls a block-oriented Simulink model, drives the Finite Element Method Magnetic simulation and manages the updating of the SolidWorks computer-aided design models of the device. The parameters involved in the different simulations and in the computer-aided design models are stored in a unique data file. Moreover, constructive drawings are automatically updated and are immediately suitable for tolerance and design constraint checks and also for the effective prototyping of the device. Constructed prototypes are immediately suitable to validate the performance predicted by the model.
Magnetorheological fluid is a controllable fluid that exhibits changeable yield stress and attractive rheological properties on the applied magnetic field. In order to enhance the yield stress of magnetorheological fluid and suppress wall slip effect in the case of transmission, the mechanism and corresponding influence factors of the wall slip effect were investigated theoretically and experimentally. Different transmittable disks and a magnetorheological transmission test-bed were built, and the influence of wall characteristics on the transmission capacity of magnetorheological fluids was investigated on the test-bed. The results showed that the material types, surface roughness, and surface textures of transmission wall have distinct influence on the transmission capacity of magnetorheological fluid. The transmission wall with a groove depth of 0.2 mm, higher material magnetic permeability, higher surface roughness, radial grooves at the surface, and higher groove density was determined as the best transmission wall.
In this article, the one-dimensional phenomenological constitutive model originally proposed by Brinson for shape memory alloys is improved to predict asymmetric behavior in tension and compression. We propose an approach that decomposes stress-induced martensite volume fraction into two parts, one in tension and one in compression. Results of numerical examples show reasonable agreement with experimental data. Moreover, we implement the proposed model in a user-defined material subroutine in the nonlinear finite element software ABAQUS/Standard as a two-dimensional Euler–Bernoulli beam element. We simulate several beam problems and a shape memory alloy staple. Regarding the results, the proposed shape memory alloys constitutive model, employed in a two-dimensional beam element, can be used to simulate various shape memory alloys applications in the design and analysis.
This article proposes a novel method for high-speed impact detection in composite panels and compares the technique with the conventional triangulation method. The proposed method uses groups of closely spaced embedded sensors to calculate the angles of the impact to these sensor groups. Angles from two groups of sensors are then used for the calculation of the impact location. The new method has reduced computational cost (and thus a faster calculation time) than the triangulation technique. The lower computational cost allows the use of cheaper, lighter, and less energy-consuming electronics, which has obvious advantages in real-time impact detection. Furthermore, because of the close proximity of the sensors within a sensor group, the novel method simplifies electronic cable routing and manufacturing. The new method is demonstrated experimentally using epoxy–fiberglass [0°/90°] composite panels with a network of embedded piezoelectric sensors and various sensor group geometries. The experiments were carried out at a high-impact speed range (>300 m/s), and each panel was subjected to multiple impacts. The proposed method is also experimentally compared with the impact location predictions using conventional triangulation from a square array of sensors. The experiments showed not only a reduced computational cost of the proposed technique but also a reduced accuracy in locating the position of the impact.
This work presented an indirect method to monitor the deformation of the flexible variable camber wing using attached fiber Bragg gratings. To measure the transverse strains resulting from deformation of flexible variable camber wing, two groups of fiber Bragg grating sensors were attached on both upper and lower surfaces of the metal sheet, which was used to replace the traditional hinges. When the flexible variable camber wing was actuated by the lower surface’s pneumatic artificial muscle actuators, the upper surface would undergo the tensile deformation. A redshift could be observed from the reflective wavelength of the fiber Bragg grating sensors located on the upper surface. On the contrary, a blueshift could also be observed from the lower surface due to the compressive deformation. The comparison of the results with those obtained from strain gauges demonstrated the reliability of fiber Bragg grating sensors. Then, the vertical displacement and deflection angle of the flexible variable camber wing were obtained through the von Karman strain–displacement relation. A finite element model of the flexible variable camber wing was developed to simulate the variation of strain and displacement, which is caused by deformation of the metal sheet. A good agreement could be seen from the vertical displacements among the fiber Bragg grating strain sensors, finite element model, and direct measurements with laser range-finders.
A galloping piezoelectric energy harvester is composed of a cantilevered piezoelectric beam and a tip bluff body. Self-excited vibration is induced when the tip bluff body is subjected to airflow. Then, the piezoelectric materials can convert the mechanical energy into electrical energy. In this article, a coupled aero-electro-mechanical model is developed to analyze a galloping piezoelectric energy harvester. A dimensionless formulation is adopted so that it is very convenient to conduct scaling and performance comparison of different galloping piezoelectric devices. Analytical approximate solution approach is employed to solve these coupled nonlinear equations using the Krylov–Bogoliubov method. Tip bluff body is assumed to have either rectangular or square section. System parameters such as galloping velocity, limit cycle oscillation amplitude, and harvested energy are determined accordingly and presented in an explicit form. Performances of galloping piezoelectric energy harvesters with different tip bluff bodies and electrical loads are characterized. In addition, experimental data are used to validate our predictions with good agreement. The galloping piezoelectric energy harvester having square section shows better performance compared to the one with rectangular section. Furthermore, the performance can be substantially improved by exploring the inherent jump phenomenon as observed in the limit cycle oscillation hysteresis response of a galloping piezoelectric energy harvester with square bluff body.
A damage identifying algorithm, named modal macro-strain vector, has been verified as efficient to locate local damages for flexural structures, with modal parameters directly extracted from the dynamic macro-strain measurements. However, the basic relation between the change in modal macro-strain vector and damage severity has not been established yet. In this article, a model-free damage identification method is proposed based on the modal macro-strain vector method to implement both damage location and quantification. In this method, one assumption is first proposed that the normalized modal macro-bending-moment is constant, as proved by the simulations. Then, damage quantification is performed with the combination of the spatial parameter of neutral axis and normalized modal macro-strain vector. In view of these, different finite element beam models are simulated with several damage cases for each specimen to verify the method. Simulation results show that the damage severity can be evaluated with a high accuracy with the proposed method. As a result, the efficiency of the method is verified through the experiments of a steel beam in the laboratory. Therefore, the proposed system is proved to be effective and useful for structural health monitoring.
Magneto-rheological materials are a class of smart materials whose rheological properties can be rapidly varied by applying a magnetic field. Magneto-rheological finishing utilizes magneto-rheological fluid, which consists of magnetic particles, non-magnetic abrasives and some additives in water or other carrier to polish the materials. Single-point diamond turning is able to remove hundreds of microns of material and generate surface with micron accuracies. Residual turning marks are the most important factor limiting the performance in diamond turning process. Magneto-rheological finishing has inherent ability to improve micro-roughness, remove subsurface damage and reduce residual stresses induced during diamond turning process. Combining single-point diamond turning and magneto-rheological finishing creates a deterministic process for manufacturing highly finished surfaces. In this article, an attempt has been made to improve the finish of diamond turned surface with magneto-rheological finishing and to investigate the effects of parameters like current, spacing, wheel speed, feed rate and magnetic field on the final surface finish. Based on the parametric study, an optimum combination of process parameters is identified using analysis of variance. Various image processing techniques have been used for the comparison of the surface analysis of diamond turned surfaces and the magneto-rheological finished surfaces.
This article offers a review of various nondestructive evaluation and structural health monitoring techniques that have been successfully utilized for assessing the damage state of woven ceramic matrix composites consisting of silicon carbide fibers and silicon carbide matrices. The techniques include acousto-ultrasonics, modal acoustic emissions, electrical resistance, impedance-based structural health monitoring, pulsed thermography, as well as thermoelastic stress analysis. The damage, in the form of distributed matrix cracks and delaminations, was introduced using multiple tactics. These included load/unload/reload uniaxial tensile tests, creep tests, and ballistic impact. Although other nondestructive evaluation techniques have been applied to this material system, the select nondestructive evaluation tools described here are limited to approaches that are of current research interest within programs at the NASA Glenn Research Center.
In this article, lead-free piezoelectric ceramics are investigated for active vibration control of piezolaminated composite shell structure. The shell structure is in the form of layered composite shell. Finite element modeling is performed to obtain vibratory response of the piezolaminated shell structure. Modeling is based on first-order shear deformation theory and linear piezoelectric theory. Fuzzy logic controller is used as controlling technique to reduce the vibration amplitude of vibrating shell using piezoelectric ceramics (both lead-based and lead-free). The simulation results reveal that Pb0.83La0.17(Zr0.3Ti0.7)0.9575O3 (lead zirconate titanate sensor) and (K0.475Na0.475Li0.05)(Nb0.92Ta0.05Sb0.03)O3 (KNLNTS actuator) combination reduces the vibration amplitude of vibrating shell structure faster than lead zirconate titanate (sensor) and lead zirconate titanate (actuator) combination. Moreover, for complete replacement of lead-based piezoelectric ceramics, 0.885(Bi0.5Na0.5)TiO3–0.05(Bi0.5K0.5)TiO3–0.015(Bi0.5Li0.5)TiO3–0.05BaTiO3 (BNKLBT sensor) and KNLNTS (actuator) combination is a potential candidate for active vibration control application.
This article reports on the modelling and experimental validation of a vibration energy harvesting approach that uses a permanent-magnet/ball-bearing arrangement and a wire-coil transducer. The harvester’s behaviour is modelled using a forced Duffing oscillator modified with quintic non-linearity, and the primary first-order steady-state resonant solutions are found using the homotopy analysis method. These solutions found are shown to compare well with measured ball-bearing displacements and harvested output power and are used to predict the wideband frequency response of this type of vibration energy harvester. A prototype harvester was found to produce a maximum output power of 16.4 mW from a 14.2 Hz, 400 milli-g excitation.
The control of vibrating structures using piezoelectric elements attached to simple control circuits, known as shunts, is a widely studied field. Many different shunt circuits have been researched that have been shown to obtain effective performance in both narrow and broadband frequency ranges. Yet, the choice for the exact parameters of the circuit elements for these vibration-suppressing shunts can be found by various methods. In this study, a new method of selecting the circuit parameters of a negative capacitance shunt is presented. The method predicts the magnitude of the strain-induced voltage caused by the vibrating substrate computed from a single voltage measurement. Therefore, minimizing the strain-induced voltage will mean that the deflection of the structure is also minimized. The tuning theory is confirmed experimentally, which validates that it is possible to experimentally obtain the shunt parameters that produce maximum control through measurement of the shunt response. The suppression ability of the shunt is also compared to the maximum power dissipated. It is found that at high frequency, the parameters that cause maximum power dissipated obtain maximum suppression, but there is no correlation between maximum power dissipated and maximum suppression at low frequency.
The magnetic field–induced and stress-induced response of magnetic shape memory alloy was investigated in the present study. Based on thermodynamic approach, a one-dimensional constitutive model was derived containing demagnetization energy and chemical energy. A cosine function was constructed to predict the variant volume fraction during reorientation process, considering the presence of residual reorientation strain. The effects of temperature on the magnetization behaviour, domain fraction and magnetization angle were discussed. Owing to the presence of residual reorientation strain, the critical threshold fields in hysteresis loop were decreased as a linear function of residual variant volume fraction. With increasing temperature, critical fields for domain and magnetic rotation to saturation were decreased, and critical threshold fields would increase for the stress-induced reorientation. The comparisons between numerical results and experimental results showed that the present model can effectively predict the macroscopic response of magnetic shape memory alloy, considering the effects of temperature and residual reorientation strain.
A tuned-mass electromagnetic energy harvester mounted on a vibrating structure is studied here, accounting for the dynamic coupling between harvester and host structure. The latter is modeled as a modal mass–spring–dashpot system, whereas the harvester device is composed of an electromagnetic transducer and a tunable secondary mass–spring–dashpot system. A thorough analytical coupled optimization of the harvested power with respect to the harvester components is presented here. Closed-form design formulas are supplied for the optimal values of the electromagnetic damping coefficient and tuning frequency, as functions of the excitation frequency, mass ratio, and mechanical damping coefficients. The optimized parameters yield a wide effective harvesting bandwidth when proper values of the mass ratio and device mechanical damping are chosen. It is shown that neglecting in the design process the dynamic coupling between harvesting device and vibrating host structure, that is, treating the latter as a mere vibration source as generally assumed in the literature, leads to a significant degradation of the harvesting performance.
In this article, we address the effect of regular and irregular distribution of phononic lattices on acoustic wave and investigate wave bending and refraction phenomena for some specific patterns of phononic crystals consisting of a square array of polyvinylchloride cylindrical rods in air matrix using finite element model. Bucay et al. have demonstrated that for a given configuration, the striking acoustic beam angle varying between 20° and 40° at 14.1 kHz central frequency shows positive, negative, and zero angle refraction inside phononic crystal and exhibits beam splitting after exiting the phononic crystal. These results are used as the benchmark in this article to validate the proposed model. Transmission spectrum in the phononic crystal has been studied for complete acoustic band gap as well as for positive and negative dispersion bands at frequencies ranging from 1 to 18 kHz. Using this established theory, in this article, the acoustic beam propagation through irregular phononic crystal structures and waveguides are investigated. It can be seen that small irregularity produces significant change in the acoustic field. It is shown that with a localized defect, resonating cavity waveguide is formed in the proposed acoustic metamaterials.
We investigate a new approach for characterizing class separability based on topological measures for use with identifying flaw severity in plates. Multi-mode Lamb waves are propagated across a flat-bottom hole of varying depth. Lamb wave tomography reconstructions are first generated to locate and size the flaw at each depth. As the flaw depth increases, scattering and mode conversion effects dominate the raw time-domain signals, obscuring information about flaw severity. Pattern classification provides an alternate means for processing the ultrasonic waveforms to identify flaw severity. High-dimensional feature spaces are generated from the Lamb wave signals using the dynamic wavelet fingerprinting technique. In order to achieve high classification accuracy, an optimal feature space is required. An intelligent feature selection routine is explored here that identifies favorable class distributions in multidimensional feature spaces using computational homology theory. Betti numbers and formal classification accuracies are calculated for each feature space subset to establish a correlation between the topology of the class distribution and the corresponding classification accuracy.
This study presents a computational model for deformation behaviour of near-equiatomic NiTi holey plates using finite element method. Near-equiatomic NiTi alloy deforms via stress-induced AM martensitic transformation, which exhibits a typical hystoelastic mechanical behaviour over a stress plateau, known as the pseudoelasticity. In this model, the transformation stress is decomposed into two components: the hyperelastic stress, which describes the main reversible aspect of the deformation process, and the hysteretic stress, which describes the irreversible aspect of the process. It is found that with increasing the level of porosity (area fraction of holes), the apparent elastic modulus before and after the stress plateau decrease, the nominal stresses for the AM transformation decrease and the strain increases, and the pseudoelastic stress hysteresis decreases. In particular, the transformation strain increases by about 25% by introducing 32% porosity. Upon loading, the strain in a holey plate made of NiTi is more uniformly distributed than in a steel plate of the same geometry. The majority of steel plate remains in a low strain range, with a small portion highly strained. In NiTi, a large volume fraction of the plate undergoes moderate strains.
Hysteresis is an important nonlinear effect exhibited by piezoelectric actuators. As a member of piezoelectric actuator family, Macro-Fiber Composite actuators can also be testified as having the same characteristics, as shown in the experimental research in this article. In order to interpret the characteristics accurately, various models were proposed previously, in which the Bouc–Wen model has gained more interest because of its capability to match a wide class of hysteretic systems. However, the model consists of a set of differential equations where multiparameters present a need to be estimated simultaneously, which is an arduous task. In view of this, the present study sets out to propose a more efficient genetic algorithm and a simplified Bouc–Wen model, on the one hand, and on the other, the genetic algorithm is applied to the model to enhance the accuracy and efficiency of the parameter estimation. Finally, a large number of experimental data are used to testify the proposed approach more efficiently and accurately than the other conventional methods. Also suggested are the implications of the present study on other hysteretic models or other complex mathematical models.
In this article, a nonlinear multiclass support vector machine–based structural health monitoring system for smart structures is proposed. It is developed through the integration of a nonlinear multiclass support vector machine, discrete wavelet transforms, autoregressive models, and damage-sensitive features. The discrete wavelet transform is first applied to signals obtained from both healthy and damaged smart structures under random excitations, and it generates wavelet-filtered signal. It not only compresses lengthy data but also filters noise from the original data. Based on the wavelet-filtered signals, several wavelet-based autoregressive models are then constructed. Next, damage-sensitive features are extracted from the wavelet-based autoregressive coefficients and then the nonlinear multiclass support vector machine is trained by a variety of damage levels of wavelet-based autoregressive coefficient sets in an optimal method. The trained nonlinear multiclass support vector machine takes new test wavelet-based autoregressive coefficients that are not used in the training process and quantitatively estimates the damage levels. To demonstrate the effectiveness of the proposed nonlinear multiclass support vector machine, a three-story smart building equipped with a magnetorheological damper is studied. As a baseline, naive Bayes classifier–based structural health monitoring system is presented. It is shown from the simulation that the proposed nonlinear multiclass support vector machine–based approach is efficient and precise in quantitatively estimating damage statuses of the smart structures.
Bistable piezoelectric generators have been demonstrated to outperform linear spring–mass–damper systems in terms of frequency bandwidth and harvested power from wideband vibrations. In this work, a nonlinear vibration energy harvester consisting of clamped–clamped buckled beams combined with a four-pole magnet across coil generator is investigated. By buckling the support beams, an elastic Duffing potential is provided so that the seismic mass can pass from being dynamically monostable to bistable. A theoretical model of the system is presented, and experimental tests are performed on a prototype. In the unbuckled state, the device exhibits higher maximum power at resonance than in the buckled, but, in general, no significant difference is noted in terms of average harvested power between monostable and bistable regimes under harmonic and band-limited stochastic vibrations. However, for an optimal acceleration level, the bistable configuration shows a factor of 2.5 times wider bandwidth and higher power outside from the natural resonance as compared with the monostable regime. It is also observed that the benefits of bistable dynamics mostly depend on the ratio between the characteristic cutoff frequency of the electrical circuit and the mechanical resonance.
In this article, we assess the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites induced by a steady fluid flow. Specifically, we consider an underwater energy harvester composed of a paddle wheel, a slider-crank mechanism, and two ionic polymer metal composites clamped at both their ends. To enhance electromechanical transduction, the electrodes of the ionic polymer metal composites are split into three parts via a selective platinum deposition process. The system is installed in a water tunnel and experiments are performed to elucidate the influence of both the flow speed and the shunting resistance on energy harvesting. To provide a theoretical interpretation of the experimental results, the classical post-buckling theory of inextensible elastic beams is adapted to predict mechanical deformations and a lumped-circuit model is utilized to estimate the harvested power.
A novel concept of a compact magnetorheological valve is proposed based on the advance characteristics of magnetorheological fluid. The structural design consists of a meandering pattern formed by multiple annular and radial gaps in order to extend the flow path length of magnetorheological fluid. Extending the flow path of magnetorheological fluid is important in order to increase the density of effective area, so that the rheological properties of magnetorheological fluid can be widely regulated in a small size magnetorheological valve. The main objective of this article is to show that the pressure drop as one of the key performance indicators in a magnetorheological valve can be significantly increased using multiple annular and radial gaps configuration. In order to demonstrate the magnetorheological valve performance, simulation work using magnetic simulation software called finite element method–based software for magnetic simulation is conducted and combined with the pressure drop calculation using the derived magnetorheological valve model. Simulation results show that the magnetorheological valve with multiple annular and radial gaps is able to improve the achievable pressure drop. The discussion on the effect of gap size variations on the achievable pressure drop and the operational range of magnetorheological valve is also presented.
Analytical and finite element electromechanical models that take into account the fact that the piezoelectric sheet does not cover the whole substrate beam are developed. A linear analysis of the analytical model is performed to determine the optimal load resistance. The analytical and finite element models are validated with experimental measurements. The results show that the analytical model that takes into account the fact that the piezoelectric patch does not cover the whole beam predicts accurately the experimental measurements. The finite element results yield a slight discrepancy in the global frequency and a slight overestimation in the value of the harvested power at resonance. On the contrary, using an approximate analytical model based on mode shapes of the full covered beam leads to erroneous results and overestimation of the global frequency as well as the level of harvested power. In order to design enhanced piezoelectric energy harvesters that can generate energy at low-frequency excitations, further analysis is performed to investigate the effects of varying the length of the piezoelectric material on the natural frequency and the performance of the harvester. The results show that there is a compromise between the length of the piezoelectric material, the electrical load resistance, and the available excitation frequency. By quantifying this compromise, we optimize the performance of beam–mass systems to efficiently harvest energy from a specified low frequency of the ambient vibrations.
This study proposes a wireless laser displacement sensor system for in situ deflection monitoring of wind turbine blades. This system consists of a tower-installed laser displacement sensor system composed of a laser displacement sensor head, controller, Zigbee transmitter, and analog-to-digital converter module, combined with a mobile host that includes a Zigbee receiver and a laptop. In contrast to the approach of blade sensor installation, the laser displacement sensor system is installed in the tower to enable noncontact blade displacement monitoring. The concepts of direct noncontact remote sensing and actuation from the tower and remote power delivery from the tower to blade-installed sensors and actuators will enable various approaches for wind turbine structural health monitoring. The proposed system can easily identify problems related to deflection. The size of wind blades increases with energy demands. Due to the large size of wind turbines, current wind turbines are installed very high above ground level. It is impractical to monitor the results from laser displacement sensor through wired connection in these cases. Hence, wired connections of laser displacement sensors to base monitoring stations must be replaced with a wireless solution. This wireless solution is achieved using Zigbee technology. The output from the laser displacement sensor is fed to a microcontroller, which acts as an analog-to-digital converter. The output from the microcontroller is connected to the Zigbee transceiver module, which transmits the data, and at the other end, the Zigbee reads the data and displays it on a PC, from which users can monitor the condition of the wind blades.
The control of piezoelectric smart structures described by large-scale finite element models typically requires construction and use of reduced-order models for the purpose of feedback controller design and implementation. However, reduced-order model–based controllers can have deleterious interactions with unmodeled modes. The unwanted controller structure interaction can cause performance degradation and even instability. The concern is that the controller structure interaction is seldom considered in conventional vibration control study of piezoelectric smart structures. In this article, a general framework within which one can study the effect of controller structure interaction is developed by integrating the reduced-order model–based controller into finite element environment. The issue of controller structure interaction is then examined numerically. The importance of including controller structure interaction effects in closed-loop simulation of piezoelectric smart structures is demonstrated. It is shown that the conventional controller design approach is very much influenced by the order of reduction of the piezoelectric smart structure. This suggests that for piezoelectric smart structures in which controller structure interaction is significant, application of the conventional control system design methods may not be adequate. Moreover, examples of controller structure interaction–induced spillover are illustrated via power spectral density of the displacement response.
This article examines the piezoelectric-based energy harvesting on civil infrastructures. Piezoelectric cantilever–based harvesters are adopted considering their wide usage. Four concrete slab-on-girder bridges that represent the majority of bridges in the United States are used as the platforms for the energy harvesting. In the simulation, the distributed-parameter model is used for the energy harvester, while four three-dimensional bridges with HS20-44 truck models are developed using ANSYS and MATLAB. Two scenarios for the bridge–vehicle systems are simulated: bridges with only one passing vehicle and bridges with a continuous vehicle flow. A parametric study is carried out to study the effect of various properties of the bridge and vehicle on energy harvesting. The simulation result shows that the energy output power increases with poorer road conditions and smaller bridge span lengths. Optimal vehicle speeds and energy harvester positions are also investigated and discussed in this article.
The performance of a traveling wave thermoacoustic-piezoelectric energy harvester is developed using an electrical circuit analogy approach. The harvester converts thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous regenerator. At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator. The resulting interaction is accompanied by a direct conversion of the acoustic energy into electrical energy. The acoustic pressure oscillations are amplified by a specially designed acoustic feedback loop that introduces appropriate phasing to make the pulsations take the form of traveling waves. Such traveling waves render the harvester to be inherently reversible and thus highly efficient. The behavior of this class of harvesters is modeled using an electrical circuit analogy approach. The developed model is a multifield model that combines the descriptions of the acoustic resonator, feedback loop, and the regenerator with the characteristics of the piezoelectric diaphragm. The onset of self-sustained oscillations of the harvester is predicted using the root locus method. The predictions are validated against published results. The developed electrical analog and the associated analysis approach present invaluable tools for the design of efficient thermoacoustic-piezoelectric energy harvesters.
A generic homogenization modeling framework which incorporates crystallographic domain features is introduced and computationally implemented for magnetoelectric multiferroics of all symmetries. The homogenization, mathematically applicable to heterogeneous media with contrasts in physical properties, replaces the heterogeneity of the multiferroics by an equivalent effective medium with uniform physical characteristics. A statistically representative unit-cell is proposed to encompass all forms of multiferroics and their composites in bulk. The variational formulation of the coupled magneto-electromechanical problem reveals the nature of interaction between mechanical, electrical, and magnetic fields of a multiferroic at a microscopic scale with high resolution. Furthermore, the mathematical homogenization theory of the multiferroic is implemented in finite element method by solving the coupled equilibrium electrical, magnetic, and mechanical fields. A "multiferroic finite element" is conceived for this purpose. The model is applied to a two-phase multiferroic magnetoelectric composite to demonstrate its validity by characterizing the equivalent physical properties.
A new design optimization methodology for the optimal design of a single-coil annular magnetorheological valve constrained in a specific volume inside a magnetorheological damper has been presented in this article. The methodology combines the finite element model, with the design of experiments and response surface techniques in order to develop approximate response surface functions for the magnetic field intensity across the activation length of a magnetorheological valve orifice with respect to identified design variables. The accuracy of the developed response surface functions over the entire design space has been verified. The developed analytical response functions have then been used in Bingham plastic model, which is based on the steady behavior of a magnetorheological fluid in order to derive the field-dependent performance functions of the magnetorheological damper, which can be effectively used in the design optimization problems. The design optimization problem has been formulated for single- and multiobjective performance functions using sequential quadratic programming technique and the genetic algorithm to find the global optimum geometrical parameters of the magnetorheological valve. Finally, a proportional–integral–derivative controller has been designed to evaluate the closed-loop performance of the optimally designed magnetorheological valve confined in a magnetorheological damper used in a quarter-car suspension model.
This study introduces micromechanical models for analyzing the overall electromechanical responses of piezoelectric composites comprising polarized piezoelectric ceramics and polymeric constituents. The polarized piezoelectric ceramics can experience nonlinear electromechanical responses due to an application of large electric fields, while the polymer exhibits viscoelastic response. Thus, the piezoelectric composites can experience significant time-dependent and nonlinear electromechanical coupling behaviors. Two micromechanical models are considered: the Mori–Tanaka and unit-cell models. Linearized micromechanical relations are first defined for obtaining the overall responses of the piezoelectric composites followed by iterative schemes in order to correct errors from linearizing the nonlinear responses. Numerical results are presented for two composite systems, that is, piezoelectric unidirectional fiber with circular/square cross section and spherical/cubic particle inhomogeneities embedded in a polymeric matrix. The linear electromechanical responses from the two micromechanical models are compared with the experimental data available in the literature. Parametric studies are performed in order to examine the effect of inhomogeneity geometry and compositions and prescribed boundary conditions on the overall time-dependent and nonlinear electromechanical responses of the composites.
Structural health monitoring has become a viable solution to monitor critical infrastructure components that show distress or are unable to pass current load ratings. This research introduces the concept of a composite layer bonded to concrete structures, which is capable of providing distributed sensing capabilities. The layer consists of carbon nanotubes that are deposited on a carrier, which form a continuous conductive skin that is exceptionally sensitive to changes in strain and the formation and propagation of micro-damage and macro-damage. It can be either structural, where the layer represents the reinforcement as well as the sensor, or nonstructural, where the layer acts as a sensing skin alone. Distributed sensing allows for increased detectability of forming or growing damage that cannot necessarily be captured with conventional point-type sensors such as strain gages or accelerometers. Once developed, this sensing skin may be able to give real-time feedback on changes in strain, temperature effects, and formation and propagation of damage. In this article, we present the fabrication and evaluation of an integrated structural sensing composite layer attached to a concrete beam specimen. The specimen was tested to failure in the laboratory. Experimental results are presented and discussed, and currently ongoing research is introduced.
The study of the electric field–induced thickness strain of ferroelectric polymers is very interesting because of the high actuating capabilities and various applications of these materials, such as electroactive materials for artificial muscles or as the active materials of membranes, due to their flexibility. This article reports on the effect on the strain properties of uniaxially and biaxially stretched β-form polyvinylidene fluoride when applying a low quasi-static triangular electric field E (100 mHz, E < 16 MV/m). For an applied electrical field at this level, the strain was proportional to the square of the electric field. The strain depended mainly on the electrostriction effect, linked to the induced reversal polarization and to interlaminar charges. The dielectric constant of the biaxially stretched polyvinylidene fluoride at 100 mHz was higher than for its uniaxially stretched counterpart. As a consequence, the induced charges and microscopic polarization for the first film exceeded those of the second one, and the electroactive strain for the biaxially stretched sample was more significant than for the uniaxially stretched film. This article first offers a description of the strain phenomenon through the polyvinylidene fluoride material during electrical excitation, after which a new model is presented. This model was developed to evaluate the induced electric current and strain phenomenon. A good agreement between simulations and experimental results was obtained.
A cellular adaptive structure concept based on fluidic flexible matrix composite is investigated for its potential of achieving multifunctionalities simultaneously. This structure consists of a string of fluidic-connected fluidic flexible matrix composite cells with different properties. When under dynamic loading, the structure exhibits distinct poles and zeros (spectral data). These spectral data can be assigned, by tailoring fluidic flexible matrix composite design, so that the structure can perform dynamic functions such as vibration absorption or actuation with enhanced authority. To fully explore the potential of the fluidic flexible matrix composite–based cellular structure, this article carries out two progressive tasks. The first task is to develop a dynamic model for the multicellular structure. This model incorporates the concept of constitutive parameters to describe the performance of individual fluidic flexible matrix composite cell. The second task is to develop a synthesis procedure to assign these constitutive parameters so that the structure can achieve the prescribed spectral data. This procedure combines genetic algorithm with discrete variables and Jacobi inverse eigenvalue problem. Case studies show that the proposed procedure is successful for synthesizing structures with three cells. The range of the achievable spectral data is found through a numerical survey, and for each set of achievable spectral data, multiple designs can be synthesized efficiently.
We report a film-type haptic actuator made with two cellulose acetate active membranes and an air gap. Two different configurations of the actuators, double cellulose acetate membranes and single cellulose acetate membrane, are investigated. Due to the intensified electrostatic attraction force between chargeable cellulose acetate membranes, the double cellulose acetate membrane case shows over 300% displacement enhancement. Under a bias electric field, the displacement can be 200% improved comparing with no bias case. When the actuator performance of the cellulose acetate membrane is compared with polyethylene terephthalate and polyvinyl chloride membranes, the cellulose acetate membrane shows superior displacement output due to its high dielectric property. The cellulose acetate double membrane actuator has a great potential as kinesthetic actuator of haptic devices.
This study investigated the mechanical and shape recovery properties of a styrene-based shape memory polymer composite reinforced by cup-stacked carbon nanotubes. Due to their unique morphology, cup-stacked carbon nanotubes could be well dispersed in the polymer matrix and offer remarkable benefits in the load transfer between the reinforcement fillers and shape memory polymer. Under the same amount of fillers, shape memory polymer composites embedded with cup-stacked carbon nanotubes exhibit superior mechanical properties in comparison with those embedded with multiwalled carbon nanotubes and carbon nanofibers. The elastic modulus, tensile strength, and flexural strength of the 2 wt% cup-stacked carbon nanotube–reinforced shape memory polymer composite increased by 61%, 66%, and 84%, respectively. It was also found that the glass transition temperature of shape memory polymer composite decreased from 61.9°C to 52.8°C by introducing 2 wt% cup-stacked carbon nanotubes, indicating that the shape recovery process could be triggered more easily by external stimulus due to the role of reinforcement fillers. Finally, under the external resistance load, the developed shape memory polymer composite was successfully driven to recover their shapes under thermal stimulus. The cup-stacked carbon nanotubes were proved to be a promising candidate for the polymer reinforcement.
In this article, the epoxy-based shape memory polymers were exposed to simulated -radiation environments up to 140 days for an accelerated irradiation. The influence of -radiation on thermal and mechanical properties was evaluated by differential scanning calorimetry, dynamic mechanical analysis, and tensile test. The glass transition temperatures (Tg) determined by differential scanning calorimetry and dynamic mechanical analysis decreased no more than 10%, and the shape recovery speed became a little faster after -radiation of 1 x 105 Gy. The tensile strength and elastic modulus could, respectively, maintain 26 MPa and 1.36 GPa after being irradiated by 1 x 106 Gy radiation, showing great potential in aerospace structural materials.
In this study, active vibration control of a cantilevered flexible beam structure equipped with bonded piezoelectric sensor/actuators is investigated. The linear quadratic regulator technique together with an observer is adopted to design the controller as well as to provide the full-state feedback. Two different approaches are subsequently used for simultaneously integrated optimization of the controller and observer parameters. In the first approach, a linear experimental model of the system is obtained using identification techniques, and the optimization is then performed based on a computer simulation of the system. However, in the second approach, a hardware-in-the-loop optimization scheme is proposed and applied to automatically tune the parameters. In both cases, a hybrid metaheuristic algorithm called tabu continuous ant colony system is utilized to find the optimal controller and observer. The integrated performance is experimentally evaluated to demonstrate effectiveness of the proposed hardware-in-the-loop optimization method. Finally, a comparison is made between the frequency response of the current controller with a pole placement controller from the literature in order to assess the improvement achieved through hardware-in-the-loop optimization.
This article presents a new iterative learning control algorithm based on inverse model to decrease the hysteresis-caused tracking error of a giant magnetostrictive actuator. The first iteration input is calculated by the inverse model of the giant magnetostrictive actuator system according to the desired output. Compared to a standard iterative learning control algorithm—in which the first iteration input usually is proportional to the desired output—the proposed algorithm converges more rapidly. Performance of the approach is demonstrated both theoretically and experimentally. The experimental results show that the inverse model–based iterative learning control converges about twice as fast as standard iterative learning control and reduces the hysteresis-caused error of giant magnetostrictive actuator to 0.5% of the total displacement range, which is comparable to the noise level of sensor measurement. Two sets of model parameters were identified by 0–1.5 and 0–5 V major hysteresis loop, respectively, and evaluated. The best convergence rate is obtained with the former case.
Ionomeric polymer transducers exhibit electromechanical coupling capabilities. The ion transport due to electric stimulus is the primary mechanism of actuation for a class of polymeric active materials known as ionomeric polymer transducers. In this article, a two-dimensional Monte Carlo simulation of ion hopping has been developed to describe ion transport in materials that have fixed and mobile charge similar to the structure of the ionic polymer transducer. Such Monte Carlo simulations were performed to study the influence of conducting powder electrodes on stationary ion distribution in actuation. Ion accumulation around the powder sphere at the cathode is clearly observed in simulation results. Moreover, based on the unique property of stationary charge density of ionomeric polymer transducers in actuation, this article proposed a novel multi-scale model connecting Monte Carlo simulation for the material boundaries and a continuum model for the central part. To validate this multi-scale model, the simulation results are compared with experimental measurements. Both transient and steady-state responses from the experiments show reasonable agreement with those from the multi-scale model.
Piezohydraulic pumps are high power density motors, which can be theoretically miniaturized with minimal loss in power output. The feasibility of using piezohydraulic pumps in pulsatile pediatric ventricular assist devices is presented in this study. A theoretical analysis is presented to calculate the piezohydraulic pump dimensions needed to meet flow and pressure requirements. In addition, an existing piezohydraulic pump was incorporated into a ventricular assist device driver to drive a pulsatile pediatric 30-mL stroke ventricular assist device as a proof of concept. The driver was tested at heart rates ranging from 50 to 110 beats per minute in an in vitro mock circulation to characterize its performance. The maximum drive pressure was 33 kPa with a peak flow rate of 6 L/min against a 10-kPa back pressure. The maximum mean flow rate from the ventricular assist device outlet was 3 L/min at 100 beats per minute operation. These results compare well to commercially available systems that output between 25 and 40 kPa drive pressure and flows between 0 and 10 L/min against 10–16 kPa pressures.
The design studies of cantilevered piezoelectric vibration energy harvesters have been focused on the optimization of the power output of rectangular cantilevered beam vibration energy harvesters. However, without clarifying the influences of the modal electromechanical coupling and mechanical behaviour clearly, the power outputs cannot be adequately optimized. In this article, a distributed parameter electromechanical model is used to predict the power output with resistive loads, and the parameters are derived using the finite element method. First, a parametric study is presented to investigate the effects of the two factors on the volumetric power of cantilevered vibration energy harvesters. Then, an optimization strategy is implemented to investigate the modal electromechanical coupling coefficient and mass ratio separately using geometric parameter study. Mass ratio represents the influences of modal mechanical behaviour on the power density directly. The findings indicate that the convergent and divergent tapered cantilevered and rectangular cantilevered beam designs with partial coverage of piezoelectric layer are able to generate higher electromechanical coupling coefficient than conventional rectangular cantilevered designs with full coverage. Besides, using convergent tapered cantilevered designs can actually decrease the power density significantly. Both using divergent tapered cantilevered structures and attaching reasonable extra masses with varied locations on vibration energy harvesters can generate larger power density.
This article demonstrates the use of embedded fibre Bragg gratings as vector bending sensor to monitor two-dimensional shape deformation of a shape memory polymer plate. The shape memory polymer plate was made by using thermal-responsive epoxy-based shape memory polymer materials, and the two fibre Bragg grating sensors were orthogonally embedded, one on the top and the other on the bottom layer of the plate, in order to measure the strain distribution in both longitudinal and transverse directions separately and also with temperature reference. When the shape memory polymer plate was bent at different angles, the Bragg wavelengths of the embedded fibre Bragg gratings showed a red-shift of 50 pm/° caused by the bent-induced tensile strain on the plate surface. The finite element method was used to analyse the stress distribution for the whole shape recovery process. The strain transfer rate between the shape memory polymer and optical fibre was also calculated from the finite element method and determined by experimental results, which was around 0.25. During the experiment, the embedded fibre Bragg gratings showed very high temperature sensitivity due to the high thermal expansion coefficient of the shape memory polymer, which was around 108.24 pm/°C below the glass transition temperature (Tg) and 47.29 pm/°C above Tg. Therefore, the orthogonal arrangement of the two fibre Bragg grating sensors could provide a temperature compensation function, as one of the fibre Bragg gratings only measures the temperature while the other is subjected to the directional deformation.
This article presents a fundamental investigation in which velocity amplification is employed in non-resonant structures to enhance the power harvested from ambient vibrations. Velocity amplification is achieved utilising sequential collisions between free-moving masses, and the final velocity is proportional to the number of masses and the mass ratios selected. The governing theory is discussed, particularly how the final velocity scales with the number of masses. This article examines n-mass velocity-amplified vibration energy harvesters and examines their performance relative to single-mass harvesters. Electromagnetic energy conversion is chosen as it is fundamental in allowing the free movement of the masses. Experimental results from two- and three-mass prototypes are presented that demonstrate a wider frequency response and a gain in power of 33 times compared to single-mass configurations under wideband random excitation. The volume of the devices was constrained, which resulted in the two-mass system outperforming the triple-mass system counter to expectations. This was caused by the triple-mass device experiencing an increased number of impact due to the volume constraint, leading to high losses in the system. It is recommended that in order to realise the full benefits of the triple-mass system, additional volume for mass actuation is required.
This article presents an analytical model for power and energy transfer between excited piezoelectric wafer active sensors and host structure. This model is based on exact multimodal Lamb waves, normal mode expansion technique, and orthogonality of Lamb waves. Modal participation factors are presented to show the contribution of every mode to the total energy transfer. The model assumptions include the following: (1) straight-crested multimodal ultrasonic guided wave propagation, (2) propagating waves only, (3) ideal bonding (pin-force) connection between piezoelectric wafer active sensors and structure, and (4) ideal excitation source at the transmitter piezoelectric wafer active sensors. Constrained piezoelectric wafer active sensor admittance is reviewed. Electrical active power, mechanical converted power, and Lamb wave kinetic and potential energies are derived in closed-form formulae. Numerical simulations are performed for the case of symmetric and antisymmetric excitation of thin aluminum structure. The simulation results are compared with axial and flexural approximation for the case of low-frequency Lamb waves. In addition, a thick steel structure example is considered to illustrate the case of multimodal guided waves. A parametric study for different excitation frequencies and different transducer sizes is performed to show the best match of frequency and piezoelectric wafer active sensor size to achieve maximum energy transfer into the excited structure.
In this article, a systematic way of structural damage assessment algorithm, including identification of damage location and damage quantification, is proposed using output-only measurement. First, the null-space-based and subspace-based damage detection methods are used to confirm the damage severity of a structure. Then, the stochastic subspace identification technique is adopted to identify the time-varying system natural frequencies from the global response measurement. Finally, the novelty index, defined as the Euclidean norm of the time–frequency Hilbert amplitude spectrum of measurement between the intact and the damaged structures, is applied to locate the damage. To quantify the damage, the complete system realization is obtained from the identified modal properties through stochastic subspace identification method. From which, the inter-story stiffness reduction ratio can be identified using the normalized stiffness matrix. For case of limited measurement, the multi-setup operational modal analysis is applied to construct the complete system matrix. Verification of the proposed damage assessment algorithm using response data from a series of shaking table test of a six-story steel structure with the cut in column member to simulate the damage is demonstrated.
Thermally conductive composites with a temperature-triggered self-healing response were produced by dispersing boron nitride or graphite particles into two types of polysulphide-based thermoset matrices. The composites produced exhibit recovery of both cohesion and adhesion properties upon thermally activated healing. Using a mild healing temperature (65°C), the materials show full recovery of their initial adhesive strength during multiple healing cycles. The composites behave differently regarding the cohesion recovery: 20%–100% recovery is achieved depending on the filler type, filler loading and the type of matrix. The thermal conductivity of the composites increases with the amount of filler. Values of 1 and 2 W/m K can be achieved for the boron nitride and graphite-based composite, respectively. The results presented in this work clearly show that multifunctional materials with different functionalities and mechanical self-healing responses can be designed using this strategy.
There have been numerous experimental reports about the environmental effects on characteristics of intelligent actuators, such as the piezoelectric motors. However, the influences of temperature coefficients of material properties, which are the fundamental reasons for the changes of motors’ output characteristics in different ambient temperature condition, are specially difficult to be acquired through experiments. Thus, the optimization for piezoelectric motors driven in extreme environments is scarce till now. This article is aimed to establish one calculating method to solve this problem. First, a theoretical model is developed for investigating the effects of ambient temperature on characteristics of piezoelectric motors by the finite element method. And then, the mechanical and electrical characteristics of a piezoelectric motor are measured to demonstrate the theoretical model. After that, the changes of critical parameters caused by the ambient temperature are discussed. Based on this, the final proportion of effects of materials’ temperature coefficients on changes of characteristics of piezoelectric motors is obtained. The results obtained by the theoretical model give useful guidelines for the optimization of piezoelectric motors operating in extreme environments.
In this article, a broadband magnet-induced dual-cantilever piezoelectric energy harvester is designed and developed. The dual-cantilever structure consists of an outer and an inner beams with magnets attached to the tips. The magnets generate nonlinear repulsive force between the two beams and make the structure bistable. In the theoretical model, each beam is considered as a single-degree-of-freedom system with magnetic force applied at the free end. From the simulation results, chaotic motion is observed in a wide frequency range. A prototype of the harvester is built and verified with the simulation results. The simulation and experimental results show good agreement with respect to the power bandwidth and amplitude. The distance between magnets is adjusted to observe its effect on the power response of the harvester. The inner and outer beams are simulated and tested independently first to observe the performance of each beam. Finally, an interface circuit is designed to combine all piezoelectric plates to acquire the overall performance. By comparing with the traditional piezoelectric energy harvester, the new design is shown to provide a significant improvement in bandwidth.
Smart material electrohydrostatic actuator based on giant magnetostrictive transducer can meet the requirements of smaller vehicles like the unmanned combat air vehicle as well as in rotating environments like helicopter rotors. In order to analyze and improve the performance of smart material electrohydrostatic actuator, the dynamic hysteresis nonlinear model of giant magnetostrictive transducer is developed based on the relationship between complex permeability and magnetic energy power loss in giant magnetostrictive material, and the inverse model is also derived to design the inverse compensator for improving the linearity of giant magnetostrictive transducer. The experiments show that with the help of inverse compensator, phase lag between the input control signal and the output displacement of giant magnetostrictive transducer is decreased. In addition, the simulation results show that because of the effect of inverse compensator, the flow rate is increased and the growth rate increases with the increase of excitation frequency.
Crystal structure and electrical properties of MnO2-doped Pb0.97La0.02(Zr0.63Sn0.26Ti0.11)O3 antiferroelectric ceramic were studied in detail in this article. X-ray diffraction analysis showed that all specimens took on single tetragonal antiferroelectric structure, and antiferroelectric phase stability enhanced with the increase of MnO2 addition, which was because that the substitution of Mn2+ or Mn3+ with large ion radius for B-site Ti4+ decreased the tolerance factor of the ceramic. In addition, it was observed that different from Mn doping reducing Tm of ferroelectric ceramics, Tm of antiferroelectric ceramics increased with the addition of MnO2, which is for the reason that MnO2 addition enlarged the zone of antiferroelectric phase. Furthermore, by increasing MnO2 content, the strain first increased and then decreased. Meanwhile, the value improved obviously as the measuring frequency decreased. The largest electric field–induced strain of 0.65% was obtained in the specimen with 0.2 mol% MnO2 doping at the frequency of 1 Hz, which lay a foundation for preparing actuator with high strain energy density.
This article deals with the data reduction technique using the principal component analysis applied to the carbon fiber–reinforced plastic panels for structural health monitoring approaches. Two carbon fiber–reinforced plastic panels subjected to damage and repair coincide with typical aircraft repair procedures found in the aircraft structural repair manual. The panels were simulated with 30 mm diameter of partial and full penetration damages using a diamond-coated router. The data (50 observations) were captured for the undamaged, damaged, and repaired conditions by placing lead zirconate titanate smart sensors at 100 mm across the damaged and repaired structures. A time-based data response was captured for post analysis during the interrogation on the structure at each condition. The raw data were captured in a Lamb waveform, and the interested features were extracted using Morlet wavelet analysis to evaluate the Condition Structural Index and Amplitude-Based Assessment for each condition retrieved from the Gaussian-like distribution. The results were evaluated using the principal component analysis technique in order to distinguish the characteristic of the undamaged, damaged, and repaired conditions. The results showed that in all cases considered, it was possible to distinguish the conditions of undamaged, damaged, and repaired states with promising accuracy and repeatability of the data.
A multi-objective optimization-based computational approach to nondestructive evaluation of damage in structural components, and more generally in solid continua, is discussed and numerically evaluated. The multi-objective approach provides a substantial improvement in the capabilities to traverse the optimization search space to minimize the measurement error and produce accurate damage estimates. Through simulated test problems based on the characterization of damage in structural steel components, including internal pipe surface geometry as well as material loss within a plate structure utilizing steady-state dynamic measurements of outer surface displacement, a multi-objective genetic algorithm optimization approach is shown to provide substantial computational improvement over single-objective strategies. The multi-objective approach consistently and efficiently produces more accurate characterization results in contrast to equivalent single-objective strategies. More importantly, the multi-objective approach is shown to exhibit consistently better tolerance to test measurement noise and measurement sparsity. Moreover, the multi-objective strategy was found to provide improved diversity in the solution estimates for ill-posed problems, which is an important step leading to insight into the necessary changes to the testing or parameterization to subsequently produce more accurate and unique solutions to such inverse characterization problems.
Localization of scattering sources via active ultrasonic inspection in plate-like structures requires knowledge of the structure’s dispersion relation and material properties. Often the dispersion relation and material properties are unknown, uncertain, or difficult to model due to material complexity and variability in material properties, geometry, and/or environment, thereby requiring in situ estimation. Two methods are presented for estimating guided wave dispersion curves (phase and group velocity) in a multimodal, multipath environment using a phased array. Phase and group velocities are estimated in situ on an aluminum and carbon fiber plate and compared to theoretical values. Scattering from plate boundaries is localized using the estimated phase and group velocity curves through beamforming and ranging via time of flight.
In cylindrical structures such as pipelines and pressure vessels, cracks are most likely to occur along the longitudinal (axial) direction, and they can be fatal to the serviceability of the structures. However, the conventional wave propagation–based crack detection techniques are not sensitive to this type of cracks. This article focuses on the identification of axial cracks in cylindrical structures using torsional wave generated by piezoelectric macro-fiber composite. The first-order torsional wave, which is a nondispersive pure shear wave propagating at a fixed wave speed, is utilized in this work because, intuitively, it is more sensitive to axial cracks than the longitudinal waves. The crack position is determined by the time of flight of the wave pack, while the crack propagation is monitored by measuring the variation in the crack-induced disturbances. Numerical simulations have been conducted to investigate the feasibility of the proposed method, and experimental tests on aluminum pipes have been carried out for verification. Macro-fiber composite transducers oriented at 45° against the axis of the specimen were used to generate and receive the torsional waves. The experimental results demonstrated that the crack position can be identified, and its growth can be well monitored with the proposed approach.
Rocket engines are complex systems which usually operate under extreme physical conditions such as very high temperature and pressure, strong erosion, and high-density energy release. Mechanical and chemical complexity, long service lives, aging materials, and designs with small margins of safety are typical for space launch vehicle components including the engine. Furthermore, these components can be exposed to various flaws and damage during the manufacturing, assembly, or ground handling phase. In regard to the engine, its performance characteristics can be significantly affected by the degradation resulting from such flaws and damages, which, in turn, might lead to failure of the entire space mission. Any manufacturing/operational damage needs to be detected at the earliest stage possible, so that the required preventive measures can be implemented, and component readiness and reliability must be checked either during manufacturing or during field inspections. This review study lists such possible flaws/damages on rocket engine components. This information could be beneficial for determining and developing the efficient techniques for reliable nondestructive evaluation and structural health monitoring.
This article presents a fully coupled, nonlinear model for the dynamic response of Galfenol-driven unimorph actuators in a cantilever configuration. The hysteretic magnetomechanical behavior of Galfenol is modeled using a discrete energy-averaged model, and the structural behavior of the unimorph is modeled using the finite element method. The weak form equations that describe bending of the unimorph are obtained using the principle of virtual work. Since the local strain and stress are nonlinearly coupled with both the vertical and horizontal displacements, a nonlinear solver is developed to approximate the coupled finite element equations. The nonlinear solver is verified against the analytical solution and experimental data for the case of a passive beam. The analytical solution is obtained using beam theory for free and harmonic responses. The analytical model and experimental data verify that the nonlinear solver correctly quantifies the first natural frequency of the composite beam. The numerical simulations match the analytical solutions for both free and harmonic responses. Finally, the dynamic response of the nonlinear magnetoelastic model is investigated and experimentally validated from 0.1 to 500 Hz, the range in which the model is accurate without the need for adjustable parameters.
The continuing decrease in size and energy demand of electronic sensor circuits allows endowing engineering structures and, to an increasing degree, materials with integrated sensing and data processing capabilities. Materials that adhere to this description are designated as Sensorial Materials. Their development is multidisciplinary and requires knowledge beyond materials science in fields like sensor science, computer science, energy harvesting, microsystems technology, low-power electronics, energy management, and communication. Development of such materials will benefit from systematic support for bridging research area boundaries. The present article introduces the backbone of an easy-to-use toolbox for layout of the energy supply of smart sensor nodes within a sensorial material. The fundamental approach is transferred from rapid control development, where a comparable MATLAB/Simulink tool chain is already in use. The main goal is to manage limited power resources without unacceptably compromising functionality in a given application scenario. The toolbox allows analysis of the modeled system in terms of energy and power and allows analyzing factors such as energy harvesting, use of predictive power estimation, power saving (e.g. sleep modes), model-based cognitive data reduction methods, and energy aware algorithm switching. It is linked to a simulation environment allowing analysis of energy demand and production in a specific application scenario. Its initial version presented here supports single self-powered sensor nodes. A broad set of application cases is used to develop scenario-dependent solutions with minimum energy needs and thus demonstrate the use of the toolbox and the associated development process. The initial test case is a large-scale sensor network with optical fiber–based data and energy transmission, for which optimization of energy consumption is attempted. The toolbox can be used to improve the power-aware design of sensor nodes on digital hardware level using advanced high-level synthesis approaches and provides input for sensor node and sensor network level.
In this article, we employ a Bayesian framework to estimate parameter and model uncertainty for shape memory alloy bending actuators. The Bayesian framework provides parameter densities, instead of ordinary least-squares optimal point estimates. Bayes’ rule relates a posterior parameter density to a prior density and likelihood. However, the posterior density is difficult to calculate directly for high-dimensional parameter spaces. Markov chain Monte Carlo methods overcome this difficulty indirectly by creating a Markov chain whose stationary density is the posterior. In this article, we utilize the Delayed Rejection Adaptive Metropolis algorithm for estimating parameter uncertainty. The shape memory alloy bending actuator is modeled using the homogenized energy framework, a computationally efficient and accurate model for various transductive materials. The model is summarized, and techniques for estimating the heat transfer parameters are presented. An algorithmic approach to quantifying uncertainty is useful for numerous reasons. The anticipated use is to quantify uncertainty for robust control algorithms. Robust control is an area of considerable research for smart materials such as shape memory alloy; however, the source of uncertainty is rarely quantified. The methods employed here would greatly aid in the design of robust controllers.
In the arena of vibration energy harvesting, the key technical challenges continue to be low power density and narrow operational frequency bandwidth. While the convention has relied upon the activation of the fundamental mode of resonance through direct excitation, this article explores a new paradigm through the employment of parametric resonance. Unlike the former, oscillatory amplitude growth is not limited due to linear damping. Therefore, the power output can potentially build up to higher levels. Additionally, it is the onset of non-linearity that eventually limits parametric resonance; hence, this approach can also potentially broaden the operating frequency range. Theoretical prediction and numerical modelling have suggested an order higher in oscillatory amplitude growth. An experimental macro-sized electromagnetic prototype (practical volume of ~1800 cm3) when driven into parametric resonance, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power density normalised against input acceleration squared (293 µW cm–3 m–2 s4 with 171.5 mW at 0.57 m s–2) in contrast to the same prototype directly driven at fundamental resonance (36.5 µW cm–3 m–2 s4 with 27.75 mW at 0.65 m s–2). This figure suggests promising potentials while comparing with current state-of-the-art macro-sized counterparts, such as Perpetuum’s PMG-17 (119 µW cm–3 m–2 s4).
The interaction of Lamb wave A0 mode with delamination and delamination detection in 16-ply carbon fiber–reinforced epoxy composite beams are investigated through three-dimensional finite element simulation and experimental studies in this article. Wave propagation in composite beams with delamination with different lengths and located at different interfaces are investigated in finite element simulations, and some unique mechanisms of interaction between A0 mode and delamination are revealed in detail. Experimental results obtained with air-coupled ultrasonic transducers are well in accordance with finite element simulation results. In an experimental study, an air-coupled ultrasonic transducer is oriented at a coincidence angle such that it generates a pure fundamental antisymmetric Lamb wave mode A0 for delamination detection in laminated composite beams. The receiving transducer can be oriented either to detect the transmitted wave propagating in the same direction as incident wave or to detect the reflected wave in contrast to incident wave. The location and size of delamination can be evaluated quantitatively using the time-of-flight of reflected wave from both ends of the delamination.
This article presents a miniature haptic actuator (or haptic button) based on magneto-rheological fluids, designed to convey realistic and vivid haptic sensations to users in small electronic devices. The haptic sensation, which is generated in the form of resistive force, should vary according to the stroke of the actuator (or the pressed depth of its plunger). Thus, a sensing method for gauging the stroke should be integrated into the proposed magneto-rheological actuator to demonstrate real-world haptic applications. To determine the pressed depth of the magneto-rheological actuator, this article proposes an impedance sensing mechanism. The proposed sensing method measures the impedance change of the solenoid coil built in the actuator in the form of voltages to estimate the pressed depth. A control system was constructed to evaluate the simultaneous sensing and actuating performance of the proposed. The results show that the sensitivity of the proposed sensing method is sufficient to regulate the output resistive force over the small stroke range of the actuator. The results further show that the controller with the proposed sensing method enables users to measure the displacement of the plunger and concurrently generate resistive forces to convey haptic sensations to users without additional sensors.
The mechanical contact during material mechanical damage evaluation with electromechanical impedance technique was investigated, and the influencing factors, such as the times of in situ contact, contact stress, and area, were studied. The resonance frequency shift f of electrical impedance signature was regarded as the damage identification index. Results show that the influence of mechanical contact on damage evaluation could not be neglected. With increasing times of in situ contact, the characteristic resonant peak shifted leftward gradually due to the resulted superficial indentations, and the f value was in the order of 10–2–10–1 kHz for each mechanical clamping. The evolution direction of the resonance peak with contact stress was reversed, and the f value was about 10–1–100 kHz. The order was equal or even more serious against that of the early-stage mechanical damage. The relationship between the f value and the contact area, however, was elusive because of the combined effects of indentation damage and the compressive stress. Simulation experiments were conducted accordingly, and the abnormality was discussed. The quantitative results were compared between the steel and the Al alloy, and the variation with material property was demonstrated. Effective precautions to avoid the influence of mechanical contact were proposed.
Curved piezoceramic unimorph actuators exhibit strong nonlinearities due to their special architecture that enables large motion amplification. Among these nonlinearities, hysteresis is the most problematic as it makes it difficult to predict the displacement of the actuator for a given input voltage. Therefore, it has been difficult to use these actuators in precision displacement control applications. In order to overcome this difficulty, this research is focused on the development of an effective reference-tracking displacement control algorithm for such actuators. For this purpose, two linear (proportional–integral and internal model) and two nonlinear (sliding mode and model predictive sliding mode) controllers are designed and implemented. These controllers are applied to the curved piezoceramic unimorph actuator to control the displacement of the actuator for multiple sinusoidal voltage inputs at various frequencies. Experimental results are obtained, and their performance is compared both qualitatively and quantitatively. As a part of the model-based controller design, a new actuator model is also developed based on the mechanical second-order equation with an additional phase lag term to describe the hysteretic effect.
This article explores the merits of shape memory alloy Negator springs as powering elements for solid-state actuators. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbor. The unique characteristic of Negator springs is the nearly constant force needed to unwind the strip for very large, theoretically infinite deflections. Moreover, the flat shape, having a high area-over-volume ratio, grants improved bandwidth compared to any solution with solid wires or helical springs. The shape memory alloy material is modeled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behavior. The mathematical model of the mechanical behavior of shape memory alloy Negator springs is provided, and their performances as active elements in constant-force, long-stroke actuators are assessed. The shape memory alloy Negator spring is also simulated in a commercial finite element software, ABAQUS, and its mechanical behavior is estimated through finite element analyses. The analytical and the numerical predictions are in good agreement, both in martensitic and in austenitic ranges.
A nonlinear damping strategy using spatial filtering aiming at attenuating multimodal vibrations in a flexible structure is proposed and applied to a clamped–clamped steel beam. Based on the mode shapes, four piezoelectric patches are symmetrically or antisymmetrically attached on the surfaces of the beam close to the clamped ends. To suppress odd modes, two antisymmetrically attached patches are intermittently connected to a switching device consisting of a digital switch and an inductor. The electronic switch is kept open unless the sum of the two piezovoltages reaches an extremum value. When the switch is closed, the antisymmetrically bonded patches and the inductor constitute an oscillator. The switching time corresponds to half a period of this oscillator until the sum of two piezovoltages has been reversed. In a similar way, symmetrical patches based on the difference signal are used for controlling even modes. Experimental setup for controlling the first two vibration modes of a clamped–clamped beam is established to validate the analytical results based on finite element method. Corresponding results showed that the proposed damping strategy using spatial filtering exhibits better performance and allows an effective bimodal control method without significantly increasing the complexity and can be easily extended to multimode control.
The load-bearing antenna approach for state-of-the-art aero-vehicle structure has been made for military aircraft in recent studies. This study presents the structural design and development of multiband aero-vehicle smart skin antenna which has been developed as a simplified structured load-bearing antenna panel compared with recent studies for aircraft. A multifunctional concept of aircraft structure combines structural and electrical functions to single structural component. The structural function of multiband aero-vehicle smart skin antenna is load-bearing member of aircraft, and its electrical function is antenna for communication and navigation of aircraft. The radar cross section and drag reduction could be achieved by using sandwich structure and composite material. Through sequential design and development process, multiband aero-vehicle smart skin antenna successfully demonstrated the design, fabrication, and structural integrity of a load-bearing multifunction antenna component subjected to flight load conditions. This study concentrated on the computational analysis using finite element to validate the structural design of multiband aero-vehicle smart skin antenna structure. In addition, structural test results were briefly introduced to compare with the analysis results. The prototype of multiband aero-vehicle smart skin antenna was fabricated and tested for the verification of each analysis within the desirable tolerance.
A novel fiber optic bolt loosening monitoring sensor is proposed and applied to an experimental model of aircraft lug assemblies. The lug assembly is fabricated with a stainless steel lug, a composite sandwich panel, and 10 carbon-steel bolts, nuts, and washers. The bolt loosening monitoring system is configured with a single-mode fiber and an optical time-domain reflectometer. Sections of the single-mode fiber line are mounted on the respective 10 bolt/nut joints and function as bending sensor nodes to detect bolt loosening events. Then, the other end of the single-mode fiber is connected to the optical time-domain reflectometer, to measure optical loss in the backscattering light attenuation trace, induced by the macro-bending of the sensor nodes. In addition, the bolt loosening angle and locations can be determined, by analyzing the optical time-domain reflectometer traces. The experiments for multi-bolt monitoring demonstrate that the single single-mode fiber line incorporated with optical time-domain reflectometer is able to detect simultaneously which bolts were loosened with an angle resolution of 1.45°, even under temperature variation. Since the optical time-domain reflectometer and SMF combination allows monitoring tens of kilometers, just one system can monitor thousands of bolt joints. Therefore, numerous bolt joints in large structures can be economically monitored in real time.
For next generation aircraft, contra rotating open rotor propulsion systems are currently discussed. Their economic advantages are in conflict with their high noise emission, which concentrates in distinct frequency bands. To bring contra rotating open rotor engines into operation at commercial aircraft and to maintain the passenger comfort level, active systems for noise reduction are considered. In this article, a contra rotating open rotor noise simulator for the future testing of active systems is presented. The simulator consists of a 14 x 8 loudspeaker array, which is placed close to a test fuselage. Driving each loudspeaker by a particular signal, complex sound pressure fields can be synthesized on the fuselage. The algorithm presented here calculates loudspeaker signals to synthesize the target sound pressure spectra on the fuselage. These target spectra were derived from numerical contra rotating open rotor engine simulations, coupled with a Ffowcs Williams–Hawkings solver to propagate the calculated sound pressure field toward virtual surface microphone positions on the test fuselage. Requirement for such synthesis is the knowledge of the transfer paths from all loudspeakers to all surface microphones. In experiments, these paths are measured, and the loudspeaker signals are synthesized by the algorithm. Finally, measurements with the loudspeaker array and a microphone array are shown which prove the concept.
In this article, ongoing studies to apply semi-active control devices to reduce undesired vibrations of civil engineering structures are investigated. In doing so, the barrier of the nonlinear inner mass single unit impact dampers is equipped by the magnetorheological fluid dampers. For convenience, this kind of impact dampers is briefly named smart impact dampers. Dynamic behavior of a vibratory system equipped with the smart impact damper is modeled based on the modified Bouc–Wen model for the magnetorheological damper. Performance of the smart impact damper to suppress free vibration of an Euler–Bernoulli beam is investigated. Furthermore, effects of varying applied current to the magnetorheological fluid damper on vibratory behavior of the beam are illustrated in user-oriented charts. The analysis results show that the smart impact dampers with optimal parameters can suppress undesired vibrations much better than conventional impact damper systems.
Shape memory alloys are thermally activated smart materials. Due to their ability to change into a previously imprinted actual shape by means of thermal activation, they are suitable as actuators for mechatronical systems. Despite the advantages shape memory alloy actuators provide (lightweight actuators, lower costs, and so on), these elements are seldom integrated by engineers into automotive systems. One reason for this phenomenon among others is the varying dynamic behavior at different ambient temperatures. A methodical approach through the problem definition, as well as the presentation of different solutions using adaptive resetting, introduces experimental results on the behavior of these actuator systems. This article presents different solutions and longtime experiments compared to conventional shape memory alloy actuators at automotive conditions. It concentrates on the possibility of utilization of a pseudoelastic resetting element working in combination with a shape memory alloy actuator.
The concept of harvesting energy from galloping oscillations of a bluff body with different cross-section geometries attached to a cantilever beam is investigated. To convert these oscillations into electrical power, a piezoelectric transducer is attached to the transverse degree of freedom of the prismatic structure. Modal analysis is performed to determine the exact mode shapes of the structure. A coupled nonlinear distributed-parameter model is developed to determine the effects of the cross-section geometry, load resistance, and wind speed on the level of the harvester power. The quasi-steady approximation is used to model the aerodynamic loads. Linear analysis is performed to investigate the effects of the electrical load resistance and the cross-section geometry on the onset speed of galloping. The results show that the electrical load resistance and the cross-section geometry affect significantly the onset speed of galloping. Nonlinear analysis is performed to determine the effects of the electrical load resistance, cross-section geometry, and wind speed on the system’s outputs and particularly the level of the harvested power. A comparison of the performance of the different cross sections in terms of displacement and harvested power is presented. The results show that different sections are better for harvesting energy over different regions of the flow speed. The results also show that maximum levels of harvested power are accompanied with minimum transverse displacement amplitudes for all considered (square, D, and triangular) cross-section geometries.
Aerodynamic buffeting load can lead to premature fatigue damage of aircraft vertical fin structures. This article presents a robust control law development strategy for active buffeting load alleviation of a smart fin structure. The impact of aerodynamic loads on the modeling uncertainties of the smart fin was investigated through extensive wind tunnel tests. Test results revealed that the airflow introduced higher damping ratio and caused frequency shift to the vibration modes. These aerodynamic effects may adversely affect the performance and robustness of active control laws. Based on the observations, the structured singular value synthesis technique was used to develop a robust control law for the smart fin using a truncated baseline dynamic model. A parametric uncertainty block was introduced to account for the changes in the modal parameters of the baseline dynamic model due to the aerodynamic effects. An additive uncertainty block was included to account for the unmodeled higher-order vibration modes as well as the modeling errors in the low frequency range. The robust performance of the control law was demonstrated through simulations as well as extensive closed-loop control experiments in the wind tunnel using various free airstreams and vortical airflows. This provided a verified control law design strategy for active buffeting alleviation applications.
Prestressed fiber–reinforced polymer composites have gained popularity as a structural rehabilitation technique; however, the prestress loss remains a critical issue in terms of material efficiency and structure safety. This article presents a fiber Bragg grating–based technique for prestress loss monitoring in reinforced concrete beams strengthened by prestressed near-surface mounted carbon fiber–reinforced polymer strips. Bare fiber Bragg grating sensors are used to monitor the time history of the prestress loss in near-surface mounted strips with different prestress levels during both the construction stage and the ultimate loading phase. The prestress losses measured by the fiber Bragg grating sensors are further compared with the data reported by the conventional electrical strain gauges. The results show that the fiber Bragg grating sensors can effectively monitor the prestress loss when properly integrated into the near-surface mounted strips. They also provide a reliable method for crack damage detection in concrete.
Conformal load-bearing antenna structures, which afford load-bearing structures with radar capability, are a promising technology to reduce weight and drag of air vehicles. This article presents an investigation of the mechanical and electromagnetic performance of slot log-spiral antenna in carbon-fibre composite structures. Compared with traditional rectangular slots, equiangular slot spiral antenna is found to offer broader bandwidth and better mechanical strength. Through experimental testing and finite element analyses, a new tip design is proposed that can significantly reduce the stress concentration of the non-load-bearing log-spiral antenna. Results of mechanical tests also show that the compressive strength of a carbon-fibre composite plate featuring a spiral slot is comparable with that pertinent to a plate with a circular hole of the same size. Filling the slots with epoxy resin can further enhance the compressive strength.
In the recent years, electromechanical impedance–based structural health monitoring has emerged as an alternate to conventional monitoring techniques, especially for aerospace structures where the surface areas are more predominant than the thickness. In the impedance–technique, piezoceramic (lead zirconate titanate) transducers are bonded on the structure to be monitored such that surface area (length x width) of the transducer is in contact with the structure. In the presence of electric field, these transducers interrogate the structure which results in a unique health signal known as admittance signatures. Any deviation in the signature during the period of monitoring indicates disintegrity in the structure. The existing impedance technique has focused on disintegrity on the surface of the structure along the length and width directions of a transducer. This article monitors the increment of load and damage severity along the thickness direction. At first, a load and the increments of load were monitored on a carbon steel gear specimen, where the load was applied parallel to the thickness of transducer such that the load was axial on the specimen. The signatures were obtained for each load increment. Later, an aluminium plate was used to study damage increment along the length and thickness directions separately. The signatures were recorded for each damage increment stage. The signatures were carefully studied and validated using three-dimensional predictive impedance model along the length and thickness directions. This study is expected to be useful for monitoring gears and shafts in mechanical systems where the thickness is predominant.
In this article a new acceleration sensor using flexoelectric barium strontium titanate cantilever was designed, fabricated, and tested for vibration monitoring. The flexoelectric sensors were configured as a trapezoidal unimorph with a barium strontium titanate layer bonded onto a steel substrate. Seismic mass was attached to the unimorph tip to amplify the transverse flexoelectric response of the barium strontium titanate layer. The theoretical model was developed and validated by vibration tests using the prototyped flexoelectric unimorph. The prototyped accelerometer with thickness of 0.1 mm and length and width in millimeters showed a stable sensitivity of 0.84 pC/g over the frequency range of 100 Hz–1.6 kHz. The aging property of the flexoelectric material was demonstrated to be much better than that of the reported piezoelectric materials right after poling. Scaling effect analysis was also performed for flexoelectric unimorphs. The test results and initial scaling effect analysis indicate that micro/nano flexoelectric sensing holds promise for a broad range of applications.
In this article, micromechanical modeling of magnetoelectroelastic composites with multicoated inclusions and functionally graded interphases are elaborated. The integral equation taking into account the continuously varying interphase properties as well as the multifunctional coating effects is introduced based on Green’s tensors and interfacial operators. Magnetoelectroelastic composites with functionally graded interphases are analyzed, and the effective properties are derived. Based on the Mori–Tanaka, Self-Consistent, and Incremental Self-Consistent models, the numerically predicted effective properties of magnetoelectroelastic composites are presented with respect to the volume fractions, shapes of the multicoated inclusions, and the thickness of the coatings. The multicoating and functionally graded interphase concepts can be used to optimize the effective properties of multifunctional composites. This can be used to design new multifunctional composite materials with higher coupling coefficients.
In this article, the coupled thermomechanical response of superelastic shape memory alloy bars and tubes in combined tension and torsion is studied both analytically and experimentally. Using the Gibbs free energy as the thermodynamic potential and choosing appropriate internal state variables, a three-dimensional phenomenological macroscopic constitutive model for shape memory alloys is derived. Taking into account the effect of latent heat during the forward and reverse martensitic phase transformation, the appropriate form of the energy balance relation is obtained. The three-dimensional coupled relations for the energy balance in the presence of the internal heat flux and the constitutive equations are reduced to a two-dimensional form for the tension-torsion case. An explicit finite difference approach is utilized to discretize the governing boundary conditions of bars. An empirical expression for the free heat convection from the surface of a shape memory alloy bar was proposed and experimentally validated. Several sets of experiments were then carried out to evaluate the mechanical and thermal responses of the model for a shape memory alloy tube subjected to uniaxial, pure torsion and non-proportional tension and torsion loading–unloading conditions. The approach could be used in the design of shape memory alloy devices undergoing combined loads with high strain rates or in the fatigue design of shape memory alloy devices subjected to cyclic loading.
This article investigates precise positioning at the micrometer scale using piezoelectric actuators. A special focus is given to the rejection of ambient vibration disturbances. An original experimental setup composed of two superposed piezoelectric actuator stages is used to evaluate the performances of the proposed approach. The bottom one is devoted to the disturbance generation, whereas the upper one allows position tracking and active stabilization. The experimental dynamic and hysteretic characterizations of the top actuator are performed. Based on the identified dynamic model, a linear controller is designed. Its performances are improved with a hysteresis compensation method. Such methods usually imply either simple symmetrical hysteresis (e.g. General Maxwell Slip) or operators able to model asymmetric loops (e.g. Preisach) at the cost of more memory usage and computational time. In the present study, a previously published lightweight asymmetric operator hysteresis is successfully used for the first time within a piezoelectric positioning closed-loop control.
We investigate the effects of shape variations of a cantilever beam on its performance as an energy harvester. The beam is composed of piezoelectric and metallic layers (unimorph design) with a rigid mass attached to its free end. A reduced-order model based on a one-mode Galerkin approach is derived. Solutions for the tip displacement, generated voltage, and harvested power are then obtained. Linear and quadratic shape variations are considered in order to design piezoelectric energy harvesters that can generate energy at low frequencies and maximize the harvested energy. The results show that the fundamental natural frequency and mode shape are strongly affected when the shape of the beam is varied. The influence of the electrical load resistance and the shape parameters at resonance on the system’s performance is discussed. It is determined that for specific resistance values, the quadratic shape can yield up to two times the energy harvested by a rectangular shape.
Macrofiber composites are low cost, durable, and flexible piezoceramic devices that are presently being considered for applications that include shape control of airfoils for improved flight performance, vibration, and noise suppression and energy harvesting. However, macrofiber composites also exhibit hysteresis and constitutive nonlinearities that need to be incorporated in models and model-based control designs to achieve their full capability. In this article, we combine constitutive relations, constructed using the homogenized energy model for ferroelectric hysteresis, with Euler–Bernoulli theory to construct a dynamic macrofiber composite model that quantifies a range of rate-dependent hysteretic behavior of macrofiber composites. Using homogenizing strategies, the macrofiber composite patch is treated as a monolithic material with effective parameters. We initially calibrate the model by estimating parameters through a least squares fit to a subset of the measured data. We find that the estimated parameters yield very accurate fits for quasistatic hysteresis. The estimated parameters also provide reasonably accurate predictions for a range of frequencies that include the first two harmonics. Second, we employ an adaptive Markov chain Monte Carlo algorithm to construct densities and analyze the correlation between parameters. The kernel density estimates derived from the Markov chain Monte Carlo chains imply that most of the model parameters exhibit non-Gaussian distributions.
The stability analysis and active control of a composite laminated open cylindrical shell in subsonic airflow are conducted using piezoelectric material. The equation of motion of the shell with piezoelectric patch is derived from Hamilton’s principle and transformed into the ordinary differential equations using Galerkin’s method. The linear potential flow theory is applied to derive the aerodynamic pressure. The displacement and acceleration feedback control strategies are used to obtain the active stiffness and mass by applying an appropriate external control voltage to activate the piezoelectric patch. The natural frequencies of the system are calculated, from which the flow velocity for the open cylindrical shell under instability can be obtained. The effects of the ply angles of the shell and the feedback control gains on the stability properties of the structural system are discussed. From the results, it can be seen that when the flow velocity becomes sufficiently high, the open cylindrical shell exhibits instability of the divergence type and the instability velocity decreases with the increase in the ply angle. The stability of the system can be improved by the displacement feedback control strategy. With the increase in the displacement feedback control gain, the instability velocity of the system increases. For the acceleration feedback control strategy, the instability velocity of the system remains unchanged, which illustrates that the active mass induced by the acceleration feedback has no effect on the instability velocity of the composite laminated open cylindrical shell.
Launch vehicles and satellites experience severe dynamic loads during flight phases. In particular, pyroshock generated from several separation events could result in malfunctions in the electric components in the launch vehicles. Shock isolators are generally applied in order to attenuate these severe shock environments; however, these isolators could amplify the low-frequency vibration generated by the engine thrust and aerodynamic loads and reduce the payload stability. When the natural frequency of the isolator is increased in order to avoid the low-frequency vibration amplification, sufficient shock attenuation could not be obtained. Thus, the isolators used in launch vehicles need to be designed with trade-offs between the low-frequency vibration amplification and the pyroshock attenuation. This article presents a novel frequency tuning method for the isolator in order to achieve both shock attenuation performance and avoidance of the vibration amplification. Compressed mesh washer isolators using the pseudoelasticity of shape memory alloy were adopted for easier attainment of the frequency tuning with a high performance in the shock attenuation.
This article presents the design and experimental test of a new electromagnetic generator optimized for vibration energy harvesting with a nonlinear energy extraction circuit (synchronized magnetic flux extraction circuit). Previous results showed that the synchronized magnetic flux extraction circuit allows the rectification and the amplification of the voltages produced by an electromagnetic transducer, as well as the optimization of the energy transfer independently of the load impedance. A new geometry of electromagnetic harvester is proposed and optimized to harvest the maximum energy with the synchronized magnetic flux extraction circuit. The studied structure, whose total volume is 10 cm3, is based on a closed ferromagnetic back iron in order to obtain a high reactance in comparison with its resistance. Experimental measurements show that with the synchronized magnetic flux extraction technique, a rectified power of 1.6 mW is harvested at 1 g, 100 Hz over a 10 Hz bandwidth.
For source location in composites based on Lamb wave techniques using direction-dependent piezoelectric rosettes sensors, the source is usually located by the intersection of wave propagation directions identified by the sensors. However, the rosettes do not measure the direction of group velocity directly. Instead, they measure the direction of principal strain. Hence, in order to accurately predict the sources in anisotropic plates, it is essential to investigate the relationship between the direction of principal strain and that of group velocity. In this study, the four vectors, namely, phase velocity, group velocity, displacement, and principal strain associated with propagating waves in anisotropic plates, are computed using semianalytical methods. The analytical results agree very well with the results of finite element method based on Abaqus, including those of the complicated SH0 mode. Moreover, it is found that the four vectors exhibit some symmetrical properties. When Lamb waves propagate along the symmetry axes, the directions of the four vectors are all the same.
In this article, the extended displacement discontinuity method is extended to study the fracture problem in a three-dimensional transversely isotropic magnetoelectroelastic medium with a planar crack vertical to the plane of isotropy. Considering the electric and magnetic fields in the crack cavity, and using the Somigliana identity along with the displacement discontinuity Green’s functions, the hyper-singular boundary integral equations for the unknown displacement discontinuities across the crack face are derived. The singularity features along the crack fronts are analyzed, and the extended field intensity factors are expressed in terms of the extended displacement discontinuities on the crack face. Numerical examples on the field intensity factors are finally calculated for a vertical square crack using the exact closed-form Green’s functions due to constant displacement discontinuities over a rectangular crack element, and some interesting features are observed, which are different from the case where the crack is located in the plane of isotropy. The influence of the electric and magnetic boundary conditions along the crack face on the field intensity factors is further studied.
A robust electromechanical updating methodology for piezoelectric structures effective coupling prediction is first presented. It combines a finite element design experiment–based a priori sensitivity analysis, a response surface method–based meta-modelling and a genetic algorithm–based multi-objective optimization procedure. Then, this methodology is applied to cantilever aluminium thick plate and thin beam structures that are bonded, respectively, with two oppositely poled large and oppositely and same poled small piezoceramic patches on their upper and lower surfaces. In order to correlate corresponding first few effective modal electromechanical coupling coefficients, a mechanical updating is first considered; it consists of identifying the stiffness parameters of linear springs, modelling the clamp, so that relative deviations between the first few experimental and finite element short-circuit frequencies are minimized; then, an electric updating is considered; it consists of finding the patches’ relative transverse blocked dielectric constants that minimize the first few experimental and finite element open-circuit frequencies relative deviations. Free vibrations are simulated using ANSYS®-coupled piezoelectric three-dimensional finite element. The obtained results have partially confirmed those from a former ad hoc updating method since the sensitivity analyses led to same stiffness parameters’ irreducible number and only some effective modal electromechanical coupling coefficient test–model correlations were enhanced.
This article presents a modular architecture for shape memory alloy actuators elastically compensated by thin beams loaded axially beyond their buckling limit. Starting from the exact equations for the elastic curve of the beams, an approximate procedure is developed for the engineering design of the entire compensating system. The theory of the compensator is validated successfully against a finite element model and experimental results. The experimental characterization of a complete prototype actuator shows that the forces generated by the compensated actuator are constant for both instroke and outstroke over the full range of displacements. The actuator concept proposed lends itself to modular assembly to multiply either the stroke covered (series combination) or the force generated (parallel combination).
An efficient C0 continuous two-dimensional finite element model for the accurate analysis of laminated composite plates embedded and/or surface bonded with piezoelectric layers and subjected to mechanical loading and/or electrical potential has been presented in this article. The problem of smart laminates involves the coupling between mechanical and electrical fields. The mechanical/structural component is modeled by an efficient equivalent single-layer plate theory, which ensures interlaminar shear stress continuity and zero transverse shear stress conditions at the top and bottom of the plate surfaces. Moreover, this theory contains unknowns at the reference plane (i.e. the mid-plane) only. The electrical field is modeled using layer-wise theory, which contains the unknowns at each layer interfaces. In order to calculate the accurate through-the-thickness transverse shear stress variations, a simple approach based on least square error method is applied to the three-dimensional equilibrium equations of the plate problem at the postprocessing stage, after in-plane stresses are calculated using the finite element model based on the above-mentioned refined plate theory and layer-wise theory. The proposed combine model, which may be called as a refined hybrid plate model, is implemented to analyze the coupled problem of piezoelectricity in laminated composites and sandwich plate bending.
This article presents the development of a torsional adaptive tunable vibration absorber using a magnetorheological elastomer for vibration reduction of a powertrain test rig. The magnetorheological elastomer used to develop the adaptive tunable vibration absorber consists of silicone polymer, silicone oil and magnetic particles with the weight percentages of 60%, 20% and 20%, respectively. Experimental testing is conducted to obtain the magnetorheological elastomer’s properties, such as Young’s modulus and the damping ratio, and effective formulas are derived to facilitate the design of the adaptive tunable vibration absorber. With the derived formulas, a magnetorheological elastomer–based adaptive tunable vibration absorber is designed and manufactured, and experimental testing is also conducted to validate the design. The results of experiments show that the magnetorheological elastomer–based adaptive tunable vibration absorber can work in a frequency range from 10.75 to 16.5 Hz (53% relative change). Both the designed and experimental results of the adaptive tunable vibration absorber’s frequencies are in good agreement. A powertrain model is used to validate the magnetorheological elastomer–based adaptive tunable vibration absorber’s effectiveness, and the numerical simulations show that the powertrain frequencies are shifted away from the resonant frequency; thus, the powertrain’s steady-state vibration can be significantly reduced. This magnetorheological elastomer–based adaptive tunable vibration absorber will be a promising new device for vibration reduction of vehicle powertrains.
A dither motor in self-sensing actuation configuration allows each of the piezoelectric (lead zirconate titanate) elements to be used concurrently for dither rate sensing and dither motion actuation, so that system of improved efficiency and reliability can be achieved. For a self-sensing actuator, bridge circuit either fixed or adaptive is usually required to resolve the mechanical response from the control signal. In this study, a new technique for accurately extracting the mechanical response from the control signal of dither motor is developed. The measured open-loop response of the dither motor in self-sensing actuation configuration compared well with the results from a separate lead zirconate titanate sensor. Closed-loop dither rate control and frequency tracing of the dither motor are implemented and verified upon temperature variations. Method for estimating the equivalent lead zirconate titanate capacitance of the dither motor more accurately online is also provided and confirmed experimentally. The maximum error between the equivalent capacitance measured online and that measured under static conditions is about 1.2%.
The dynamic stability of a composite laminated cylindrical shell containing a throughout delamination along circumferential direction integrated with piezoelectric layers at both inner and outer surfaces is investigated in this article. The Heaviside step function is used to describe the displacement components in the regions with and without delamination. Based on the classical shell theory, linear piezoelastic constitutive relationship, and variational principle, the governing equations of motion are derived and then solved by employing Rayleigh–Ritz method and Bolotin method to obtain the principal unstable region. Numerical results are presented in both tabular and graphical forms to show the effects of the piezoelectric layer; the length, depth, and location of the delamination; and the static axial force on the resonance frequency and the principal unstable region of the delaminated piezoelectric laminated shell.
A cylindrical piezoelectric transformer with an imperfect interface operating with thickness-shear modes is used within the three-dimensional equations of piezoelectricity. The shear–slip interface model is used to simulate the effect of viscoelastic imperfect interface. The influence of interface parameters on the transforming ratio, input admittance, power density, efficiency, and the displacement and stress distributions along the radius direction is discussed. Numerical results show that the weak interface lowers the performance of the transformer overall, which may provide theoretical guidance for the design of piezoelectric transformers.
Shape memory alloy actuator wires undergo a significant (~4%) contraction and a corresponding change in resistance because of a temperature- and load-induced phase transformation. When a restoring force such as a pre-stretched bias spring is placed in series with a shape memory alloy wire, the system becomes an actuator that can generate a repeatable force. Simultaneously, the resistance of the wire can be correlated to strain and enable self-sensing, eliminating the need for external feedback sensors. The self-sensing task, however, is complicated in applications requiring multiple coupled wires, for example, advanced two-dimensional or three-dimensional positioning. The presence of coupled (passive or active) actuator wires with nonlinear, hysteretic force–displacement characteristics has a strong impact on an individual wire’s resistance behavior that has not been systematically studied to date. This article expands upon previous work that studied a single-shape memory alloy–spring system by adding a second opposing shape memory alloy wire and focusing on the resistance to strain mapping that is crucial for self-sensing applications. Systematic stress–strain and resistance–strain experiments are presented alongside physics-based modeling results that help to identify several sources of hysteresis in the resistance–strain behavior and facilitate intelligent calibration schemes for multifunctional self-sensing and actuation applications.
This article presents a combined finite element method and analytical process to predict the one-dimensional guided-wave propagation for nondestructive evaluation and structural health monitoring application. Analytical methods can perform efficient modeling of wave propagation but are limited to simple geometries. In response to today’s most complex cases not covered by the simulation tools available, we aim to develop an efficient and accessible tool for structural health monitoring application. This tool will be based on a hybrid coupling between analytical solution and time-domain numerical codes. Using the principle of reciprocity, global analytical calculation is coupled with local finite element method analysis to utilize the advantages of both methods and obtain a rapid and accurate simulation method. The phenomenon of interaction between the ultrasonic wave, the defect, and the structure, leading to a complex signature, is efficiently simulated by this hybrid global–local approach and is able to predict the specific response signal actually received by sensor. The finite element mesh is used to describe the region around the defects/flaws. In contrast to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the time domain using the explicit solver of the commercial finite element method software ABAQUS.
Structural health monitoring refers to the interdisciplinary engineering field whose objective is to monitor and evaluate the integrity of mechanical structures. Often times, structural health monitoring diagnostics utilize piezoelectric (lead zirconate titanate) transducers bonded to the surface of the structure monitored. Nonetheless, unexpected variations in the mechanical properties of the adhesive film could affect the dynamic behavior of the system and potentially mischaracterize the fitness for service of a structure. In this article, we presented an analytical model to describe the dynamic coupling between the structure and the lead zirconate titanate transducer that includes the adhesive layer. An electromechanical impedance–based method capable of assessing the integrity of the adhesive bondline was developed based on the proposed analytical model. Our study found that the phase angle of the transducer’s electrical admittance was correlated to the mechanical impedance of the adhesive film following a power law behavior. Validation of the proposed model was carried out both by testing transducers bonded to aluminum plates and through a numerical parametric study. In the future, the method proposed could be used to detect preexisting defects in the adhesive bondline, to estimate the adhesive’s thickness at manufacturing, and to monitor the degradation of the adhesive material during the life of the system.
Oscillation-based linear energy harvesters are often excited by random, band-limited, slowly varying forces. When the excitation bandwidth is limited such that natural frequencies of electromechanical energy harvester are not excited, linear devices lose their efficiency, and nonlinear structures with negative stiffness can be used to enhance the conversion efficiency by performing frequency up-conversion. It is shown here that nonlinear, bistable oscillators perform considerably better than their linear counterpart under band-limited excitation, in certain regions. This is contrary to commonly modeled, wideband, or white noise excitation, where nonlinear potential has no or little effect on the energy output. A sharp increase in performance is observed for band-limited random excitation along a well-defined region in the input-level and bandwidth plane. Having defined this region, the harvesting device can be adaptively tuned in order to keep the power output levels high. The results of simulated, partially analytical, and experimental studies are compared and analyzed to obtain cross-validation.
Reinforced concrete is subjected to deterioration due to aging, increased load, and natural hazards. To minimize the maintenance costs and to increase the operation lifetime, researchers and practitioners are increasingly interested in improving current nondestructive evaluation technologies or building advanced structural health monitoring strategies. Acoustic emission methods offer an attractive solution for nondestructive evaluation/structural health monitoring of reinforced concrete structures. In particular, monitoring the development of cracks is of large interest because their properties reflect not only the condition of concrete as material but also the condition of the entire system at structural level. This article presents a new probabilistic approach based on Gaussian mixture modeling of acoustic emission to classify crack modes in reinforced concrete structures. Experimental results obtained in a full-scale reinforced concrete shear wall subjected to reversed cyclic loading are used to demonstrate and validate the proposed approach.
Self-healing materials capable of autonomic crack healing are potentially important in terrestrial and space applications. Where damage-causing forces and healing forces compete, it is of interest to consider ways to increase the healing rate. This article investigates the use of acoustic energy for this purpose. As a means for targeted acoustic energy delivery to the crack site, we study time-reversal mirrors (iterative time reversal and playback) for stress wave focusing at a discontinuity. The article begins with a discussion of the key analytical results. Both pulse propagation and eigenfrequency vibrations are analyzed, and it is argued that if sufficient time is allowed between successive time-reversed playbacks, the focused pulse amplitude grows faster than the eigenfrequency vibrations. Experimental implementations of iterative time-reversed playback on solid circular steel and nylon rods with artificially introduced discontinuities show that even in the one-dimensional propagation studies here, time-reversal mirrors produce satisfactory focusing for a multitone pulse. Based on the significant amplification seen in the steel rods and the more dispersive and dissipative nylon rods, it appears that acoustic energy could be delivered in a targeted manner to a crack using iterative time-reversal mirrors.
Triboluminescent materials are promising in the field of structural health monitoring for real-time crack detection and related damage assessment. This study presents a simple, but novel, image processing protocol to detect and quantify luminescence from crack formation in cement-based matrices. Mortar cubes of 2'' x 2'' (5.1 cm x 5.1 cm) were loaded in compression with an external coating of manganese-doped zinc sulfide (ZnS:Mn) triboluminescent material. The concentration of triboluminescent material and rate of loading were varied to evaluate luminescence response. A digital single lens reflex camera was employed to capture luminescence from the resulting cracks, which formed and propagated during failure. The images were then analyzed with an image processor, and total luminescence/pixel along the cracks was quantified. Results show that overall luminescence increases with the increase in triboluminescent concentration as well as with the rate of loading. This article presents a novel method that can be applied to monitor crack formation in cement-based materials, providing reliable accuracy in luminescence quantification.
Physics-based computational models play a key role in the study of wave propagation for structural health monitoring and the development of improved damage detection methodologies. Due to the complex nature of guided waves, accurate and efficient computation tools are necessary to investigate the mechanisms responsible for dispersion, coupling, and interaction with damage. In this article, a fully coupled electromechanical elastodynamic model for wave propagation in a heterogeneous, anisotropic material system is developed. The final framework provides the full three-dimensional displacement and electrical potential fields for arbitrary plate and transducer geometries and excitation waveform and frequency. The model is validated theoretically and proven computationally efficient. Studies are performed with surface-bonded piezoelectric sensors to gain insight into the physics of experimental techniques used for structural health monitoring. Collocated actuation of the fundamental Lamb wave modes is modeled over a range of frequencies to demonstrate mode tuning capabilities. The displacement of the sensing surface is compared to the piezoelectric sensor electric potential to investigate the relationship between plate displacement and sensor voltage output. Since many studies, including the ones investigated in this article, are difficult to perform experimentally, the developed model provides a valuable tool for the improvement of structural health monitoring techniques.
A package-level peristaltic piezoelectric micropump has been designed and fabricated in utilizing multilayer ceramic fabrication methods. The device was fabricated using commercially available low-temperature cofired ceramic materials and a custom-designed low-temperature cofired ceramic compatible piezoelectric ceramic composition. The assembled multilayer pump structure was sintered in single cofiring step. Performance testing resulted in observed unloaded bidirectional flow rates of 450 µL/min and a blocking pressure of 1.4 kPa when the pump was operated at a voltage of 100 Vpp (with a phase difference of 120°) with a frequency of 100 Hz. It was further shown that incorporation of diffuser elements into the microfluidic interconnects was used to increase the blocking pressure capabilities at the expense of flow rate and bidirectional flow characteristics. Alternatively, by maintaining a uniform channel width but varying channel cross section width over height ratio (W/H), an unloaded flow rate of 630 µL/min with an enhancement of blocking pressure (1.55 kPa) was achieved for W/H = 3 (and the same drive conditions as above). The resulting multilayer ceramic-based piezoelectric micropump offers a compact planar pump design, with significant performance advantages, and design flexibility compared to competing micropump technologies.
This article presents a novel composite magnetorheological fluid clutch design that is based on both disc- and cylinder-type clutches. Combining the two types within the clutch, all of the area of the input plate can be used to transmit torque. The transmittable torque can be 1.45 times larger than the existing disc-type clutches with the same input plate diameter. An analysis of the structure created a torque transmission model that produced results consistent with the experimental results. Through the combination of structure analysis and experimental study, the relationship between the magnetic flux leakage coefficient and input current is obtained. The magnetic flux leakage coefficient of the novel structure increases with the input current, reaching a maximum of 2.5. These results can be used for the design of similar clutches.
A novel real-time acousto-ultrasonic sensor system using a phase-shifted fiber Bragg grating rather than a normal fiber Bragg grating was investigated. The spectrum of the phase-shifted fiber Bragg grating was simulated and analyzed, which indicates that a phase-shifted fiber Bragg grating has superior properties when compared to a normal fiber Bragg grating. Based on theoretical considerations, a novel real-time acousto-ultrasonic sensor system was proposed. Two identical 5-mm phase-shifted fiber Bragg gratings, with slightly different Bragg wavelengths, were used as the filter and the sensor. An amplified spontaneous emission light source and an apodized fiber Bragg grating were connected to illuminate the phase-shifted fiber Bragg gratings. The design allows the strain resulting from the ultrasonic wave to be precisely received and converted to the fluctuation of the output voltage. An ultrasonic wave generated in a carbon fiber–reinforced plastic plate using a macrofiber composite actuator was detected by both the phase-shifted fiber Bragg grating sensor system and a sensor system based on a normal fiber Bragg grating and arrayed waveguide grating. Comparison of the temporal and spectral responses of these two systems indicates that the phase-shifted fiber Bragg grating sensor system has a higher sensitivity than the fiber Bragg grating system. The results show that the phase-shifted fiber Bragg grating system does not require data averaging for noise reduction to measure the Lamb wave modes in a carbon fiber–reinforced plastic plate.
It is imperative to study the damage detection methods of steel truss structures that are always employed in extreme environment. Accurate structural damage localization is still a challenge due to high noise and low accuracy of the structural finite element model. To develop a dependable damage localization technique for truss structural health monitoring, a novel idea of damage localization is proposed: the curvature difference method of strain waveform fractal dimension, based on fractal theory and curvature method. To validate the approach, a simply supported bailey steel truss benchmark model has been designed and constructed in the laboratory. Based on the model, both experimental and numerical simulation results using the procedure under pulse excitation indicate that it is feasible and effective to detect the change of boundary conditions and the stiffness reduction of a truss member. In addition, the proposed technique exhibits highnoise insusceptibility (e.g. it works for noise levels up to 20% for a 10% truss member stiffness reduction). Moreover, the proposed technology is robust against the accuracy of the finite element model of measured structures, which decrease the workload of model updating dramatically. All these lay a good foundation for its engineering application.
In robotics and haptics, actuators that are capable of high force output with compact size are desired for stable and stiff interfaces. Magnetorheological brakes are viable options for such implementations since they have large force-to-volume ratios. Existing linear magnetorheological brakes have limited strokes, are relatively large, and have high off-state friction forces mainly due to the piston-cylinder internal design. The main contribution of this research is a new alternative internal design for linear magnetorheological brakes. The proposed approach uses the serpentine flux path concept to eliminate the piston-cylinder arrangement. It leads to significantly less off-state friction and infinite stroke. To the best of our knowledge, this is the first such linear magnetorheological brake. Our new brake can produce 173-N force. In comparison, a conventional linear magnetorheological brake with the same size can only produce about 27-N force. Our results showed that the ratio of the off-state friction force to the maximum force output in the prototype linear brake is about 3% compared with more than 10% for most similar devices in the literature and 27% for a commercial brake. At the same time, the compactness was improved as our prototype is about half the size of a commercially available product.
Dielectric elastomer actuators, a promising transducer technology, have received much attention due to their high efficiency and large deformation. However, in addition to electrical breakdown, dielectric elastomer actuators may also be easily affected by electromechanical instability. These failure modes inhibit the full potential actuation of dielectric elastomers. This study examines the parametric range for which electromechanical instability can be avoided for a dielectric elastomer plate actuator while achieving large actuation. It is found that the electromechanical instability can altogether be eliminated by boundary constraints. With control of the boundary conditions, consideration should also be given to the possible mechanical buckling failure that may occur. Simulation results based on Gent constitutive model are presented to show how these failure modes can be controlled and to what extent the performance of the dielectric elastomer actuator can be improved. This work should provide a better understanding on how to achieve the desired actuation performance of dielectric elastomers, thus leading to a better and controlled design for the applications of these smart materials in transduction technologies.
In this study, a mathematical model of a monotube magnetorheological (MR) shock absorber is presented and verified with an emphasis on leakage flow mechanisms and their impact on the damping force output. The model can be used in shock absorber design studies as well as vehicle simulations. To copy the force increase with yield stress, the authors employed the generic biplastic Bingham model for capturing the hydraulic resistance of the annular flow path in the piston. Moreover, the authors considered the impact of high-speed losses, fluid chamber compressibility, cavitation, elastic deformation of cylinder, fluid inertia, floating piston inertia, gas chamber pressure and Coulomb friction between damper components and the cylinder. The presented MR shock absorber model of is verified against experimental data involving three prototype shock absorber units. One shock absorber unit was a conventional unit with only one annular flow path, the second one employed the thru-core flow bypass for force roll-off at low piston velocities. The third unit utilized a so-called flux bypass to lower the magnetic field strength in the annulus to initiate the flow of MR fluids at lower yielding pressures across the piston. The flux bypass was located in the annulus. Except for the bypass features, all units were identical. All secondary flow features affect on the damping force at low piston velocities in particular. The experiment covered all key flow regimes of MR shock absorber operation from low speed to high speed. The results show that the proposed approach is capable of capturing key characteristics across the examined range of piston velocities and coil current levels.
Air-coupled nondestructive testing is an attractive technique that allows easy scanning inspection capability due to its noncontact nature with the specimen. A piezoelectric air-coupled transducer has been combined with a laser ultrasonic propagation imaging system as a fixed noncontact sensor. However, the large impedance mismatch between air and a specimen and its narrowband frequency range has prevented it from being efficiently used in real-world applications as a laser-air-coupled transducer ultrasonic propagation imaging system. Therefore, instead of combination with a piezoelectric air-coupled transducer, a combination between a laser and a capacitance air-coupled transducer is proposed through a comparative analysis between the capacitance and piezoelectric air-coupled transducers as the ultrasonic detector of the ultrasonic propagation imaging system. Under the same conditions, a series of experiments was conducted to examine the damage sensitivity in metal and composite specimens that have a hidden crack and barely visible impact damages, respectively. This noncontact system was further improved using repeat-scanning technique to enhance the signal-to-noise ratio and to overcome high attenuation problems, especially in composite specimens.
Spatially periodic structures, such as bladed disks, are widely used as components in rotating machines. The recent advent of blade-tip-timing sensing technique has allowed the extraction of vibratory response information of blades during rotation for damage detection purposes. The decision making in damage detection of a periodic structure based on such measurement, however, is difficult primarily because of the clustered natural frequencies and high modal density, which is further complicated by inevitable structural uncertainty/variation. Our underlying idea is to integrate piezoelectric transducers together with circuitry elements onto the periodic structure to alter its dynamic characteristics during the inspection stage to improve the sensitivity and robustness of vibration-based damage detection. In particular, it has been identified that a properly designed piezoelectric inductive circuitry can amplify the response anomaly under external excitation. Such amplification nevertheless diminishes as the mechanical damping in the periodic structure increases. In this research, it is shown that the adverse effect of mechanical damping to anomaly amplification can be effectively reduced, by incorporating negative resistance elements into the piezoelectric circuitry network. The negative resistance elements are synthesized using operational amplifier circuits and can offset the mechanical damping through the dynamic interaction between the piezoelectric circuitry and the host structure. The stability boundary of the negative resistance integration is identified, where the frequency-dependent inherent resistance of the piezoelectric transducer is taken into consideration explicitly. The effectiveness of the enhanced circuitry network for amplifying damage signature in periodic structures under large damping is illustrated with detailed case studies.
The ability of using measurements collected through a sensor network for detecting and locating damage via structural health monitoring algorithms relies on accurate sensor measurements from the deployed sensor network, and therefore, it can be affected by the presence of malfunctioning and/or faulty sensors. In this article, three sensor fault detection and identification techniques based on statistical monitoring, using latent-variable techniques, were implemented, evaluated, and compared with respect to their capability to detect and identify faulty sensors using case studies from an analytical three-dimensional truss and from an actual cable-supported bridge in the metropolitan Los Angeles, California region. It is shown that the leading sensor fault detection algorithms are effective in detecting certain classes of sensor failure mechanisms but are of limited utility when dealing with representative types of sensor faults encountered in typical structural health monitoring of civil infrastructure systems.
Motivated by their structural monitoring and energy harvesting applications, in this article, we study the modeling and inverse compensation of cantilevered ionic polymer–metal composite sensors that are excited at base. The proposed dynamic model is physics based, combines the vibration dynamics of a flexible beam under base excitation and the ion transport dynamics within an ionic polymer–metal composite, and incorporates the effect of a tip mass. Excellent agreement is demonstrated between the model prediction and experimental measurement in both the magnitude and the phase of the frequency response, for the frequency range of 10–150 Hz. For the purpose of real-time signal processing, we further reduce the model to finite dimension by combining techniques of Padé approximation and Taylor series expansion. For the reconstruction of the base excitation signal given the sensor output, we present an inverse compensation scheme for the reduced sensor model, where stable but noncausal inversion and leaky integration are introduced to deal with zeros that are unstable and on the imaginary axis, respectively. The effectiveness of the scheme as well as the underlying model is validated experimentally in the reconstruction of structural vibration signals, when the structure to which the ionic polymer–metal composite is attached is subjected both to periodic vibrations and to an impact.
This article discusses the development of a high-rate shape memory alloy–driven actuator. The concept of the actuator was developed to act as aerodynamic load control surface on wind turbines. It was designed as a plate or beam-like structure with prestrained shape memory alloy wires embedded off its neutral axis. Moreover, the shape memory alloy material was embedded in channels through which air was forced to actively cool the wires when the recovery load was to be released. Wires were implemented on both sides of the neutral axis to deflect the beam in both directions. Thermal analysis of the cooling channels showed that they increased the cooling rate up to 10-fold in comparison to the same set-up without forced convection. Subsequently, a fuzzy logic controller was designed to control the thermo-mechanical system. The inputs were the error between the deflection and the set point, the value of the set point and the time derivative of the set point. The output consisted of two signals to the valves that controlled the flow through the channels and a signal heating signal that was split into both sets of wires, depending on its sign. The controller was tested on an antagonistic set-up, through which a similar thermo-mechanical behaviour as with the actuator was obtained, but eliminating the beam dynamics. The results were satisfactory; an actuation bandwidth of 1 Hz was attained. Subsequently, the controller was tested on the actuator. With increasing actuation frequency, until 0.6 Hz, a relatively small error between the set point and the actual deflection was observed. Above that frequency, the error increased, but the sinusoidal response was lost. This is believed to be due to snap-through behaviour around the neutral position of the actuator. This was substantiated by the apparent inability of the actuator to track the set point around the neutral position in tracking a composite sinusoidal set point.
Piezoceramic materials are widely used in solid-state actuators and sensors. Since the shear piezoelectric coupling coefficient d15 is much higher than the other piezoelectric coefficients d31 or d33, the application of shear actuators is of particular interest. Shear-induced vibrations in piezoceramics are more complex to describe mathematically than longitudinal or transverse vibrations. Furthermore, as the complexity of the model increases, the coupling of electrical and mechanical terms precludes the analytical solution of the field equations for all but the simplest case. For a moderately complex piezoceramic model, the implementation of an analytical method to obtain the closed-form solution is very challenging. The use of approximate energy methods, such as the Rayleigh–Ritz method, is explored in this work to obtain the eigenvectors and eigenfrequencies for annular piezoceramic actuators. Series comprising orthogonal polynomial functions, generated using the Gram–Schmidt method, is used in the Rayleigh–Ritz method to formulate the linear eigenvalue problem. The advantage of the presented methodology lies in its adaptability for software implementation, which reduces the efforts to obtain fairly accurate results for more complex piezoceramic structures in future. The efficacy of the presented approximate method is assessed by comparing the results with the experiments.
This article presents a resonance-type vibration energy harvester with a Duffing-type nonlinear oscillator that can perform effectively in a wide frequency range. To mitigate the power-bandwidth trade-off in conventional linear harvesters, the resonance frequency band of the harvester is expanded by introducing a Duffing-type nonlinear oscillator in order to enable the harvester to generate larger electric power in a wider frequency range. Such a nonlinear oscillator, however, can have multiple stable steady-state responses in the resonance band with different levels of regeneration energy. In this study, the principle of self-excitation is utilized to destabilize the solutions, except for the highest energy solution. A load circuit with a switch between the conventional load circuit and a negative resistance circuit and the switching control law, which depends on the amplitude of the oscillator’s response, are introduced to impart the self-excitation capability in order to entrain the oscillator with the excitation only in the highest energy solution. Theoretical and numerical analyses are conducted to show that the proposed harvester can respond in a large amplitude in a wide frequency range, and a significant improvement in the regenerated power is achieved as compared to the one without self-excitation control.
This article presents the dynamic analytical solution of piezoelectric composite stack transducers under external harmonic mechanical loads, which is based on the linear theory of piezoelasticity. The solution is obtained by using the displacement method. The effects of the load frequency, the load amplitude, and the thickness of electrode on the dynamic characteristics of the transducers are discussed. Experimental results strongly verify the validity of the proposed theoretical analysis.
The shape memory behavior of polymers derives from a combination of their molecular architecture and thermomechanical history. In this study, several epoxies with various network architectures were prepared using mixtures of a diepoxide resin, a monoepoxide resin, and an aliphatic diamine hardener. A nonconventional cold-working programming, carried out below Tg, was employed to set the materials in a temporary configuration and allowed to fix considerable amounts of the applied strain. The shape memory behavior was evaluated through transient heating and isothermal recovery tests. All the resins are capable of complete recovery, which occurs as a sequence of an early process taking place below Tg and a major one close to Tg, which acted as the switching temperature (Tswitch). The proximity of the deformation temperature to Tg influenced the amount of strain recovered within each process. It was shown that resins with different structures, although presenting similar Tswitch, may have different recovery kinetics, and the roles of the network density and the chain stiffness on the recovery rate were evidenced.
In this article, modal feedback control is proposed to reduce the sound transmission through finite double panels using lead zirconate titanate ceramic sensors and actuators bonded to the structure. Active control allows adding virtual modal damping and mass to the structure by the use of modal velocities and accelerations. In a first step, the equations describing the structure, the actuators, the acoustic excitation, and the acoustic radiation are detailed. Next, the state space formulation of the smart structure is presented. In a second step, the implementation of active control is illustrated through the use of numerical examples. Finally, simulations are performed using two actuators, allowing five modes to be controlled. The transmission loss factors of the controlled and uncontrolled structure are shown as a function of the required command voltage. These results are also compared with those achieved using other vibroacoustic control techniques.
Among many shape memory alloys, nickel–titanium (NiTi) alloys are popular due to their superior properties in shape memory effect and superelasticity. They are presently often used in microengineering and medical technology especially in orthopedic and orthodontic implants due to their specific properties. In this study, the electric discharge machine characteristics of NiTi shape memory alloys have been fully investigated by full factorial design. Analysis of mean showed that the material removal rate of NiTi in the electric discharge machine process significantly related to the electrodischarge energy, involving the pulse current and pulse duration. Many electrodischarge craters and recast layers were observed on the electric discharge machine surface of NiTi samples. In addition, there was no significant difference between copper (Cu) and tungsten–copper (W-Cu) electrodes in material removal rate but work stability of W-Cu electrode was longer. On the contrary, quantity of impurity on the surface of the Cu electrode was lower. The specimen’s hardness near the outer surface could reach 1200 Hv, which originated from the hardening effect of the recast layer. Here, the microstructure, composition, and hardness of electric discharge machine surfaces are also discussed.
Ferroelectric and ferromagnetic materials have the advantage of broadband and dual actuator and sensor capabilities. Ferroelastic compounds such as shape memory alloys have large energy densities and are biocompatible. However, to take full advantage of these properties, it is necessary to employ models and control designs that account for the rate-dependent hysteresis, creep, and constitutive nonlinearities inherent to the materials. Inverse compensation is one technique that achieves this purpose. We present an inversion algorithm based on a binary search of a discretized input grid and apply this to the homogenized energy model for modeling hysteresis. The inversion algorithm is shown to provide a reasonable balance between accuracy and computational speed. Numerical examples are presented for three specific cases of the homogenized energy model.
In the wavelength-division multiplexing network, high-performance optical wavelength converters are desired. This article will report very stable second harmonic generation by using tellurite glasses, second harmonic generation comparison in glass materials, and time-dependent change of second harmonic generation. We obtained 9 times larger second harmonic generation using TeO2 (60 mol%)–WO3 (30 mol%)–Bi2O3 (10 mol%) than using TeO2 (60 mol%)–WO3 (30 mol%)–PbO (10 mol%) glass. This value corresponds to 4.6 times higher than d11 constant of Y-cut quartz (0.4 pm/V). We have succeeded permanent poling by measurement of time-dependent change of second harmonic generation because there could not be found second harmonic generation intensity change after 6 months of poling at room temperature, and there was no decay of second harmonic generation intensity after 4 h of heating at 100°C.
Early fatigue life behavior is important for the prediction of residual useful life of aerospace structures via computational modeling. In particular, the influence of rolling-induced anisotropy on fatigue properties has not been studied extensively, but it is likely to be an important effect. Therefore, fatigue behavior of a 2024-T351 plate was studied using notched uniaxial samples with load axes along either longitudinal or long transverse directions. Interrupted fatigue testing at stresses close to yielding was performed to nucleate and propagate short cracks, and local nucleation sites were located and characterized using optical and electron microscopy techniques. Results show that crack nucleation occurred due to fractured particles for longitudinal samples, while either debonded or fractured particles led to nucleation for transverse samples. Crack nucleation from debonded particles reduced life till matrix fracture because sharper flaws were generated when compared to those from fractured particles. Longitudinal samples experienced multisite crack initiation because of preferential fracture of inclusions for that loading direction. Conversely, long transverse samples showed reduced particle fracture, which eliminated multisite cracking. Crystallography of individual grains also played a role related to bulk plasticity in the grains, as estimated by their individual Taylor factors, and to environmental effects.
Cracking is one of the main distresses responsible for the service life reduction of asphalt pavement. On the contrary, self-healing is a process that reverses to cracking and increases the service life. Understanding of the cracking and healing behavior of bituminous materials is very important for service life predictions. Instead of a complex and time-consuming fatigue test, a modified direct tension test with a loading–healing–reloading procedure was developed in this article to characterize the cracking and healing behavior of bituminous mastics. A displacement-controlled loading was applied to obtain damaged specimens with different crack sizes at various postpeak elongations. After unloading and healing, the reloading was applied to quantify the healing behavior under different conditions. The healing behavior is very dependent on rest periods, crack phases, and material types. A clear difference in self-healing property between a polymer-modified bituminous mastic and a conventional penetration grade bituminous mastic was observed for different phases of crack. As a result, the modified direct tension test is believed to be an effective tool for characterizing the self-healing capability of bituminous mastics.
An integrated sensor system that continuously monitors the structural integrity of an aircraft’s critical composite components can have a high payoff by reducing risks, costs, inspections, and unscheduled maintenance, while increasing safety. Hybrid sensor networks combine or fuse different types of sensors. Optimal sensor fusion tries to find the optimal number and location of different types of sensors such that their combined probability of detection is maximized. Optimal hybrid sensor networks can be more robust, more accurate, and/or cheaper than networks consisting only of homogeneous sensors. A generic sensor fusion approach that combines the probabilities of detection of heterogeneous sensors is described. A fast greedy optimization approach that provides approximate solutions is described and demonstrated. Computable lower and upper bounds of a probability of detection objective function were determined. Fiber Bragg grating sensors can be inserted in layers of composite structures to provide local damage detection, while surface-mounted piezoelectric lead zirconate titanate sensors can provide global damage detection for the host structure under consideration. The generic approach is demonstrated on such combinations of fiber Bragg grating and lead zirconate titanate sensor networks. It is demonstrated that the proposed approach can be used to answer structural health monitoring network design problems such as the following: (1) Given a number of sensors, what is the maximum probability of detection that the sensors can attain and where should they be positioned to provide the maximum probability of detection? (2) If a given probability of detection is desired, the minimum number, types, and locations of sensors that are needed to attain this probability of detection can be determined. The approach is generic, that is, it can be extended to any number or types of sensors for which probabilities of detection can be defined.
The development of embedded sensors, connected to a large-scale sensor network and integrated within the host material, is a first step toward intelligent sensorial materials. This article discusses selected common sensor principles used, in particular, for structural health monitoring in composite materials and presents a new approach developed by the authors that is based on intelligent electronic sensor nodes, interconnected by optical fibers. Both a high-speed data link and power supply are realized via the optical fibers, making batteries or other local energy sources for the sensor nodes superfluous.
In this study, an inverse procedure based on stress guided waves is proposed for the characterization of the elastic moduli of composite plates. The characterization is carried out via genetic algorithms by minimizing the discrepancy between experimental and numerical group delay curves for different directions of propagation along the plate. Experimentally, for a given distance source–receiver, the group delay curves are obtained by processing the guided waves time–transient signals via a time–frequency transform. For the same distance, a fast and reliable semi-analytical finite element formulation is used for the forward computation of the group delay curves. Here, pseudo-experimental data, generated by means of the semi-analytical finite element model for an assumed known set of elastic coefficients, are used to test the reliability of the proposed procedure. The results obtained for three different plates are promising. Since semi-analytical finite element formulations can also handle plates with uniform curvature, this identification procedure could be extended to composite shells. The authors believe that this procedure could support the on-field nondestructive evaluation and structural health monitoring of composite plates and shells.
We present microcantilevers that utilize magnetic actuation for use as mass sensors for bioapplications. The microcantilevers are made of electroplated cobalt–nickel that has low coercivity and high saturation magnetization. The microcantilevers are actuated by applying magnetic fields, and the deflection is measured using a laser Doppler vibrometer. The microfabrication of the microcantilevers is based on two lithography steps, an electroplating step and a sacrificial layer etching step. The magnetic actuation and optical readout using the fabricated cobalt–nickel microcantilever were successfully demonstrated in air under atmospheric pressure and in deionized water. A feedback circuit is used to enhance the quality factor of the microcantilever. The quality factor increased from approximately 550 to 1600 in air and from 7.3 to 10.6 in deionized water. The microcantilevers can be readily functionalized with selective binding molecules and used as a biomass sensor.
High-strain environments, such as are found in automobile tires, provide deformation energy that can be harvested using piezoelectric materials, for instance, for powering electronics such as wireless sensors. Despite numerous efforts, none of the present devices easily satisfy the stringent operating and lifetime requirements for use inside a car tire, such as mechanical (accelerations of up to 3000 m/s2) and thermal requirements (temperatures of –40°C to 120°C), often leading to complex and costly solutions. Polymer–piezoelectric ceramic composite properties can be designed to fulfill the operating requirements. Furthermore, these materials are suitable for low-cost mass production and easy integration in the tire itself. Composite materials with increased output can be manufactured using the dielectrophoretic processing technique, which causes the alignment of the piezoelectric particles inside the polymer matrix, to obtain materials with adequate flexibility combined with a high energy density. In this study, we present the design, synthesis, and integration of novel composite material foils in automobile tires. The advantage of these dielectrophoretically structured composite materials is demonstrated and their output is compared to conventional piezoelectric composites. Furthermore, the charge signal output of a number of foil-based prototypes tested using an automobile tire test rig is evaluated and discussed with respect to energy harvesting performance.
New generations of chemical sensors require both innovative (evolutionary) engineering concepts and (revolutionary) breakthroughs in the fundamental materials chemistry, such as the emergence of new types of stimuli responsive materials. In recent years, intensive research in those fields has brought interesting new concepts and designs for microfluidic flow control and sample handling that integrate high-quality engineering with new materials. In this article, we review the recent developments in this fascinating area of science, with particular emphasis on photoswitchable soft actuators and their incorporation into fluidic devices that are increasingly biomimetic in nature.
This article investigates an energy-based multiscale damage criterion for a biaxial loading case. The criterion incorporates crystal plasticity at the microscale that produces a damage tensor, representing the local damage state derived from a least squares method. The damage tensor, driven by modification of strain energy density on each potential slip system, is averaged from local to grain level to obtain a damage vector for each grain. The Kreisselmeier–Steinhauser function, which produces an envelope function for multiobjective optimization is adopted to predict the failure of a meso–representative volume element, and to calculate the damage index for meso–representative volume element. A weighted averaging method is also used to simultaneously provide the most potential cracking directions for meso–representative volume element. In order to verify that the developed method is capable of producing an acceptable prediction of fatigue damage initiation and growth under multiaxial loading conditions, a cruciform specimen is used for biaxial loading. A biaxial torsion MTS machine is used to conduct fatigue tests on the cruciform specimen. Numerical fatigue analysis is also performed based on the multiscale fatigue damage criterion. Comparing the simulation results with the experimental data shows that the multiscale fatigue damage model can provide acceptable prediction of failure of meso–representative volume element and crack direction.
Crack-repairing technology via embedded capsules with healing agents is becoming a promising approach to sustain the performance of cementitious materials. In this article, the practical crack patterns in cementitious materials caused by various mechanisms are simplified to be the linear cracks in two-dimensional plane and the planar cracks in three-dimensional space, respectively. Then, based on the assumption that the length of the capsules embedded is larger than the average spacing between the adjacent cracks, via the theory of geometrical probability, the analytical solutions on the exact dosage of capsules required are developed for the different types of crack pattern models in a probabilistic point of view. Furthermore, the reliability of these analytical solutions is verified via computer simulation.
With very simple methods, we fabricate photoelectrical devices using a regular paper as substrate; these sensors are able to detect ultraviolet, visible, and infrared radiation using different paper additives. The experiment we made to test detection of ultraviolet and visible light consists in irradiating light of different wavelengths over a device made of paper and semiconductor crystals; electrical current of these devices increases importantly when the bandgap energy of the semiconductor crystal is reached. To test the sensitivity to infrared, we use paper devices impregnated with salts and glycerol to increment its electrical conductivity due to the augmentation of ionic current carriers. We observe that the ionic conductivity on paper increases when the paper is irradiated by infrared light from hot objects; this phenomenon might be due to the molecular structure of cellulose that absorbs energy in the infrared part of the spectrum.
This article presented the application of an energy-based multiscale damage criterion for crack initiation and life prediction in crystalline metallic aerospace structural components under fatigue loading. A novel meso statistical volume element model was developed to improve computational efficiency compared to traditional meso representative volume element models. The key microscale factors affecting the mechanical properties of crystalline materials, including grain orientation, misorientation, principal axis direction, size, aspect ratio, and shape were considered in the formation of the statistical volume element model. The effect of several factors was studied to assess the importance in the overall macroscopic response of the material. Fatigue tests of lug joint samples were performed to validate the damage criterion as well as the statistical volume element model. Crack initiation was predicted within 29% accuracy, and orientation was predicted within a 2° range, which was comparable to other methods. The simulation efficiency of the statistical volume element model was improved 15 times over the traditional representative volume element models.
A self-healing polymer system is created by incorporating reversible covalent bonds into an epoxy–amine-based network structure. The self-healing concept is based on the reversible Diels–Alder reaction between furan and maleimide functional groups. The thermal and mechanical properties of the reversible network structure are tailored in order to achieve good self-healing properties for the corrosion protection of metal surfaces. Atomic force microscopy is proposed as a technique to study the self-healing behavior of coatings. Local thermal analysis techniques are used to study the local thermomechanical behavior of the reversible network. Nanosized defects in the coatings are made by means of nanolithography. The actual self-healing behavior is studied by atomic force microscopy imaging before and after the heating steps. The healing capability of elastomeric and glassy model systems is compared.
Thermoresponsive TiO2/SiO2 one-dimensional photonic crystals (Bragg stacks) fabricated via sol–gel processing methods represent a promising class of environmentally responsive nanostructures featuring optically encoded temperature and humidity detection. The thermo-optic response of the layer materials is amplified by their inherent porosity owing to adsorption/desorption of ambient humidity into the mesoporous multilayer structure. Based on a comprehensive analysis of the impact of layer thickness, refractive index and thermo-optic coefficient on the stop band position, and width of various Bragg stack architectures, design criteria for thermoresponsive Bragg stacks operating in the visible range of the optical spectrum are put forward. A large and well-defined thermo-optic signature is expected for material combinations featuring individually high thermo-optic coefficients with the same sign or allowing for large changes in the effective refractive indices due to water adsorption in the porous layers reinforcing the thermo-optic response, as observed in the TiO2/SiO2 couple. Important practical aspects of the performance of thermoresponsive Bragg stacks are addressed, including the hysteresis properties of TiO2/SiO2 Bragg stacks during multiple heating/cooling cycles, as well as response and recovery times (~2–4 s) of the multilayer system during external changes in ambient humidity.
Impact damage has been identified as a critical form of defect that constantly threatens the reliability of composite structures, such as those used in aircrafts and naval vessels. Low-energy impacts can introduce barely visible damage and cause structural degradation. Therefore, efficient structural health monitoring methods, which can accurately detect, quantify, and localize impact damage in complex composite structures, are required. In this article, a novel damage detection methodology is demonstrated for monitoring and quantifying the impact damage propagation. Statistical feature matrices, composed of features extracted from the time and frequency domains, are developed. Kernel principal component analysis is used to compress and classify the statistical feature matrices. Compared with traditional principal component analysis algorithm, kernel principal component analysis method shows better feature clustering and damage quantification capabilities. A new damage index, formulated using the Mahalanobis distance, is defined to quantify impact damage. The developed methodology has been validated using low-velocity impact experiments with a sandwich composite wing.
This article presents the dynamical modelling of a novel active aeroelastic structure. The adaptive torsion wing concept is a thin-wall, two-spar wingbox whose torsional stiffness can be adjusted by translating the spar webs in the chordwise direction inward and towards each other using internal actuators. The reduction in torsional stiffness allows external aerodynamic loads to induce twist on the structure and maintain its deformed shape. Here, the adaptive torsion wing system is considered as integrated within the wing of a representative unmanned aerial vehicle to replace conventional ailerons and provide roll control. The adaptive torsion wing is modelled as a two-dimensional equivalent aerofoil using bending and torsion shape functions to express the equations of motion in terms of the twist angle and plunge displacement at the wingtip. The full equations of motion for the adaptive torsion wing equivalent aerofoil were derived using Lagrangian mechanics. The aerodynamic lift and moment acting on the aerofoil were modelled using Theodorsen’s unsteady aerodynamic theory. A low-dimensional, state-space representation of an empirical Theodorsen’s transfer function was adopted to allow time-domain analyses. Four actuation strategies were investigated. Figures of merit, including plunge displacement, twist angle, actuation forces and actuation powers, were quantified and discussed for each of the scenarios. This study allows the conceptual design and sizing of the internal actuators that are required to drive the webs.
To impart self-healing ability to epoxy, styrene-loaded and benzoyl peroxide–loaded microcapsules were prepared by in situ polymerization in emulsion using melamine–formaldehyde resin as the wall former. Afterward, the two types of microcapsules were embedded in epoxy to produce self-healing epoxy composite. Upon fracture of the material, the core substances in the broken capsules were released and polymerization of styrene initiated by benzoyl peroxide took place, rebinding the cracked planes. The parameters for manufacturing the microcapsules and the factors that influence healing efficiency of the system were discussed in detail.
In this study, a hydrogenated amorphous carbon (a-C:H) film with a high electrical resistance is developed for use in embedded sensors in an abrasive environment. The a-C:H and a-C:H:Si films were deposited by magnetron sputtering. Graphite targets were sputtered by means of bipolar pulsed-direct current power supply and addition of acetylene, argon, and krypton. The a-C:H:Si films were deposited using graphite targets with small silicon inserts. To optimize the adhesion, a chromium nitride interlayer was deposited prior to the carbon layer. The influence of bias voltage, acetylene flow, deposition pressure, and silicon doping on the electric resistance was investigated. Hardness, hydrogen content, and bonding status of the coating were also determined. It was found that the resistance of the film increases with decreasing negative bias voltage and increasing acetylene flow and deposition pressure. With increasing resistivity of the film, the hardness decreases. This was attributed to higher hydrogen contents in these films. The silicon doping of the films has no significant effect on the electrical resistance.
Silicon microcantilevers are realized and tested using different ferromagnetic thin films as active actuators. The exploited design is optimized for operating the sensor in a liquid environment. Different magnetic materials are used as actuator elements: a soft layer of face-centered cubic Co, a hard layer of Co80Cr20 (subscript: atomic composition in percentage) and a (Co5Cu10)5 multilayer (superscript: thickness; subscript: number of repetitions). The thin film magnetizations are characterized both in the film plane and out of it. We characterize the devices in air and in water comparing piezoelectric and magnetic actuation, confirming that nanostructured magnetic multilayers represent a new and promising route to optimize the actuation of magnetic microcantilevers. Complete sets of dynamical measures, consisting of stability plots, are discussed. Finite element simulations performed with a commercial code and inherent to a static analysis of different magnetic microcantilevers are commented, casting more light on the importance of having a nanostructured actuator for a high-efficiency energy transfer. This opens the route to new challenging devices, where the spin arrangement at the nanoscale is used to induce either mechanical deformations or movements by effect of an electromagnetic field.
An ionomer, which is able to self-heal the damage after ballistic impact of a projectile, was studied using dynamic puncture tests. A temperature increase in this polymer is a fundamental part of the self-healing process. Therefore, the temperature during the puncture tests was measured using embedded thermocouples. These adiabatic temperature measurements allow for some first conclusions about the processes that are involved in the heating of the material during an impact process.
Interest in structural health monitoring/management is attracting lots of attention across a spectrum that ranges from sensor developers to end users. The US military, in particular, is making a concerted effort to implement condition-based maintenance as a means of reducing the life cycle costs and improving availability of various weapon platforms. Despite this effort, the majority of installed health monitoring systems are limited to rotating machinery such as engines, transmissions, and other gear boxes. The goal of this workshop was to bring together representatives from military, industry, and academia covering the spectrum from hardware developers to end users and platform managers and have them discuss issues that must be addressed as structural health monitoring systems mature to the point that managers will implement them. This article describes those discussions and highlights important issues that need to be addressed as structural health monitoring systems make the transition from laboratory scale demonstrations to real-world use.
Concrete cracks due to its low tensile strength. The presence of cracks endangers the durability as they generate a pathway for harmful particles dissolved in fluids and gases. Without a proper treatment, maintenance costs will increase. Self-healing can prevail in small cracks due to precipitation of calcium carbonate and further hydration. Therefore, the use of microfibres is proposed to control the crack width and thus to promote the self-healing efficiency. In the current research, crack sealing is also enhanced by the application of superabsorbent polymers. When cracking occurs, superabsorbent polymers are exposed to the humid environment and swell. This swelling reaction seals the crack from intruding potentially harmful substances. Mortar mixtures with microfibres and with and without superabsorbent polymers were investigated on their crack sealing and healing efficiency. Regain in mechanical properties upon crack healing was investigated by the performance of four-point-bending tests, and the sealing capacity of the superabsorbent polymer particles was measured through a decrease in water permeability. In an environment with a relative humidity of more than 60%, only samples with superabsorbent polymers showed healing. Introducing 1 m% of superabsorbent polymer gives the best results, considering no reduction of the mechanical properties in comparison to the reference, and the superior self-sealing capacity.
In the current research, a mathematical model for bacterial self-healing of a crack is considered. The study is embedded within the framework of investigating the potential of bacteria to act as a catalyst of the self-healing process in concrete, which is the ability of concrete to repair occurring cracks autonomously. Spherical clay capsules containing the healing agent (calcium lactate) and nutrients for bacteria are embedded in the concrete structure. Water entering a newly appearing crack initiates the release of the capsule content and activates the bacteria to convert calcium lactate to calcium carbonate (limestone). The crack is sealed through the metabolically mediated limestone precipitation. The model of the self-healing process is based on a moving boundary problem in which two fragments of the boundary move resulting from calcium carbonate precipitation and the dissolution of the capsule content, respectively. A Galerkin finite element method is used to solve the diffusion equations. The moving boundaries are tracked using a level set method.