Composite automated placement shows great potential for efficient manufacturing of large composite structures. In order to realize online layup quality detection and parameter optimization with high speed and desired layup quality, a methodology is developed based on assumed inherent sensor inversion. First, it is necessary to conduct sensitive analysis in order to analyze the importance of process parameters and their changes. Then the relationship between these process parameters and the layup quality could be established by assumed inherent sensor inversion, which is considered as the basis of parameter optimization. Simultaneously, genetic algorithm combined with the multi-objective optimization theory is applied to determine the optimum set for obtaining desired composite components with high speed and best layup quality. A series of experiments had been conducted to verify the feasibility of the developed approach. Results demonstrate that the model has high precision, and significant improvement could be achieved through parameter optimization.
It is proposed that an impregnation model can predict the porosity of composites for power-law fluids impregnation in fabric. The impregnation model takes the material properties and fabric characteristic dimensions into account. In order to verify the model, glass fabric reinforced polypropylene (PP) composites are fabricated by using compression molding procedure. The impregnation model is validated by a series of comprehensive experiments, and the experimental results are perfectly consistent with the impregnation model’s value. The impregnation process is studied respectively through the model and the experiment. The results of it have shown that the impregnation time can indeed be shortened for compression molding procedure by increasing the processing temperature or increasing the applied pressure.
As one of the most common defects induced by Automated Fiber Placement, in-plane fiber micro-buckling is characterized by a macroscopic value and its influence on composites tensile properties are studied in this article. The mathematical relationship between fiber microscopic distribution and geodesic curvature of non-geodesic fiber path is derived. Influences of in-plane fiber micro-buckling on tensile properties are analyzed by off-axis tensile theory and finite element analysis, and verified by experiments. Actual fiber microscopic distribution of in-plane fiber micro-buckling shows that it is reasonable to evaluate the scale of fiber micro-buckling by the geodesic curvature radius of curved fiber trajectory. Longitudinal tensile properties of lamina are dramatically influenced by in-plane fiber micro-buckling, while the influences of in-plane fiber micro-buckling on transversal tensile properties can be ignored. When A/L reaches 0.023, the longitudinal tensile modulus and strength of lamina decreased by 25.5% and 57.7%, respectively, compared with the lamina without any defects. Based on the conclusions made in this article, the scale of in-plane fiber micro-buckling can be predicted without metallographic observation. And the increase of structural efficiency and the loss of mechanical performance in consequence of non-geodesic fiber path could be evaluated for the optimization of fiber trajectory.
Since holes comprise the necessary features of many structural components, a comprehensive understanding of the behavior of composite plates containing an open hole is a crucial step in their design process. In the present manuscript, an extensive numerical study has been conducted in order to investigate the effects of material nonlinearity on the stress distribution and stress concentration factors in unidirectional and laminated composite materials. To attain this objective, various models with different configurations were studied. In unidirectional composites, the maximum deviation of stress distribution around the hole (from the linear solution) happens in 45° lamina in which includes a high level of shear stress. However, the maximum difference in the stress concentration factor occurs in 15° lamina and is 15.1% at the onset of failure. In composite laminates, the maximum deviation of nonlinear stress concentration factor from the linear solution is reported 24.3% and it occurs in [+45/–45] s laminate. In the last section, Neuber’s rule is employed to find the stress concentration factors of the laminated composites, with a reasonable accuracy.
This paper presents an experimental investigation of the compression behaviour of Carbon Fiber Reinforced Plastics (CFRP) tubes with different off-axis ply orientations. A series of compression tests with effective end-reinforcement were conducted on [04/±theta] CFRP tubes, with equal to either 0°, 30°, 45°, 60°, or 90°. Various failure progressions and fracture morphologies were measured using a high-speed camera and a scanning electron microscope. The failure modes and mechanisms of CFRP tubes with different stacking sequences were analysed in detail. The results indicate that the off-axis ply orientation greatly influences the compression behaviour. The adopted end-reinforcement ensures that nearly all of the CFRP tubes fail within the gauge length. When < 45°, the tubes exhibit various failure modes, and the scatter of strength is large. However, when ≥ 45°, the sole failure mode is a shear fracture of the inner 0° layers, and their scatter of strength is minor. A new shear failure mechanism is instrumented: the shear fracture direction changes from inclining along the circumferential direction to inclining along the radial direction when varies from 45° to 90°. The failure strength and off-axis ply orientation display a complex non-linear relationship. When = 60°, the compression strength becomes maximum at an average value of 602 MPa, and the scatter of strength is 2.71%.
This paper presents molecular dynamics (MD) simulations on the effects of carbon nanotubes (CNTs) without and with chemical functionalization, on the mechanical properties of bisphenol E cyanate ester (BECy) – a potential structural resin. Atomistic models of CNTs, functionalized CNTs (fCNTs), BECy resin, CNT-BECy and fCNT-BECy resins with definite quantity of CNT/fCNT are built. Using these atomistic models, mechanical properties of the above nanosystems are estimated through a computational method involving geometric optimization and equilibration through MD by judiciously establishing various parameters. Adoptability of the approach taken up in this work to model and solve complex nanosystems capturing interactions in the interfacial region between CNT/fCNT and the resin to understand the mechanical behaviour has been highlighted. These investigations have yielded interesting and encouraging results to arrive at optimum quantity of CNTs/fCNTs to be added to achieve enhanced mechanical properties of BECy resin that validate the previous experimental studies carried out by the authors infusing similar quantities of CNTs and fCNTs into BECy.
An adequate dispersion of fine particles is essential for improved properties in particle-reinforced composites. State-of-the-art methods mainly rely on mechanical (shearing) dispersion methods that do not yield the requested homogeneity within the final composite. This leads to a deterioration and inhomogeneity of mechanical properties. Other non-conventional methods such as in-situ polymerisation or solution compounding are not yet applicable on an industrial scale. This study tackles these problems and provides a novel method for the fabrication of well-dispersed particle-reinforced polymer composites while making use of conventional machinery on the one hand and allowing industrial applicability on the other hand. The presented technique makes use of the pyrolysis of a low thermally stable polymer within a conventional melt compounding process to produce well dispersed carbon particles throughout a thermoplastic matrix in an in-situ process. For this purpose, Carboxymethylcellulose particles are used. The selection of decomposition parameters around the processing temperature of polypropylene yields well-dispersed carbon particles, as evidenced by scanning electron microscopy. This further interprets the resulting promising mechanical properties.
The effect of geometric discontinuities can be reduced by appropriate choice of parameters affecting the stress distribution around cutout. This is possible if the effective parameters are accurately calculated. In this study, using genetic algorithm, the optimum parameters are introduced in order to achieve the minimum value of stress around cutout. Here, design variables are fiber angle, load angle, aspect ratio of cutout, shape of cutout, rotation angle of cutout, and bluntness parameters. Using the Lekhnitskii’s method, stress distribution around various cutouts is determined. The effect of the aforementioned parameters on the stress values around various shapes of cutouts such as quasi-triangular, quasi-square, and hypotrochoid cutouts is examined. Also, the optimal parameters for each cutout are introduced. The results showed that these parameters have significant effects on stress distribution around the cutouts and the structural load-bearing capacity will increase without changing the type of material if the parameters are correctly chosen.
In this paper, the effect of layer shifting on out-of-permeability of 0°/45° alternating multilayer fabrics was studied. Three mathematical models with three extreme structures were developed to predict the out-of-plane permeability, respectively. By segmenting the unit cell into several different zones according to characteristic yarn arrangement, the global permeability was modeled by using a rule of mixture of local permeability. The influences of local permeability of each zone on the global value of unit cell were carefully researched. In addition, experimental measurements of the permeability were carried out to validate the analytical models. And the differences of the results of three extreme structures with respect to fiber volume fraction were also investigated.
The change of mold normal curvature along the trajectory may result in out-of-plane waviness during the automated laying process, on which the layup speed and temperature would have an effect. A new parameter, deformation rate, was defined by combining the effect of mold curvature change rate and layup speed. A predicting model was proposed based on the fiber waviness and interlaminar sliding model to calculate the relationship between stiffness retention and the layup process parameters, including deformation rate and temperature. An experimental study on the effect of different deformation parameters on the tensile performance of composites was carried out based on a new manufacturing method of plated specimens with different levels of waviness by means of a four-point bending fixture. The experimental results showed that when the deformation temperature increases from 20℃ to 80℃, the tensile strength increases first and then decreases while the tensile module keeps increasing. While the deformation rate decreases from 0.40 to 0.04 mm–1/s, both tensile strength and module showed an increasing trend. The predicting model being validated by experimental results can be utilized to optimize the layup process parameter to satisfy the quality and efficiency requirements.
A feasibility study was conducted to determine the use of polyphthalamide/glass-fiber and polyphthalamide/glass-fiber/polytetrafluoroethylene-based composites as substitutes for aluminum and steel, respectively, in the production of motorcycle oil pump parts (housing, shaft/inner gerotor and outer gerotor). New and used (80,000 km) oil pumps were subjected to performance tests, whose results indicated that the pressure and temperature of the used pump reached a maximum of 1.8 bar and 93℃, respectively. Thermogravimetric analysis indicated that the materials are stable at the maximum operating temperature, which is 20℃ lower than the minimum glass transition temperature obtained by dynamic mechanical analysis for both materials at the analyzed frequencies (defined after calculations based on rotations in neutral, medium and high gear). The pressure value was multiplied by a safety factor of at least 1.6 (i.e., 3 bar), which was used as input for a finite element analysis of the parts, as well as the elasticity modulus at glass transition temperatures obtained by dynamic mechanical analysis. The finite element analysis indicated that the von Mises stresses to which the composite parts were subjected are 7 to 50 times lower than those the materials can withstand. The results suggest that it is feasible to manufacture motorcycle oil pump parts with these composites.
A series of para-phenylene terephthalamide pulp modified damping materials were prepared. The dynamic mechanical properties, differential scanning calorimetry, vibration damping properties, vulcanization property, tensile strengths as well as scanning electron microscopy micrographs of the damping materials were studied theoretically and experimentally. The dynamic mechanical properties of para-phenylene terephthalamide pulp modified damping materials were also compared with aramid short-cut fiber, E-glass staple fiber and carbon fiber powder modified damping materials. The results showed that para-phenylene terephthalamide pulp modified damping materials exhibited the best damping property and highest modulus in comparison with the other types of fibers. The storage modulus (E'), loss modulus (E'') and tensile strength of the materials were all increased significantly with increasing pulp content, and this trend was significantly greater in machine direction rather than in cross-machine direction. The second, third and fourth modes modal loss factors () of the steel beams coated with para-phenylene terephthalamide pulp modified damping materials increased substantially up to a maximum, and then became stable with increasing pulp amount. The optimal in machine direction was achieved as the mass ratio of butadiene-acrylonitrile rubber to para-phenylene terephthalamide pulp was 100:30. Excellent damping property was mainly attributed to the extremely high interfacial contact area which significantly improved the efficiency of energy dissipation of internal friction, interfacial sliding and dislocation motion between para-phenylene terephthalamide pulps and butadiene-acrylonitrile rubber chains. Since para-phenylene terephthalamide pulp modified damping materials offer a high E', excellent vibration damping properties, broad damping temperature and frequency ranges, it is ideal for free-damping structures which are widely utilized in industrial vibration and noise control applications.
The purpose of this study was to determine the influence of fibre architectures on the interlaminar fracture toughness and tensile toughness of flax fibre epoxy composites. The fracture toughness was investigated for both Mode I (GIC) and Mode II (GIIC) for seven flax-epoxy architectures: one plain weave, two twill 2 x 2 weaves, a quasi-unidirectional and a unidirectional architecture, the UD’s being tested in both [0,90] and [90,0] composite lay-ups. The results of the Mode I and Mode II showed promising results of the flax-epoxy composite performance. The addition of flax fibre increases the GIC and GIIC of the composites over that of the unreinforced brittle polymer by at least two to three times. Further improvements are made with the use of woven textiles. The tensile toughness was found to be a good indicator of the capacity of a material to sustain perforation or non-perforation impact.
It is not common to accompany material development by a Life Cycle Assessment (LCA) during the research and development phase. It is the aim of the study at hand to present environmental aspects of the manufacturing of different polypropylene composites by injection moulding in comparison to the neat polypropylene. The process analysis following two injection-moulding experiments revealed that the total specific energy consumption of injection moulding of seven different materials and on different scales ranges from 1.6 MJ/kg to 3.5 MJ/kg. On the level of an ex-ante LCA from cradle-to-factory gate, injection moulding can be rated from being a negligible to an important contributor.
A critical limitation of fibre reinforced plastic is its large variability on mechanical performance, especially the longitudinal compressive strength. The influence of fibre random packing and waviness on the compressive strength of UD fibre reinforced plastic is studied in this paper. Three-dimensional geometrically non-linear finite element model is constructed to investigate the compressive behaviour, and an improved approach named Latin hypercube sampling based on random sequential expansion is proposed to generate random fibre distribution across the cross-section. Latin hypercube sampling based on random sequential expansion provides high computation efficiency and good distribution characteristics in comparison to previously proposed methods. Fibre waviness defect with different misalignment angles is also incorporated in the finite element model. It is shown that random fibre packing tends to result in a stochastic detriment of fibre reinforced plastic compressive strength in comparison with uniform fibre packing condition, and the stochastic variation of compressive strength tends to follow normal or lognormal distribution.
The main objective of this work is an experimental investigation and an analytical modeling of ablation and to analyze the thermophysical properties of nanocomposites based on novolac resin/short carbon fiber/graphite nanocrystalline powders in oxyacetylene flame test. The composite consisting of 40 wt.% carbon fiber was prepared as reference sample of which matrix was modified with three different percentages (6, 9 and 12 wt.%) of nano-sized graphite powders as reinforcement. Ablation is calculated by mass balance equation. Some parameters in the ablation modeling are evaluated by simultaneous thermal gravimetric analysis technique. Results of this work show that ablation rates decrease by the addition of graphite powders. The theoretical ablation rates are 33–38% less than the experimental data analyzed by oxyacetylene flame tests. This difference is reasonable because the effect of fluid stream force of oxyacetylene flame that causes the thermomechanical erosion of the surface is omitted in theoretical calculations. Therefore the model only calculates thermochemical erosion. Also, the thermophysical properties change due to heating is analyzed. Moreover, in nanocomposite with 9 wt.% graphite nanopowders, the rate of ablation and thermal diffusivity coefficient decreased by 10% and 50%, respectively, and thermal stability increased by 12% compared to the reference sample.
This paper mainly focuses on flexural behavior of U-shape HFRP profile-concrete composite beams under static and cyclic loading. Four-point-bending experiments of eight pieces of HFRP-RC composite T-shaped beams with shear keys combined with wet-bond interface under both static and cyclic loads were conducted. The fiber-reinforced polymers profiles were produced by using vacuum infusion molding process. Experiment phenomena were detailed, and flexural performance such as failure mode, capacity, stiffness and load–displacement curves was also analyzed. Result shows that the shear keys combined with wet-bond interface is effective. Meanwhile, the flexural performance of the fiber-reinforced polymers-reinforced concrete beams under cyclic load was simulated based on the OpenSees software, in which special constitutive models of different materials were chosen to consider the cyclic loading. The simulation results and the experimental results such as the load–displacement curves, unloading stiffness, residual displacements, etc. were compared. The results show that OpenSees system can simulate the flexural performance of the fiber-reinforced polymers-reinforced concrete beams under both monotonic loads and cyclic loads very well. And then parameters study was conducted by using simulation method, and the influence factors such as concrete strength, steel bar ratio, fiber-reinforced polymers types, tensile stiffness of the longitudinal fiber-reinforced polymers, etc. were analyzed. Meanwhile, the recoverability of the fiber-reinforced polymers-reinforced concrete composite beams was evaluated, and a modified formula for the residual deformation was put forward. Finally, an idealized type of fiber-reinforced polymers-reinforced concrete beams with a medium reinforcement ratio and high post-yield stiffness was proposed, and reasonable values of the secondary stiffness ratio (defined as post-yield tangent stiffness divided by post-crack tangent stiffness) are recommended.
Lots of studies have investigated the shear contribution of the fiber-reinforced polymer of reinforced concrete beams with externally bonded fiber-reinforced polymer (FRP). In this paper, based on more than 200 collected experimental results of reinforced concrete beams shear strengthened with U-jacketing fiber-reinforced polymer composites, four existing design guidelines on the fiber-reinforced polymer shear contribution of strengthened reinforced concrete beams are compared in terms of the effect of the shear span-to-effective depth ratio, beam size, and stirrup ratio. These three influence factors are found to play significant roles in the prediction accuracy of different design guidelines. This paper, therefore, proposes an advanced shear strength model, which considers the effect of shear span-to-effective depth ratio, beam size, and stirrup ratio. The proposed model can provide better predictions of fiber-reinforced polymer shear contribution.
An automated tool has been developed for generation of permeability predictions for multi-layered unit cells utilising textile modelling techniques. This tool has been used to predict the permeability tensor of a woven textile. Single-layer predictions were carried out and the predicted permeabilities obtained were in close agreement to the permeability behaviour captured experimentally. The tool was used to capture the effects of textile variability on its permeability, isolating the influence of individual parameters. A complete textile sample was also analysed, predicting its permeability map. The concept of estimating the permeability of a textile with variability using an average single unit cell was explored. The prediction tool was also used to study the effect of preform structure on its permeability, including consideration of the number of layers, ply shift and applied compaction.
We investigate the unsaturated resin flow behavior in a dual scale porosity preform by observing the pressure distribution and the void content. The experimental data show that the pressure profile in the unsaturated flow is nonlinear with positive curvature whereas that in the saturated flow is linear as expected from the classical Darcy’s law. To address this issue, the governing equation for mass conservation is modified by introducing a mass sink term. Eventually, it has been found that the discrepancy between the unsaturated and saturated permeability values comes from a misinterpretation of the pressure gradient at the flow front in the unsaturated permeability measurement method and the permeability for a given preform is a unique value regardless of measurement method or flow condition. Based on this investigation, the ratio of unsaturated permeability to saturated permeability is represented as a dimensionless number in terms of void content.
In this paper we extend Kollár and Pluzsik’s thin-walled anisotropic composite beam theory to include multiple cells with open branches and booms, and present a finite element formulation utilizing the stiffness matrix obtained from this theory. To recover the 4 x 4 compliance matrix of a beam containing N closed cells, we solve an asymmetric system of 2N + 4 linear equations four times with unitary section loads and extract influence coefficients from the calculated strains. Finally, we compare 4 x 4 stiffness matrices of a multicelled beam using this method against matrices obtained using the finite element method to demonstrate accuracy. Similarly to its originating theory, the effects of shear deformation and restrained warping are assumed negligible.
Natural fiber has been a focus for environmental and recyclable polymer composite. Liquid composite molding process is an attractive manufacturing technique for natural fiber-reinforced polymer composites with high quality and low cost. Understanding the permeability along different directions of fiber preform is important for liquid composite molding to design and optimize mold and processing parameters. This paper addresses issues of the permeabilities along longitudinal direction of ramie fiber bundles and through-thickness direction of ramie fabric stack. Two simple methods were designed to detect axial and transverse infiltration with assistance of external vacuum pressure in ramie bundles and ramie fabric stack, respectively. Different surface chemical treatments, including flame retardant, silane and alkali treatments, were done on ramie fabric. The effects of fiber content, liquid type and surface treating method on the permeability and capillary pressure were studied. The results show that surface treatment obviously changes the surface morphology and surface energy of ramie fiber. The relationships between defined relative velocities of penetration flow and applied pressure for ramie fiber bundles and fabrics perfectly follow linear relationships, indicating that Darcy’s law is suitable for describing permeation behavior in ramie fibers. Moreover, fiber content and liquid type, including silicone oil and epoxy resin, significantly impact axial permeability and capillary pressure. Surface treatment significantly decreases the permeability along the thickness direction of ramie fabric stack followed by increasing capillary pressure, which are attributed to the changes of treated ramie fibers in surface energy and morphology. Finally, a unique difference in the permeabilities along axial and thickness directions was pointed out.
In unidirectional carbon fiber-reinforced plastic laminates, the distance between fibers can varies from submicron to micron length scales. The mechanical properties of the matrix at this length scale are not well understood. In this study, processing methods have been developed to produce high quality epoxy micro-fibers with diameters ranging from 100 to 150 µm that are used for tensile testing. Five types of epoxy resin systems ranging from standard DGEBA to high-crosslink TGDDM and TGMAP epoxy systems have been characterized. Epoxy macroscopic specimens with film thickness of 3300 µm exhibited brittle behavior (1.7 to 4.9% average failure strain) with DGEBA resin having the highest failure strain level. The epoxy micro-fiber specimens exhibited significant ductile behavior (20 to 42% average failure strain) with a distinct yield point being observed in all five resin systems. In addition, the ultimate stress of the highly cross-linked TGDDM epoxy fiber exceeded the bulk film properties by a factor of two and the energy absorption was over 50 times greater on average. The mechanism explaining the dramatic difference in properties is discussed and is based on size effects (the film volume is about 2000 times greater than the fiber volume within the gage sections) and surface defects. Based on the findings presented in this paper, the microscale fiber test specimens are recommended and provide more realistic stress–strain response for describing the role of the matrix in composites at smaller length scales.
This article includes the results of blast tests that were performed with the aim of comparing the energy absorption and protection efficiencies of protective boots with different sole configurations. The tests were performed using a frangible leg model vestured with protective boots. Strain values were measured during the blast tests to determine the protection efficiencies of different sole configurations of the protective boots. Filling honeycomb cells with glass microspheres dramatically increased the energy absorption. In the type-3 samples, which were produced with these microspheres, the strain through the tibia axis decreased 83–47% for different explosive weights compared with the type-1 samples and 52–13% for different explosive weights compared with the type-2 samples; the type-1 and type-2 samples do not have glass microspheres. Bone damage and mine trauma score values show that the type-3 boot provides absolute protection against 40 g of Trinitrotoluene (TNT) and that the injuries that occurred in the tests performed using 70 and 110 g of TNT can be reduced to a curable level without amputation.
Optimum structural design of composites is a research subject that has drawn the attention of many researchers for more than 40 years with a growing interest. In this study, a review of the literature on this subject is presented. The papers are classified according to the type of the composite structure optimized in those studies, the loading conditions, the objective function, the structural analysis method, the design variables, the constraints, the failure criteria, and the search algorithm used by the researchers.
A hot-press tackifying process was used to improve the mechanical properties of cured laminates in vacuum-assisted resin transfer molding by placing a thermoplastic film into the preforms at various pressures and temperatures. Three modified preforms were prepared at 0.1, 0.3, and 0.6 MPa using an autoclave, and the laminates were then produced via vacuum-assisted resin transfer molding. The mechanical properties of the modified laminates were tested and compared to those of the unmodified ones. The fiber volume fractions of the modified laminates decreased with increasing pressure. The tensile strength of the modified laminates at the three pressures improved by 16.78%, 41.21%, and 29.47%, respectively, compared to the unmodified samples. Modified laminates at 0.3 MPa showed better results than those at 0.1 and 0.6 MPa, which were all better than the unmodified samples. The modulus of the modified laminates from vacuum-assisted resin transfer molding was improved by 2.48%, 19.01%, and 13.22%, respectively. The effect of the hot-press tackifying in improving the tensile strength and modulus of a laminate on a pre-impregnated laminate (prepreg) using the autoclave was studied and compared to that of the unmodified case. Here, the tensile strength increased by 32.5% and 12.3%, respectively.
Delamination is a potential risk of failure considered as one of the failure modes and frequently occurs in composites due to its relatively low inter-laminar fracture toughness. In recent years, the majority of activities in this field have been focused on raising the level of sensitivity of these devising methods for detecting tiny damages. In this article, damage detection method via wavelet transform has been examined, and an appropriate procedure has been proposed to increase sensitivity of this transform for damage detection. Among the inherent impediments of classical wavelet transforms, the generality of these transforms and ignoring the studied signal can be mentioned. Consequently, various wavelet selection algorithms leading to provide appropriate wavelet functions with respect to the characteristics of the signal have been examined. As a novelty in the field, the correlation between wavelet and strain energy signal is considered as a criterion for optimal wavelet selection. In wavelet transforms, in addition to original wavelet functions, the signals used for damage detection are also of high importance. To achieve this goal, the frequency-weighted strain energy ratio signals resulting from intact and damaged forms have been exploited. Also, the edges’ effects were removed through stringing of plane mode shape signals. Moreover, by summing wavelet coefficients in all scale factors plus natural frequencies, the focus can bring to the detection of one or more damages in a laminated composite plate with symmetric layup. Finally, a quantitative measure to compare different wavelets has been presented.
This study aimed to evaluate the load-carrying capacity of reinforced concrete rectangular columns confined with fiber-reinforced polymer composites and subjected to small eccentric loading. Seven design-oriented models of fiber-reinforced polymer-confined concrete were implemented in OpenSees software to establish the theoretical axial force-moment interaction diagram for rectangular columns. The examined models were categorized into two types: stress–strain models developed for fiber-reinforced polymer-confined non-circular concrete tested under the effect of concentric loading and others designed for fiber-reinforced polymer-confined non-circular concrete subjected to eccentric loading. The accuracy of these models was examined against the experimental results of eccentrically loaded fiber-reinforced polymer-confined reinforced concrete rectangular columns. Results indicated that the local stress–strain law obtained from the concentric compression tests would not reflect very well the local behavior of the compression zone of fiber-reinforced polymer-reinforced concrete members subjected to the combined effect of flexural and axial loadings. Adoption of a rational approach reflecting the impacts of eccentric loadings on the stress–strain relationship of the fiber-reinforced polymer-confined concrete revealed a much better evaluation of the load-carrying capacity of both reinforced concrete rectangular columns and plain concrete square columns under the effect of axial loads with various eccentricities.
Critical energy release rate for delamination initiation in composites as a material property, supposed to be independent from non-material variables. However, a thorough literature review presented in this study shows that in many cases it may vary with the variation of layup configuration or geometrical and dimensions. This study is aimed to investigate the effect of interface layers orientation on fracture toughness by eliminating the other influential parameters such as stacking sequence, by selecting the anti-symmetric layup configuration of Double Cantilever Beam,
Epoxy-based adhesives reinforced with silica and alumina fillers (20, 40, and 60 phr) were prepared and successfully applied for lap-joint bonding of carbon fiber composite with steel. The mechanical properties of adhesives were assessed as different cure temperatures to find optimum cure temperature. Morphology of the reinforced epoxy adhesives was observed by optical microscopy to disclose the interplay between composite properties and distribution fashion of the silica and alumina fillers within the epoxy matrix. Thermal stability and interfacial interaction situation were explored by thermogravimetric and Fourier transform infrared spectroscopy analyses, respectively. Rheological behavior of the composite samples was also studied. Lap shear test was an indication for a considerable improvement of about 12% and 20%, compared to unfilled epoxy/hardener systems, for composites containing 60 phr of alumina and silica, respectively. However, the presence and population of voids in case of samples cured at elevated temperature deteriorated lap shear strength. Of note, the storage and loss modulus of the latter adhesive have been increased by 797% and 472%, respectively. Thermal stability on the basis of initial degradation temperature and char yield (> 500℃) of the assigned adhesive under N2 and air have also been enhanced. Higher performance of silica-based adhesives was mechanistically and morphologically discussed on the bedrock of formation of a 3D inter-connected network of filler particles.
Design and analysis of parts constructed from weft-knitted textile composites need the elastic and fracture behavior of the composite. To avoid time-consuming and expensive experimental procedures, micromechanical models and finite element simulations can be used to estimate stiffness matrix of these composites. In the present study, at first, a 3D model of a plain weft-knitted fabric is presented. Then a micromechanical approach is proposed to derive the mechanical properties of the weft-knitted composite using this geometrical model. A finite element simulation is carried out to extract the elastic properties of the composite as an alternative procedure. Finally, obtained moduli from both methods are validated by comparing them with existing experimental values. Results show a good agreement between the calculated and measured data. It can be concluded that the proposed micromechanical approach can predict weft-knitted composite behavior well without any great effort; however, the finite element analysis gives acceptable results too. The effects of composite variables on the stiffness are investigated and discussed.
In this study, the effect of graphene content on quasi-static and fatigue mechanical properties of basalt fiber reinforced polyamide 6 is investigated. Hybrid composites and reference monocomposites were melt compounded, and then specimens were injection molded. Although the presence of graphene caused moderate change in quasi-static tensile properties, remarkable increment in the fatigue properties of hybrid composites was experienced. Hybrid composites with low graphene content withstood higher number of cycles in fatigue tests at the same loading compared to basalt fiber reinforced monocomposites. Scanning electron microscopy of the fracture surfaces revealed proper dispersion of reinforcement in the hybrid materials, an explanation to the better fatigue performance at lower graphene contents.
A method to predict the tensile strength of needle-punched carbon/carbon composites is elaborated in this paper. Based on the geometric characters gained by using optical microscope, the structures of the material can be classified as five typical unit cells, which can reflect the mutual alignment relationship of planar fiber tows and needle fiber tows. With the elliptical inclusion theory and Puck’s strength criterion, the stress–strain curves and progressive damages of these five unit cells are obtained. Based on these results, the mechanical behavior of needle-punched carbon/carbon composites under tensile loading can be predicted. It is found that the predictions of the composite under unidirectional tensile loading agree well with the experimental data.
In this paper, the creep of short (chopped) basalt fibre reinforced poly(lactic acid) composites was investigated; 5, 10, 20 and 30 wt.% short basalt fibre reinforced composites were prepared by using twin-screw extrusion followed by injection moulding. Differential scanning calorimetry measurements revealed that the basalt fibres had nucleating effect on the poly(lactic acid)grade used in this study, while scanning electron microscopy demonstrated that there was strong adhesion between the fibre and the matrix. Fibre distribution analysis showed that there was no significant statistical difference between the average fibre lengths of all of the produced composites. Finally, creep mastercurves were constructed using the single creep curves obtained by applying 10, 20, 30,..., 90% of the tensile strength of the composites as a static creep loading force. It was demonstrated that the basalt fibres as reinforcements can effectively reduce the strain and increase time to failure of the composites during creep load and thus could open the possibilities for poly(lactic acid)-based composites to be used in long-term constantly loaded structural or engineering applications.
In order to explore competitive bio-products to meet the requirements of the engineering structural member with high-strength, light-weight and low cost, bamboo bundle and wood laminated veneer lumbers (BWLVLs) with well-designed laminated structures have been regarded as potential candidate. Eight different assemble patterns of BWLVLs were designed and their mechanical performances with elastic range and ultimate bearing failure stage including the deflection, stress distribution, and stress transferring between adjacent layers were investigated using finite element simulations. The results showed that the finite element predicting model with a high accuracy could be used to optimize the design of laminated structures for bamboo bundle and wood veneer laminated composites. The relative error of the simulation results from the predicting model and the experimental results for different laminated composite panels was substantially less than 10%. The rank order for the VonMises stress of eight assemble BWLVLs were (7B) > (BBPPPBB) (BBPBPBB) > (BPBPBPB) > (BPPPPPB) (BPPBPPB) > (PBPBPBP) > (7P), (P) poplar, and (B) bamboo. The stress in laminated composites was transferred from poplar layers with low modulus to bamboo bundle layer with high elastic modulus.
This paper presents an experimental and numerical investigation of reinforced concrete beams strengthening by means of different combinations of externally bonded hybrid fabrics-reinforced polymer composite: Carbon and glass fabric–reinforced polymer composite and another fabric-reinforced polymer composite based on vegetable fiber it is the jute fiber. The objective of this study is the conjugation of the properties of each type of fiber fabric to increase the load capacity, rigidity, and ductility of reinforced concrete beams and obtaining a typical model of reinforcement beams, which provides both these three desired mechanical properties. Three control beams and 27 beams strengthened in flexural–shear with Carbon, glass, and jute fabric–reinforced polymer composite and hybrid fiber fabrics were conducted and tested under three points bending. The load–deflection response, ductility, and associated failure modes of the tested specimens have been recorded and analyzed. In addition to the experimental investigations, numerical simulation using ABAQUS was developed to predict the load–deflection response and the failure modes, the results were compared with the corresponding experimental results, a good correlation was obtained.
The formation of longitudinal splitting alleviates the extremely high stress concentration at notch tips of fiber-reinforced composites under remote tension. Theoretical foundation is provided to show that the true stress field along the potential splitting routes can be accurately modelled by inserting cohesive zones in finite element models, such that strength-based criteria can be used to predict damage initiation. Progressive failure analyses are performed to study the in-plane size effect of double-notched quasi-isotropic composite laminates. To capture the stress relief effect of longitudinal splitting during the loading process, surface-based cohesive contacts are introduced along the fiber directions to model the longitudinal splitting. To predict the possible delamination, interface cohesive contacts are also inserted between plies with different fiber orientations. The advantage of the surfaced-based cohesive contact method over the conventional cohesive element method is that it allows different mesh configurations for plies with different fiber orientations. Failure patterns and failure loads predicted by finite element analyses of three scaled composite laminates were compared with experimental results from open literature.
Self-reinforced poly(ethylene terephthalate) laminates were prepared from woven fabric by compression moulding. The fabric was stretched to different degrees during heating before hot consolidation to simulate a manufacturing process where the material is stretched through forming. High tenacity poly(ethylene terephthalate) fibres with different degrees of stretching were prepared for a comparison to laminates. Tensile tests were made to characterize mechanical properties, while dynamical mechanical analysis, differential scanning calorimetry, FTIR spectroscopy and X-ray diffraction analysis were employed to study microstructural changes caused by the stretching. Tensile tests show that 13% stretching of the fabric increases the laminate tensile stiffness by 34%. However, same degree of stretching for pure fibres increases the fibre tensile stiffness by 111%. Crystallinity and molecular conformations are not influenced by stretching while shrinkage upon heating increases with degree of stretching. Shrinkage is known to be related to disorientation of non-crystalline regions whereof the conclusion from this study is that the increased tensile properties are due to orientation of the non-crystalline regions of the fibre.
Thermal conductivity is one of the key material properties to understand the effective thermo-mechanical behavior of advanced composites. Experimental studies show that when highly conductive inclusions are embedded in a less thermally conductive matrix, the effective thermal conductivity of the composite changes drastically with the increase of volume fraction (Vf) of the inclusions. This study presents a theoretical model to predict the effective thermal conductivity of two-phase particulate composites containing highly conductive inclusions in a polymeric matrix. The probabilistic approach presented by Tsao (1961) has been modified and extended for predicting the effective thermal conductivity of two-phase composites. The expression for the effective thermal conductivity of a unit cube of two-phase composite is derived implicitly in terms of distribution function, Vf and thermal conductivity of the constituents. Different distribution functions of the inclusions are proposed and the optimum function is obtained to describe the effective thermal conductivity of highly conductive particulate composites. Results of the effective thermal conductivity of a cubic unit cell obtained from different distributions of inclusions are compared with published experimental data, and other analytical and numerical models for particulate composites available in the literature. The results show a linear distribution of inclusions gives reasonable estimates of the effective thermal conductivity of the particulate composites. It is anticipated that the proposed approach can be used to develop models for the effective thermal conductivity of advanced composites containing highly conductive inclusions.
To conform to the fiber path, deformation of prepreg tow occurred inevitably in automated fiber placement process which would have great impact on layup quality. In order to evaluate whether fiber trajectory could be laid without prepreg distortion, fiber path layup quality was proposed and evaluated by prepreg tow deformation characteristic on free-form surface in this paper. Critical buckling radius of plane lateral bending was proposed as evaluation index for tow deformability. Layup quality of fiber trajectory was evaluated by the relationship between geodesic radius of trajectory and critical buckling radius. If the former radius was larger than the latter radius, layup quality of fiber path was fairly good, but not vice versa. A series of layup experiments were conducted to verify the evaluation criterion. Results showed that fiber trajectory layup quality could be well evaluated by this criterion proposed in this paper. And fiber modulus, prepreg thickness, and process parameters played important roles in determining fiber trajectory layup quality evaluated by prepreg deformability. By adjusting layup process parameters during automatic layup process, deformation ability of prepreg tow can be improved and the layup quality of fiber path could be enhanced to a higher level.
A facile and efficient method was developed to gain accurate prediction of the resin fillet size for self-adhesive prepreg skin to honeycomb core bonding in sandwich composites fabricated by co-curing process. The proposed method mainly contained numerical simulation of the fiber compaction and experimental measurement of the resin fillet. The influences of processing parameters, including pressure applying moment and processing pressure, on the resin fillet size were analyzed and discussed. Some other factors such as skin thickness and initial resin content of prepreg, which are difficult to be investigated using traditional test method, were also researched by means of this method. The obtained results were in good agreement with the experimental data, which indicated the accuracy of this method. These outcomes are greatly helpful to establish and optimize the processing parameters of co-cured honeycomb sandwich composite materials.
We conducted a feasibility study on the pultrusion of glass fiber-reinforced vinyl ester/nano-mica matrix composites through a proprietary in situ method. The matrix prepolymer for pultrusion is to be prepared by blends of vinyl ester, initiator (t-butyl perbenzoate), and nano-mica. It is desired to investigate the process feasibility and parameters of the unidirectional glass fiber-reinforced vinyl ester/nano-mica matrix composites through in situ pultrusion. The characteristics of long pot life, high reactivity, and excellent glass fiber wet out of the vinyl ester/nano-mica matrix confirmed its excellent process feasibility for in situ pultrusion. The effects of the optimal process parameters, including die temperature, pulling rate, postcure temperature and time, filler (nano-mica) content, and glass fiber content, were investigated. The optimal die temperature was determined on the basis of a differential scanning calorimetry diagram and conversion of the vinyl ester/nano-mica matrix. The mechanical properties of pultruded composites decreased with increasing pulling rate and increased at a suitable postcure temperature and time. Furthermore, the properties decreased because of the degradation of pultruded composites for a long postcure time. The mechanical properties of pultruded composites achieved maximum values at 2 phr and 75.6 vol% corresponding to nano-mica and glass fiber content and then decreased.
In filament-wound composites, the existence of fiber undulation introduces unique challenges in the calculation of compressive modulus and strength using traditional composite theories. In the current work, a previously developed three-dimensional continuum representation of undulated fibers was incorporated into a multi-scale homogenization process to simulate the effective longitudinal stress-strain behavior of filament-wound cylinders and compressive failure in the undulation regions. Calculated properties were compared to previously obtained experimental data for carbon fiber cylinders made with various matrix materials and winding parameters. The average difference between predicted and measured properties was 14% and the predicted failure modes were consistent with the experimental observations.
In this paper, the phenomenon of delamination under static and dynamic loading of a composite made of an epoxy matrix and carbon fiber reinforcement has been studied, analyzing its fracture behavior under mixed mode I/II loading employing an asymmetric double cantilever beam test. Under static loading, some of the most representative formulations for calculating the energy release rate were analyzed, finding a good agreement between the results obtained by means of the different formulations. Under dynamic loading, the number of cycles necessary for the crack onset was determined (determination of G – N fatigue curves and number of cycles necessary for the delamination onset for a given energy release rate). As regards the experimental results, apparent fatigue limits of the order of 38% of the critical fracture energy were obtained for an asymmetry coefficient of 0.1. Subsequent statistical analysis of the results enabled the fatigue limit to be defined more accurately. This was found to be 15% for this material, indicating the need to use these tools for the actual determination of the infinite fatigue life of the material. Finally, an optical study of the fracture surfaces was carried out which confirmed the presence of mixed mode fracture typologies.
Automated fibre placement was used to optimise the tow steering of carbon fibre reinforced plastic/polymer whereby the minimum defect-free steering radius (Rmin) achievable. The results revealed that in the case of the woven ply surface with unheated tool the Rmin, using 1/4 inch tows, is found to be 1350 mm. For the bare tool surface, the tool temperature had to be raised to 30℃ in order to achieve the same Rmin of 1350 mm. To attain a seamless transition from part design to manufacture using CAD, automated fibre placement was equipped with software tools (TruPLAN and TruFIBER). From the results of software validation and steering trials on a variable radius tool having a pre-laid UD ply, it is found that the ability to steer around a tighter radius was a vast asset of the 1/8 inch tow over the 1/4 inch one, which makes it the preferred choice for the more geometrically complex parts.
In this study, a three-phase multiscale model is developed to study the elastic behavior of the carbon nanotube-reinforced polymer composites. The cohesive zone model is implemented to model the carbon nanotubes debonding. The effects of weight fraction and aspect ratio of the carbon nanotubes as well as the strength of the interfacial adhesion on the effective elastic response of the nanocomposite have been investigated. A good agreement is obtained between the predicted and available experimental results when the cohesive interface is introduced in the model. The results show that carbon nanotube/polymer interfacial strength has more significant effect on the nanocomposites modulus and stiffness for higher values of weight fraction and aspect ratio.
An experimental investigation was performed to study the mechanical performance of 3D carbon/phenolic composites subjected to bending and impact forces. T300-3 k dry preforms were tufted using carbon threads of 396, 800, and 1600 tex. Also, the tufting densities varied from sparse density (tufted 16 x 16: areal density = 0.37 cm–2) to moderate density (tufted 11 x 11: areal density = 0.82 cm-2) and high density (tufted 5.5 x 5.5: areal density = 3.30 cm–2). The tufted preforms were then infiltrated by phenolic resin through the vacuum pressure infusion process. The three-point bending tests results revealed that the flexural strength loss of tufted composites ranged from 17 to 34%. In untufted composites, the specified crack grew quickly along the composite while through-the-thickness reinforcements stopped the crack growth and led to crack branching along the thickness of composite. With the presence of through-the-thickness yarns, damage behavior changed and the tufted composites exhibited a slower rate of decrease in the level of stress. These composites also showed higher levels of after-failure stress values. The experimental results of the impact test demonstrated that tufting had different effects on the energy absorption of composites. In a number of tufted composites, the energy absorption increased by 14.6% and in the other ones, it reduced by 8%.
Owing to the increased demand of long endurance flight, lightweight, and high strength envelope becoming the main point of the stratospheric airship design, especially the research on the envelope mechanical properties a novel stratospheric airship envelope material was developed in this paper. According to the structure of the woven fabric composite, nonlinearity and orthotropy are two main characteristics of the envelope. Uniaxial tensile test was performed to study the stress–strain curves of the envelope material. It is seen that the force–displacement curve can be divided into two significant nonlinear regions and three quasi-linear regions by the analysis of the test results. To analyze the force–displacement curve with different regions by the statistical method, Monte Carlo simulation based on the Ising model was developed. It is found that the simulation curves coincide well with the experiment curves both in the warp and weft directions. And the results show that parameters of the envelope material including fabric strength, functional layer strength, interfacial bonding strength, and so on, are the important factors affecting the mechanical properties and they decide the force–displacement curve shape.
For the purpose of improving the energy absorption performance of capped carbon fiber reinforced plastic tubes, a semi-circle grooved crush-cap is proposed and a series of experiments and improvements has been conducted. Tubes, which are respectively built by carbon fiber laminate and carbon fiber woven cloth, with semi-circle grooved crush-caps, combined (notched-end and crush-cap) failure mechanisms were investigated to identify the optimal configuration that would result in the most stable initial peak load while providing the highest possible specific energy absorption. Experimental results show that the new crush-caps lower the initial load, effectively yielding a high specific energy absorption. These results are significantly influenced by the semi-circle radii of the crush-caps. Furthermore, two failure modes have been observed in tests by changing the external trigger and tube material. The failure mode changes from splaying mode to fragmentation mode with the decrease of radii. The combined failure triggers proved the reduction in the initial load without smoothing the load-displacement curve, therefore, they reduce the energy absorption capability of carbon fiber reinforced plastic tubes. In our experiments, the tested tube which is made by T300/5208 woven cloth with R3 trigger is ground into powder, resulting in an specific energy absorption as high as 101.7 kJ/kg also with a smooth load-displacement curve.
In this work, nonwoven kenaf fibre/epoxy composites were produced by using resin transfer moulding. The effect of kenaf fibre volume fraction on the composites’ tensile properties and Poisson’s ratio was investigated. Experimental results show that highest tensile properties and Poisson’s ratio were attained at volume fraction = 0.42. A simple method has been developed to predict the fibre transverse modulus and has allowed the characterisation of kenaf fibre’s elastic anisotropy. The performance of the Tsai–Pagano model in predicting the composites’ tensile modulus and Poisson’s ratio was compared with the Manera and Cox-Krenchel model. Results showed that the consideration of fibre’s elastic anisotropy in the Tsai–Pagano model yielded a good prediction of both composites’ modulus and Poisson’s ratio. Meanwhile, the Bowyer–Bader model produced a better tensile strength prediction owing to the inclusion of fibre length and orientation factors in the model.
The present study provides a comparative investigation and discussion on the influence of laminate thickness uncertainty on reliability of laminated composite. Laminate thickness uncertainty in three different scenarios is considered: component level thickness uncertainty, fiber-dominated ply level thickness uncertainty and matrix-dominated ply level thickness uncertainty. Monte-Carlo and Markov-chain Monte-Carlo methods are employed to calculate failure probabilities of symmetric and balanced laminate panels bearing uniaxial and multiaxial loads. It is shown that conventional considerations on laminate thickness uncertainty in the component level could underestimate or overestimate the composite failure probability. Ply level thickness uncertainty primarily caused by fiber or matrix quantity may also result in very different failure probabilities. This study highlights the importance of a thorough analysis and classification of the laminate thickness uncertainty in the ply level in order to achieve confident reliability evaluation of composite structures.
The bond–slip behavior between carbon fiber reinforced polymer (CFRP) plates and steel is crucial for predicting the structural behavior of CFRP-strengthened steel members. In this paper, the CFRP-to-steel bonded joints with different bond lengths and adhesive thicknesses were tested to investigate the bond–slip behavior of CFRP-to-steel bonded interfaces. The digital image correlation (DIC) technique was used to measure the displacement and strain data. The test results, including the failure mode, ultimate load, displacement distribution, and CFRP strain distribution, are presented and discussed. The non-linear bond–slip curves of CFRP-to-steel bonded interfaces are determined by a fitting procedure for CFRP strain distributions. A bilinear bond–slip relationship is further proposed to simplify the non-linear bond–slip curve. The test results indicate that the adhesive thickness has an influence on the failure mode, ultimate load, and bond–slip behavior. Similar to a CFRP-to-concrete bonded interface, an effective bond length also exists for a CFRP-to-steel bonded interface. The development of the interfacial shear stress is analyzed based on the determined non-linear and bilinear bond–slip curves. Finally, two theoretical models are employed for the prediction of the ultimate load, effective bond length and bond–slip curve. This study shows that the DIC method is suitable for investigating the bond–slip behavior of CFRP-to-steel bonded joints.
In the current paper, the modal characterisation of aramid–carbon fiber hybrid composites (ACFRP) and ACFRP reinforced with silica nanoparticles (nACFRP) is investigated through the analytical-experimental transfer function method. The modal properties, such as resonant frequencies and modal loss factors, are measured by vibrating cantilever beam specimens with an impact hammer, while the vibratory response is detected through an acceleration transducer. The procedure for the identification of analytical-experimental transfer functions is carried out using a genetic algorithm by minimising the difference between the measured response from tests and the calculated response, which is a function of the modal parameters. The analytical transfer functions provide a substructuring process to identify modes, as a function of damped natural frequencies and loss factors of a complex structure, and it is insensitive to experimental noise as well as the modal coupling effect. The validation of the proposed method is verified with 10 degrees of freedom mass-spring dashpot model. The effectiveness of the proposed method is demonstrated by investigating the static and dynamic behaviour of the ACFRP and nACFRP specimens. Results indicate that the inclusion of nanosilica particles increase the stiffness of the ACFRP, although the damping response of the reinforced specimens is moderately improved.
In the current research enterprise, behavior of novel bio-composites incorporating Aloe Vera fibers in biopolymer matrix (polylactic acid) has been experimentally examined in comparison to Sisal fiber reinforced bio-composites. These bio-composites were melt blended using single screw extruder prior to injection molding. The effect of fiber weight fraction (10–20–30%) and fiber surface modification on mechanical behavior of developed bio-composites was investigated. Alkaline treatment using sodium hydroxide concentration of 5% was used for fiber surface modification. Both alkali treated and raw fibers were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscope. Thermal stability of the fibers improved after alkaline treatment. The mechanical characteristics of developed bio-composites exhibited an improvement with increasing fiber concentration. Alkaline treatment of fibers further improved the tensile, flexural and compressive properties of developed bio-composites, while their impact properties declined compared to raw fiber reinforced bio-composites. Moreover, from the results, it is evident that the characteristics of Aloe Vera fiber reinforced bio-composites are comparable to Sisal fiber reinforced bio-composites and the developed bio-composites have the potential to be used in various automotive, furniture and architectural applications.
Parameterized unit-cell models of three-dimensional n-directional (n = 5, full-5, 6, or 7) braided structures are established based on the internal structures of three-dimensional braided composites. Braiding structures are characterized by model parameters, and the relationships between fiber volume fraction and model parameters are analyzed in this study. A finite element stiffness prediction is conducted using the parameterized models, and the simulation results are found to be consistent with the experimental data. Model parameters’ influence on elastic constants of the composites is studied through finite element method. The research shows that the models can describe braiding structures precisely and are applicable to stiffness performance analyses, and provides an available approach to mesoscopic mechanical analysis and structural optimization design of three-dimensional braided composites.
Ultra-thin chopped carbon fiber tape-reinforced thermoplastics, which belong to a class of randomly oriented strands and are characterized by enhanced strength, stiffness, and formability properties, have been prepared via a paper-making method from ultra-thin thermoplastic prepregs. The failure of ultra-thin chopped carbon fiber tape-reinforced thermoplastics under static tensile loading was studied in detail using various observation techniques, such as high-speed camera imaging, thermography, and optical microscopy. The obtained results revealed that the tensile fracture of ultra-thin chopped carbon fiber tape-reinforced thermoplastics exhibited three main patterns: fiber breakage, splitting of chopped tapes, and pulling out of chopped tapes. In contrast to conventional randomly oriented strands, the utilization of ultra-thin prepregs decreased the tensile strength scattering. An increase in the ultra-thin prepreg tape length resulted in an increase in the strength average magnitude, reaching saturation at a length of 18 mm. The results of this study can be used for constructing tensile strength prediction models and expanding the ultra-thin chopped carbon fiber tape-reinforced thermoplastics application range.
This article deals with the static response of thin circular clamped GLAss REinforced fiber–metal laminates subjected to oblique indentation. The indentation response is initially predicted using ANSYS software and a three-dimensional nonlinear finite element analysis with geometric and material nonlinearities. From this analysis, the load-indentation and the strain energy-indentation curves are calculated. Postprocessing of the obtained Finite Element Method (FEM) results reveals how GLAss REinforced plates respond to oblique indentation. Then, analytical formulas are derived to predict the GLAss REinforced plate indentation load and strain energy as a function of the oblique indentor’s displacement and the direction of indentation. The derived analytical formulas are applied successfully for circular GLAss REinforced plates with various diameters and indentation directions. The analytically predicted load-indentation and strain energy-indentation curves are compared with corresponding Finite Element Method (FEM) results and a very good agreement is found.
Elastically prestressed polymeric matrix composites exploit the principles of prestressed concrete, i.e. fibres are stretched elastically during matrix curing. On matrix solidification, compressive stresses are created within the matrix, counterbalanced by residual fibre tension. Unidirectional glass fibre elastically prestressed polymeric matrix composites have demonstrated 25–50% improvements in impact toughness, strength and stiffness compared with control (unstressed) counterparts. Although these benefits require no increase in section dimensions or weight, the need to apply fibre tension during curing can impose restrictions on processing and product geometry. Also, fibre–matrix interfacial creep may eventually cause the prestress to deteriorate. This paper gives an overview of an alternative approach: viscoelastically prestressed polymeric matrix composites. Here, polymeric fibres are subjected to tensile creep, the applied load being removed before the fibres are moulded into the matrix. Following matrix curing, viscoelastic recovery mechanisms cause the previously strained fibres to impart compressive stresses to the matrix. Since fibre stretching and moulding operations are decoupled, viscoelastically prestressed polymeric matrix composite production offers considerable flexibility. Also, the potential for deterioration through fibre–matrix creep is offset by longer term viscoelastic recovery mechanisms. To date, viscoelastically prestressed viscoelastically prestressed polymeric matrix composites have been produced from fibre reinforcements such as nylon 6,6, ultra-high molecular weight polyethylene and bamboo. Compared with control counterparts, mechanical property improvements are similar to those of elastically prestressed polymeric matrix composites. Of major importance, however, is longevity: through accelerated ageing, nylon fibre-based viscoelastically prestressed viscoelastically prestressed polymeric matrix composites show no deterioration in mechanical performance over a duration equivalent to ~25 years at 50℃ ambient. Potential applications include crashworthy and impact-absorbing structures, dental materials, prestressed precast concrete and shape-changing (morphing) structures.
Impact properties of flax fibre-reinforced polymer composites were investigated using two different impact test methods, i.e. drop-weight test and Charpy test. The drop-weight impact tests were conducted with varying drop height. For the drop-weight tests, the perforation energy and the energy absorbed by a specimen are used to study the impact response of the flax fibre-reinforced polymer composite. In a series of Charpy tests, the energy absorbed per unit width of the specimen was investigated. Impact force and Hertzian force were analysed and were found to increase with composite thickness. The ductility index decreased as the composite thickness increased. The failure of flax fibre-reinforced polymer composites started as micro-cracks, progressed to larger cracks and perforation occurred at last. However, the damage to flax fibre-reinforced polymer composites differed with the thickness of the specimens.
The novel composite pyramidal truss core sandwich panels with reinforced joints are manufactured by the water jet cut and interlocking assembly method. Here, the relative density
The Tandon–Weng model has been used for polymer nanocomposites in previous reports. However, some complex parameters and questionable accuracy of this model have limited its application. In this work, the original Tandon–Weng models for bulk and shear moduli of isotropic composites containing 3D randomly oriented particles are simplified for polymer/clay nanocomposites. Additionally, the effects of main parameters on the predictions of the simplified models are evaluated. According to the simplified models, the moduli of polymer/clay nanocomposites depend to moduli of polymer matrix and nanoparticles, Poisson ratio of matrix, and nanofiller concentration, while some parameters such as aspect ratio of platelets cannot play a significant role. Also, the similar effects of matrix Poisson ratio and nanofiller concentration on the shear and Young’s moduli are observed, but a different trend is fund for bulk modulus.
Strong wind causes damages and losses around the world. The windborne debris carried by strong wind might impact on building and create openings on the building envelop, which might threaten the occupants and cause further damages to the building. To address this issue, some wind loading codes including the Australian Wind Loading Code (AS/NZS 1170:2:2011) give design requirements. The resistance capacity of oriented strand board skins structural insulated panel was investigated and proved having low resistance to the projectile impact, and could not meet the impact resistance requirement for application in cyclonic region C and D defined in Australian Wind Loading Code. In this study, basalt fibre cloth is used to strengthen oriented strand board structural insulated panel to increase its capacity to resist windborne debris impact. This paper presents experimental and numerical study of structural insulated panel with or without basalt fibre cloth strengthening under windborne debris impact. Five specimens with different configurations were tested. The dynamic responses were quantitatively compared in terms of residual speed of debris after impact. The results indicate that basalt fibre cloth enhanced the resistance capacity of oriented strand board structural insulated panel. A numerical model is developed in LS-DYNA to simulate the debris impact. The testing results are used to verify the accuracy of the numerical model, which can be used in subsequent parametric studies.
In this study, an optimization procedure is proposed to find the optimum stacking sequence designs of laminated composite plates in different fiber angle domains for maximum buckling resistance. A hybrid algorithm combining genetic algorithm and trust region reflective algorithm is used in the optimization to obtain higher performance and improve the quality of solutions. As a novelty, Puck fiber and inter-fiber failure criteria are directly implemented to the optimization problems as nonlinear function constraints, which have allowed more consistent and feasible results. The performance of the hybrid algorithm is demonstrated by comparing with the individual performances of genetic and trust region reflective algorithms via test problems from the literature. Also, a study is performed to exhibit the effectiveness of the selected failure criterion as constraint among the other common criteria. The proposed procedure is used to solve many problems including various design considerations. The results indicate that reliable stacking sequence designs can be achieved in specific configurations even for the composite plates subjected to superior buckling loads when Puck physically based (3D) failure theory is considered as a first ply failure constraint in the buckling optimization.
The mechanical recycling of polylactic acid composites reinforced with wood fibres was studied by multiple extrusions. The composite material was extruded seven times, and the mechanical and thermal properties were monitored by tensile tests, flexural tests, differential scanning calorimetry, Fourier-transform infrared and scanning electron microscopy. The results showed that the material retained its mechanical properties relatively well, for up to five cycles after which the tensile strength decreased by 23%. Thermal characterisation further showed that the glass transition temperature (Tg) shifted several degrees centigrade towards lower temperatures, further indicating degradation of the polylactic acid polymer. Characterisation was also done on composite material, which was aged hydrothermally between each extrusion cycle in order to simulate post-consumer recycling of composite products, which had been exposed to water. Samples were aged at 50℃ in distilled water for 5 days. The thermal and mechanical testing showed that the material survived the ageing test fairly well.
The demand for natural fiber composites in the automotive industry in both Europe and the United States has been forecasted to increase in the coming years. The natural fiber composites based on highly commercialized fibers such as flax, hemp, and sisal has grown to become an important sector of polymeric composites. However, little attention has been addressed to expanding natural fiber composites to include new sources of emerging natural reinforcements, such as reclaimed algae fibers, that have a multiple environmental benefits. Not only are extracted algae fibers biodegradable, the reclamation process has the added benefit of restoring health of waterways choked with algae. This study focuses on the processability of algae fiber–epoxy composites. Short fibers, chemically extracted from raw reclaimed algae, were prepared for natural fiber composite products in two ways. First, randomly oriented mats were produced using the wet-laid process to create layered, compression-molded laminates. Second, loose fibers were dispersed directly into the thermoset matrix to produce a bulk molding compound that was further compression molded into composite lamina. The effect of processing variables such as compaction pressure, temperature, and time were addressed. Moreover, the effect of fiber volume fraction (f) and fiber form were considered. Enhanced mechanical properties were found when 56% f algae fiber was used for the compression-molded laminates composite. This variant exhibited an improvement on the flexural and tensile modulus of 70% and 86% when compared to the neat epoxy. However, the volume of porosity on the same variant was 11% due to lack of compression in some of the fibers. The effect of porosity on the theoretical stiffness was estimated by using the Cox–Krenchel model. Furthermore, an empirical exponential model was formulated to characterize the multi-scale effect of compaction pressure on the overall fiber volume fraction, f.
There has been a vast growth in manufacturing of fiber reinforced plastics by means of liquid composite molding such as resin transfer molding and vacuum-assisted resin transfer molding processes. In these processes, compression of the porous media and pressure of the injected resin result in in-mold forces that need to be determined. Limited information exists regarding the processing parameters and extent of reinforcing potential natural fibers have in polymer matrices. Current study investigates the effect of different variables such as fiber volume fraction, shive content, fiber size, wax content, and resin viscosity on permeability of five different natural fiber mats. Flax fiber with low-, medium-, and high-shive content as well as hemp and kenaf fiber mats was selected for this study and an original experimental device was setup to measure the permeability of the mentioned fiber mats based on different variables. It was found that increasing fiber volume fraction will result in reduction of permeability of all mats. The presence of shive and larger fiber size increased the permeability. Higher wax content lowered the permeability. These competing factors could be used by manufacturers to produce a mat which had optimum permeability while still maintaining acceptable strength.
The effect of boehmite alumina nanofiller on properties of polylactide/polypropylene blend compatibilized with 3% maleic anhydride grafted polypropylene was investigated. Boehmite alumina nanoparticles were finely dispersed in polylactide/polypropylene/boehmite alumina blend up to 7 wt.% to form blend nanocomposites which were prepared by twin-screw melt compounding. The morphology, thermal, mechanical, heat distortion temperature, thermomechanical and degradation characteristics were investigated. Scanning electron microscopy indicated a tubular morphology with increasing boehmite alumina in the blend matrix particularly at 5 and 7 wt.% of boehmite alumina loadings with few agglomerates. Transmission electron microscopy indicated a highly dispersed boehmite alumina in the blend nanocomposites. Boehmite alumina nanoparticles significantly influenced the thermal properties and a nucleation of the blend matrix. A significant improvement in the tensile modulus and tensile strength upon addition of boehmite alumina in the blend nanocomposites was obtained. However, beyond 3 wt.% of boehmite alumina addition, there was a clear deterioration in mechanical properties.
Carbon fiber-reinforced plastics (CFRP) have been widely applied in aerospace industry as structural components due to their excellent mechanical and physical properties. Meanwhile, the drilling process is indispensable for machining the assembly holes of CFRP. However, in the conventional drilling process of CFRP, it is prone to produce the defects including delamination, spalling, fuzzing, and tool wear. In recent years, the rotary ultrasonic-assisted drilling (RUAD) with diamond core drill, as a novel machining method, has been employed to reduce the defects. But this is few reported investigations on chip adhesion of tool surface and machined rod jamming into core drill tool during RUAD of CFRP. Therefore, this paper detailedly reported a study on removal analyses of chip and rod in RUAD of CFRP using core drill under no cooling condition for the first time. To begin with, the principle analysis on RUAD of CFRP was presented to illustrate the removal process of chip and rod. And then, the experiment analysis on RUAD of CFRP was carried out to observe the removal effects of chip and rod. The experimental results indicated that compared with the common drilling of core drill, when the vibration amplitude reached 5.0 and 7.5 µm in RUAD, the cutting ability of core drill tool was greatly enhanced, excellent removal effects of chip and rod were obtained, which obviously reduced the chip adhesion, rod jamming, rod fragmentation, thrust force, cutting temperature, and surface roughness, improved the dimensional accuracy of machined hole and rod diameter, prolonged the tool life, as well as acquired superior surface integrity of machined hole and flat fibers fracture surfaces. Furthermore, the experimental results also validated the accuracy of the principle analysis.
This paper aims at comparing the mechanical behaviour of different composite materials constituted of twill flax and glass fabrics-reinforced liquid thermoplastic and thermoset resins. The main objective is to study the possibility of thermoplastic to replace thermoset matrix, and flax fibre to replace glass fibre. For this purpose, the studied composites were fabricated using the vacuum infusion technique. Next, they were subjected to several monotonic and load-unload tensile tests in order to determine their mechanical properties and their evolution with damage. Two elastic damage and elastic-plastic damage models were also considered to predict their behaviour. The obtained results show that the used thermoplastic resin could constitute an interesting alternative to the thermoset resin for the vacuum infusion process. Furthermore, the flax fibre composites, in particular those based on the thermoplastic resin, present specific tensile moduli close to those of glass composites.
A simulation model of carbon fiber-reinforced polymer composites (CFRP) exposed to simulated lightning current was constructed based on the pyrolysis behavior of resin, in which temperature dependent material properties due to resin pyrolysis were took into account, such as thermal conductivity, electrical conductivity, specific heat, and density. The damage behavior of CFRP caused by lightning strike has been modeled and validated by experiments. Based on the model, CFRP damage propagation behavior during lightning strike and influence of lightning current parameters to damage behavior of CFRP were investigated. Results indicated that, during lightning strike, damage depth and damage area of CFRP propagate rapidly at the initial stage of lightning strike, and then become slowly, damage of each layer formed under the act of resistive heating generated by electricity conduction in-plane of the layer and heat transmit between connected layers, and then propagate directionally; with the increase of peak current and waveform parameters, damage of the CFRP will be increased.
In this work, computational fluid dynamics simulations are performed to predict the temperature distribution on a part during an autoclave run. Data from an experimental study are used as input to the simulations and also for comparison with the numerical results. A conjugate heat transfer approach was used for the simulations, where best agreement with experiments was obtained from the simulation that included thermal radiation and utilized an experimentally obtained velocity profile as inlet velocity. A yet more detailed inlet velocity profile and more advanced turbulent model could result in an even better agreement.
This study explored the use of J-integral approach for characterizing mode I, mode II and mixed-mode I/II interlaminar fracture toughness of composites materials. Delamination tests were conducted to measure the fracture toughness and the resistance curve (R-curve) for double cantilever beam, end-notched flexure and mixed-mode bending specimens. The J-integral approach and the well-established ASTM standard methods based on LEFM were compared in this work. The results obtained from both methods are in very good agreement. However, the J-integral method has the advantages of being applicable to materials with large fracture process zone (e.g., composites with fiber bridging) and provides a simpler experimental procedure with fewer inputs. More importantly, the presented method avoids the ambiguity in visual measurements of delamination length required by the ASTM standard methods. In this study, an image-processing program based on Hough transform was developed to obtain the rotation angles of the specimen. The method provides good accuracy and has lower requirements for image resolution, light and material surface compared to previous methods.
During the last few years, the hybrid composite materials are replacing the conventional composite materials because of their superior properties. In the present communication, unidirectional banana–jute hybrid fiber-reinforced epoxy composites were prepared by varying the fiber content from 0 to 40 wt% with different weight ratios. The physical and thermal properties of the hybrid composites were tested as per ASTM standards. The influence of fiber content on density, thermal conductivity, specific heat, thermal diffusivity, thermal stability, and water absorption of hybrid composites was investigated. A new micromechanical model for the transverse thermal conductivity of hybrid fiber-reinforced polymer composites is developed using the law of minimal thermal resistance and equal law of specific equivalent thermal conductivity. The results are validated with the results obtained by experimental, numerical simulation, and analytical methods existing in the literature. In numerical, steady state heat transfer simulations were performed to calculate thermal conductivity by using ANSYS software. It is encouraging to notice that the experimental and numerical results are in close approximation with the values predicted by the micromechanical model suggested in this work. It is found that the measured properties of the hybrid composites are suitable for building components and automobiles in order to decrease energy consumption.
Technology development is tied strongly to our ability to engineer materials that cope with the fast evolving requirements of innovative products. The best way to build this ability is by establishing a material design process from atomic scale to the system scale. An important building block of this process is micromechanical models that bridge microscale to mesoscale. Unfortunately, current micromechanical models remain short from material design perspective. To be able to improve these models, one must first assess and apprehend their prediction capabilities. In this respect, this paper seeks to analyze and compare some prominent micromechanical models with the objective to emphasize those capable of evaluating accurately the effective properties for composites. These models can, then, be candidates for a potential integration in the material design process. This work begins, therefore, with an overview of some well-known models, namely Mori–Tanaka model, self-consistent model, Lielen’s model, effective self-consistent, and its extension interaction direct derivative. The double-inclusion model in its original and new version is introduced and explained. Subsequently, the limitations of all the aforementioned models are discussed and their predictions in the case of both two-phase and multiphase composites are compared. Consequently, it is shown that the improved Double-inclusion model version of Aboutajeddine and Neale can be seen as a unified model, which includes some of the previously existing models as special cases. In addition, this last model is the only model that gives satisfactory predictions in the case of multiphase composite materials.
The objective of this paper is to present an investigation of resistance welded thermoplastic joints using stainless steel wire mesh and polyethylene terephthalate (PET) with unidirectional E-glass fiber reinforcement. Five weld pressures and six heating element types were investigated to achieve high quality welds. Scanning electron microscope (SEM) images of welded heating element cross-sections were analyzed to provide a phenomenological description of the weld. Welded joints were also subjected to experimental lap shear evaluation and joint strengths were compared with values from the literature to assess the overall quality of welded joints. Characteristic B-basis strengths and corresponding SEM images are compared to lead to a recommended weld pressure of 345 kPa with a stainless steel wire mesh with 100 openings per inch.
Laboratory compressive tests and acoustic emission analysis have been used to investigate the failure of pultruded fibre reinforced polymer materials after they have been subjected to temperature stress and compressive loading. The acoustic emission approach is then compared with the experimental values of energy released by each sample through the corresponded load-displacement curve. Samples subjected to severe thermal conditions showed more evidence of brittle failure mechanism. This analysis has been conducted in order to confirm the potential capacity of fibre reinforced polymer materials, known currently for their strength and lightweight but often ‘brittle’ physical characteristics, to perform under exaggerated conditions of temperature and compressive stress.
The static and vibrational properties of randomly oriented shape memory alloy short wires reinforced epoxy resin are determined considering the interface effect between shape memory alloy wires and the resin. First, experimental pull-out test is utilized to obtain the interfacial shear strength between the reinforcement and the matrix. Then, using the finite element simulation, the elastic modulus of the equivalent fiber is determined. Micromechanics model based on Eshelby’s equivalent inclusion and Halpin-Tsai method is used to predict the elastic modulus of shape memory alloy/epoxy composites theoretically. Experimental tensile tests in the present work beside the reported vibration results in the literature are used in order to validate the accuracy of the model. The results showed that ignoring the interface effect in modeling the behavior of shape memory alloy/epoxy composites causes significant errors, especially in high-volume fraction of the shape memory alloy wires. Moreover, the critical aspect ratio of the shape memory alloy wires is obtained as a function of temperature. The critical values for the aspect ratio are about 30, 40 and 42 for 50℃, 25℃ and 0℃, respectively.
The tensile properties of prestressed fabric-reinforced composites have been investigated. A method of applying an equi-biaxially fabric prestressing prior to and during the curing process of a plain-weave fabric composite was performed. A novel fibre prestressing equipment was built to apply and measure the tension load in the principal yarn directions of a fabric. The equi-biaxial fabric prestressing level, ranged from zero to 100 MPa, was used. Tensile tests were performed for the batches with different fabric prestressing levels to estimate the optimum level that gives the maximum tensile performance. The samples were also tested at different orientation angles, precisely from warp to bias direction. Prestressing the fabric enhanced the tensile performance such as elastic modulus and critical stress to first fracture of the composite by 10–20%. Most tensile properties, for instance tensile modulus and critical stress, reached their ultimate values at 50 MPa of prestressing level; however, the tensile-limited toughness was maximum at a level of fabric prestressing of ~75 MPa.
Bamboo fibers reinforced with non-woven fabric polypropylene composites were prepared via compression molding. Three types of bamboo fibers were used in the research: untreated, treated with a sodium hydroxide solution and treated with a sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of the preformed structures and chemical treatments on the composite performances were investigated. The results showed that the composite attained optimum mechanical properties at an alkali concentration of 5% and at a silane coupling reagent concentration of 3%. The preformed structure composed of materials with bamboo fiber/polypropylene mass ratios of 50/50 and 70/30 exhibited ideal mechanical properties. The moisture absorption behavior of the composites with different bamboo fiber contents exhibited good agreement with Fick’s law. Scanning electron microscopy showed that the composites prepared using alkali-silane-treated fibers demonstrated better bonding between the fibers and matrix and had fewer voids in the composites. We also confirmed that the modifications of the bamboo fibers improved the hygrothermal properties of the composites because of the improved interfacial adhesion between the fiber and matrix.
Graphene nanoplatelets are two-dimensional carbon structure materials with single or multilayers graphite plane which possesses attractive characteristics. In this study, the environmental aging effect on interlaminar properties of graphene nanoplatelet containing different proportions (0.25, 0.50, 0.75 wt%) reinforced epoxy/carbon fiber (carbon fiber reinforced plastic) composite laminates including interlaminar shear strength and fracture toughness were investigated. The interlaminar properties of graphene nanoplatelets/carbon fiber reinforced plastic composite laminates were improved over that of neat carbon fiber reinforced plastic composite laminates. Experimental results showed that the composite laminates containing graphene nanoplatelets possesses the appreciable improvement. The mechanisms responsible for the interlaminar enhancement were identified by studying the fracture surfaces using field emission scanning electron microscopy.
This paper presented a review of 84 confinement strength models developed for predicting the ultimate compressive strength of carbon fiber-reinforced polymer-confined concrete subjected to uniaxial compression. Among these models, 64 design-oriented models and 12 analysis-oriented models were selected and evaluated by a comprehensive database including the experimental results of 1475 carbon fiber-reinforced polymer-confined concrete specimens through three statistical indicators: the mean (μ), the coefficient of determination
Generally, a grid layer is used as an orthotropic layer to reinforce plates and shells or as an independent structural element. The proposed laminated grid plate is composed of different grid layers with different orientations. Consequently, the grid layers with different fibers, patterns and orientations can be used, resulting in laminates with enhanced stiffness and coupling effects. In the present study, to investigate the efficiency of the laminated grids, the vibration and buckling responses of a conventional and laminated grid plates are compared. The first-order shear deformation plate theory along with Ritz method is used to obtain the buckling load and natural frequencies of the plates. The effectiveness of increasing the number of layers on mechanical responses of the laminated grids is also studied. The analytical results of vibration frequencies are compared and validated by finite element method and experimental analysis of two manufactured grid plates. The results indicate that thoughtful selection of stacking sequences of the laminated grids considerably enhances the response of the laminated grids in comparison with conventional grids.
The influence of different layering pattern on the thermal and mechanical properties of the hybrid lyocell/rayon woven fabric reinforced polyester composites is demonstrated in this research work. The effect of different layering pattern was studied and characterized with tensile, open hole tensile, flexural, and impact testing. Composites manufacture with rayon/rayon/lyocell pattern reinforcement has the best tensile and flexural properties. The tensile and flexural strength increased by 36.5% and 43.79%, respectively, with reference to neat resin. It is also noted that the tensile modulus reduced by 31.1% when compared to neat resin. This represents an increase of material ductility in comparison with neat resin. It is observed that placing of high strength lyocell fabric at the extreme layer as reinforcement would result in enhanced properties. In case of rayon/lyocell/rayon hybrid tensile composites it can be seen that there is only 8% increase in tensile properties in comparison with neat resin due to rayon fabric placed as a skin rather than core. A negative effect of 6–26% reduced tensile strength was observed for the open hole (6 mm diameter) samples of all pattern of textile composites. This was due to fiber and inter fiber (matrix) fracture. A more detailed microfractography analysis was used to determine the crack growth direction and initiation. While in impact properties the lyocell/lyocell/lyocell pattern reinforcement showed the best impact strength of 3.36 kJ/m2 compared to rayon/rayon/rayon and other tri-layer composites. Thermal analysis showed higher thermal stability for the rayon/rayon/lyocell pattern reinforcement.
This article deals with the dynamic response of thin circular clamped GLARE (GLAss REinforced) fiber-metal laminates subjected to low-velocity impact by a lateral hemispherical impactor, striking at the center with constant kinetic energy. The laminates have equal total thickness and consist of GLARE 2A-3/2-0.4, GLARE 2A-4/3-0.238, GLARE 3-3/2-0.4, GLARE 4-3/2-0.317, and GLARE 5-3/2-0.233 standard grades. Three different plate diameters are considered for each GLARE grade. Their dynamic response is predicted by solving previously published differential equations of motion corresponding to a spring-mass modeling of the impact phenomenon. The obtained results are analyzed and compared in order to understand and evaluate the performance of the examined material grades along with the effect of different plate radius. With reference to the radius variation, it is found that it affects substantially the overall impact behavior of a GLARE plate. As far as the examined material grades are concerned, similarities and differences related with their impact behavior are recorded and a comparative evaluation is implemented. Characteristic variables associated with the low-velocity impact response of fiber-metal laminates are discussed and pertinent design recommendations are proposed.
The non-linear deformation response of plain woven carbon fiber-reinforced composites is experimentally studied at meso-scales. Stereovision digital image correlation is utilized to capture the full-field strain distribution over a 10 x 10 mm2 area of interest located at the center of the specimens. The evolution of local strains on the fiber bundles and matrix-rich regions as a function of loading is extracted. The effect of fiber orientation angle on fiber bundles stretch ratio and their angle of rotation (fiber trellising) and the related underlying failure mechanisms are analyzed using the measured full-field displacement data. The results indicate that the local load-bearing mechanisms are different in on-axis and off-axis loading conditions, whereas the larger global failure strain noticed in off-axis conditions is attributed to the occurrence of fiber rotation. The fiber trellising is also shown to promote high local shear strain and consequently leads to the protrusion of the matrix material on the deformed specimen surface.
In recent years, the amount of research on natural fibres and natural-fibre-based products has increased substantially. The reason for this increase is due to a greater awareness of the environment and the ever depleting trend of petroleum supplies. Natural fibre composites and in general, natural fibres have a big role to play towards a sustainable environmentally friendly future. The automotive industry is taking big steps toward a more eco-friendly product chain by implementing natural fibres as a base for making various components, such as seat backs, door panels, spare tyre and boot linings. The world production of natural fibres is increasing since the product base is increasing. Each year, more synthetic fibres and high energy consuming products are being replaced by natural-fibre-based products. The reason for this trend is not only due to an increased environmental awareness but also because natural fibres have excellent properties, such as light weight, and they have relatively low costs. This study attempts to review the most commercially important natural fibres and their automotive application and also looks at the properties, chemical composition and cost of some natural fibres being used in industry.
Fiber metal laminates (FML) combine the strength of carbon fiber composite layer with ductility of the aluminum layer for desirable mechanical characteristics. For these composites, progressive failure behavior can be complex and require attention. In this study, two carbon fiber reinforced aluminum laminates (CARRAL) with a 3/2 configuration, with aluminum in the outer layer for the first case and one with carbon fiber composite layer in the outer layer were prepared using a vacuum press without any adhesive layer between the layers—a significant departure from similar aerospace materials. Epoxy from the prepreg provides adequate adhesion during consolidation in these lower cost FMLs with a pressure level of 0.35 MPa. Three-point flexural behaviors of these two material systems were evaluated under static loading and failure modes were recorded. Primary failure modes observed were crack in lower aluminum layer, carbon fiber (CFRP) layer fracture and delamination between upper aluminum and CFRP layer. A major contribution of this study was to predict the flexural response of these FMLs using LS-DYNA finite element code. Modeling the progressive damage behavior of FML by considering stress based material failure and shear stress based delamination failure between adjacent layers were key aspects of finite element modeling. Predicted mechanical behavior matches well with experimental results and the progressive nature of damage are recovered in the model.
Weld line is aesthetically unpleasant and affects the mechanical strength of injection molded parts. Because of the ever-increasing requirements for parts performance, lots of researchers have performed various studies related to the weld lines optimization. However, research about the computer determination of weld lines in injection molding remains scarce. In this paper, a weld line computer determination method based on filling simulation with surface model is proposed, from which the positions and lengths of the weld lines can be predicted. According to the characteristics of the surface model, all weld lines are classified into two different types. Initial welding node searching and revision algorithms for the two different types of weld lines are first developed. Starting from initial welding nodes, weld lines are then extended by a pre-extension algorithm and an extension algorithm. In the weld line extension algorithm, 135° is set as a welding angle threshold for forming weld lines. Finally, the effects of cavity thickness, process parameters, and mesh densities have been investigated. Moreover, Moldflow simulation results and real parts in production have been conducted to verify the proposed determination method, which demonstrate that the proposed method is correct and effective in actual production.
Viscose fabric-reinforced unsaturated polyester composites were successfully prepared through vacuum infusion process. Unidirectional viscose fabric was modified by two different organosilane coupling agents and by acetylation treatment. The main objective was to study the influence of fabric treatment on the mechanical and water absorption properties of the composites. Flexural, tensile and impact properties of composites were studied. The results from mechanical testing of composites pointed out that 3-aminopropyltriethoxy silane treatment increased the flexural and impact strengths of the composites with respect to untreated fabric composite. The impact strength of 3-aminopropyltriethoxy silane-treated fabric composites almost doubled compared to the value of untreated fabric composite. Among all the composites under study, those with fabrics treated by 2 vol% 3-aminopropyltriethoxy silane in ethanol/water (95:5) solution exhibited significant improvement in water uptake resistance. An unsaturated polyester gelcoat and topcoat were applied as the outer surface on the composites with untreated fabric. This was done in order to investigate the visual surface appearance and evaluate the gelcoat and topcoat effect on water absorption after accelerated water immersion test. The regenerated cellulose fibre as reinforcement shows high potential to be used as an alternative for natural bast fibres, especially, when toughness of material matters. Chemical treatment of regenerated cellulose fibres could result in improvement in properties of polymer composites, considering that the appropriate treatment method is selected for the corresponding fibre–matrix system.
Capillary rise affects void inclusion during the impregnation of fiber reinforcements in resin transfer molding. A new model of effective capillary radius has been developed to investigate the effect of pore size distribution on capillary flow in unidirectional fiber bundles. With the image analysis method, the statistical results showed that the pore size distribution could be very different even for the same fiber volume fraction. Then, the classical Washburn equation, in conjunction with different models for calculating effective capillary radius, was applied to predict the capillary rise rate. Compared with the experimental results, we found that the new model performed better than traditional models where the effective capillary radius was obtained using average pore radius or hydraulic radius.
Fibre-reinforced composites are an important field of composite research and are used in an enormous range of applications from special high-tech applications such as aeronautics to consumer goods such as sporting goods. The objective of this study is to assess the monetary value of fibres to be used for reinforcement in composites by the relation of price and certain fibre properties. To model this, relationship data from different types of technical fibres were used. An economic approach is used to identify the determinants of fibre value. In total, four regression models were calculated. The models give an impression of the impact of the explanatory variables. This work shows that the evaluation of the economic value of a reinforcement fibre by technical properties is feasible.
Impact-induced delamination propagation on both tufted and untufted carbon fibre-reinforced plastics composite laminates was investigated. High-velocity impacts were performed on a ballistic gas gun. Initial and residual velocities were monitored with optical sensors especially developed for this study. Energy-absorption abilities were compared for different tufting parameters. The perforated specimens were inspected with an original technique allowing the observation of interlaminar delamination area for each interface. The existence of preferential propagation direction is highlighted. It is concluded that tufting helps to contain delamination and provides improved energy absorption depending on the tufting pitch.
In this study, two micro-mechanical models for analyzing the stress transferring in single-fiber composites composed of the fiber, the matrix, and the interphase are developed based on the shear-lag theory. The analytical model has taken into account two micro-damage modes, that is, the interficial debonding and the matrix damage, respectively. So, the real distribution of the shear stress at the interface and the axial stress in the fiber in single-fiber composites under loading can be obtained. An approach based on combining the micro-mechanical model with the single-fiber fragmentation test was utilized to determine the property of the interphase. The more accurate and real shear strength of the interphase in single-fiber composites is determined compared with the previous methods.
Microwave curing of epoxy/glass fiber composites was investigated in this paper. By studying the reaction characteristics of the resin matrix, detailed curing processes were established. With the use of a self-designed pressure-exerting device, the resin weight fraction of the composites was controllable. The glass transition temperature was measured by differential scanning calorimetry, and the mechanical properties were determined by three-point-bend and uniaxial tensile tests at room temperature. The tensile failure surfaces of both microwave and thermally cured composites were observed with scanning electron microscope. A comparison of the microwave and thermal processes was conducted to evaluate the advantage of microwave curing process. The microwave process (a) and thermal process (b) were regarded as the optimized process for each curing method. It was concluded that the epoxy/glass composites cured by microwave radiation had slightly higher T g, comparable flexural strength and better tensile properties. Furthermore, the microwave process had a great advantage in saving the cycle time.
Chopped carbon fibers reinforced wood plastic composites were fabricated using a two-step extrusion process. As a coupling agent, maleic anhydride polyethylene was added for improving the interfacial adhesion between the chopped carbon fibers and plastic matrix. The results showed that the mechanical properties of the maleic anhydride polyethylene–added composites were significantly improved compared to that without maleic anhydride-grafted polyethylene. Tensile strength, flexure strength and impact strength were increased by 97%–133%, 113%–119% and 181%–251%, respectively, which were very close to the strengths of structural timber. The adding of maleic anhydride polyethylene also influenced the electrical property of chopped carbon fibers reinforced wood plastic composites. The volume electrical resistivity of the composites with maleic anhydride polyethylene was higher. The scanning electron microscopy was used to examine the morphology of brittle fracture cross-section paralleled to the extrusion direction. It was observed that the interfacial adhesion was improved with the incorporation of maleic anhydride polyethylene. Chopped carbon fibers were coated by high-density polyethylene and the bonding connections were formed on the fiber surfaces. The distribution direction of chopped carbon fibers was parallel to the extrusion direction and dispersed more uniformly in the maleic anhydride polyethylene–added composites.
In this paper, an effort has been made to investigate the incorporation of carbon nanotubes in structural composites in order to improve damage characteristics, such as delamination. The nanocomposite material is introduced in the damage-prone regions of complex aerospace stiffener sections; the methodology proposed is an alternative to traditional approaches used to suppress delamination in composites, such as the use of metallic fittings. Numerical simulations are conducted using a multiscale modeling framework. The effective properties of the nancomposites are computed using a micromechanics-based approach and the results are compared with those obtained using a Kalman filter algorithm. The information is then used to analyze the structural response of a hat stringer using detailed finite element models. The stringer is analyzed under different loading conditions and varying levels of defects in the structure. Results obtained indicate that the use of nanocomposites improves the structural performance by improving the initial failure load. It is anticipated that the use of carbon nanotubes during the manufacturing process will help delay the onset of initial damage and damage growth, which can ultimately lead to a more robust structural design with enhanced performance against unique composite failure modes.
In this study, we investigated the physical, mechanical, and thermal properties of polypropylene/old corrugated container fibers and polypropylene/poplar fiber composites, which were treated with 1, 2, 3, and 4 wt% of hexamethylenediisocyanate coupling agent. Compounding was conducted by a counter-rotating twin-screw extruder, and samples for measurements of tensile, flexural, and impact properties were prepared by an injection molding machine. Thermal properties of composite samples were studied by thermogravimetric analysis and differential scanning calorimetry techniques. Thermal stability and crystallinity content of the prepared composites were determined, as well. The obtained results showed that the addition of coupling agent increased the thermal properties of the composites. Mechanical resulting indicated that by the addition of coupling agent, there was improvement in the tensile and flexural properties but there was declination in impact properties. Scanning electron micrographs taken from failed surfaces of the composite samples showed that the addition of coupling agents resulted in the improvement of bonding between wood fibers and polymer matrix at their interface.
This paper deals with the evaluation of water absorption properties of natural fibre composites consisting of bamboo fibre as reinforcement, epoxy as matrix and cenosphere as particulate filler at different environmental conditions. Hand lay-up technique is used to fabricate the composites with varying number of layers of bamboo fibre and cenosphere filler content. Water absorption kinetics of the composites is presented in this paper. It is observed that the rate of water absorption depends on the fibre content as well as filler content. Addition of filler in the layered bamboo–epoxy composite decreases the moisture absorption capacity and maximum reduction is observed to be 21% and 32% for distilled and sea water conditions, respectively, in seven-layered composite with 3.0 wt% filler.
Studies aimed at improving the tensile, flexural, impact, thermal, and physical characteristics of wood–plastic composites composed of Paulownia wood flour derived from 36-month-old trees blended with polypropylene were conducted. Composites of 25% and 40% w/w of Paulownia wood were produced by twin-screw compounding and injection molding. Composites containing 0–10% by weight of maleated polypropylene were evaluated and an optimum maleated polypropylene concentration determined, i.e., 5%. The particle size distribution of Paulownia wood filler is shown to have an effect on the tensile and flexural properties of the composites. Novel combination composites of dried distiller’s grain with solubles mixed with Paulownia wood (up to 40% w/w) were produced and their properties evaluated. Depending on the composite tested, soaking composites for 872 h alters mechanical properties and causes weight gain.
Curved section is regarded as the weak point of composite structures because of the delamination caused by the stress concentration. In the present work, L-shaped specimens made of randomly oriented short fiber-reinforced polypropylene were prepared to investigate the effect of the radius of the curved section of composite structures on the strength and the damage modes. The results of tensile tests and finite element analysis indicated that the radius greatly affects on the stress distribution and the damage modes, and showed good agreement with former researches using different composites. The strengths of the materials were extrapolated from the results of tensile tests and finite element analysis in this research. Finally, allowable radii of the curved section of the composite structures of two kinds of materials were given respectively.
Compression resin transfer molding (CRTM) is an effective process for the manufacturing of composite parts with large size and high fiber content. The analysis of the resin flow and stress distributions can only be performed by directly solving the coupled flow/deformation equations, but it is difficult to handle the complicated preform deformation models and geometry models; therefore, the simulation precision and application range are extremely limited. In this paper, an alternative approach is introduced to overcome the above problems, in which the preform deformation and the accompanying resin release during the secondary compaction phase are calculated in an additional element associated with each unit of the discretized model geometry instead of solving the coupled governing equations directly, so the complex compaction models can be adopted. Three simulation examples are presented to demonstrate the accuracy and capability of the above numerical approach on velocity-controlled, force-controlled 3D CRTM processes.
This is the second paper in a two-part study into the numerical simulation of the light resin transfer moulding (LRTM) process. It focuses on the development of empirically derived models for the permeability and compaction behaviour of Unifilo during light resin transfer moulding. A detailed review of relevant literature allowed identification of important material parameters, and appropriate testing procedures were devised accordingly. Previously published approaches were used to construct light resin transfer moulding specific permeability and compaction models. A material response for each stage of the process was quantified and then inputted into the light resin transfer moulding simulation developed in the Part I of this study. Results were verified using data from an empirical testbed, and the completed light resin transfer moulding model was then applied to a 6-kW wind turbine blade case study to evaluate different infusion strategies and minimise fill time. Finally, it was used to compare the light resin transfer moulding, resin transfer moulding and liquid resin infusion processes for the manufacture of this part.
The first part of this two-part study introduces an approach for a numerical model of the composite manufacturing method light resin transfer moulding. Discussion of process physics and relevant literature is used to develop a coupled finite element and infusion software simulation of both the structural and flow elements of the method, with the aim of producing an accurate and comprehensive model. This theoretical overview of the model acts as a precursor to the final part of the research where results are presented and verified and a wind energy case-study application will be demonstrated.
Sheet molding compound compression molding is a complicated manufacturing process. The main goal of the present research is to determine the required molding axial compression stress of the sheet molding compound in different conditions, using minimum experimental data. In the present research, the effective process parameters on molding forces such as the initial sheet molding compound temperature, the axial punch velocity, and the temperature of the mold surface are studied. It is shown that considering the charge under isothermal condition, especially in the filling stage is not a reasonable assumption. Thus, the applied rheological model of sheet molding compound flow is modified by accounting the thermal variations during the filling stage. The power law model is implemented to propose a novel model for prediction of the hydrodynamic friction as the dominant friction of the sheet molding compound compression molding process. Finally, a model has been developed to predict the molding axial compression stress under non-isothermal conditions. The proposed model is simple and general and does not need any extra experimental parameters. The results obtained by the model are in a very good agreement with the available experimental data.
The purpose of this paper is to discuss the role of multiwalled carbon nanotube in the swelling of polyacrylamide–multiwalled carbon nanotube composites. Swelling experiments were performed in water at various temperatures by real-time monitoring of the decrease in pyranine (Py) and emission light intensity (I em). The Stern–Volmer equation is modified for low-quenching efficiencies to interpret the behavior of pyranine intensity during the swelling of polyacrylamide–multiwalled carbon nanotube composites. The Li–Tanaka equation was used to determine the swelling time constants, , and cooperative diffusion coefficients, D, from fluorescence intensity, weight, and volume variations of the composite at various temperatures. It was observed that when decreased, naturally D increased by increasing temperatures.
The effect of the 0°-tow waviness on axial stiffness of cross-ply non-crimp fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90°-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90°-layer material.
Poly(ether–ester)/cerium oxide (CeO2) composites with CeO2 nanoparticles of 0, 1, 2, 3, 4, and 5 wt% were prepared from dimethyl terephthalate, 1,4-butanediol, polytetramethylene glycol, and CeO2 nanoparticles by traditional melt polymerization. The Fourier transform infrared, scanning electron microscopy, thermal gravimetric analysis, tensile strength, thermal stability, aging resistance, ultraviolet resistance, and low-temperature elastic recovery of these composites were characterized. The results indicated that introduction of CeO2 nanoparticles into poly(ether–ester) can enhance the mechanical, thermal, low-temperature elastic recovery properties and ultraviolet resistance of traditional poly(ether–ester). In particular, the incorporation of 2 wt% CeO2 nanoparticles endowed poly(ether–ester) with the best performance in mechanical and low-temperature elastic recovery properties.
The compression behaviors of 2D plain woven basalt/vinyl ester resin composites along the thickness direction under high strain rates have been investigated experimentally and by use of finite element analyses. The compression stress–strain curves, compressive damage, and rate sensitivity of the compressive behaviors was obtained experimentally. The dynamic responses including the compression stress–strain curves, compression damages, and energy absorptions of the plain woven composite samples were predicted based on finite element analyses at the microstructure level. From the finite element analyses results, it was concluded that the plain woven fabric structure and the rate dependent behaviors of the matrix were the key factors which affect the strain rate sensitivity of the compressive properties. The plain woven fabric structure distortion, instability of woven architecture, and matrix crack were the main failure modes of the plain woven composites under high strain rate compression. The compressive behaviors of plain woven composite could be improved with better design of the woven fabric structures and superior matrix properties.
In this study, the shear-lag model considering the micro-structure "interphase" and the two separate micro-damages, "interphase" debonding and matrix damage, in single fiber composite is developed firstly. So the more actual stress distribution on the fiber fragmentations during the process of stress transferring in single fiber composite is obtained. Then based on the present shear-lag model, the Monte-Carlo simulation for the process of the single-fiber fragmentation is established to predict the number of fiber fragmentation during the process of the test. The predicted result of the simulation is in accordance with the result of the single-fiber fragmentation test. At last, the factors including the statistical parameter of fiber strength distribution, the properties of the matrix and the state of the "interphase" in the single fiber composite, which affect the process of single-fiber fragmentation are analyzed.
Thermoplastic vulcanizates (TPVs) based on high impact polystyrene (HIPS)/high vinyl polybutadiene rubber (HVPBR) composites were prepared by dynamic vulcanization, and then compatibilized by styrene–butadiene–styrene (SBS) block copolymer. The effects of SBS compatibilizer on mechanical properties, Mullins effect, morphological and dynamic mechanical properties of the TPVs were investigated systematically. Experimental results indicated that SBS had an excellent compatibilization effect on the dynamically vulcanized HIPS/HVPBR composites. Compared with those of HIPS/HVPBR composite, the tensile strength, elongation at break and tearing strength of HIPS/HVPBR composite with 12 phr SBS incorporation were improved by about 163%, 312% and 67%, respectively. Mullins effect results showed that the compatibilized HIPS/HVPBR TPVs had relatively lower residual deformation and internal friction loss than those of HIPS/HVPBR composites, indicating the improvement of elastic reversibility. Morphology studies showed that the interface interaction of the TPVs was enhanced and the particle sizes of the dispersed phase were decreased with the incorporation of SBS compatibilizer. Dynamic mechanical analysis studies showed that the Tg s of HIPS and HVPBR phases were slightly shifted toward low temperature with the incorporation of SBS, which indicates the significant improvement of the compatibility.
Low-velocity impact tests have been conducted on sandwich beams and panels based on [0°, 90°] glass fibre-reinforced epoxy skins with an aluminium honeycomb core. The sandwich beams were placed on simple supports positioned at different separations to investigate the effect of target size on their impact response. Two thicknesses (13 and 26 mm) of honeycomb core were investigated. Following impact, damage within the beams was assessed by sectioning the samples and observing them under a low-power microscope. An energy-balance model was used to predict the maximum impact force for subsequent comparison with the experimental results. The energy-balance model was used to partition the energy absorbed during the impact event, giving an understanding of the energy absorption process. Finally, a limited number of tests have been conducted on square sandwich panels in order to investigate the effect of impact loading on their indentation behaviour. An examination of the cross-sections of impacted samples highlighted regions of core buckling and local plastic folding. At higher energies, damage in the form of localized fibre fracture was observed in the top skin close to the point of impact. The energy-balance model predicted the elastic response of the sandwich beams with reasonable success. The accuracy of the model decreased as damage became more extensive in the beams. It has been shown that the level of permanent indentation in both the beams and the square panels collapsed onto a single curve when the data are plotted against maximum impact force.
Repair of a cracked aircraft structure by an adhesively bonded composite patch has gained lot of importance in extending the fatigue life as well as improving the structural integrity of it. In the present work, an experimental study is carried out using digital image correlation (DIC) technique to analyze the behavior of single and double-sided adhesively bonded patch repair of an inclined center cracked aluminium panel subjected to uniaxial tensile loading. Further, the shear strain distribution in the adhesive layer is also estimated using the DIC technique. Shear strain concentration at the overlap edge in the adhesive layer is very high leading to patch debonding. Further, optimum patch dimension and patch thickness for the given cracked panel are arrived using a genetic algorithm-based optimization technique in conjunction with finite element analysis (FEA). With the optimum patch configuration, a 3-D FEA is further carried out and the obtained results are compared with the experimental prediction from DIC. The DIC prediction correlates with FEA contours on overall basis.
Graphene has drawn a great attention in the recent research innovations mainly due to its structural geometry, which is composed of one-atom thick planar sheet of hexagonally arrayed sp2 carbon atoms. Development of nanocomposites utilising graphene as the nanofiller offer desired properties to the added polymer matrix. Furthermore, incorporation of functional groups such as hydroxyl, epoxy, carboxyl, etc. on the basal plane of graphene enhances the interaction with the polymer matrices. Better interaction between the nanofiller and the polymer leads to exfoliation of the nanofiller in the matrices, which indeed significantly improves the physical, mechanical, thermal, electrical, electronic properties, etc., of the polymer. The review article explores the recent research findings on the development of polymeric nanocomposites utilising pure and functionalised graphene. The article focuses on the method of synthesis of graphene and functionalised graphene, followed by their characterisation methods and inferences. It also summarises the routes for the preparation of graphene and modified graphene-based polymer nanocomposites. The work highlights the enhancement of properties observed due to the addition of graphene and modified graphene to the polymer matrices. Several surface modifications done on GNS in order to achieve better dispersion of the same in the polymer matrix has been discussed. The review article portrays the recent research reports on graphene and modified graphene-based polymer nanocomposites. Techniques such as cryomilling, latex technology and lyophilisation as applied to polymer nanocomposites have been reviewed. Also, each of the literatures has been reviewed under the synthesis of filler and the preparation of the polymer nanocomposite separately which would serve as a guidance for future research. Literatures in which different carbon nanofillers have been compared to find the optimum filler has also been discussed.
External torque on circular composite shafts produces linearly decreasing shear stresses along radial direction. The inner layers never stressed as much as outmost layer. Accommodating fiber stiffness of each layer based on these linearly decreasing stresses may be advantageous. To reduce the cost of carbon fiber-reinforced composite drive shaft, inner layers of shaft can be reinforced by hybrid fiber systems with less stiffness. To achieve that, while the top layer is still reinforced with carbon fiber, inner layers can be reinforced with the mixture of glass and carbon fiber. Without changing the fiber volume fractions, replacement of some carbon fiber with glass fiber will reduce the overall stiffness of fiber system. Mixture ratio or hybrid ratio can be calculated using linearly decreasing stress levels and the rule of mixture. These hybrid composite shafts can be manufactured by filament winding technique. During filament winding, composite shafts are wound layer by layer and filament type can be changed between the layers. The proper mixing ratio can be achieved by arranging the fiber count in each filament bundle. The relation between geometrical parameters and hybrid fiber volume fractions of composite shaft was derived. Finite element analysis on carbon fiber and functionally hybridized glass/carbon fiber shafts with same geometry was conducted. Stress, strain, and moment behavior of both shafts were compared. The possible advantages and disadvantages of hybridization were discussed.
Natural fibre-reinforced polymer composites are seen as a possible substitute to synthetic fibre-based composites to face the environmental issues related to non-biodegradable nature of synthetic fibres. Due to their high specific strength and modulus, natural fibre-reinforced polymer composites are receiving widespread attention. In the present research initiative, natural fibre-reinforced thermoplastic composites have been developed with microwave curing technique. Two types of natural fibres namely sisal and grewia optiva, and two types of thermoplastic polymers (polypropylene and ethylene vinyl acetate) were used for fabrication of composites. Microwave wattage and exposure time were optimized for successful curing of thermoplastic composites. Results of tensile, flexural and impact strength of developed composites showed improvement in the properties as compared to neat polymers. The results suggest that microwave energy provides a feasible, environmental friendly option for curing of natural fibre-based thermoplastic composites.
In this research work, copper wires with 0.0564 mm, 0.0502 mm, and 0.0447 mm diameters were selected as a conductive filler of core material for producing various resultant count of copper core yarn with cotton fibers and polyester fibers as sheath material. The copper core yarns with a resultant count of 118 Tex, 98 Tex, and 84 Tex were produced by G5/1 ring spinning machine with the core attachment device. From the produced copper core yarn different types of fabrics were produced by using a weaving machine. In order to improve the electromagnetic shielding effectiveness of copper core yarn woven fabrics, nano silver finishing was given. The copper core fabrics were treated by nano silver particles with various levels of nano silver concentration, ethanol, time, and copper wire diameter using Taguchi design experiments. The morphology structure, bonding nature, and size of silver nanoparticle treated copper core cotton and polyester fabrics were studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy analyzer and X-ray diffraction. The effect of antibacterial properties of silver nano treated copper core cotton and polyester fabrics were also analyzed. X-ray diffraction and Raman spectroscopic studies have confirmed the crystalline structure of silver nanoparticle over surface of copper core cotton and polyester fabrics. Scanning electron microscopic and energy-dispersive X-ray spectroscopic studies revealed that the silver nanoparticles were formed and dispersed with spherical shape of about 30 to 50 nm. On increasing the nano silver concentration an increase in nano silver deposition and electromagnetic shielding has been observed in 500–12,000 MHz frequency range. The electromagnetic shielding effectiveness of nano silver finished fabrics were improved by 20–55% to that of the untreated copper core yarn fabrics.
Selective laser sintering was used for producing uniformly porous and graded porous polyamide structures. The porous structures were infiltrated with epoxy to produce composites. The porous and composite specimens were physically and mechanically characterized. Within the capabilities of the selective laser sintering machine and the materials used, porosities in the range 5–29% could be obtained in a controlled, repeatable manner. The ultimate tensile strength of the produced uniformly porous polyamide structures ranged from 20 MPa (for 29% porosity) to 44 MPa (for 5% porosity). The graded porous structures exhibited continuously changing porosity grades. As the number of grade increments rose, the grade profile fit closely with the design grade profile. The grades need to be constructed at porosities 9% or more for clear grade variation. Five percent porosity remained in all epoxy-polyamide composites after infiltration of the polyamide preforms with epoxy resin. Improvement in strength with epoxy infiltration was observed for preform porosities above 9%. The composite strength varied from 37 MPa to 44 MPa with respect to epoxy resin volume fraction. The maximum strength of the composites was found to be the same as the strength of the sintered polyamide powder (44 MPa).
The specific properties of fibre reinforced polymers give them a lot of advantages over traditional materials but the long life of polymeric composites poses serious environmental threats raising sustainability concerns. The other issue of importance concerning the innovators and environmentalists in the mass usage of this material is its health impacts on human beings. This paper thus attempts to highlight and surface out the issues related to fibre reinforced polymers’ sustainability and their health impacts on human beings, by reviewing past studies on the subject, to examine critically the extensive body of published data, prior observations and ideas on the subject in order to identify and analyse those features that are intrinsic and unique to fibre reinforced polymers. This would thus serve as a conceptual model for future research on fibre reinforced polymer composites sustainability and health concerns.
During the preforming stage of woven reinforcement, in the first step of the resin transfer moulding process, the phenomenon of friction occurring at the tool–reinforcement interfaces and the reinforcement–reinforcement interfaces is one of the key parameters of the forming process. This behaviour must be correctly taken into account when modelling the process and a better understanding of the contact and friction phenomena occurring during the woven fabric preforming process is necessary for realistic simulation of the preforming process. Although some existing studies concerning friction of reinforcement have been published, the complex frictional behaviour of fabrics is still not completely clear. The experimental characterization of the frictional behaviour of a specific carbon woven reinforcement (G1151) used for aeronautical applications is the aim of this article and three interfaces have been studied (G1151/G1151, G1151/Plexiglas, G1151/aluminium). The Coulomb coefficients of friction occurring during contact between two layers of fabric and between the fabric and other materials have been determined. The effect of the variation of normal pressure and temperature on the frictional behaviour of this reinforcement has also been analysed. Comparisons between several frictional models, described in the literature, are also conducted in associated with these experimental results. This study highlights a significant tribological anisotropy of the G1151 reinforcement and a dependence of the frictional characteristics on the applied pressure and the temperature.
Composite is prepared by filling acrylonitrile–butadiene–styrene copolymer with stainless steel fiber. Its physical properties and electromagnetic shielding effectiveness are tested. When the mass percent of stainless steel fiber is 15%, shielding effectiveness of composite is 21–59 dB in frequency band of 15 MHz to 3 GHz and cylindrical shell is made of it. Experiments under radiation of X-band high power microwave and ultra-wideband electromagnetic pulse are conducted in microwave anechoic chamber while magnetic fuzes connected with electrical fire head are placed at the center of cylindrical shell. Results show good agreement with test. Coupling effect is analyzed while shell has a hole or slot of millimeter level.
The demand for energy efficient, low weight structures has boosted the use of composite structures assembled using increased quantities of structural adhesives. Bonded structures may be subjected to severe working environments such as high temperature and moisture due to which the adhesive gets degraded over a period of time. This reduces the strength of a joint and leads to premature failure. Measurement of strains in the adhesive bondline at any point of time during service may be beneficial as an assessment can be made on the integrity of a joint and necessary preventive actions may be taken before failure. This paper presents an experimental approach of measuring peel and shear strains in the adhesive bondline of composite single-lap joints using digital image correlation. Different sets of composite adhesive joints with varied bond quality were prepared and subjected to tensile load during which digital images were taken and processed using digital image correlation software. The measured peel strain at the joint edge showed a rapid increase with the initiation of a crack till failure of the joint. The measured strains were used to compute the corresponding stresses assuming a plane strain condition and the results were compared with stresses predicted using theoretical models, namely linear and nonlinear adhesive beam models. A similar trend in stress distribution was observed. Further comparison of peel and shear strains also exhibited similar trend for both healthy and degraded joints. Maximum peel stress failure criterion was used to predict the failure load of a composite adhesive joint and a comparison was made between predicted and actual failure loads. The predicted failure loads from theoretical models were found to be higher than the actual failure load for all the joints.
Fiber-reinforced composites play an important role in enabling the industrial composites industry including automotive, pressure vessels etc. to meet ever increasingly aggressive fuel efficiency requirements. Modeling and analysis is often employed in composite development as a tool to achieve faster and more cost-effective solutions to both product and process designs. Thermal conductivity measurements play a critical role in enhancing the fidelity of these models, especially in scenarios involving non-isothermal processing. Accurate characterizations of anisotropic thermal conductivities that are typical of dry fibrous preforms are especially challenging because of their highly porous and complex structures. In this article, an inverse approach is developed to estimate the anisotropic thermal conductivities of a dry preform made of biaxial [0°/90°] stitched glass-fiber mats based on the measurements of thermal conductivities of cured epoxy-matrix composites. This method is found to not only yield more accurate results than direct preform measurements but also provide the capability to characterize preforms in multiple directions rather than only through-thickness direction. The estimated thermal conductivities are used in preform heating simulation that is validated against experiments.
Bio-based fibers (wood and bamboo)-filled high-density polyethylene composites were prepared in a twin-screw extruder using two types of coupling agents: maleated polyethylene and glycidyl methacrylate-grafted polyethylene. The effect of bio-fibers used as filler on the mechanical properties of composites was studied. It was observed that mechanical properties such as tensile and flexural strengths of the composites with coupling agent increased with increasing filler loadings. Tensile strength and flexural strength exhibited improvement up to 66% and 90%, respectively, over virgin high-density polyethylene. The maximum enhancement in the properties was observed with wood pulp when compared with wood- or bamboo flour-filled composites. Effect of coupling agents on the performance of composites was evaluated at 30% filler loading with wood flour as the filler. The study suggested that glycidyl methacrylate-grafted polyethylene exhibited better tensile and flexural properties as compared with maleated polyethylene. Impact strength of the composites prepared with coupling agent was found to be more than uncoupled composites. Among the fiber type, the impact strength of wood-fiber-filled composites was superior than that of bamboo flour-filled composites. Moisture absorption study indicated that even at 40% filler loading, moisture gain by the wood fiber- and bamboo flour-filled composites was merely 1.55% and 2.60% after 600 h of water immersion test, which suggests encapsulation of filler material by the polymer matrix.
This study deals with the preparation and characterization of thermoplastic composites using polypropylene, high-density polyethylene and polylactic acid matrices and including whole chicken feathers as reinforcement. The behaviour of the composites was determined in terms of physical and mechanical properties, which were related to the fibre–matrix compatibility analysed by Fourier transform infrared spectroscopy and scanning electron microscopy. The results showed that the addition of chicken feathers into the thermoplastic matrices results in a slight increase in the stiffness when small amounts of chicken feathers (5–10% vol/vol) were incorporated into the composites. Tensile strength at maximum load, elongation at break and toughness properties decreased when the chicken feather concentration was increased. Results for chicken feather–polypropylene composites were analogous to chicken feather–high-density polyethylene and chicken feather–polylactic acid composites. The Fourier transform infrared spectroscopic study and the scanning electron micrographs suggest that the insufficient compatibility of chicken feather and polymer matrices is the main reason for the decrease in tensile properties.
Generally, in functionally graded material structures, a ceramic material as reinforcing part is distributed in a metallic matrix. These structures benefit the merits of both their metallic and ceramic parts such as the mechanical strength and thermal resistance. An important aspect in the function and study of functionally graded material structures is the effect of temperature. Usually, the resulted thermal stresses are so high that partial failure of structure is inevitable. In this paper, by using of different exact and approximate mathematical models and solution techniques, the yielding of a functionally graded material cylindrical pressure vessel is studied. Different solution techniques such as closed form solution, FE solution of ABAQUS and semi-analytical solution of variable material properties are used. Based on the von Mises and Tresca’s yield criteria, the shape of plastic zone are obtained and compared. The influences of different structural parameters as well as the effect of failure criterion upon the results are studied. Accordingly, some justifications are made regarding the selection of different material parameters or failure models.
External confinement of concrete columns by means of carbon fiber reinforced polymer (CFRP) sheets can be considered as an efficient technique for their structural strengthening. An experimental research program including 18 circular short column specimens were tested under axial compression load, to investigate the gain strength of reinforced concrete (RC) columns confined with CFRP sheets. The parameters studied were both the volume and configurations of CFRP sheets, the size of cross-section, the percentage of main reinforcement, and the volume of internal stirrups. On the basis of the obtained results, mathematical models (Egyptian code and American Concrete Institute code) proposed to predict the axial compressive strength of non-slender RC column strengthened by means of CFRP sheets are evaluated. These codes showed an underestimation in predicting the axial compressive strength of RC strengthened columns. This, from the authors' point of view, is attributed mainly to the fact that the proposed models overlooked the amount of internal stirrups when calculating the strength of strengthened columns. Therefore, modifications in the studied models were considered. The modifications take the effective lateral confining pressure due to presence of internal steel stirrups into account. The modified codes showed an acceptable approach to the experimental results.
In order to study the interlayer bond property of airport double-layer pavement, the cement concrete cube splitting tensile test and double-layer beam test were conducted. The bond mechanism of fiber grid and airport double-layer pavement was analyzed. The deflection and strain of upper and lower beams of double-layer beam were measured. The splitting tensile strength of new and old cement concrete cubes, the strain ratio, deflection difference and coupling coefficient of the double-layer beam were taken as criteria for the interlayer bond property of airport double-layer pavement. The result demonstrates that the splitting tensile strength is maximal when the basalt fiber grid with dimension of 5 mm was adopted, the old cement concrete and fiber grid surface treatment have great influence on splitting tensile strength, but the maximum grain size of coarse aggregate have few influence on it. The friction between double-layer beam reduces the strains of the bottom of the lower and upper beams by 44.44–98.46%. The fiber grid and old cement concrete surface treatment not only increase the coupling coefficient with the range of 4.60–15.73% but also decrease the deflection difference, the number of which ranges from 0.004 mm to 0.016 mm, thus improve the integral force performance and deformation ability of double-layer beams.
This paper presents a review of the state-of-the-art concerning composite hull structures subjected to wave-induced slamming load. Slamming is one of the critical load components that can influence the behavior of marine structures and can result in micro- or macro-level damage. Emphasis of the review is placed on fundamental issues with regard to the interaction between composite hulls and slamming events, including material characteristics, structural configurations, hydroelasticity, and the nature of wave-generated impact load. Practical aspects such as design implementation are also discussed. Recent developments in predictive approaches (e.g. multi-scale modeling) and hybrid testing methodologies are elaborated. Current research needs are identified and technical topics requiring further study are suggested.
The stress–strain response of an offshore pipe riser subjected to combined internal pressure, tension and bending is studied. Finite element analysis was used to study three conditions of pipe riser – uncorroded, corroded and corroded and repaired with designated laminate orientation of carbon/epoxy or E-glass/epoxy fibre-reinforced composite. The behaviour of the pipe riser (grade API 5L X60 steel) was studied using Ramberg–Osgood model. Two composites laminate systems, a pre-cured prepreg (grade AS4 3501-6 carbon/epoxy) and a wet-layup filament-wounded composite (grade Gevetex LY556/HT917/DY063 E-glass/epoxy), were characterised. Design conditions were determined via a limit analysis known as the double-elastic slope method. The results showed that under combined hoop, tensile and bending loads, the riser tends to approach failure at a much lower strain compared with each of these loads being applied individually. The limiting design factor of the composite repair system was due to excessive tensile strain experienced in a bent riser while the compressive stress caused by reversing the bending load occurred well within the linear-elastic region. With respect to the types of composite repair system, carbon fibre displayed a much better strength rehabilitation over glass fibre. In the aspect of laminate orientation, off-axis plies [90°/ ± 30°]s and [90°/ ± 45°/0°]s laminates were found capable of restoring the strength of the corroded riser and provide superior reinforcement in both hoop and axial directions.
Contemporary world is facing numerous bomb explosion attacks on public and civil buildings causing huge loss of property and human lives. As a consequence, the society needs more safety and protection for the existing structures against blast loads. Among the various strategies, one effective way to enhance the blast resistance of reinforced concrete and masonry structures is through retrofitting using various types and forms of fibrous and composite materials. This work presents an up to date review of available literature and publications on the fibrous and composite materials utilized for blast protection of structural elements and highlights the lacking areas where further research is required.
The application area of wood–plastic composites is growing rapidly, which is reflected in massive research activity. In the present study, comparative analysis of cellulosic fillers of different macro- and micro-sized particles in reinforcing polypropylene-based wood–plastic composites is performed. The mechanical properties of composites manufactured with three different types of spruce wood flour (coarse, 20-mesh and Arbocel C320) particles are compared. The study shows that composites with 20-mesh wood flour have better tensile, flexural and impact properties. The possibility of using a microfibrillated cellulose as the reinforcing filler in wood–plastic composite is also studied. The combination of microfibrillated cellulose (10 wt%) with coarse wood flour resulted in improvement in almost all mechanical parameters of the wood–plastic composite. In addition, it is shown that a wood–plastic composite manufactured using pure cellulose fibres has the weakest mechanical properties. The water absorption and thickness swelling of the composite, as well as the durability of the composites exposed to three cycles of water immersion, freezing and thawing are observed. The microstructure of the composites is examined by scanning electron microscope. The superior properties of microfibrillated cellulose-containing wood–plastic composites are described for the first time.
In the present work, the influence of organo-modified montmorillonite loading on the solid particle erosion of carbon fabric-reinforced epoxy composites was investigated. The development of a multi-component composite system consisting of thermoset epoxy resin reinforced with carbon fabric and organo-modified montmorillonite nanoparticles, the erosion behaviour was studied for various erodent size, impact velocity, loading of organo-modified montmorillonite and for different impingement angles. For this purpose, erosion test rig and the design of experiments approach utilizing Taguchi’s orthogonal arrays were used. Of all the above factors, the erodent size has the greatest effect on the reduction in the erosion wear rate. The erosion wear rate variation was found to be in the range of 1.33 x 10–4–48.02 x 10–4 g/g. The lowest erosion wear rate was found in the case of unfilled carbon fabric-reinforced epoxy composite under erodent size of 600 µm, impact velocity of 30 m/s and erodent time of 1 min. Further, the results showed strong dependence of the erosive wear on the erodent size. The organo-modified montmorillonite filled carbon fabric-reinforced epoxy composite showed brittle erosion behaviour with maximum weight loss at 75° impingement angle. Analysis of variance was performed on the measured data and signal to noise ratios were found. The morphology of eroded surfaces was examined using scanning electron microscopy and damage mechanisms were discussed.
Twelve identical concrete prisms were strengthened with Carbon Fibre-Reinforced Polymer (CFRP) laminate strips on two opposite faces and the laminates were anchored using the newly developed CFRP -anchor. Prisms were tested in tension to investigate the effectiveness of the anchor to possibly delay delamination and/or to prevent the complete separation of the laminate from the prism. The salient feature of the anchor is its wide head to resist high interfacial shear stresses and its shanks that were inserted in predrilled holes to provide mechanical anchorage and to resist pull-out. The anchor doubled the tensile load-carrying capacity, effectively delayed delamination and prevented the CFRP laminate from full separation. Furthermore, the strengthened prisms experienced noticeable deformation.
In this paper, interfacial adhesion of epoxy resin/ultra-high molecular weight polyethylene fibre composites by polymerization grafting of glycidyl methacrylate onto fibre surface was investigated. To optimize the grafting process, experiment design method was applied using the time and monomer concentration as grafting variables. In order to confirm the formation of glycidyl methacrylate bonds onto the polyethylene chains, attenuated total reflectance-infra red test was performed. Besides, Pull-out test was utilized to measure the interfacial shear strength of fibres with the matrix for both modified and unmodified ultra-high molecular weight polyethylene fibre composites. Tensile test was carried out. Three amounts, 11%, 25%, and 40%, of polymerized glycidyl methacrylate grafted onto the fibre surface was obtained. The grafting percent of glycidyl methacrylate onto the fibre showed enhancement by increasing the amount of glycidyl methacrylate monomer and the reaction time which was bigger by monomer increment. The interfacial shear strength of 11%, 25%, and 40% glycidyl methacrylate grafted fibres with epoxy matrix showed 126%, 195%, and 220% enhancements, respectively, in comparison with untreated fibre. The tensile strength of 11% glycidyl methacrylate grafted polyethylene fibre-epoxy composite showed about 10% enhancement; however, the tensile strengths of 25% and 40% glycidyl methacrylate grated polyethylene fibre-epoxy composites showed decrement. Toughness results showed improvement for 11% glycidyl methacrylate grafted composite due to appearing of energy absorbing mechanisms while fracturing.
In this work, the normal (0°) and oblique (30° and 45°) ballistic impact behavior of glass fiber-reinforced aluminum laminates (fiber metal laminate, FMLs) impacted by a rigid cylindrical projectile (with a flat nose) has been investigated from an experimental point of view. The ballistic impact tests were conducted on the FMLs using a one-stage gas gun at different impact angels, i.e. 0°, 30° and 45°. A high-speed camera was used to capture and record the experimental images and data during the impacting process. Different failure patterns were observed in the FMLs under oblique and normal impact, with the differences concentrated on the initial crack (in the back surface) and plugging damage (in both the front and back surface). The angular change in direction of the projectile during perforation was only observed during oblique impact tests while the maximum value of the angular change was observed when the impact velocity was close to its ballistic limit velocity. In addition, the angular change decreases with increasing impact velocity and is almost constant when the value of vi /v50 reaches a critical value. It can also be observed from the impact test results (both normal and oblique impacts) that FMLs exhibited the lowest ballistic limit velocity when the impact angle was close to 30°. In particular, normal impact shows a higher ballistic limit velocity than that of oblique impact while the ballistic limit velocity at impact angle 45° is slightly higher than that at 30°.
The objective of this study is to investigate the performance of bamboo fabric–poly(lactic acid) composites manufactured by compression moulding. The effects of compression moulding parameters on the mechanical properties of the bamboo fabric–poly(lactic acid) composite sheets were evaluated. Optimum compression moulding parameters to achieve the "best" mechanical properties of the composites was determined using the Taguchi method of experimental design. A rheology test was also conducted to measure the viscosity of the poly(lactic acid) at different temperatures. The processing parameters were found to affect the consolidation and quality of the composites. It appeared that the impact strength of the bamboo fabric–poly(lactic acid) composites in warp direction was enhanced by 240% in comparison to pure poly(lactic acid), whereas the improvements of tensile and flexural properties were lower than expected. When compared with theoretical predictions, the measured values of warp and weft tensile modulus show good agreement than those predicted by rules of mixture. On the other hand, the experimental values of tensile strength were lower than theoretical values due to poor fibre matrix adhesion.
Mixed acid and rare-earth (RE) solution were used as the surface modifiers to functionalize multi-walled carbon nanotubes (CNTs). Fourier transform infrared spectra reveal that the carboxylic groups were induced on the surface of acid-functionalized and RE-functionalized CNTs, and the presence of C–N bond suggests that the ethylenediamine tetraacetic acid molecules were successfully grafted on the surface of RE-functionalized CNTs. Raman analysis indicates that acid-treatment and RE-treatment did not significantly change the structure of pristine CNTs. X-ray photoelectron spectroscopy analysis shows that both acid-treatment and RE-treatment improved the number of carboxylic groups on treated CNTs surfaces compared to pristine CNTs, and RE-treatment is superior to acid-treatment to improve the oxygen to carbon ratio on the CNTs surfaces. Transmission electron microscope and scanning electron microscope observations indicate that RE-functionalized CNTs have better dispersion in solvent and in polytetrafluoroethylene (PTFE) matrix than acid-functionalized CNTs, respectively. Thermal stability analysis and mechanical tests display that RE-functionalized CNTs/PTFE nanocomposite has the highest thermal stability and mechanical properties than acid-functionalized CNTs/PTFE nanocomposite and pristine CNTs/PTFE nanocomposite.
The years long in preparation World Wide Failure Exercise II has been completed and the final results and conclusions published. The overall purpose of the World Wide Failure Exercise II was to evaluate the failure criteria/failure theories to be used in the analysis of fiber composite materials. An in-depth consideration of the results from the failure exercise is laid out here. Many critical issues are examined and the status and significance of the World Wide Failure Exercise II is assessed. These results may be of interest and use to researchers and practitioners in the field of composite materials and structures.
In this study, the effect of compounding principles on the properties of Polymer Bonded Soft Magnetic Nanocomposites (PBSMNs) was discussed. The polymethylmethacrylate /Fe3O4 magnetic nanocomposites (Fe3O4: 30 wt%) were prepared by the in situ process based on the solution and spray drying method, as well as by the ex situ process based on the kneading machine. As reference, the process combining these two compounding principles was also carried out for the PBSMN preparation, named as in-between process. The morphology structures, thermal, mechanical and magnetic properties of the magnetic nanocomposites achieved with different compounding principles were characterized. The results show that compounding principles have significant influence on the properties of the magnetic polymer nanocomposites. In the end, their contributions to the power electronic applications were discussed as well.
Flexural fatigue behaviors were investigated experimentally for unidirectional glass fiber (U)/random glass fiber (R)/epoxy hybrid composite laminates. Three different hybrid composites, i.e. [0.5R/U/U]S, [U/0.5R/U]S and [U/U/0.5R]S were fabricated using hand lay-up technique with 37% total fiber volume fraction (VfT), unidirectional glass fiber relative volume fraction (VfU/VfT) = 0.8 and of 5.5 ± 0.2 mm thickness. Flexural fatigue tests were performed at zero mean stress. A 20% reduction of the flexural stiffness was taken as a failure criterion. The effects of layer stacking sequences on both initial stress–no. of cycles to failure relationships and the relative surface temperature increase of the mentioned composites were investigated. The specimen failure modes have been recorded and discussed. The S–N curves and fatigue safe workability areas for the fabricated hybrid composites have been constructed as design curves. Two-parameter Weibull distribution function was used to obtain the scatter in the experimental results and to construct the reliability graphs for the fabricated hybrid composites.
Biocomposites were prepared using epoxidized linseed oil and flax fibre reinforcements in different assemblies. Epoxidized linseed oil was cured by two different anhydrides to check how its thermomechanical properties can be influenced. As reinforcements, nonwoven mat, twill weave and quasi-unidirectional textile fabrics with two different yarn finenesses were used. Their reinforcing effect was determined using dynamic mechanical analysis in flexure. Dynamic mechanical analysis served to determine the glass transition temperature (Tg) also. Shape-memory properties were derived from quasi-unconstrained flexural tests performed near to the Tg of the epoxidized linseed oil and its biocomposites. Flax reinforcement reduced the Tg that was attributed to off-stoichiometry owing to chemical reaction between the hydroxyl groups of flax and anhydride hardener. The shape-memory parameters were moderate or low. They were affected by both textile content and type.
Poly(ethylene-co-vinyl acetate), acrylonitrile butadiene copolymer, and their blend (50/50 wt%) loaded with different concentrations of high-abrasion furnace were prepared. Mechanical, thermal, and electrical properties as well as the morphology and the swelling behavior have been investigated in view of filler loading. The tensile strength values increase with increasing high-abrasion furnace loading while the elongation at break and the swelling index decrease. Also, the thermal stability was improved. The addition of high-abrasion furnace in poly(ethylene-co-vinyl acetate)/acrylonitrile butadiene copolymer improves the interaction and the compatibility between the two polymers as shown by scanning electron microscope.The presence of acrylonitrile butadiene copolymer in the blend increases the thermal stability and the swelling resistance, whereas poly(ethylene-co-vinyl acetate) enhances the tensile strength values of the blends. The permittivity ' and the dielectric loss '' values indicate that an abrupt increase was noticed when the concentration of high-abrasion furnace reaches 10 phr for all investigated systems. This increase indicates the tendency of conductivity chain formation through the aggregation of high-abrasion furnace particles network. The percolation theory was applied to detect the percolation threshold for each composite. The effect of thermal aging on mechanical and electrical properties was also studied.
Polyether ether ketone (PEEK) is a commonly used engineering plastic but has poor friction and wear properties when compared to those of ultra-high-molecular-weight polyethylene (UHMWPE), whereas UHMWPE has good tribological properties but relatively weaker mechanical strengths. An optimum combination of these two materials is expected to have both sides’ goodness without adverse effects to a certain extent. Adding an optimum amount of PEEK powder filler into UHMWPE to form composite has shown better friction, wear and compressive strength properties. The mechanism of wear resistance improvement is found largely due to counterface transfer film but less because of the filler strengthening effect. Adding PEEK could improve the compressive strength of the composite due to high hardness of PEEK particles.
This paper reports a melt blend of poly(lactic acid)/liquid natural rubber with Cloisite C30B (C30B). The mechanical, thermal and morphological properties of poly(lactic acid)/liquid natural rubber and nanocomposites were investigated. Results indicate that Young’s modulus and flexural modulus increased with the addition of C30B to the poly(lactic acid)/liquid natural rubber blend. The elongation at break of poly(lactic acid)/liquid natural rubber increased significantly as compared to nanocomposite with 1% of C30B, i.e. from 37.3% to 62.4%. Nevertheless, the elongation at break and impact strength decreased gradually when nanoclay content increased above 3%, suggesting the addition of clay changed the strain response in the blend systems. The incorporation of nanoclay in the poly(lactic acid)/liquid natural rubber blends lowered the glass transition temperature values relative to poly(lactic acid). This behavior may be associated with more free volume available in the nanocomposite blend systems compared with pure poly(lactic acid). Morphological analyses by scanning electron microscope and transmission electron microscope revealed that different types of morphologies exist for poly(lactic acid)/liquid natural rubber and nanocomposites. This study indicates that poly(lactic acid)/liquid natural rubber-toughened nanocomposites with a higher modulus and that thermal stability could be produced.
This paper presents a multi-scale correlating model to simulate the elastic and failure behavior of two-dimensional tri-axial braided composites. Unlike the traditional information-passing multi-scale approaches, the present analytical model enables a two-way coupling of scales through a bottom-up homogenization procedure and a top-down decomposition procedure, based on the continuum mechanics and homogenization method. The main feature of this model is that it not only concurrently obtains the stress/strain fields in multiple scales but also allows the application of constituent-based failure criteria to reveal local failure mode, failure sequence and the resulting failure progression of the composites. Using the multi-scale correlating model, the stiffness and strength of a braided composite are predicted solely from its corresponding constituent properties and braid geometrical parameters, which can be easily obtained. The predicted failure events and the corresponding stiffness degradation are in good agreement with experimental data found in the literature. Parametric studies are also performed to examine the effect of various geometrical parameters such as braid angle, tow undulation and manufacturing-induced defects on the resulting mechanical properties. It is found that micro-structural imperfections play a role in the strength reduction, and the most detrimental factors are the defects of bias tow.
The post-fire integrity of pultruded phenolic/glass and polyester/glass floor gratings, of the type used offshore and elsewhere, was investigated. The aim was to determine whether glass/phenolic gratings may be safely walked on, post-fire, by offshore workers and fire-fighting teams. The load to be resisted was identified as equivalent to a running person carrying a load, the combined mass being 150 kg. The maximum resulting dynamic strains were determined by strain gauges on the undersides of the individual beam elements of gratings. This enabled target values of post-fire bending resistance to be identified. Individual beam elements from the gratings were exposed to heat fluxes of 12.5, 37.5 and 100 kW/m2 using a propane burner, for periods up to 16 min, after which the residual strength was measured. Phenolic gratings showed longer ignition times, with lower flame and smoke emission, as well as greater post-fire strength compared to polyester ones. At the lowest flux, 12.5 kW/m2, all gratings remained serviceable beyond 16 min. At higher heat fluxes, the phenolic gratings retained some post-fire strength, assisted by the formation of a carbonaceous char binding the fibres. However, this was somewhat below the target level. A study of the effect of testing speed indicated that fire-exposed gratings are not especially strain-rate sensitive.
In this study, a new biodegradable hybrid composite material is developed with natural Vetiveria zizanioides (vetiver), woven jute, and commercially available E-glass as reinforcing fibers and vinyl ester as the resin. Vetiver fibers are pretreated with distilled water and alkali followed by heat treatment. Nine composite specimens are prepared by varying the proportions of natural and glass fibers in each and maintaining the resin content as a constant. The specimens are tested for tensile, compressive, flexural, and impact strengths. The results revealed that the chemical treatment to the vetiver fiber shows a substantial improvement in the mechanical properties of hybrid composite material. Also, by proper selection of fiber proportions, glass fibers can be replaced by natural fibers without losing the mechanical properties.
The natural fiber-reinforced polymer composite materials offered extensive range of properties which are suitable for large number of engineering application. The natural fibers have been abundantly available in the world. It has unique properties compared to synthetic fiber and reduces the plastic usage. This article reports the extraction process of natural fibers, characterization of natural fibers, and preparation of natural fiber-reinforced composites. The mechanical properties such as tensile, flexural, impact, and dynamic properties as well as thermal and machinability properties of the composites with and without chemically treated fibers were reported. The water absorption capability of the composites and its effect on mechanical properties were also reported.
Snake grass fibers are subjected to various chemical surface modifications such as alkali, benzoyl peroxide, benzoyl chloride, potassium permanganate and stearic acid. These fibers are utilized to fabricate the longitudinal oriented fiber-reinforced composites at 40% weight fraction of fiber. The mechanical properties of treated fiber composites are found to be higher than those of raw ones. Potassium permanganate treated fiber composites has optimum mechanical properties than other chemicals treated snake grass fibers composites. The scanning electron microscopic images of the tensile and impact fractured composites containing treated and untreated fibers have been examined. The fiber pull-out from the specimen has been found low for the treated fibers compared to untreated fiber composites. The kinetics of water absorption of the composites studied at various time intervals and temperature reveals that the treated fiber-reinforced composites has less water uptake compared to untreated one.
Out-of-autoclave processable fiber/resin systems have been gaining much attention due to the elimination of needing a costly autoclave large enough to hold the part to be cured. For large composite structures this can pose a challenge. However, for these fiber/resin systems to replace conventional autoclave fiber/resin systems for use on aerospace structures, the damage tolerance capabilities need to meet (or exceed) those of current autoclave fiber/resin systems. In this experimental study, compression-after-impact strengths of two commercially available out-of-autoclave fiber/resin systems are compared to compression-after-impact strengths of a conventional autoclave fiber/resin system used as a baseline in this study. compression-after-impact testing was chosen since this is the most common method to assess laminates damage tolerance capabilities. Three different levels of impact severity were chosen and information on damage size and morphology are assessed along with compression-after-impact strength values. The results show the two out-of-autoclave fiber/resin systems examined in this study have similar damage tolerance characteristics to the autoclave fiber/resin system used in this study.
The mechanical and structural properties of novel melt processed poly-ethylene terephthalate (PET)-hemp fiber composites for engineering applications were investigated. First, four reinforcement formulations were compared with the PET modified with poly-epsilon-caprolactone: hemp, Clay/hemp, pyromellitic dianhydride/hemp and glycidyl methacrylate/hemp. Next, the effect of hemp fibers concentration as well as the effect of heat treatment was analyzed. A significant difference was observed in the mechanical and structural properties of the composites. Moreover, we observed a good fiber–matrix interface without the use of a coupling agent, particularly in the absence of additives. Our data suggest that a careful trade-off between the additives, the hemp fiber concentration and the desired engineering applications is key requirement for the applications of high melting polymers-reinforced with natural fibers.
Cellulose nanofibers have shown great potential to improve mechanical and physical properties in polymer-based composites. We aimed to extract the cellulose nanofibers from waste newspaper as a high-yield cellulosic source. First the newspaper was treated chemically and physically in order to extract individualized cellulose nanofibers from their cellulosic matrix. Then acid hydrolysis and mechanical treatments resulted in the cellulose nanofibers of diameter between 10 and 40 nm. The reinforcing effect of obtained cellulose nanofibers from waste newspaper was investigated by composing with a starch-based dispersion-type biodegradable resin CP-300, Miyoshi Oil & Fat Co. Ltd, Japan. Commercially available cellulose nanofiber-reinforced composites were used as comparison to newspaper cellulose nanofiber-reinforced composites. The tensile test results show significant enhancement in mechanical properties of reinforced composites for both composites. However, commercially available cellulose nanofiber-reinforced composites showed greater enhancement than newspaper cellulose nanofiber-reinforced composites.
This article is concerned with the reliable test method for measuring the tensile strength in the longitudinal direction of unidirectional carbon fiber-reinforced plastics. A filament-wound resin-impregnated carbon fiber strand (carbon fiber-reinforced plastics strand) was employed as the specimen. The most important improvement for reliable tests is that the bonding strength of the end tabs with carbon fiber-reinforced plastics strand should be higher than the tensile strength of CFRP strand. We improved the bonding strength by co-curing the carbon fiber-reinforced plastics strand with end tabs. The improved method was applied to two kinds of carbon fiber-reinforced plastics strands and the reliable tensile strengths were obtained.
Novel epoxidized hemp oil-based biocomposites containing jute fibre reinforcement were produced at the Centre of Excellence in Engineered Fibre Composites (CEEFC) owing to the need to develop new types of biobased materials. Mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), thermo-mechanical properties (glass transition temperature, storage modulus and crosslink density) and moisture-absorption properties (saturation moisture level and diffusion coefficient) were investigated and compared with samples containing commercially produced epoxidized soybean oil and a synthetic bisphenol A diglycidyl ether-based epoxy control, R246TX cured with a blend of triethylenetetramine and isophorone diamine. Scanning electron microscopy was also performed to investigate the fibre–matrix interface. Epoxidized hemp oil-based samples were found to have marginally superior mechanical, dynamic mechanical and similar water-absorption properties in comparison to samples made with epoxidized soybean oil bioresin; however, both sample types were limited to bioresin concentrations below 30%. Synthetic epoxy-based samples exhibited the highest mechanical, dynamic mechanical and lowest water-absorption properties of all investigated samples. This study has also determined that epoxidized hemp oil-based bioresins when applied to jute fibre-reinforced biocomposites can compete with commercially produced epoxidized soybean oil in biocomposite applications.
Construction sector is one of the largest markets for fibre reinforced polymers (FRPs) globally. FRP composites are used in a wide range of applications in construction ranging from rehabilitation of existing structures to the full-scale use for new projects because of the benefits they provide over conventional building materials. Such advantages include but not limited to lightness, high mechanical performance and possibility of production in any shape, ease of installation and lesser requirement for supporting structure, controlled anisotropy, high specific strength and specific stiffness. All these multifarious features of FRPs are knocking the doors for new avenues of myriad applications in the Construction Industry, but unfortunately polymeric composites are susceptible to heat and moisture when operating in changing environmental conditions dispelling the biggest myth of them being invincible. The heat response of FRPs is also a major issue of importance in dictating the fate of FRPs future acceptability and applicability. This paper thus attempts to review the specific areas of the current utilization trend of FRPs in the Construction Industry and draw their advantages to support the future applications in a variety of construction processes. It is also being attempted to juxtapose the applicability and the durability concerns of FRPs in a single literature for assessing the versatility and scope of FRPs, by shedding light on the past available studies on the related matter.
In this research, the mechanical properties and fracture behavior of composites based on recycled high-density polyethylene and recycled Tetrapack have been investigated. The matrix and filler were recovered from landfills, ground into flakes of ~1.6 cm2 size, washed and physically mixed before putting the mixture in a cast, introduced in an oven at 250°C, and pressed applying 1 Metric Ton pressure. Mixtures with varying concentration of tetrapack flakes were prepared. Mechanical properties such as Young’s modulus, yield stress, and ultimate tensile stress were obtained from uniaxial tensile deformation tests carried out at room temperature. The results showed that the tetrapack flakes were effective reinforcers, increasing the Young’s modulus and yield stress relative to neat high-density polyethylene. However, it was also found that the filler acts as stress concentrator where mechanical failure initiates. Scanning electron microscopy showed that fracture of the composite occurred mainly by the lack of adhesion between polymer matrix and filler. Moreover, a percolation threshold was reached at about 5% g/g concentration of tetrapack, beyond which mechanical properties are severely compromised. Interestingly, this investigation also showed that the color of the high-density polyethylene flake, that is, the pigment, strongly influences the mechanical properties of the composite. Thus, boards hot-pressed from individual colors were also investigated. The results showed that pigments, like those used in gray color, favored higher degree of crystallinity, as measured by differential scanning calorimetry, and therefore higher Young’s modulus.
Nanocomposites of cellulose-based adhesive and doped polypyrrole (PPy) have been prepared via colloidal dispersion method. Cellulose was chemically modified with epoxy to incorporate adhesion property. PPy nanoparticles were synthesized via oxidation reaction using toluenesulfonic acid as a doping agent. Field emission scanning electron microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis and high-frequency impedance spectroscopy were used to characterize the nanocomposites. Toluenesulfonic acid-doped PPy synthesized at pH 1 resulted in rod-shaped particles with a diameter and a doping level of about 80–100 nm and 25%, respectively. Toluenesulfonic acid-doped PPy synthesized at pH 3 and pH 4 produced spherical-shaped particles with doping level of 21% and 17%, respectively. Toluenesulfonic acid-doped PPy particles synthesized at pH 3 is smaller (76–100 nm) compared to the one prepared at pH 4 (97–254 nm). The electrical and thermal conductivities obtained for toluenesulfonic acid-doped PPy synthesized at pH 1 were 8.422 x 10–3 S cm –1 and 0.431 W m–1 K–1, respectively. Whereas, the one synthesized at pH 3 and pH 4 exhibited lower electrical and thermal conductivities. Nanocomposite with a composition of 70 : 30 (toluenesulfonic acid-doped PPy:epoxypropyl cellulose) gave the highest electrical and thermal conductivities.
Intermediate crack-induced debonding is often a dominant failure mode in fiber-reinforced polymer (FRP)-strengthened reinforced concrete (RC) beams in flexure. It has been extensively studied for RC beams externally strengthened with unstressed FRP laminates. However, very little work has been done on FRP debonding for RC beams strengthened with prestressed FRP. This article presents a sectional analysis model for predicting the flexural capacity of RC beams strengthened with prestressed FRP laminates with due consideration of different failure modes. The focus is placed on the effective strain in the prestressed FRP at the ultimate states of intermediate crack-induced debonding or rupture of debonded FRP. Through back-calculation analysis of 51 RC beams strengthened with post-tensioned FRP laminates, a model for predicting the effective strain of prestressed FRP for ultimate strength prediction based upon sectional analyses was developed and validated through comparisons with test results.
Recently, natural fiber-reinforced composites are becoming a viable alternative to synthetic fiber composites in many applications. Secondary processing in terms of hole making in composites is an almost unavoidable operation for facilitating the assembly operations. In the present experimental investigation, the drilling process of natural fiber-reinforced thermoplastic bio-composites has been evaluated in terms of the drilling forces. The cutting speed, feed rate and the drill point geometry have been taken as the input process parameters. Two types of drill geometries (solid and hollow in shape) have been used for drilling in the present work. The cutting mechanism of solid and hollow drill point geometry are substantially different which consequently affects the drilling forces and drilling-induced damage.
A new hyperdispersant agent with maleic anhydride monoester as anchoring group, butylmethacrylate as solventable chain, and styrene (St) as functional group was synthesized, and named SMB. Also, the effects of nanometer-TiO2 (nano-TiO2) modification and concentration on the mechanical properties of polypropylene/polyamide/maleic anhydride-grafted polypropylene (70/30/5 by weight) composites were investigated. The experimental results indicated that the mechanical properties of polypropylene/polyamide 6/M blend reduced with the addition of p-TiO2 (unmodified nano-TiO2) due to the aggregation of nanoparticles, but improved by the addition of t-TiO2 (modified by titanate coupling agent TDI) or SMB-TiO2 (modified by hyperdispersant agent SMB), and SMB-TiO2 seemed to be more effective. The optimum content of SMB-TiO2 was found to be 3 wt%. In order to understand the reinforcing mechanisms of nanoparticles, SEM and TEM pictures were carried out, which revealed that SMB-TiO2 mainly distributed at the interface of polypropylene and polyamide 6 in nanoscale as compatibilizer. It could be due to the surface of nano-TiO2 coated with SMB, and the carboxy group of SMB could react with the functional group of PA6; meanwhile, the solventable chain had good compatibility with PP, and so the interaction between PP and PA6 increased in the presence of SMB-TiO2. Consequently, PP/PA6/M blend could be simultaneously strengthened and toughened by SMB-TiO2.
Aerogels are highly porous solids formed by replacing the liquid in a gel by air, without changing the original structure. The present cellulose aerogels are made by sublimating the water from a colloidal suspension of cellulose nanofibers. The nanofibers form three-dimensional networks, crosslinked by hydrogen bonds bridging the surface hydroxyl groups and also by mechanical entanglements between nanofibers. Although the studies on aerogels from cellulose nanofiber hydrogels by freeze-drying reported so far had produced small samples, improved cooling techniques that produces larger samples were attempted and the obtained cellulose nanofiber aerogels were impregnated with epoxy resin to fabricate composites. The highly porous structure allowed complete impregnation of resin and translucent composites were produced. The modulus of composites was increased in relation to neat epoxy, but due to high brittleness the ultimate strength was decreased. This is likely to be caused by nanofiber agglomerations of uneven pore sizes acting as stress concentrators. The evaluation of the mechanical properties of composites serves as an indirect way to assess the quality of the aerogels produced.
As the new composite connection technology, pre-tightened teeth connection can play better mechanical performance for composite materials. To this connection technology, the ultimate bearing capacity of the first tooth is very important. In this article, the ultimate bearing capacity of the single tooth is researched by the experiment and theory. Firstly by the experiment, the optimal tooth depth and an effective teeth length are obtained. Secondly on the basis of reasonable simplified load model of a single tooth, the theoretical solution of the interlaminar stress distribution on a single tooth is worked out. And depending on the interlaminar stress distribution theory, the concepts of optimal tooth depth and tooth length are explained and their determination methods are given out. Finally combined with tests, the approach to determine the ultimate bearing capacity of the single tooth is put forward, hence offering design method for the final connection.
This article focuses on the study of the mechanical properties of the reinforced concrete columns with different specifications under different loading rates. The dynamic properties of the reinforced concrete column under bidirectional loading conditions are investigated as well. The initial stiffness, stiffness degradation, strength degradation, ductility, ultimate resistance capacity, yield resistance capacity, energy absorption and damage of members are analyzed according to experimental results. Based on the above analyses, some significant conclusions are obtained for engineering practice.
This article is concerned with the numerical modelling and analysis of the mechanical behaviour of composite pipes used for offshore oil and gas applications. Specifically, the bending of the reinforced thermoplastic pipes during the reeling process of reel-lay installation is modelled using non-linear finite-element procedures. In particular, the possible buckling of the reeled composite pipes has been investigated. Composite pipes reinforced with one angle-ply and two angle-ply layers are considered and the effects of different diameter-to-thickness ratios and different angle-ply combinations on the mechanical behaviour of these pipes have been studied.
During curing process of composite overwrap the die shows a significant influence on the temperature field, curing degree distribution, and curing deformation. The curing process can thus not be accurately simulated without a die. In this paper, a model of the composite overwrap with a die and two models without dies were respectively created. The finite element method was employed to solve the equations for describing the thermo-chemical model coupled with the cure kinetic model. The validity of the simulation was experimentally verified. The temperature distribution and the curing degree field of the composite overwrap were outlined and the effect of the die on the curing process was evaluated for each model. With the aid of the thermal analysis, the curing deformation as a result of the thermo-chemical shrinkage was presented and the difference in thermal expansion coefficients between the composite overwrap and the die was illustrated. The effect of the stacking sequence of multi-layers on the curing deformation of the composite overwrap was also evaluated, taking into account the changes in the resin properties during the curing process.
Thermal and morphological behavior of epoxy nanocomposite system was investigated under the influence of barium sulfate nanoparticles. Initially, epoxy resin and nano-BaSO4 were synthesized under controlled ultrasound cavitation technique. At the time of epoxy resin synthesis, nano-BaSO4 (2–10 mass% loading) was added under controlled ultrasound. The intense collapse effect was arising due to cavitation, which enhances the polymerization process with uniform mixing of nano-BaSO4. The effect of nano-BaSO4 on thermal and functional group linkage was studied using differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy, respectively. Addition of nBaSO4 accelerates the rate of epoxy resin curing during composite formation with uniform dispersion of nano-BaSO4 under controlled ultrasonic waves (50 kHz), which shows remarkable change in cross-linking density. The thermal stability of epoxy resin nanocomposite was found to be improved as compared to neat epoxy resin. The increasing amount of loading of nano-BaSO4 shows enhancement in thermal properties of epoxy nanocomposite. It was demonstrated that ultrasonic synthesis is a unique and ultimate way for preparation of epoxy resin with nanoaddition. Due to controlled ultrasonic waves, formation of long-term stable polymerization occurs, which consists of polymer/inorganic nanoparticles composite.
Sound absorption properties of natural fiber-reinforced sandwich structures based on the structure of the fabrics were investigated in this work. The sound absorption coefficients of the sandwich structures were measured by the impedance tubes with the aid of the transfer function. Effects of yarn sizes, fiber diameters and hybrid stacking of different fibers on the sound absorption properties were studied. The flow resistance and characteristic impedance of the reinforcing fabrics which were correlated with the fabric structures were calculated and compared. It was concluded that the thicker the fabric yarn and the bigger the fiber diameter were, the better the sound absorption properties were for natural fiber-reinforced sandwich structures.
With successful applications in every other field, composites have been used in making boats, offshore structures and various marine structural applications for past few decades, owing to their superior strength-to-weight ratio and performance-to-cost ratio. Usually, marine environment poses serious challenges to the choice of materials due to the presence of corrosive seawater which significantly decreases their life-time. Slowly, nanocomposites are increasingly becoming popular because of nanoscale effects, large interface area and strong interfacial interactions between nanoparticles and polymer. In the present study, Silicon dioxide nanofillers were used as additive in order to enhance the barrier property of composites against water diffusion and hence to prevent it from mechanical degradation. Being one of the most commonly used resin for making composites, unsaturated polyester was chosen for study. Resistance to sea-water diffusion and water absorption rate was studied while varying parameters like ambient temperature and salinity of water. It was observed that the presence of nanoparticles significantly decreases the maximum water uptake and moisture diffusivity in the composite. It was also found that as the salinity of sea-water increases and temperature decreases, degradation due to water absorption decreases.
Millable polyurethane (MPU) rubber nanocomposites were prepared on a two-roll mill and molded on a compression molding machine. The amount of loading of Mg(OH)2 nanoparticles (nMg(OH)2) was from 0.5 to 2.5 wt% followed by the addition of dicumyl peroxide (as a curing agent). The compounded matter was subjected to compression molding so as to get a cure sheet (130 x 130 x 3 mm). Mechanical (tensile strength, elongation at break (%) and abrasion resistance index), physical (hardness and swelling index), and thermal properties (flammability retardency and degradation stability) were studied. The extent of dispersion of nMg(OH)2 particles was studied using scanning electron microscope and atomic force microscope. nMg(OH)2 was synthesized using continuous ultrasonic cavitation technique. The size and shape of nMg(OH)2 was confirmed using X-ray diffraction and transmission electron microscopy, which was found to be ~20–60 nm with quasi shape. MPU:nMg(OH)2 nanocomposites show improved mechanical, physical, and thermal properties compared to pristine MPU. This improvement was due to very fine grain size of nMg(OH)2, which facilitates uniform dispersion of nMg(OH)2 within MPU rubber matrix. However, higher loading of nMg(OH)2 shows marginal decrement in properties due to agglomeration, especially at 2.5 wt%.
Glass fiber-reinforced plastic composites are particularly attractive as bridge deck systems due to their high strength, low density, and excellent corrosion resistance, which are of importance to the bridge industry. According to ACI 440.3R–04, the tests consisting of 100 glass fiber-reinforced plastic bridge deck samples were conducted to evaluate the mechanical behaviors of glass fiber-reinforced plastic bridge decks (including tensile property and flexural property) in terms of temperature of the alkaline solution and time period. The parameters of temperature included 40°C and 60°C, and the investigated corrosion time included 3.65 days, 18 days, 36.5 days and 92 days, respectively. The micro-formation of the glass fiber-reinforced plastic bridge deck samples surface were surveyed under scanning electron microscopy, which indicated that corrosion pits on the surface of glass fiber-reinforced plastic bridge decks became obvious and the interface between fibers and resins was severely damaged with the aging time and temperature increased. After being exposed to alkaline solution for 92 days at 40°C and 60°C, the tensile strength of glass fiber-reinforced plastic bridge decks decreased by 35.43% and 40.58%, respectively, while the flexural strength decreased by 21.36% and 42.10%, respectively. In addition, the degradation model of tensile strength and flexural strength of glass fiber-reinforced plastic bridge deck under alkaline solution were proposed based on Arrhenius equation.
Dynamic mechanical thermal analysis was used to evaluate temperature-dependent mechanical performance of wheat straw/talc polypropylene composites intended for automotive components as well as thermal properties of the produced formulations. Dynamic mechanical thermal analysis results were also correlated with impact tests and static bending test results. Isotactic and impact-modified copolymer polypropylene composites with various amounts of wheat straw or talc were prepared using extrusion followed by injection molding. Different thermal transitions as well as mechanical performance of the composites were evaluated and the effects of fiber loading, matrix type, filler type and hybridization were studied. Results indicated different mechanical behaviors of the two fillers within and between the two matrices. Modulus retention term and relative storage modulus were used as parameters defining mechanical performance at various temperatures. It was found that wheat straw composites were generally comparable to talc composites with better performance at very low or very high temperature regions. The correlations between the dynamic mechanical loss factor values at room temperature and impact strength data revealed a good relationship only for the isotactic polypropylene composites whereas statistically significant correlations were established between flexural strength and impact data for all formulations.
Nanocomposites were formed by curing the dispersion of carbon nanofillers—nanographene platelets and vapor grown carbon nanofibers—in resole type phenolic resin. X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy, thermal expansion, and thermogravimetric and flexure testing were carried out to study the morphology and thermal and mechanical properties of the manufactured nanocomposites. The coefficient of thermal expansion decreased by 15.36% (73.83 µm/m°C) and 14.23% (74.81 µm/m°C) with 1.5 wt% nanographene platelets and 1.5 wt% vapor grown carbon nanofibers, respectively, compared with neat phenolic (87.23 µm/m°C) in the temperature range 60–80°. The flexure strength of neat phenolic resin increased by 31.62% (48.57 MPa) and flexure modulus by 42.23% (2.9 GPa) at 0.5 wt% nanographene platelets. Comparatively, vapor grown carbon nanofibers at 1.5 wt% increased the flexure strength by 14.3% and flexure modulus by 23.5%. Nanographene platelets and vapor grown carbon nanofibers increased the char content of neat phenolic resin. The char content increased by 200% at 800°C in 5 wt% nanographene platelet nanocomposites, compared with 75% increase in 3 wt% vapor grown carbon nanofibers nanocomposite. Nanographene platelets were more effective than vapor grown carbon nanofibers in lowering the coefficient of thermal expansion of neat phenolic, in improving its flexure strength and modulus and in increasing the char yield. The results indicate that nanographene platelets can be effectively used as carbon nanofiller in the manufacture of carbon/carbon composites.
This paper presents a new three-dimensional method to braid a net-shape preform with rounding chamfer. This new method is mainly based on the 4-step method. It needs six steps to finish one cycle. For the traditional braiding method it needs eight steps to form a L- shape preform. Due to the different braiding processes referred above the yarn topology is different. After the preforms are impregnated with matrix, the interior unit cells between the two kinds of composite referred above are compared. The interior unit cell of the composite with rounding chamfer consists of four yarns while the other contains five yarns. The corner of the L-shape composite is cut to form the same dimensional rounding chamfer. The specimen of the two kinds of composites is tested. The flexural experiment shows that composite manufactured by the new method performs better due to the structural integrity.
This article is devoted to study the factors affecting the performance of the adhesively bonded joints between rubber composites and metal substrates. The mechanical strength of the adhesively bonded joint is assessed with regard to several parameters as the type of rubber, type and/or concentration of black fillers, type of adhesive system and type of metallic substrate. The mechanical properties of the adhesively bonded composites were measured under different modes of deformation such as the uniaxial extension, shear and peel tests. The results showed that the presence of black filler and/or polar group in the rubber composites enhanced adhesion effectiveness between the rubber composites and the metal substrate. This was confirmed by Fourier transformed infrared spectroscopic analysis and the swelling characteristics in benzene. Moreover, the two-component adhesive system was more effective in adhesion than the one-component adhesive.
The influence of temperature and relative humidity on the moisture content of paper honeycomb sandwich panels was studied, and the ideal three-dimensional diagram between the moisture content of paper honeycomb sandwich panels and the temperature and relative humidity was constructed by the GAB model. The evaluation equation of critical stress and plateau stress were obtained. The results indicate that the moisture content of paper honeycomb sandwich panels rises with the increase of relative humidity and declines with the increase of temperature; as the moisture content increases, the critical stress and plateau stress of paper honeycomb sandwich panels decline linearly; with the increase of the moisture content, the energy absorption of paper honeycomb sandwich panels increased firstly and then decreased; the evaluation equation of critical stress and plateau stress can predict the mechanical properties of paper honeycomb sandwich panels in different temperatures and relative humidities.
Plasma spray technology is being widely used for the development of protective coatings to prevent degradation of critical components working under severe conditions. Plasma sprayed alumina–titania have many industrial applications. These coatings provide a dense and hard surface which is resistant to abrasion, corrosion, cavitation, oxidation, and erosion. Plasma sprayed alumina–titania coatings are regularly used for wear resistance, electrical insulation, thermal barrier applications, etc. Alumina pre-mixed with titania powder is deposited on mild steel substances by atmospheric plasma spraying. Microstructure of the coating is analyzed by SEM. Adhesion strength of alumina–titania coatings are measured. The response of plasma sprayed alumina–titania coatings to the impingement of solid particles has been presented in this study. The erosion rate is calculated on the basis of ‘coating mass loss’. It is observed that the erosion wear rate varies with erodent dose, angle of attack, the velocity of erodent, standoff distance, and size of the erodent. Cumulative coating mass loss varies with time of erosion.