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In the article, we propose a new method to generate representative volume element (RVE) of random spatial distributions with cylindrical fibers and spherical particles based on the Improved Artificial Bee Colony (IABC) algorithm. In this employed bee phase of IABC, the proposed algorithm adopts a new search strategy, which improves the computational efficiency. To analyze the differences between the fiber distribution generated by this algorithm and the actual fiber distribution, we conducted statistical analysis on the distribution of the generated RVE. The statistical analysis results of the nearest neighbor distance (NND), Second-order intensity function, and pair correlation function were in good agreement with the experiment and complete spatial randomness (CSR) patterns. In addition, the predicted elastic properties were compared with experimental measurements and theoretical prediction methods. The results demonstrate the accuracy and efficiency of the proposed algorithm. This algorithm can quickly generate the RVE of cylindrical fibers and spherical particles with volume fractions of 80% and 62%, and the calculation time for generating the RVE of cylindrical fibers is about 17s. [ABSTRACT FROM AUTHOR]

Tidal turbine infrastructure is currently in the large-scale prototype and short-term demonstration phase. However, the immediate requirement is to develop materials, processes and long-term life predictive facilities for tidal turbine plant that has decades of operational lifetime requirements. Computational modelling is a key tool to interpret the experimental data, understand the relevant mechanisms and provide a predictive capability for the performance of aged components for industries. The goal of this paper is a prediction of the long-term life of marine-based glass/epoxy and carbon/epoxy composite laminates aged in artificial seawater with 3.5% salinity based on Arrhenius degradation theory and tensile strength retention over 180 days ageing at room temperature and 60°C. Three different analytical models (linear and exponential) were implemented to calculate time shift factors and corresponding life in a real marine environment. Additionally, multi-scale modelling has been implemented via a representative volume element approach for square and hexagonal cells, and two-step homogenization of textile composites in accordance with nanoindentation testing for matrix/resin cells and fibre constraint cells after 90 days of immersion in saltwater. In general, the multi-scale modelling in ABAQUS and TexGen4SC was able to approximate (with about 10% difference) the mechanical properties of dry and aged composite laminates. [ABSTRACT FROM AUTHOR]

Inter-fibre failure analysis of carbon fibre-reinforced polymer (CFRP) composites, under biaxial loading conditions, has been a longstanding challenge and is addressed in this study. Biaxial failure analysis of IM7/8552 CFRP unidirectional (UD) composites is conducted under various stress states. Two widely accepted failure criteria, the interactive Tsai-Wu and non-interactive Hashin failure criteria, are comprehensively assessed with finite element-based micromechanical analysis. High-fidelity three-dimensional representative volume elements (RVEs) are subjected to biaxial loadings with imposed periodic boundary conditions. Carbon fibres are assumed to be transversely isotropic and linearly elastic. The Drucker-Prager plastic damage constitutive model and cohesive zone model are utilised to simulate the mechanical response of the matrix and fibre-matrix interface, respectively. Coulomb friction is assumed between the fibres and matrix after interface failure. Two sets of biaxial loading scenarios (i.e. transverse stress dominated and shear stress dominated) with the associated failure modes are selected for the failure analysis and assessment of these failure criteria. A data-driven failure envelope for the composites under biaxial loadings is developed using a univariate cubic spline function. Failure mode transition points are determined under biaxial loadings. It is found that the micromechanics-based numerical model is effective in assessing these two existing criteria. [ABSTRACT FROM AUTHOR]

Onset Theory (previously known as Strain Invariant Failure Theory) is a physics-based composite failure criterion attempting to predict failure at the level of constituents rather than for a homogenized ply. Applying Onset Theory correctly requires a number of steps. As a starting point for other researchers, a consistent approach is developed by resolving contradictions found in literature. This includes the micromechanical FEA process used to determine the individual fiber and matrix strains, such as correct choice of representative volume elements (RVEs), the use of transformed RVEs, boundary conditions, and the location of data extraction points. Analytical expressions are provided to determine the full state of strain in a ply, including in-plane and out-of-plane Poisson's strains and thermally induced mechanical strains. Literature definitions of the critical invariants are discussed, and a trend in critical distortional invariants is observed. Assumptions and limitations of the theory are identified. Finally, a failure envelope is compared to World Wide Failure Exercise test data. [ABSTRACT FROM AUTHOR]

In this study, the effect of various microcapsule sizes on the mechanical properties of microcapsule-based polymeric materials was investigated using the finite element method and validated with experimental outcomes. Specimens containing 5wt. % of microcapsules were fabricated to calculate the elastic modulus, and maximum tensile stress, and to validate numerical results. To consider the error, five tests were performed for all samples, and results were reported on average. The average errors between the numerical outcomes and experimental results were 4.74% and 5.35% for maximum tensile stress and elastic modulus, respectively. The coaxial electrospraying method was used for synthesizing microcapsules made of alginate (shell) and epoxy (core). A scanning electron microscope (SEM) was used to calculate the diameter of the capsules. To develop an empirical model for the average microcapsule diameter (AMD) and carry out the optimization process, response surface methodology (RSM) with central composite design was used. Also, analysis of variance was employed to validate the accuracy of the model. The effects of three parameters, including voltage, needle size, and the distance between the tip of the needle to the collector, on average microcapsule diameter, were investigated. The empirical model was validated by a confirmation run, and the determined error (1.93%) between the predicted and experimental results indicates the precision of the model. The numerical study indicated that microcapsule-based self-healing polymers containing smaller microcapsules tolerate higher stresses. However, the effect of the microcapsules' size on the elastic modulus of a representative volume element was negligible. [ABSTRACT FROM AUTHOR]

Macroscopic properties of ferroelectrics are controlled by processes on the microscale, in particular the switching of crystal unit cells and the movement of domain walls, respectively. Besides these microscopic levels, the grains of a polycrystalline material constitute the mesoscopic scale. Interactions of grains with statistically distributed orientations, as a consequence of mechanical and electrostatic mismatch, give rise to for example, residual stress which in turn affects domain switching. A multiscale modeling thus has to incorporate at least three interacting scales. In this context, the condensed method has recently been elaborated as an efficient tool with low computational cost and effort of implementation. It is extended toward statistical distributions of grain sizes in a representative material volume element and amended with regard to the modeling of domain evolution. Each of the few parameters of the constitutive approach has a unique physical meaning and is adapted to available experimental values of macroscopic quantities of barium titanate taken from various sources. [ABSTRACT FROM AUTHOR]

In the failure analysis of composite materials, the damage of fiber and matrix is always noticed rather than the debonding of interface which is responsible for transferring the load between matrix and fiber. The stress amplification factors of fiber, matrix, and interface were extracted by establishing representative volume element model with interface and the strength of corresponding constituent is calculated in our work. Micro mechanics of failure served as the initial failure criterion of material components, and user-material subroutine (UMAT) was applied to realize progressive damage analysis of fiber metal laminate (FML) under different loading angles. The analysis results show that it is not strictly correct to directly use the stress on the matrix to calculate interface stress, and the damage trend of interface is consistent with that of fiber. The strain hardening phenomenon of FML decreases with larger loading angle, and the mechanical response of FML is about 45° symmetric due to its structure symmetry. The simulation results are in good agreement with the experiment results. [ABSTRACT FROM AUTHOR]

A two-scale concurrent topology optimization method based on the couple stress theory is proposed for maximizing structural fundamental eigenfrequency. Because of the fact that the classical mechanics theory cannot reveal the size effect because of neglecting the influence of microstructure, the theory of couple stress including the microscopic properties of materials can be used to describe the size effect in deformations. On the foundation of the couple stress theory, the two-scale optimization model for finding optimal configurations of macrostructures and their periodic composite material microstructures is built. And the fundamental eigenfrequency of the macrostructure is maximized. The effective macroscopic couple stress constitutive constants of macrostructures are calculated by the representative volume element method. And a modified solid isotropic material with a penalization model is used to effectively avoid the localized mode. The optimization algorithm based on the bidirectional evolutionary structural optimization method is proposed. The optimal results of numerical examples show that the optimal topologies and natural frequencies obtained by the couple stress theory may differ significantly from those obtained by the typical Cauchy theory. It is obvious that couple stress theory can effectively describe the size effect in topology optimization. [ABSTRACT FROM AUTHOR]

Recent researches show that the embedment of hollow spheres in the matrix phase of composite materials improves the strength of these structures against crack propagations. Rare studies are reported for calculating equivalent elastic constants of fiber reinforced composites containing hollow spheres. In this paper, the effects of hollow spheres on mechanical characteristics of fiber reinforced composite are studied for the first time. To achieve this aim, a micromechanics based finite element method is employed. Representative volume elements (RVEs) including hollow spheres with different radius, thickness and volume fraction of hollow spheres, are modeled by using 3D finite elements. The equivalent elastic constants are calculated through homogenization technique. The results are compared with available experimental works. Good agreements find between two sets of results. Also, the volume fraction, number and thickness of hollow spheres as effective parameters on mechanical properties of composite were investigated. The results show the equivalent elastic properties increase with increasing the volume fraction and number of hollow spheres and decrease with increasing the number of hollow spheres. Furthermore, the equivalent Young's modulus in transverse directions to the fiber direction and shear modulus of the composite increase with increasing the thickness of hollow spheres. As a final result, the presence of hollow spheres in the matrix phase generally increases the equivalent elastic constants without significant changes in the weight of structures. [ABSTRACT FROM AUTHOR]

Over the last decade, vibration energy harvesting has received substantial attention of many researchers. Piezoelectric materials are able to capture energy from ambient vibration and convert it into electricity which can be stored in batteries or utilized to power small electronic devices. In order to benefit from the 33-mode of the piezoelectric effect, interdigitated electrodes have been utilized in the design of macro fiber composites which are made of piezoelectric fibers of square cross sections embedded into an epoxy matrix material. This paper presents an analytical model of a macro fiber composite bimorph energy harvester using the 33-mode. The mixing rule is applied to determine the equivalent and homogenized properties of the macro fiber composite structures. The electromechanical properties of a representative volume element composed of piezoelectric fibers and an epoxy matrix between two successive interdigitated electrodes are coupled with the overall electro-elastodynamics of the harvester utilizing the Euler–Bernoulli theory. Macro fiber composite bimorph cantilevers with diverse widths are simulated for power generation when a resistive shunt loading is applied. Stress components in the Kapton layers, which are typically a part of any macro fiber composite patch, and in the bonding layers have been included in the model contrary to previously published studies. Variable tip mass, attached at the free end of the beam, is utilized in this paper to tune the resonance frequency of the harvester. The generated power at the fundamental short circuit and open circuit resonance frequencies of harvesters having three different widths is analyzed. It has been observed that higher electrical outputs are produced by the wider macro fiber composite bimorph using (M8528-P1 patches). [ABSTRACT FROM AUTHOR]

This paper presents a micromechanics-based 3D finite element model for predicting the damage initiation, propagation, and failure strength of TC33/Epoxy carbon fiber reinforced polymer (CFRP) unidirectional lamina under biaxial loadings. The finite element model is generated by introducing representative volume element (RVE) with a random distribution of fibers and a non-zero thickness, numerically identified interface phase via cohesive elements. In the finite element model, the carbon fibers are considered as elastic, while the elasto-plastic behavior and damage of the matrix are governed by extended Drucker–Prager plastic yielding model and ductile damage criterion. By imposing periodic boundary conditions to the RVEs, various cases subjected to uniaxial and biaxial loading conditions are carried out. During the combined transverse and in-plane shear stress states, a failure transition from compression- or tension-dominated to shear-dominated is captured, and the effects of the interfacial strength on the transition damage mechanisms are discussed. The corresponding failure locus is compared with the upper bound and lower bound predictions of three phenomenological failure criteria (Hashin, Tasi–Wu, and Puck failure criteria) for composites. It was found that in the interface-dominated failure of a CFRP lamina with a weak interface, the Hashin failure criterion performs best among the currently popular failure criteria. However, in the matrix-dominated failure with a strong interface, the Puck failure criterion performs best. Comparing these three criteria, it can be seen the Tsai–Wu may be generally better than both of others as it presents more neutral predictions in both of the examined cases. [ABSTRACT FROM AUTHOR]

Polymer matrix composites are developed by reinforcing biodegradable rubber seed shell, cashew nut shell and walnut shell powder in epoxy resin. Theoretically, elastic modulus is calculated using Hashin–Shtrikman bounds using variational principles. Investigation of the elastic modulus of the composites is extended by varying filler weight up to 25% in Digimat 2017-MF which applies Mori–Tanaka mean field homogenization and ANSYS 15.0 Workbench which uses a three-dimensional model of representative volume element having spherical shaped filler particles to calculate elastic modulus. Elastic modulus is the measurement of resistance of the material under tensile load. The corresponding stress–strain relationship predicts the stiffness of the material. The results are confirmed with experimentation approach for 5% wt filler content. Elastic modulus obtained from these approaches show a maximum error of 7% with experiment results. Investigation further reveals that elastic modulus of composites increases with increase in weight fraction of fillers. However, above 15% wt of filler content, no significant increase in the elastic modulus of the composites is observed. [ABSTRACT FROM AUTHOR]

The paper aims to investigate the correlation of microstructural characteristics and machinability of unidirectional carbon fiber reinforced polymer composites by a modified analytical model. A representative volume element was selected to present the microstructure and analyze the force distribution, in which the interphase between the fiber and the matrix was considered significantly. And the microstructure can be obviously measured by using microscopic observation, especially the interphase was found to be around 0.3 μm in the used carbon fiber reinforced polymer composites. To study the representative volume element effect on the cutting behavior of unidirectional carbon fiber reinforced polymer composites, the prediction of cutting force was done by using a modified force model. Compared with the experiments, the developed model can well predict the cutting forces and subsurface damage in the carbon fiber reinforced polymer composites cutting. It was found that surface integrity as well as subsurface damage has a coincident varying trend with the fiber orientations, as confirmed by the observations of the machined surface at different fiber orientations. The good surface integrity can be obtained at the low fiber orientation of 0° and the poor surface occurs at the large fiber orientation of 135°. Moreover, the effect of interphase and the fiber volume fraction in representative volume element were further investigated. The results show that the cutting forces increase with increasing the fiber volume fraction as well as the interphase volume fraction, and the interphase affects the cutting force in the transverse direction is significantly higher than that in longitudinal direction. [ABSTRACT FROM AUTHOR]

Carbon nanotube-reinforced polymers belong to a class of composite materials, which have been largely investigated due to their special electrical, thermal and mechanical properties. In the case of electrical conductivity of carbon nanotube-reinforced polymer, a critical amount of carbon nanotubes as a filler material enables a sharp increase of electrical conductivity. At this certain volume fraction of carbon nanotubes, the material turns into a conductor because of the percolation effect. This effect occurs due to the formation of a closed pathway of filler material through the system. Mesoscopic simulation models of these materials were carried out to predict their electrical conductivity. In this paper, the effects of carbon nanotube curvature and their alignment parallel or perpendicular to the electrical flow direction inside a representative volume element were analysed and an optimized carbon nanotube distribution is presented. A network with a longest average path length per (rigid) carbon nanotube but also cross-linking (only nearly isotropic alignment) shows the best conductivity in the preferred direction. [ABSTRACT FROM AUTHOR]

The purposes of this paper are sixfold. First, any micromechanics model for predicting elastic property (stiffness) of a composite is applicable to a reasonable prediction of a composite strength, provided that the homogenized internal stresses in the matrix are converted into true values. The conversion for all of the stress components free of biaxially transverse loads is presented in the paper. Second, the predictability of 12 well-known micromechanics models for stiffness and strength of a unidirectional composite is assessed against the measured data of all of the nine unidirectional composites used in three world-wide failure exercises. An accuracy ranking is made accordingly. Third, it is demonstrated that the smallest fiber volume in a representative volume element for a finite element approach plays a more dominant role than other issues such as a random fiber array to achieve the highest simulation accuracy. This feature has been largely ignored in the current literature. Fourth, a consistency of a micromechanics model in calculating the internal stresses in the fiber and matrix of the composite is an issue that should be taken into account. Among the 12 models considered, only Bridging Model is consistent. A non-consistency implies that a full three-dimensional approach should be used to predict an effective property of the composite even though it is subjected to a uniaxial load. Fifth, an effective method to detect an interface debonding between the fiber and matrix subjected to an arbitrary load is presented in the paper. Only a transverse tensile strength of the composite, in addition to the original fiber and matrix properties, is needed. Whereas essentially any load can cause the interface to debond earlier before a composite failure, only a transverse tensile load carrying capacity of the composite is influenced significantly by the debonding. Specifically, an interface debonding has insignificant effect on a shear strength of the composite. Sixth, a fiber misalignment-induced kink band failure is analyzed by virtue of the original fiber and matrix properties, and a longitudinal compressive strength is predicted micromechanically. [ABSTRACT FROM AUTHOR]

Interior fibers in yarns of plain woven carbon fiber-reinforced composite are distributed randomly, which further influences the mechanical properties of yarns. To explore the stochastic nature of fibers’ distribution in yarn and its effect on the properties of yarn, this study proposes a new perturbation algorithm named Sequential Random Perturbation algorithm to reconstruct the microstructure of randomly distributed fibers, based on which representative volume element micromechanical models consisting of three phases to accurately predict the mechanical properties of yarn are established. The algorithm is based on successive smart perturbations of fibers to gain microstructures of arbitrary volume fraction, and statistical study shows that the algorithm is in good agreement with experimental results. Finally, representative volume element models are simulated to predict the whole mechanical properties of composite yarns to reflect the failure mechanisms and microstructure–property relations. The randomness of fiber distribution has some degree of influence on mechanical properties of yarn, especially strength responses. The failures under axial tension and compression are dominated by fiber breakage, while under transverse and shear loading conditions, the failures are mostly decided by interface debonding and matrix damage. [ABSTRACT FROM AUTHOR]

Determination of effective composite properties for a real distribution of piezoelectric particles in cement matrix is considered using a representative volume element. The scaled boundary finite element method is proposed to analyse cement-based piezoelectric ceramic composites. Quadtree hierarchical meshing structure is utilized to provide a mesh that captures the material variation in the representative volume element effectively based on the colour of the piezoelectric composite’s image. Analyses with carefully selected boundary conditions are performed to obtain the effective material properties of various samples. [ABSTRACT FROM AUTHOR]

Carbon nanotube reinforced polymers belong to a class of composite materials, which have been largely investigated due to their specific electrical, thermal and mechanical properties. In the case of electrical conductivity of carbon nanotube reinforced polymers, a critical amount of filler material ensures a sharp increase of conductivity. The material forms a percolation pathway and instantly turns the composite into a conductor. Mesoscopic simulations of these materials were carried out to predict electrical conductivity of carbon nanotube reinforced polymers and their critical amounts. This research work deals with percolation thresholds, converging representative volume elements and the effect of the discontinuous behaviour of conductivity considering tunnelling effects found in atomistic approaches on mesoscopic simulation models. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effect of carbon nanotube reinforcement in conventional carbon fiber reinforced composite on the buckling and postbuckling behavior of the laminated nanocomposite plate made of carbon nanotube and carbon fiber reinforcements in a matrix material. The method of representative volume element is utilized to perform the multiscale modeling of the problem. Initially, Boolean-based random sequential adsorption algorithm is utilized to model a nanoscale representative volume element of nanocomposite material to mimic the effect of randomly distributed (i.e. having random orientation and position) carbon nanotubes in a matrix material. After estimating the elastic properties of the nanocomposite material using representative volume element, another microscale representative volume element of carbon fiber reinforced in the nanocomposite (i.e. carbon nanotube reinforced matrix material) is modeled to evaluate the stiffness properties of the lamina formed of carbon nanotube–carbon fiber reinforced nanocomposite. The laminae are further stacked in the sequence of (45°/−45°/−45°/45°) to model a laminate. Thereafter, the evaluated stiffness properties of the lamina are employed to predict the effect of carbon nanotube reinforcement on buckling and postbuckling behavior of the laminated plates through nonlinear finite element method formulation based on the first-order shear deformation theory and von Karman’s assumptions. It is established that carbon nanotube reinforcement in carbon fiber reinforced composite lamina results in the enhancement of stiffness properties of the resulting carbon nanotube–fiber nanocomposite lamina, with more prevalent effect on the matrix-dominated properties—transverse and shear moduli—than the axial modulus. The increased stiffness properties result in the substantial improvement in the buckling load and postbuckling strength of the laminated plate made of carbon nanotube–carbon fiber nanocomposite material, for all volume fractions of carbon nanotube, loading and boundary conditions, geometric parameters (i.e. aspect ratio and width-to-thickness ratio), and matrix materials. [ABSTRACT FROM AUTHOR]

The finite element method is proposed to analyze coated fiber composites with piezoelectric and piezomagnetic phases. The computational homogenization technique is applied for fiber composites with magnetoelectroelastic properties to determine effective material parameters. The evolution of the magnetoelectroelastic fields at the macroscopic level is resolved through the incorporation of the microstructural response. The microstructural analyses are performed on the representative volume element, where essential physical geometrical information about the microstructural components is included. Circular cross section of fibers is considered in numerical analyses. A thin coating layer is considered on the surface of the piezoelectric fiber which is embedded in the piezomagnetic matrix. Influence of the coating layer on the effective material properties is analyzed. [ABSTRACT FROM AUTHOR]

The micromechanical prediction of mechanical properties of composites, using a finite element method, is highly affected by selecting a suitable representative volume element. In the present research, the effects of the representative volume element aspect ratio on the stiffness of aligned short fiber composites have been studied. First, an analytical method is suggested to predict the longitudinal and transverse moduli of composites considering the representative volume element aspect ratio. Then, the optimum aspect ratio of the representative volume element is estimated by comparing the results obtained by the present method with those of a micromechanical method. Comparing the stiffness of the optimized representative volume element with some experimental results available in the literature shows that the result of the present method is also in a good agreement with experiments. [ABSTRACT FROM AUTHOR]

In this paper, a set of failure criteria for transverse failure in non-crimp fabric-reinforced composites is presented. The proposed failure criteria are physically based and take into account the orthotropic character of non-crimp fabric composites addressing the observed lack of transverse isotropy. Experimental data for transverse loading out-of-plane in combination with in-plane loads are scarce. Therefore, to validate the developed criteria, experimental data are complemented with numerical data from a representative volume element model using a meso-micromechanical approach. The representative volume element model also provides a deeper understanding of how failure occurs in non-crimp fabric composites. Strength predictions from the developed set of failure criteria show good agreement with the experimental and numerical data. [ABSTRACT FROM AUTHOR]

The mechanical properties of shape memory alloy/epoxy composites are evaluated using cylindrical representative volume element for long and short shape memory alloy wires considering the effect of interface between shape memory alloy wires and epoxy resin. The cohesive zone model is used to simulate the interface region between the shape memory alloy wire and the resin. An experimental pullout test is performed on the cylindrical specimens of resin containing single-shape memory alloy wire in order to achieve cohesive zone parameters. The finite element method is utilized to characterize the elastic properties of shape memory alloy/epoxy composites including axial modulus, transverse modulus, and Poisson’s ratio. The effect of length ratio between the shape memory alloy wire and the representative volume element on the mechanical properties of composite is investigated. Moreover, the critical aspect ratio for short shape memory alloy wires is calculated using shear-lag model. [ABSTRACT FROM AUTHOR]

This study investigates the influence of void microstructure on the effective elastic properties of high fiber volume fraction discontinuous fiber-reinforced composites with randomly oriented fibers. A void microstructure is characterized by using parameters such as the number of voids, void volume fraction, void Aspect Ratio and void size distribution. In order to overcome the difficulties associated with the creation of high fiber volume fraction representative volume element models containing voids, a novel automation program called “ArtiComp” is developed. This program is used to generate representative volume element models of discontinuous fiber-reinforced composites containing randomly oriented straight fibers, curved fibers and spheroidal voids. The effective properties of discontinuous fiber-reinforced composites are computed using a finite element-based micromechanics approach. For comparison, the Mori-Tanaka method is used to compute the effective properties of unidirectional discontinuous fiber-reinforced composites and then orientation averaging is performed on these properties to obtain the effective properties of discontinuous fiber-reinforced composites with randomly oriented fibers. The comparison shows that the finite element predicted properties are stiffer than the analytically predicted properties. The results indicate that the finite element predicted properties are dependent on the number of voids used to represent the void volume. It is seen that the effective properties significantly decrease when void volume fraction is increased. The void Aspect Ratio and void size distribution are found to have a negligible influence on the effective properties. Finally, it is observed that straight fiber composites with voids perform better than the corresponding curved fiber composites with voids. [ABSTRACT FROM AUTHOR]

Based on the representative volume element (RVE) model of single layer in multilayer-connected biaxial weft-knitted (MBWK) fabric-reinforced composites, the elastic properties of multilayer-connected biaxial weft-knitted fabric-reinforced composites have been developed and presented hereafter. The average stiffness matrix of the multilayer-connected biaxial weft-knitted fabric-reinforced composites, taking into account the contribution the final geometrical of the knitting loops, can be obtained by the volume average stiffness of the unidirectional composites with different local coordinate system, and the engineering elastic constants of this kind of composites have been figured out. Numerical predictions have compared to the results of tensile tests performed on composite samples. The percentage error of the numerical prediction results and the experimental results is less than 10%. [ABSTRACT FROM AUTHOR]

The representative volume element method is used to investigate the interface debonding of fiber-reinforced composites due to curing residual stress. First, the interface debonding behavior is characterized by means of the cohesive zone model, and the effects of curing residual stresses on the fiber/resin interface debonding are also studied using the cure hardening instantaneously linear elastic model. Second, debonding envelops of the representative volume element are obtained for tension loading, shear loading and mixed loading, respectively, which indicate that the curing residual stresses will have an important influence on the maximum principal stress and have no effects on the debonding initiation location and the propagating path. Finally, the relationships between the fiber versus resin aspect ratio γ and the maximum principal stress at the fiber/resin interface of the representative volume element in fiber-reinforced composites are investigated as well. [ABSTRACT FROM AUTHOR]

In this paper, micromechanical modelling and simulation were performed for unidirectional fibre reinforced composites subjected to transverse and in-plane shear by finite element method. Representative volume element consisting of fibre, matrix and interface was established for the simulation, considering random fibre distribution. The two dominant damage mechanisms of fibre reinforced composites, matrix plastic deformation and interfacial debonding were taken into account in the simulation. Periodic boundary conditions were applied to the representative volume elements. The simulation results indicate that the failure behaviour of the composites under transverse shear is dominated by matrix plastic damage, while the in-plane shear damage is initiated by interfacial debonding and then ultimate failure is caused by matrix damage. Fibre distribution is found to have a more significant effect on the failure behaviour of the composites under transverse shear than in-plane shear. The predicted in-plane shear strength and failure strain show reasonable agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Representative volume element-based three-dimensional models with various nanofiller geometries and process parameters are presented for the design and analysis of composite materials. Analytical, computer-aided design, and computer-aided engineering tools are integrated to develop user interface tools with automated three-dimensional models for mechanical and electrical analyses. Various process parameters in the manufacture of nanocomposites are quantified using image analysis techniques. A filler-to-filler distance algorithm is incorporated in developing a three-dimensional network of fillers within matrix representative volume element to account for filler–filler interactions and compatibility. The stress–strain behavior of metal matrix nanocomposites, the effective modulus, and the electrical conductivity of polymer nanocomposite fibers are presented as case studies to demonstrate the capabilities of the developed representative volume element-based design and analysis tools. The unique automated design and analysis framework presented in this study integrates various software tools, quantifies the effect of process parameters of experimental composites with nanofillers, and provides quick what-if analysis for manufacturing application-specific composites. [ABSTRACT FROM AUTHOR]

A multiscale numerical approach is established to model damage in random glass fiber composites. A representative volume element of a random glass fiber composite is employed to analyze microscale damage mechanisms, such as matrix cracking and fiber-matrix interfacial debonding, while the associated damage variables are defined and applied in a mesoscale stiffness reduction law. The macroscopic response of the homogenized mesoscale damage model is investigated using finite element analysis and validated through experiments. A case study of a random glass fiber composite plate containing a central hole subjected to tensile loading is performed to illustrate the applicability of the multiscale damage model. [ABSTRACT FROM AUTHOR]

A theoretical model for the evaluation of the elastic modulus and thermal expansion coefficient of particulate composites is presented in this study. This model takes into consideration the influence of neighboring spherical particles on the thermomechanical constants of the composites material consisting of matrix and filler. A microstructural composite model which represents the basic cell of the composite at a microscopic scale was transformed to a six-phase spherical representative volume element in order to apply the classical theory of elasticity to this. The obtained theoretical results using this model were compared with experimental results carried out on iron particles reinforced epoxy resin composites as well as with other theoretical values derived from expression given in the literature. [ABSTRACT FROM PUBLISHER]

This article presents a computational procedure for evaluating effective homogenized material properties of polycrystalline piezoelectric materials and constructing two- and three-dimensional realistic microstructure models based on electron backscatter diffraction crystal orientation measurement. Microstructural features of a polycrystalline piezoelectric material, barium titanate, were investigated through electron backscatter diffraction measurements using an amorphous osmium coating to prevent charging. Realistic crystal orientations obtained from the electron backscatter diffraction measurements were introduced into multiscale finite element simulations based on homogenization theory to reveal the relationship between the macrostructure and the microstructure. First, a two-dimensional microstructural model was constructed, and the effect of the sampling area of the electron backscatter diffraction–measured crystal orientations was analyzed. We discuss the representative volume element determined from two points of view: the macroscopic homogenized material properties and the microscopic localized material behavior in response to external loads. Second, the surface of specimen was ground and polished at regular intervals and was measured by electron backscatter diffraction iteratively. Then a three-dimensional microstructural model was constructed by stacking in-plane crystal orientations in series along the out-of-plane direction, and the influence of the microstructural thickness, which indicates the stacking dimension in the out-of-plane direction, was investigated. We compare the macrostructural homogenized material properties between the two- and three-dimensional microstructures. [ABSTRACT FROM PUBLISHER]

This work quantifies geometric effects of randomness in unidirectional fiber packing arrays over a 0.1-0.9 fiber volume fraction range. Investigated parameters are equivalent symmetry angle, nearest neighbor distance, number of touches per fiber, and specific fiber volume fraction. Ten-thousand different fiber array configurations were analyzed to generate statistical results. These results are presented as plots and least squares approximating functions. It is shown that, for fiber volume fractions exceeding 0.6, truly random fiber packing is unlikely to occur. A sample problem is also included to illustrate benefits of accounting for random behavior in simple models. [ABSTRACT FROM AUTHOR]

Applicability of the finite element method (FEM) in predicting the effective transverse thermal conductivity of fiber reinforced composites is systematically studied. Four different boundary condition combinations representing the periodicity of the temperature field are employed for ideal composites having perfect bond between fiber and matrix. Both circular and square cross-section fibers are studied. Comparisons of present FEM results with available analytical and experimental results reveal that periodicity realized by prescribed temperatures yields most accurate results up to high fiber volume fractions. In composites with interfacial thermal barrier resistance the effective conductivity varies in a wide range depending on the interfacial conductance between fiber and matrix. Best fit with available experimental results is obtained for both circular and square fibers when the dimensionless interfacial conductance is about 30. By employing the modeling practice found successful in the cases for which analytical andlor experimental results exist, some typical combined effects of partial debonding and matrix cracking, for which no such results exist, are finally considered. [ABSTRACT FROM PUBLISHER]

The idea of fiber commingling is proposed to increase compressive strengths and the effect of fiber commingling is evaluated by considering two different failure models, buckling failure and shear failure. Micro-buckling failure theory is extended to account for the nonlinear effects of the fiber and matrix by using Ramberg-Osgood stress-strain relations and the tangential modulus concept. In the case of shear failure, a more appropriate method to estimate the shear strength of each component is proposed. The effect of fiber commingling can be estimated from the controlling mode. [ABSTRACT FROM PUBLISHER]