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When an elastoplastic material undergoes large plastic deformations, the elastic law and particularly the stiffness tetrad will evolve. This evolution is strongly dependent on the particular material. In the present paper, we consider a fiber-reinforced composite with fibers in different distinct directions. These directions introduce the anisotropy into the material behavior, particularly into the elastic law. Under plastic deformations, these directions are deformed together with the material (in contrast to crystal plasticity). This effect is called material plasticity and gives the basis for our new method. It consists of superimposing transversely isotropic stiffnesses for each fiber direction at any stage of the deformation process. A comparison for different composites and deformation paths shows the range of applicability of this method.

The macroscopic properties of composite materials depend on the microscopic properties of the constituents and the geometric arrangement of their phases. Therefore, it is essential to predict heterogeneous materials’ mechanical properties by simulating microstructural finite element models. The present article aims to analyze particle reinforced composites composed of spherical alumina inclusions surrounded by a glass matrix using a tridimensional representative volume element. Herein, microstructures are artificially created considering a regular or random arrangement of the inclusions. Two materials systems previously studied in the literature were analyzed. The discretization of the models was performed to have periodic mesh, thus enabling the use of periodic boundary conditions. A finite element model is created using Abaqus software. Numerical results show that the macroscopic properties can be estimated with high accuracy for the temperature where linear matrix behavior stands. The predictions were compared to experimental data from the literature. The models with a regular arrangement of inclusions show a difference inferior to 10%, while random arrangements show a difference inferior to 3.9%. The developed numerical algorithms can be modified to include new features, such as other dispersed phase arrangements or nonlinear material behavior.

Grain size distribution and orientation distribution functions are combined in a single multivariate continuous grain size orientation distribution function (GSODF). Several examples of practical applications to low carbon steels are presented, in which it is shown how the GSODF can be used in the analysis of 2D and 3D electron backscatter diffraction data, and as input in full-field and mean-field crystal plasticity simulations., Two of the microstructural parameters most influential in the properties of polycrystalline materials are grain size and crystallographic texture. Although both properties have been extensively studied and there are a wide range of analysis tools available, they are generally considered independently, without taking into account the possible correlations between them. However, there are reasons to assume that grain size and orientation are correlated microstructural state variables, as they are the result of single microstructural formation mechanisms occurring during material processing. In this work, the grain size distribution and orientation distribution functions are combined in a single multivariate grain size orientation distribution function (GSODF). In addition to the derivation of the function, several examples of practical applications to low carbon steels are presented, in which it is shown how the GSODF can be used in the analysis of 2D and 3D electron backscatter diffraction data, as well as in the generation of representative volume elements for full-field models and as input in simulations using mean-field methods.

In the present study, Composite material consisting of an elastic homogeneous isotropic matrix in which are embedded coated elastic isotropic inclusions, widely used in many applications is investigate by homogenization approach coupled to the finite elements method. A finite element model is proposed to predict the Young and Shear modulus of the three-phase composite containing spherical inclusions surrounded by a spherical or ellipsoid interphase layer. Three cases of particles volume fractions and interphase was considered with addition of two interphase morphology. Young modulus of interphase region was varied from soft to hard than the matrix properties. We note that interphase morphology and properties plays an important role in the elastic properties of composite with increasing the volume fraction of inclusions and interphase. The results were compared to the first order bounds Voigt and Reuss, and the mean field homogenization techniques. A sensitive study of the effect of mesh density on the results of the von Mises stresses and elastic properties has been made.

Micromechanics models of composite materials are preferred in the analysis and design of composites for their high computational efficiency. However, the accuracy of the micromechanics models varies widely, depending on the volume fraction of inclusions and the contrast of phase properties, which have not been thoroughly studied, primarily due to the lack of complete and representative experimental data. The recently developed microstructure-free finite element modeling (MF-FEM) is based on the fact that, for a particulate-reinforced composite, if the characteristic size of the inclusions is much smaller than the composite representative volume element (RVE), the elastic properties of the RVE are independent of inclusion shape and size. MF-FEM has a number of advantages over the conventional microstructure-based finite element modeling. MF-FEM predictions have good to excellent agreement with the reported experiment results. In this study, predictions produced by MF-FEM are used in replace of experimental data to compare the accuracy of selected micromechanics models of particulate composites. The results indicate that, only if both the contrasts in phase Young’s moduli and phase Poisson’s ratios are small, the micromechanics models are able to produce accurate predictions. In other cases, they are more or less inaccurate. This study may serve as a guide for the appropriate use of the micromechanics models.

Damping performance of the plates with constrained layer damping (CLD) treatment mainly depends on the layout of CLD material and the material physical properties of the viscoelastic damping layer. This paper develops a concurrent topology optimization methodology for maximizing the modal loss factor (MLF) of plates with CLD treatment. At the macro scale, the damping layer is composed of 3D periodic unit cells (PUC) of cellular viscoelastic damping materials. At the micro scale, due to the deformation of viscoelastic damping material affected by the base and constrained layers, the representative volume element (RVE) considering a rigid skin effect is used to improve the accuracy of the effective constitutive matrix of the viscoelastic damping material. Maximizing the MLFs of CLD plates is employed as the design objectives in optimization procedure. The sensitivities with respect to macrodesign variables are formulated using the adjoint vector method while considering the contribution of eigenvectors, while the influence of macroeigenvectors is ignored to improve the computational efficiency in the mesosensitivity analysis. The macro and meso scales design variables are simultaneously updated using the Method of Moving Asymptotes (MMA) to find concurrently optimal configurations of constrained and viscoelastic damping layers at the macro scale and viscoelastic damping materials at the micro scale. Two rectangular plates with different boundary conditions are presented to validate the optimization procedure and demonstrate the effectiveness of the proposed concurrent topology optimization approach. The effects of optimization objectives and volume fractions on the design results are investigated. The results indicate that the optimized layouts of the macrostructure are dependent on the objective mode and the volume fraction on the meso scale. The optimized designs on the meso scale are mainly related to the objective mode. By varying the volume fraction on the macro scale, the optimized designs on the meso scale are different only in their detailed size, which is reflected in the values of the equivalent constitutive matrices.

Natural fiber composites (NFCs) also termed as biocomposites offer an alternative to the existing synthetic fiber composites, due to their advantages such as abundance in nature, relatively low cost, lightweight, high strength-to-weight ratio, and most importantly their environmental aspects such as biodegradability, renewability, recyclability, and sustainability. Researchers are investigating in depth the properties of NFC to identify their reliability and accessibility for being involved in aircrafts, automotive, marine, sports’ equipment, and other engineering fields. Modeling and simulation (M&S) of NFCs is a valuable method that contributes in enhancing the design and performance of natural fibers composite. Recently many researchers have applied finite element analysis to analyze NFCs’ characteristics. This article aims to present a comprehensive review on recent developments in M&S of NFCs through classifying the research according to the analysis type, NFC type, model type, simulation platform and parameters, and research outcomes, shedding the light on the main applicable theories and methods in this area, aiming to let more experts know the current research status and also provide some guidance for relevant researches.

In the automotive field, piezo-resistive strain sensors have been increasingly integrated into “intelligent tyres”, to monitor the operating parameters, and to transmit them in real-time to the ECU. This work deals with polymer based piezo-resistive strain sensors with Carbon NanoTubes (CNT) embedded. CNTs slightly increase the mechanical strength of the sensor while improve the conductive and piezo-resistive behaviour of the polymer. A numerical methodology based on the Representative Volume Element (RVE) is proposed to predict the mechanical and electrical response of CNT-polymer. Finite Element method has been applied to obtain equivalent properties, which have been compared to experimental data available in the literature. Good estimate of the mechanical (i.e. Young’s Modulus) and electrical (i.e., resistivity) parameters has been achieved. The proposed methodology is thus suitable to identify electrical and mechanical properties of polymers with dispersed nanofibres.

We investigate numerically the small-strain, elastic–plastic response of statistically isotropic materials with non-uniform spatial distributions of mechanical properties. The numerical predictions are compared to simple bounds derived analytically. We explore systematically the effects of heterogeneity on the macroscopic stiffness, strength, asymmetry, stability and size dependence. Monte Carlo analyses of the response of statistical volume elements are conducted at different strain triaxiality using computational homogenisation, and allow exploring the macroscopic yield behaviour of the heterogeneous material. We illustrate quantitatively how the pressure-sensitivity of the yield surface of the solid increases with heterogeneity in the elastic response. We use the simple analytical models developed here to derive an approximate scaling law linking the fatigue endurance threshold of metallic alloys to their stiffness, yield strength and tensile strength.

The development of additive manufacturing technologies has been followed by an increase in material variety, especially by the introduction of numerous types of reinforcements to enhance the mechanical performance of basic polymers. Since the microstructure of these novel composites may vary in types, sizes, shapes, and ratios of reinforcements, it is necessary to optimize these parameters before conducting experimental validation. Hence, a microscale analysis based on representative volume element modeled according to the statistically significant constituent’s data acquired from the microscopic analysis is proposed. Moreover, to account for the weak fiber/matrix bounding in comparison with the ideal bond assumption, cohesive behavior can be prescribed at these interfaces. According to the type of reinforcement, three variations of RVE-s have been modeled in the Abaqus CAE environment utilizing periodic boundary conditions, and each was tested for longitudinal, transverse, and shear loading cases. The validation has been conducted on two unidirectional [0] and [90], as well as one multidirectional [45/−45]4s carbon fiber reinforced composite specimens. The experimental tests have been performed quasistatically and monitored using a digital image correlation system. Experimental and numerical results have been systematically compared with the published data, proposing a guideline for the protocol applicability and the necessity for further improvements.

The impact of real sintering structures on the macroscopic stress state and yield locus of sintered silver was investigated and a novel continuum modelling approach that predicts the macroscopic properties in an accurate, simple and efficient way was derived. Focused-Ion-Beam (FIB) tomography was utilized to study silver films, which were sintered under a wide range of processing conditions. With reconstructed three-dimensional representative volume elements (RVE), linear elastic and linear elastic–perfect plastic Finite-Element-Analyses were performed for a variety of loading states. The stress state ratios and the plastic yielding were investigated with respect to the mesostructural quantities obtained from the FIB tomography. The specific pore surface area and the fractional density were found to represent characteristic scalar measures for the sintering structure, which were further used to formulate a thermodynamic consistent continuum model for the macroscopic stress state and yield locus. An assessment of the modelling approach showed good coincidence of the macroscopic stress state with experiments and simulations from literature and a 43 % better prediction accuracy for the yield locus compared to established modelling approaches. The transferability of the model parameters to different silver sintering raw materials was partially proved by literature results and promises reduced parameterization effort.

An algorithm for post-processing of the grayscale 3D computed tomography (CT) images of porous structures with the automatic selection of filtering parameters is proposed. The determination of parameters is carried out on a representative part of the image under analysis. A criterion for the search for optimal filtering parameters based on the count of "levitating stone" voxels is described. The stages of CT image filtering and its binarization are performed sequentially. Bilateral and anisotropic diffuse filtering is implemented; the Otsu method for unbalanced classes is chosen for binarization. Verification of the proposed algorithm was carried out on model data. To create model porous structures, we used our image generator, which implements the function of anisotropic porous structures generation. Results of the post-processing of real CT images containing noise and reconstruction artifacts by the proposed method are discussed.

This study presents a systematic evaluation of the physical, thermal and mechanical performance of medical-grade semi-crystalline PLLA undergoing thermally-accelerated degradation. Samples were immersed in phosphate-buffered saline solution at 50 °C for 112 days and mass loss, molecular weight, thermal properties, degree of crystallinity, FTIR and Raman spectra, tensile elastic modulus, yield stress and failure stress/strain were evaluated at consecutive time points. Samples showed a consistent reduction in molecular weight and melting temperature, a consistent increase in percent crystallinity and limited changes in glass transition temperature and mass loss. At day 49, a drastic reduction in tensile failure strain was observed, despite the fact that elastic modulus, yield and tensile strength of samples were maintained. Brittleness increase was followed by rapid increase in degradation rate. Beyond day 70, samples became too brittle to test indicating substantial deterioration of their load-bearing capacity. This study also presents a computational micromechanics framework that demonstrates that the elastic modulus of a semi-crystalline polymer undergoing degradation can be maintained, despite a reducing molecular weight through compensatory increases in percent crystallinity. This study presents novel insight into the relationship between physical properties and mechanical performance of medical-grade PLLA during degradation and could have important implications for design and development of bioresorbable stents for vascular applications.

A microstructure-based numerical simulation is performed to understand the mechanical properties and fracture of a Ti-Al3Ti core-shell structured particulate reinforced A356 composite ((Ti-Al3Ti)cs/A356). A series of two-dimensional (2D) representative volume element (RVE) models are generated automatically by embedding Ti-Al3Ti core-shell structured particulates in an A356 matrix. Microstructure-based 2D RVE of monolithic Al3Ti particulate reinforced A356 composite (Al3Tip/A356) is also simulated for comparison. The ductile fracture of both Ti core and A356 matrix as well as the brittle fracture of the Al3Ti shell are considered. The simulation confirms that the high elongation of the (Ti-Al3Ti)cs/A356 composite is attributed to the uniform distribution of the overall ductile globular reinforcing particulates, which prevent a premature failure effectively by reducing local stress concentration both on and inside the core-shell structured particulates. The surrounding ductile phases of the Al3Ti shell blunt the crack tips effectively and, therefore, restricting the propagation of the cracks in a nominal strain range of 2.2%–6.1%. For both (Ti-Al3Ti)cs/A356 and Al3Tip/A356 composites, the simulation results are in good agreement with microstructural observations during an in-situ tensile test in a scanning electron microscope.

International audience; A numerical method to compute the Effective Thermal Conductivity (ETC) of granular media surrounded by a stagnant fluid is presented. Based on the geometry and size of grains, a Representative Volume Elements (RVE) of the granular media is created using the Discrete Element Method (DEM) while the ETC of this RVE is estimated with Fast Fourier Transform (FFT) computations. To bridge the gap between the DEM and the FFT, a discretization algorithm (voxelisation of convex polyhedra) was developed. Since their physical properties are poorly defined, "fuzzy" voxels associated with solid-gas interfaces or solid-solid contacts, domains inherent in a granular medium, are clearly identified during this step. The assignment of extreme properties to these voxels, assuming negligible radiation, allows to establish lower and upper ETC bounds. This methodology is applied to granular media of Uranium dioxide particles immersed in stagnant Helium; packed beds for which experimental data are available in the literature. First, the effect of RVE and discretization sizes on the simulated ETC are investigated and optimal values of RVE size and discretization ratio are defined. Next, the significant deviation of simulated DEM-FFT ETC bounds, observed at high solid to gas conductivity contrasts, exhibits the key role of interfaces on the computed ETCs. An improved modelling of solid-gas interfaces based on the Knudsen effect and a modelling correction for solid-solid interfaces is therefore proposed. The new modelling is shown to adequately bound and estimate the ETC of considered granular media at high (∼100) solid to gas thermal conductivity contrasts.

The microstructure-based finite element modeling (MB-FEM) of material representative volume element (RVE) is a widely used tool in the characterization and design of various composites. However, the MB-FEM has a number of deficiencies, e.g., time-consuming in the generation of a workable geometric model, challenge in achieving high volume-fractions of inclusions, and poor quality of finite element mesh. In this paper, we first demonstrate that for particulate composites the particle inclusions have homogeneous distribution and random orientation, and if the ratio of particle characteristic length to RVE size is adequately small, elastic properties characterized from the RVE are independent of particle shape and size. Based on this fact, we propose a microstructure-free finite element modeling (MF-FEM) approach to eliminate the deficiencies of the MB-FEM. The MF-FEM first generates a uniform mesh of brick elements for the RVE, and then a number of the elements, with their total volume determined by the desired volume fraction of inclusions, is randomly selected and assigned with the material properties of the inclusions; the rest of the elements are set to have the material properties of the matrix. Numerical comparison showed that the MF-FEM has a similar accuracy as the MB-FEM in the predicted properties. The MF-FEM was validated against experimental data reported in the literature and compared with the widely used micromechanical models. The results show that for a composite with small contrast of phase properties, the MF-FEM has excellent agreement with both the experimental data and the micromechanical models. However, for a composite that has large contrast of phase properties and high volume-fraction of inclusions, there exist significant differences between the MF-FEM and the micromechanical models. The proposed MF-FEM may become a more effective tool than the MB-FEM for material engineers to design novel composites.

The paper is devoted to finite element method based study of stress field heterogeneity at microstructure level of two-phase cemented carbides. Special attention is put on investigation of influence of the microstructure model type on the stress field distributions. Two- and three-dimensional models of the microstructures have been generated. Moreover, two different representations of the microstructure have been considered. The first one assumes uniformly distributed cobalt phase forming continuous boundaries between tungsten carbide particles. The second one assumes that the cobalt phase shape and distribution are created in a way that allows for no differentiation of continuous boundaries between tungsten carbide grains. Finite element analyses have been carried out with different microstructure models. The results of the simulations are stress distributions in each phase of the material. Furthermore, a numerical homogenization has been conducted to investigate the phase properties’ influence on the effective elastic constants of the cemented carbide.

In this work we develop a multi-scale model to characterise the large scale constitutive behaviour of a material featuring a small scale fibrous architecture. The Method of Multi-scale Virtual Power (MMVP) is employed to construct the model. At the macro-scale, a classical continuum mechanics problem is formulated in the finite strain regime. At the micro-scale, a network of fibres, modelled as one-dimensional continua, composes the representative volume element (RVE). The MMVP provides a full characterisation of the equilibrium problem at the RVE, with consistent boundary conditions, as well as the homogenisation formula which defines the first Piola–Kirchhoff stress tensor. Particular attention is given to the fact that the macro-scale continuum could be considered incompressible. Numerical experiments are presented and model consistency is verified against well-known phenomenological constitutive equations. Scenarios departing from the hypotheses of such phenomenological material models are discussed. Fil: Rocha, Felipe Figueredo. Laboratório Nacional de Computação Científica; Brasil. Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica; Brasil Fil: Blanco, Pablo Javier. Laboratório Nacional de Computação Científica; Brasil. Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica; Brasil Fil: Sánchez, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Feijóo, Raúl Antonino. Laboratório Nacional de Computação Científica; Brasil. Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica; Brasil

A multiscale framework for the analysis of fracture is developed in order to determine the effective (homogenized) strength and fracture energy of a composite material based on the constituent's material properties and microstructural arrangement. The method is able to deal with general (mixed-mode) applied strains without a priori knowledge of the orientation of the cracks. Cracks occurring in a microscopic volume element are modeled as sharp interfaces governed by microscale traction-separation relations, including interfaces between material phases to account for possible microscale debonding. Periodic boundary conditions are used in the microscopic volume element, including periodicity that allows cracks to transverse the boundaries of the volume element at arbitrary orientations. A kinematical analysis is presented for the proper interpretation of a periodic microscopic crack as an equivalent macroscopic periodic crack in a single effective orientation. It is shown that the equivalent crack is unaffected by the presence of parallel periodic replicas, hence providing the required information of a single localized macroscopic crack. A strain decomposition in the microscopic volume element is used to separate the contributions from the crack and the surrounding bulk material. Similarly, the (global) Hill–Mandel condition for the volume element is separated into a bulk-averaged condition and a crack-averaged condition. Further, it is shown that, though the global Hill–Mandel condition can be satisfied a priori using periodic boundary conditions, the crack-based condition can be used to actually determine the effective traction of an equivalent macroscopic crack.

In order to provide an accurate thermal analysis method of fiber-reinforced composites, a novel model based on a probabilistic representative volume element (RVE) is presented in this paper. Monte Carlo methods, probability analysis and finite element analysis have been applied together. The effective transverse thermal conductivity, heat flux field, and thermal gradient field of typical fiber-reinforced composites are examined. The criteria of RVE have been determined, and the minimal size for thermal analysis is obtained using the main statistics and the cross-entropy theory. At the same time, the fiber-to-matrix ratio of thermal conductivity and volume fraction have been changed to determine the influence on heat transfer inside fiber-reinforced composites. It is shown that different purposes of simulations lead to different minimal RVE sizes. The numerical results indicate that the non-dimensional minimal RVE sizes for calculating the effective thermal conductivity, heat flux, and thermal gradient are 30, 80, and 80, respectively. Compared with the volume fraction, the fiber-to-matrix ratio of the thermal conductivity has a more significant effect on minimal RVE size. When the thermal conductivity ratio increases, the minimal size of the RVE increases at first, then it remains almost unchanged.

For unidirectional loaded specimens consisting of isotropic-homogeneous ductile materials, an analytical elastoplastic model for the equivalent stress and strain of the representative volume element at the median point were derived based on energy density equivalence and dimensional analysis. Then, a data processing method for various specimen types was proposed to obtain the equivalent stress–strain in real time without presetting the constitutive parameters. Finite element analyses of six specimen types and experiments with four selected specimen types were conducted to verify the method. The results show that the stress–strain curves obtained using this method were consistent with the preset stress–strain curves in the finite element analysis and with the standard tensile results. Using the proposed model and relevant data processing method to obtain the stress–strain curves is effective and, with the theoretical basis, could promote the application of non-tradition and small specimens for obtaining the material mechanical properties.

This work addresses the multi-scale modeling of fluid flow in highly complex media based on the concept of Representative Volume Element (RVE). The Method of Multi-scale Virtual Power developed by the authors is employed to construct a coarse-scale model from standard fluid flow model at a fine-scale. Kinematic conservation principles, duality arguments and the balance of virtual power between scales are employed to set the grounds of the scale transition of physical fields. This allows to derive in a variationally consistent manner (i) the fine-scale problem to be solved at the RVE, and (ii) the homogenization formulae for coarse-scale dual quantities, namely, the force-like and stress-like fields. Examples of application of flow in permeable media are presented to show the potential of the present approach. Fil: Blanco, Pablo Javier. Instituto Nacional de Ciência E Tecnologia Em Medicina Assistida Por Computação Científica; Brasil. Laboratorio Nacional de Computacao Cientifica; Brasil Fil: Clausse, Alejandro. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina Fil: Feijóo, Raúl Antonino. Laboratorio Nacional de Computacao Cientifica; Brasil. Instituto Nacional de Ciência E Tecnologia Em Medicina Assistida Por Computação Científica; Brasil

Mesoscale geometric modeling of cellular materials is not strictly related only to tomography reconstruction, but it can be applied also in Finite Element Analysis: (a) to better understand load distribution at the interfaces; (b) to develop and calibrate material models; (c) for sensitivity analysis to different loads or shape parameters. This paper aims to examine some of the most applied techniques for geometric modeling of cellular materials at a mesoscale level discussing their advantages and disadvantages for Finite Element Analysis. Among them, two of the most applied techniques, the Voronoi approach and the reverse engineering reconstruction, are here applied to simulate the behavior of aluminum foams under compression. These applications compared to some experimental evidences confirm the capability of mesoscale analysis, highlighting possible enhancement of the geometric modeling techniques.

Glioblastomas represent a challenging problem with an extremely poor survival rate. Since these tumour cells have a highly invasive character, an effective surgical resection as well as chemotherapy and radiotherapy is very difficult. Convection-enhanced delivery (CED), a technique that consists in the injection of a therapeutic agent directly into the parenchyma, has shown encouraging results. Its efficacy depends on the ability to predict, in the pre-operative phase, the distribution of the drug inside the tumour. This paper proposes a method to compute a fundamental parameter for CED modelling outcomes, the hydraulic permeability, in three brain structures. Therefore, a bidimensional brain-like structure was built out of the main geometrical features of the white matter: axon diameter distribution extrapolated from electron microscopy images, extracellular space (ECS) volume fraction and ECS width. The axons were randomly allocated inside a defined border, and the ECS volume fraction as well as the ECS width maintained in a physiological range. To achieve this result, an outward packing method coupled with a disc shrinking technique was implemented. The fluid flow through the axons was computed by solving Navier–Stokes equations within the computational fluid dynamics solver ANSYS. From the fluid and pressure fields, an homogenisation technique allowed establishing the optimal representative volume element (RVE) size. The hydraulic permeability computed on the RVE was found in good agreement with experimental data from the literature.

In this study, we investigate the effect of the heterogeneous micromechanical stress fields resulting from the grain-scale anisotropy on the redistribution of hydrogen using a diffusion coupled crystal plasticity model. A representative volume element with periodic boundary conditions was used to model a synthetic microstructure. The effect of tensile loading, initial hydrogen content and yield strength on the redistribution of lattice (CL) and dislocation trapped (Cx) hydrogen was studied. It was found that the heterogeneous micromechanical stress fields resulted in the accumulation of both populations primarily at the grain boundaries. This shows that in addition to the well-known grain boundary trapping, the interplay of the heterogeneous micromechanical hydrostatic stresses and plastic strains contribute to the accumulation of hydrogen at the grain boundaries. Higher yield strength reduced the amount of Cx due to the resulting lower plastic deformation levels. On the other side, the resulting higher hydrostatic stresses increased the depletion of CL from the compressive regions and its diffusion toward the tensile ones. These regions with increased CL are expected to be potential damage initiation zones. This aligns with the observations that high-strength steels are more susceptible to hydrogen embrittlement than those with lower-strength.

In this research, the effect of 2D and 3D Representative Volume Element (RVE) on the ductile damage behavior in single-phase (only ferrite) and dual-phase (ferrite and martensite) steels is analyzed. Physical and fitting parameters of the constitutive model for bcc-ferrite and bcc-martensite phases are adapted from the already published work. Crystal plasticity (CP) based numerical simulations without damage consideration are run and, later, ductile damage criteria for the ferrite phase is defined for all cases. The results of the non-damage (-nD-) and damage (-D-) simulations are compared to analyze the global and local differences of evolving stresses and strains. It is observed that for the same model parameters defined in all cases, damage initiation occurs at the overall higher global strain in the case of 3D compared to 2D. Based on statistical data analysis, a systematic comparison of local results is carried out to conclude that the 3D RVEs provide better quantitative and qualitative results and should be considered for such full phase simulations. Whereas 2D RVEs are simple to analyze and provide appropriate qualitative information about the damage initiation sites.

This paper presents a new metallurgical model for the ausferritic transformation of ductile cast iron. The model allows predicting the evolution of phases in terms of the chemical composition, austenitization and austempering temperatures, graphite nodule count, and distribution of graphite nodule size. The ferrite evolution is predicted according to the displacive growth mechanism. A representative volume element is employed at the microscale to consider the phase distributions, the inhomogeneous austenite carbon content, and the nucleation of ferrite subunits at the graphite nodule surface and at the tips of existing ferrite subunits. The performance of the model is evaluated by comparison with experimental results. The results indicate that the increment of the ausferritic transformation rate, which is caused by increments of austempering temperature and graphite nodule count, is adequately represented by this model. Fil: Boccardo, Adrian Dante. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; Argentina Fil: Dardati, Patricia Mónica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; Argentina Fil: Celentano, Diego J.. Universidad Católica de Chile; Chile Fil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina

The present article deals with micromechanical composite modeling. Both analytical and computational micromechanics approaches are described as well as micromechanical modeling of damage. Based on micromechanics of failure theory, a user subroutine including a progressive damage algorithm is programmed for finite element analysis. Three theory-experiment correlations of tubes under a three-point bending test have been carried out using the bi-phase material model developed along with this project. These studies include three-ply schedules., All the presented work was carried out within the project MATISSE funded by European Commission’s 7th Framework Programme.

We present a new numerical methodology to build a Representative Volume Element (RVE) of a wide range of 3D woven composites in order to determine the mechanical behavior of the fabric unit cell by a mesoscopic approach based on a 3D finite element analysis. Emphasis is put on the numerous difficulties of creating a mesh of these highly complex weaves embedded in a resin. A conforming mesh at the numerous interfaces between yarns is created by a multi-quadtree adaptation technique, which makes it possible thereafter to build an unstructured 3D mesh of the resin with tetrahedral elements. The technique is not linked with any specific tool, but can be carried out with the use of any 2D and 3D robust mesh generators.

Crystal plasticity models attempt to reproduce the complex deformation processes of polycrystalline metals based on a virtual representation of the real microstructure. When choosing this representation, a compromise must be made between level of detail at the local level and statistical significance of the aggregate properties, also taking into account the computational cost of each solution. In this work, the correlation between crystallographic orientation and grain size is considered in the definition of virtual microstructures for the simulation of the mechanical behavior of AISI 420 stainless steel (consisting of a ferrite matrix with large carbide precipitates), in order to improve the accuracy of the solution without increasing model complexity or computation time. Both full-field (DAMASK) and mean-field models (Visco Plastic Self Consistent (VPSC)) are used together in combination with experimental results to study the validity of the assumptions done in each of the models.

This study aims to establish a strategy for bridging the microstructure and mechanical properties of fine-grain-structured dual-phase steel. A complete workflow is built up commencing with the microstructure observations and characterization in both phase and grain levels by assorted experimental techniques. An assessment criterion is proposed to quantitatively examine the representativeness of synthetic microstructure models in terms of the refined microstructural features including phase fraction, grain size, grain shape, and texture for each phase of the steel. The criterion is employed to define a two-step optimization procedure for building the synthetic microstructure model for the dual-phase steel with nanoscale grain size. The crystal plasticity model is employed to describe the material deformation behavior. The corresponding material parameters are calibrated by an inverse approach combining the nanoindentation test and the macroscopic uniaxial tensile test. The simulation with the calibrated parameters and the synthetic microstructure model gives an excellent prediction of the Lankford coefficient of the dual-phase steel. Benefiting from the strategy, a virtual laboratory is conducted to investigate the micro-structure sensitivity on the mechanical properties, which serves a basis for the microstructure design with desired properties.

A nanoscale representative volume element has been developed to investigate the effect of interphase geometry and property on the mechanical behavior of silica/epoxy resin nanocomposites. The role of interphase–matrix bonding was also examined. Results suggested that interphase modulus and interfacial bonding conditions had significant influence on the effective stiffness of nanocomposites, while its sensitivities with respect to both the thickness and the gradient property of the interphase was minimal. The stiffer interphase demonstrated a higher load-sharing capacity, which also increased the stress distribution uniformity within the resin nanocomposites. Under the condition of imperfect interfacial bonding, the effective stiffness of nanocomposites was much lower, which was in good agreement with the documented experimental observations. This work could shed some light on the design and manufacturing of resin nanocomposites.

ResumenLa fundición nodular es una aleación metálica de Fe-C-Si cuya microestructura está formada por una matriz, en general compuesta por ferrita y perlita, en la cual se encuentran embebidos nódulos de grafito. Al ser este un material microscópicamente heterogéneo, su comportamiento está definido por las propiedades, la morfología y la topología de las fases que lo componen. En este trabajo se plantea como objetivo hallar el valor de las constantes elásticas, el módulo de Young y el coeficiente de Poisson, de un material homogéneo equivalente que caracteriza el comportamiento macroscópico de una fundición nodular. Para la estimación del comportamiento elástico se utiliza el método de homogeneización asintótica. Este método se aplica a celdas multipartículas tridimensionales y bidimensionales que se analizan mediante el método de los elementos finitos (MEF). Para la determinación del elemento de volumen representativo (RVE [representative volume element]) del comportamiento del material se utilizan 2 criterios, uno físico y otro geométrico, encontrándose que el tamaño del RVE es sensible al criterio utilizado para su definición. Las principales características microestructurales son extraídas de una simulación computacional de la solidificación del material. Se comparan los resultados obtenidos de la aplicación de los modelos tridimensionales y bidimensionales y se analiza la influencia del modelo utilizado en las propiedades analizadas. Del análisis de los resultados obtenidos se observa que los modelos que emplean celdas multipartícula tridimensionales requieren tamaños menores de la misma para ser representativos de la fundición nodular, es decir, los tamaños de los RVE tridimensionales son menores que los correspondientes bidimensionales. Se observa también que estos últimos presentan una respuesta elástica menos rígida en relación con los primeros.AbstractNodular cast iron is a Fe-C-Si metallic alloy whose microstructure consists of a matrix, composed in general of ferrite and pearlite, with graphite nodules embedded in it. Owing to its microscopical heterogeneity, the material response is governed by the properties, morphology and typology of the phases involved. This work reports on the evaluation of the elastic properties, i.e., Young's modulus and Poisson's ratio, of an equivalent homogeneous material that characterizes the macroscopic response of a nodular cast iron. Asymptotic homogenization is used to this end. This approach is applied to both 3D and 2D multiparticle cells simulated via the finite element method. Two different physically and geometrically-based criteria are considered to estimate the representative volume element (RVE), where the size of the RVE is found to be sensitive to the chosen criterion. The main microstructural features are obtained from a computational simulation of the solidification process of the material. The numerical predictions computed for the 3D and 2D cases are compared and discussed in terms of the resulting elastic properties. It is observed that the models employing 3D multiparticle cells require lower RVE sizes than the corresponding 2D models, where the latter present a stiffer elastic response.

In order to describe irreversible deformation during metal forming processes, the yield surface is one of the most important criteria. Because of their simplicity and efficiency, analytical yield functions along with experimental guidelines for parameterization become increasingly important for engineering applications. However, the relationship between most of these models and microstructural features are still limited. Hence, we propose to use micromechanical modeling, which considers important microstructural features, as a part of the solution to this missing link. This study aims at the development of a micromechanical modeling strategy to calibrate material parameters for the advanced analytical initial yield function Barlat YLD 2004-18p. To accomplish this, the representative volume element is firstly created based on a method making use of the statistical description of microstructure morphology as input parameter. Such method couples particle simulations to radical Voronoi tessellations to generate realistic virtual microstructures as representative volume elements. Afterwards, a nonlocal crystal plasticity model is applied to describe the plastic deformation of the representative volume element by crystal plasticity finite element simulation. Subsequently, an algorithm to construct the yield surface based on the crystal plasticity finite element simulation is developed. The primary objectives of this proposed algorithm are to automatically capture and extract the yield loci under various loading conditions. Finally, a nonlinear least square optimization is applied to determine the material parameters of Barlat YLD 2004-18p initial yield function of representative volume element, mimicking generic properties of BCC and FCC steels from the numerical simulations.

Monotonic deformation behavior of ferrite-martensite dual phase steels with martensite volume of 13-43 % have been analyzed in the current investigation using micromechanics based finite element simulation on representative volume elements. The effects of martensite volume fraction on the strain partitioning behavior between soft ferrite matrix and hard martensite islands in dual phase steels during tensile deformation have been investigated. As a consequence of strain incompatibility between hard martensite and soft ferrite phases, inhomogeneous deformation and finally deformation localization occur during tensile deformation. Restricted local deformation in ferrite phase caused by the adjacent martensite islands triggers the local stress triaxiality development. As the martensite volume fraction increases, the local deformation restrictions in ferrite phase also increases and which results in higher stress triaxiality development. Similarly the strain partitioning behavior between ferrite matrix and martensite island is also influenced by the volume fraction of martensite. The strain partitioning coefficient increases with increasing martensite volume fraction.

Many composite materials, widely used in different engineering fields, are characterized by random distributions of the constituents. Examples range from polycrystals to concrete and masonry-like materials. In this work we propose a statistically-based scale-dependent multiscale procedure aimed at the simulation of the mechanical behavior of a two-phase particle random medium and at the estimation of the elastic moduli of the energy-equivalent homogeneous micropolar continuum. The key idea of the procedure is to approach the so-called Representative Volume Element (RVE) using finite-size scaling of Statistical Volume Elements (SVEs). To this end properly defined Dirichlet, Neumann, and periodic-type non-classical boundary value problems are numerically solved on the SVEs defining hierarchies of constitutive bounds. The results of the performed numerical simulations point out the importance of accounting for spatial randomness as well as the additional degrees of freedom of the continuum with rigid local structure.

Two phase masonry model, which contains elastic mortar and elastic bricks, is analyzed numerically in order to evaluate sensitivity of effective elastic moduli and strength properties to a deviation in the masonry structural parameters. Different methods of masonry homogenization are studied. Effective elastic moduli of the masonry representative volume element are obtained by means of direct finite element simulation and homogenization procedure. Influence of variation in the heterogeneous material microstructure characteristics (influence of brick aspect ratio and orientation angle) on the local stress-strain state and mechanical properties of the representative volume element of the composite considered is analyzed. Mechanical properties obtained by direct finite element modeling and other methods in various literary sources are compared. These studies are relevant for the design of composite materials with a structure similar to masonry.

A numerical approach based on a computational constitutive multi-scale model is used in this work to predict the effective Young’s modulus and Poisson’s ratio of a pearlitic nodular cast iron. The Representative Volume Element (RVE) is defined based on a set of micrographs acquired from an optical device. For each micrograph, two RVE with different shape, rectangular and hexagonal, are defined. The volume fraction of graphite and metal matrix and the boundary of each object were identified on each RVE by using a procedure of image enhanced and segmentation. The set of RVE obtained was meshed with triangular finite elements. The numerical results obtained with rectangular and hexagonal RVE are compared with results obtained by means of an analytical expression. The influence of graphite fractions, aspect ratios and nodularity are investigated. The results show that graphite fraction has the largest influence on the effective modulus E. This feature is independent of the external shape of the RVE. Only one multi-scale model show a good agreement with the analytical expression in the effective modulus E. Also, the influence of the graphite volume fraction on the effective Poisson’s ratio is investigated by means of multi-scale simulation. Fil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; Argentina Fil: Giusti, Sebastian Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Civil; Argentina Fil: Boccardo, Adrian Dante. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Civil; Argentina Fil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina

In this paper the estimation of residuals for the homogenized solution in elastic problem is taken into account. The case of the beam with Young's modulus randomly varying along the axis is considered. The analysis is performed by means of numerical simulation which is validated by comparison with particular solutions reported in the literature. The convergence to the homogenized solution and the behavior of the residuals are studied in terms of the parameter ɛ , which represents the ratio between the microscopic and the macroscopic scale. After validation with the literature results, the procedure is used to analyze the influence on the convergence of the correlation law of Young's modulus with log-normal distribution. Moreover the particular case of the two-phase beam is considered. The effect of different boundary conditions is also investigated.

A sequential method is proposed to investigate the influence of material parameters identified at different scales (atomic, grains and phase) on fracture properties of tungsten carbide-cobalt (WC-Co) drill bit material used for hard rock drilling. The study includes four commercial WC-Co grades. The representative volume element (RVE) approach was used to account for microstructural features such as volume fraction and distribution of the phases and average size of grain. Different RVEs representing the grades materials were generated and implemented in a FE model incorporating the anisotropic elastic response of the constitute grains. Brittle fracture is assumed in the phases and an energy based failure criterion using the work of separation for the WC/WC, WC/Co and Co/Co interfaces has been identified using the density functional theory (DFT). This criterion was implemented in the finite element model to determine fracture strength for the investigated grades. The elastic properties and fracture strength predicted by the model were discussed with respect to the influence of volume fraction of the phases and average grain size in the investigated WC-Co grades.

The present work investigates by finite element (FE) analysis the effects of volume fraction and distribution of martensite phase on the strain localization in three commercial dual-phase (DP) steels. Strain localization is considered here as a precursor to fracture. The microstructures of the investigated steels were explicitly represented in the FE model using the representative volume element (RVE) approach. The properties of the ferrite and the martensite were determined from tensile test data for the investigated steels using an inverse identification procedure. The strain field in each phase was determined and related to the distribution of the martensite in the soft ferrite phase. Strain localization in the hard martensite phase was discussed with respect to fracture initiation and propagation in the investigated DP steels. The numerical results are coherent with microstructural observations of fracture initiation in DP steels.

Dual-phase steels have become a favored material for car bodies. In this study, the deformation behavior of dual-phase steels under uniaxial tension is investigated by means of 2D Representative Volume Elements (RVE) model. The real metallographic graphs including particle geometry, distribution and morphology are considered in this RVE model. Stress and strain distributions between martensite and ferrite are analyzed. The results show that martensite undertakes most stress without significant strain while ferrite shares the most strain. The tensile failure is the result of the deforming inhomogeneity between martensite phase and ferrite phase, which is the key factor triggering the plastic strain localization on specimen section during the tensile test.

Carbon nanotubes (CNTs) are allotrope of carbon having a cylindrical structure. They have remarkable mechanical, thermal and electrical properties. The properties of CNTs depend on how the flat sheets of graphene are rolled up (atomic arrangement), diameter and length of nanotubes and morphology of nanostructure. In this paper effective thermal conductivity of Multiwalled Carbon nanotube (MWCNT) based polymer composites are evaluated using a square Representative Volume Element (RVE) in Finite Element Method (FEM). COMSOL Multiphysics 4.2 has been used for making the models and doing the simulations. Effective thermal conductivity of a single MWCNT based polymer composites are evaluated analytically and validated by simulation technique. Continuum model developed by Bagchi A. and Nomura, S. has been used to calculate theoretical conductivity of single MWCNT based polymer composite. Mathematica ® code has been written for theoretical calculation of thermal conductivity. The effect of varying CNT diameter, length, volume fraction and thermal contact conductance on effective thermal conductivity of MWCNT reinforced composites is estimated and analyzed.

Glioblastomas represent a challenging problem with an extremely poor survival rate. Since these tumour cells have a highly invasive character, an effective surgical resection as well as chemotherapy and radiotherapy is very difficult. Convection-enhanced delivery (CED), a technique that consists in the injection of a therapeutic agent directly into the parenchyma, has shown encouraging results. Its efficacy depends on the ability to predict, in the pre-operative phase, the distribution of the drug inside the tumour. This paper proposes a method to compute a fundamental parameter for CED modelling outcomes, the hydraulic permeability, in three brain structures. Therefore, a bidimensional brain-like structure was built out of the main geometrical features of the white matter: axon diameter distribution extrapolated from electron microscopy images, extracellular space (ECS) volume fraction and ECS width. The axons were randomly allocated inside a defined border, and the ECS volume fraction as well as the ECS width maintained in a physiological range. To achieve this result, an outward packing method coupled with a disc shrinking technique was implemented. The fluid flow through the axons was computed by solving Navier–Stokes equations within the computational fluid dynamics solver ANSYS. From the fluid and pressure fields, an homogenisation technique allowed establishing the optimal representative volume element (RVE) size. The hydraulic permeability computed on the RVE was found in good agreement with experimental data from the literature.

The thickness of the hot component in a turbine engine is usually small. Therefore, the traditional prediction model of anisotropic thermal conductivity (ATC) based on the periodic hypothesis may be improper for use in the thermal analysis of ceramic matrix composite (CMC) components with a thin-wall structure. Thus, the prediction model for the ATC of a 2.5-D braided CMC was investigated, taking into account the actual thickness of the CMC thin-wall structure. An RVE (Representative Volume Element) model with a periodic boundary and a full-size model with the actual thickness were built to study the temperature field, the heat flux field, and the effective thermal conductivity of the CMC. A validation experiment was carried out to verify the accuracy of the two prediction models. The effect of the composite&rsquo, s thickness on the ATC and the critical thickness suitable for the RVE model were also studied. The results showed that in the thermal analysis of the thin-wall structure, the RVE model had a large deviation in the estimation of the effective thermal conductivity in the thickness direction. The relative error between the numerical data based on the RVE model and the experimental data reached 10.93%, while the relative error was only 3.53% for the full-size model. Additionally, with increasing thickness, the effective thermal conductivities, based on the RVE model and the full-size model, were close to each other. For the critical thickness for the RVE model, which would be suitable for the prediction of the ATC, if the material&rsquo, s thermal properties such as the absolute value ratio and the level of anisotropy changed, the corresponding critical thickness was also different. For the ATC of the SiC/SiC composites used in this study, the critical thickness was found to be 18.4 mm, nearly 31 times larger than the RVE model&rsquo, s thickness.

Accurate numerical homogenization necessitates the thorough determination of the Representative Volume Element (RVE). There exists several seminal works on the notion of the RVE in homogenization, its definitions and methods of determination for efficient computation of composite effective properties. The objective of the current work is to assess the ability of numerical RVE determination methods to deliver accurate effective properties of composite materials. This paper demonstrates that common and well-established RVE determination methods, based on studying the convergence rate of the effective properties with respect to the volume element size, are invalid for the case of composites reinforced by randomly oriented fibers and yield erroneous estimates of their effective properties. Following the failure of traditional RVE determination methods, we proposed a new RVE determination criterion that is not based on the average property stability, but its statistical variations. Our new proposed criterion has been shown to be more accurate than other criteria in computing the effective properties of composites for aspect ratios up to 60. Moreover, the proposed criterion does not necessitate a convergence study over the volume element size, hence reducing considerably the RVE determination cost. Finally, our work questions the validity of many published works dealing with composites including heterogeneities of high aspect ratios.

A method for the numerical modeling of mechanical behavior of nanocomposite materials reinforced with the carbon nanotubes, based on the computational homogenization as a multiscale method, is presented. The matrix reinforcement interactions, based on the weak van der Waals forces are incorporated into the multiscale model and are represented by the nonlinear rod elements. The reinforcements, i.e. carbon nanotubes, are modeled as a space frame structure, using beam finite elements. Computational homogenization and representative volume element (RVE) are the basis of the presented numerical model of the nanocomposites. Nanoscale model is based on beam and non-linear rod finite elements. An algorithm is developed for the analysis of the presented nanostructure, and for the purpose of the software verification, examples, i.e. models of the nanocomposite material are presented. Also, the nanocomposite model with various vacancy defects in the reinforcement, i.e. nanotube, has been prepared and the obtained results are compared and discussed.Keywords Nanocomposite materials · Carbon nanotubes · Multiscale modelling · Computational homogenization

International audience; This work describes a computational homogenization methodology to estimate the effective elastic-plastic response of random two-phase composite media. It is based on finite element simulations using three-dimensional cubic cells of different size but smaller than the deterministic representative volume element (DRVE) of the microstructure. We propose to extend the approach developed in the case of elastic heterogeneous media by Drugan and Willis (1996) and Kanit et al. (2003) to elastic-plastic composites. A specific polymer blend, made of two phases with highly contrasted properties, is selected to illustrate this approach; it consists of a random dispersion of elastic rubber spheres in an elastic-plastic glassy polymer matrix. It is found that the effective elastic-plastic response of this particulate composite can be accurately determined by computing a sufficient number of small subvolumes of fixed size extracted from the DRVE and containing different realizations of the random microstructure. In addition, the response of an individual subvolume is found anisotropic whereas the average of all subvolumes leads to recover the isotropic character of the DRVE. The necessary realization number to reach acceptable precision is given for two examples of particle volume fractions.

This work is a combined analytical and numerical study of the extreme values of the thermal and elastic fields occurring in a propellant composite material, a granular medium containing dense self-assembled spheroidal grains embedded in a matrix. First, a 3D microtomography image of a representative sample is segmented using morphological operators. Second, the local temperature and heat flux in the quasi-static thermal response is computed numerically, making use of the segmented microstructure and of experimental values of the heat conductivity in each phase. Such fields are readily derived by means of a Fast Fourier Transform method. Emphasis is put on the maximum values of the local fields: even at low contrast of properties between the grain and the matrix, the heat flux patterns is made of hot-spot zones located in-between grains that are close to each other with preferential directions. Third, the local extrema of the fields are investigated in the context of linear elasticity. Finally, analytical approximations are examined at low and high contrast of properties, on a simple hard-core model of cylinders, which is tantamount to a 2D granular microstructure.

We perform Monte Carlo analyses of the anisotropic viscoelastic response of random RVEs representing the microstructure of UD fibre composites. Both fibres and matrix are taken as isotropic viscoelastic solids; the fibres have different shapes including circular, elliptical, Reuleaux and star-shaped; they are separated from the matrix by interphase regions of different mechanical properties and thicknesses. The analyses allow determining the sensitivity of the transversely isotropic, viscoelastic response of UD composites to fibre volume fraction, fibre shape, interphase volume fraction and interphase properties.