Representative elementary volume

About: Representative elementary volume is a(n) research topic. Over the lifetime, 4105 publication(s) have been published within this topic receiving 86863 citation(s).

Determination of the size of the representative volume element for random composites: statistical and numerical approach

Abstract: The representative volume element (RVE) plays a central role in the mechanics and physics of random heterogeneous materials with a view to predicting their effective properties. A quantitative definition of its size is proposed in this work. A RVE size can be associated with a given precision of the estimation of the wanted overall property and the number of realizations of a given volume V of microstructure that one is able to consider. It is shown to depend on the investigated morphological or physical property, the contrast in the properties of the constituents, and their volume fractions. The methodology is applied to a specific random microstructure, namely a two-phase three-dimensional Voronoi mosaic. Finite element simulations of volumes of different sizes are performed in the case of linear elasticity and thermal conductivity. The volumes are subjected to homogeneous strain, stress or periodic boundary conditions. The effective properties can be determined for large volumes and a small number of realizations. Conversely, smaller volumes can be used providing that a sufficient number of realizations are considered. A bias in the estimation of the effective properties is observed for too small volumes for all types of boundary conditions. The variance of computed apparent properties for each volume size is used to define the precision of the estimation. The key-notion of integral range is introduced to relate this error estimation and the definition of the RVE size. For given wanted precision and number of realizations, one is able to provide a minimal volume size for the computation of effective properties. The results can also be used to predict the minimal number of realizations that must be considered for a given volume size in order to estimate the effective property for a given precision. The RVE sizes found for elastic and thermal properties, but also for a geometrical property like volume fraction, are compared.

A micromechanics-based nonlocal constitutive equation and estimates of representative volume element size for elastic composites

Abstract: A variational formulation is employed to derive a micromechanics-based, explicit nonlocal constitutive equation relating the ensemble averages of stress and strain for a class of random linear elastic composite materials. For two-phase composites with any isotropic and statistically uniform distribution of phases (which themselves may have arbitrary shape and anisotropy), we show that the leading-order correction to a macroscopically homogeneous constitutive equation involves a term proportional to the second gradient of the ensemble average of strain. This nonlocal constitutive equation is derived in explicit closed form for isotropic material in the one case in which there exists a well-founded physical and mathematical basis for describing the material's statistics: a matrix reinforced (or weakened) by a random dispersion of nonoverlapping identical spheres. By assessing, when the applied loading is spatially-varying, the magnitude of the nonlocal term in this constitutive equation compared to the portion of the equation that relates ensemble average stresses and strains through a constant “overall” modulus tensor, we derive quantitative estimates for the minimum representative volume element (RVE) size, defined here as that over which the usual macroscopically homogeneous “effective modulus” constitutive models for composites can be expected to apply. Remarkably, for a maximum error of 5% of the constant “overall” modulus term, we show that the minimum RVE size is at most twice the reinforcement diameter for any reinforcement concentration level, for several sets of matrix and reinforcement moduli characterizing large classes of important structural materials. Such estimates seem essential for determining the minimum structural component size that can be treated by macroscopically homogeneous composite material constitutive representations, and also for the development of a fundamentally-based macroscopic fracture mechanics theory for composites. Finally, we relate our nonlocal constitutive equation explicitly to the ensemble average strain energy, and show how it is consistent with the stationary energy principle.

Mechanics of Composite Materials: A Unified Micromechanical Approach

Abstract: 1. Fundamentals of the Mechanics of Composites. Representative volume element. Volumetric averaging. Homogeneous boundary conditions. Average strain theorem. Average stress theorem. Effective elastic moduli. Relations between averages-direct approach. Relations between averages - energy approach. 2. Basic Models in the Mechanics of Composites. The Voigt approximation. The Reuss approximation. Hill's theorem. The dilute approximation. The composite spheres model. The self-consistent scheme. The generalized self-consistent scheme. The differential scheme. The mori-tanaka theory. Exhelby equivalent inclusion method. 3. The Micromechanical Method of Cells. The method of cells for fiber reinforced materials. Coefficients of thermal expansion. Hill's relations. Thermal conductivities. Specific heats. The method of cells for short-fiber composites. Randomly reinforced materials. Periodically billlminated materials. 4. Strength and Fatigue Failure. Micromechanics prediction of composite failure. 5. Viscoelastic Behaviour of Composites. Linearly viscoelastic composites. Thermoviscoelastic behaviour of composites. Nonlinear viscoelastic behaviour of composites. 6. Nonlinear Behaviour of Resin Matrix Composites. Macromechanical analysis. Micromechanical analysis. 7. Initial Yield Surfaces of Metal Matrix Composites. The initiation of yielding in isotropic materials. Initial yielding of metal matrix composites. Investigation of the convexity of initial yield surfaces. 8. Inelastic Behaviour of Metal Matrix Composites. Constitutive equations of plasticity. Unified theories of viscoplasticity. Bodner-partom viscoplastic equations. Inelastic behaviour of laminated media. Inelastic behaviour of fibrous composites. Matrix mean-field and local-field. Subsequent yield surfaces prediction of metal matrix composites. Metal matrix composite laminates. Short-fiber metal-matrix composites. 9. Imperfect Bonding in Composites. General considerations. The flexible interface imperfect bonding model. Periodically billaminated materials. Fiber-reinforced materials. Short-fiber and particulate composites. The Coulomb frictional law for the modeling of interfacial damage in composites. Index.

Multi-scale constitutive modelling of heterogeneous materials with a gradient-enhanced computational homogenization scheme

Abstract: A gradient-enhanced computational homogenization procedure, that allows for the modelling of microstructural size effects, is proposed within a general non-linear framework. In this approach the macroscopic deformation gradient tensor and its gradient are imposed on a microstructural representative volume element (RVE). This enables us to incorporate the microstructural size and to account for non-uniform macroscopic deformation fields within the microstructural cell. Every microstructural constituent is modelled as a classical continuum and the RVE problem is formulated in terms of standard equilibrium and boundary conditions. From the solution of the microstructural boundary value problem, the macroscopic stress tensor and the higher-order stress tensor are derived based on an extension of the Hill-Mandel condition. This automatically delivers the microstructurally based constitutive response of the higher-order macro continuum and deals with the microstructural size in a natural way. Several examples illustrate the approach, particularly the microstructural size effects.

Prediction of composite properties from a representative volume element

Abstract: A vigorous mechanics foundation is established for using a representative volume element (RVE) to predict the mechanical properties of unidirectional fiber composites. The effective elastic moduli of the composite are determined by finite element analysis of the RVE. It is paramount in such analyses that the correct boundary conditions be imposed such that they simulate the actual deformation within the composite; this has not always been done previously. In the present analysis, the appropriate boundary conditions on the RVE for various loading conditions are determined by judicious use of symmetry and periodicity conditions. The non-homogeneous stress and strain fields within the RVE are related to the average stresses and strains by using Gauss theorem and strain energy equivalence principles. The elastic constants predicted by the finite element analysis agree well with existing theoretical predictions and available experimental data.