The use of strain gradient theory for analysis of random media (original) (raw)

Random Residual Stresses in Elasticity Homogeneous Medium with Inclusions of Noncanonical Shape

International Journal for Multiscale Computational Engineering, 2012

We consider a linearly elastic composite medium, which consists of a homogeneous matrix containing a statistically inhomogeneous random set of noncanonical inclusions. The elastic properties of the matrix and the inclusions are the same, but the stress-free strains are different. The new general volume integral equation (VIE) is proposed. These equations are obtained by a centering procedure without any auxiliary assumptions such as the effective field hypothesis implicitly exploited in the known centering methods. The results of this abandonment are quantitatively estimated for some modeled composite with homogeneous fibers of nonellipsoidal shape. New effects are detected that are impossible within the framework of a classical background of micromechanics.

Elastic heterogeneity of soft random solids

Europhysics Letters (EPL), 2007

Spatial heterogeneity in the elastic properties of soft random solids is investigated via a twopronged approach. First, a nonlocal phenomenological model for the elastic free energy is examined. This features a quenched random kernel, which induces randomness in the residual stress and Lamé coefficients. Second, a semi-microscopic model network is explored using replica statistical mechanics. The Goldstone fluctuations of the semi-microscopic model are shown to reproduce the phenomenological model, and via this correspondence the statistical properties of the residual stress and Lamé coefficients are inferred. Correlations involving the residual stress are found to be long-ranged and governed by a universal parameter that also gives the mean shear modulus.

Effective constitutive properties of a disordered elastic solid medium via the strong-fluctuation approach

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1999

A general scheme is developed for estimating the effective constitutive properties of a randomly disordered elastic solid medium. The presented methodology, already known in electromagnetics and acoustics, is based on renormalizing the conventional equations of motion. The resulting equations lend themselves to an approximate averaging procedure, which holds for strong fluctuations in the constitutive properties of the disordered medium provided the renormalization constants are chosen appropriately and the length-scales of the random perturbations are small. As an example, the homogenization of anisotropic spherical inclusions randomly dispersed in an isotropic host medium is considered, and the effective Lamé constants of the homogenized disordered medium evaluated and discussed.

A HOMOGENIZATION APPROACH FOR THE DETERMINATION OF THE EFFECTIVE PROPERTIES OF GRADIENT ELASTIC MEDIA

The aim of this paper is to provide the macroscopic elastic properties of a gradient elastic media from a homogenization framework. To reach this objective, the clas-sical conditions at the boundary of the representative volume element (RVE) are replaced by nonlinear boundary conditions. The macroscopic measures associated to polynomial boundary conditions are obtained along the lines of Rodin (2007). The RVE is constituted of an elastic matrix containing voids randomly distributed within the RVE. The elastic matrix comply with Cauchy equations at the microscopic scale. Nonlinear boundary con-ditions are taken under the form of a polynomial function which depends explicitly of the strain gradient or the hyperstress. The generalization of the homogenization approach in this context consists in replacing the RVE by an equivalent gradient elastic medium at the macroscopic scale. The macroscopic model which is thus obtained takes into account the effect of the strain gradient and a char...

Stochastic modeling of mesoscopic elasticity random field

Mechanics of Materials, 2016

In the homogenization setting, the effective properties of a heterogeneous material can be retrieved from the solution of the so-called corrector problem. In some cases of practical interest, obtaining such a solution remains a challenging computational task requiring an extremely fine discretization of microstructural features. In this context, Bignonnet et al. recently proposed a framework where smooth mesoscopic elasticity random fields are defined through a filtering procedure. In this work, we investigate the capabilities of information-theoretic random field models to accurately represent such mesoscopic elasticity fields. The aim is to substantially reduce the homogenization cost through the use of coarser discretizations while solving mesoscale corrector problems. The analysis is performed on a simple but non-trivial model microstructure. First of all, we recall the theoretical background related to the filtering and multiscale frameworks, and subsequently characterize some statistical properties of the filtered stiffness field. Based on these properties, we further introduce a random field model and address its calibration through statistical estimators and the maximum likelihood principle. Finally, the validation of the model is discussed by comparing some quantities of interest that are obtained either from numerical experiments on the underlying random microstructure or from model-based simulations. It is shown that for the case under study, the information-theoretic model can be calibrated with a limited set of realizations and still allows for accurate predictions of the effective properties.

A Random Field Formulation of Hooke’s Law in All Elasticity Classes

Journal of Elasticity

For each of the 8 symmetry classes of elastic materials, we consider a homogeneous random field taking values in the fixed point set V of the corresponding class, that is isotropic with respect to the natural orthogonal representation of a group lying between the isotropy group of the class and its normaliser. We find the general form of the correlation tensors of orders 1 and 2 of such a field, and the field's spectral expansion.

Relation Between Microscopic and Macroscopic Mechanical Properties in Random Mixtures of Elastic Media

Journal of Engineering Materials and Technology, 2007

A material composed of a mixture of distinct homogeneous media can be considered as a homogeneous one at a sufficiently large observation scale. In this work, the problem of the elastic mixture characterization is solved in the case of linear random mixtures, that is, materials for which the various components are isotropic, linear, and mixed together as an ensemble of particles having completely random shapes and positions. The proposed solution of this problem has been obtained in terms of the elastic properties of each constituent and of the stoichiometric coefficients. In other words, we have explicitly given the features of the micro-macro transition for a random mixture of elastic material. This result, in a large number of limiting cases, reduces to various analytical expressions that appear in earlier literature. Moreover, some comparisons with the similar problem concerning the electric characterization of random mixtures have been drawn. The specific analysis of porous ran...

Correlation functions for strain fields in elastic-plastic composites with random microstructure

2016

A technique has been developed and implemented to compute the correlation functions of strain fields in a representative volume of elastic-plastic composites under different loading conditions and for various isotropic physicalmechanical characteristics of components. The correlation functions of fields are obtained from the solution of a stochastic elastic-plastic boundary value problem based on full correlation approximation. The constants characterizing the properties of the components of a representative volume and which are part of integral expressions, as well as the geometrical properties of the components and representative volume, determined by the structural moments of functions, act as input parameters for calculations. Some case studies of the representative volumes of composites with randomly arranged porous spherical inclusions are considered, for which the correlation functions of the strain fields are constructed.