Fabrice Cormery

Some Remarks on the Damage Unilateral Effect Modelling for Microcracked Materials

This study deals with the macroscopic modelling of the mechanical behaviour of microcracked materials and particularly with the unilateral aspect of such damage which leads, at the closure of microcracks, to a partial damage deactivation. By means of a micromechanical analysis, the aim of this article is first to point out the influence of the opening–closure of microdefects on the effective elastic properties of a microcracked medium. According to these considerations,a new elastic moduli recovery condition at damage deactivation is proposed. The introduction of this condition within the anisotropic damage model proposed by Halm and Dragon, 1996 allows its micromechanical background to be extended while preserving its main advantages, in particular the continuity of the stress–strain response and the symmetry of the stiffness tensor.

On uniqueness and localization in elastic-damage materials

Abstract We consider isotropic elastic-damage behaviour such that the evolution law of the unique scalar internal variable characterizing material damage is associative (“ d -associativex201D; model). Two particular variants of modelling are considered. More precisely, and because of some analogies between these models and non-associative plasticity, we attempt to compare the loss of positiveness of second-order work and the localization criteria. These criteria are written in terms of critical damage. Thus, the damage value at loss of positiveness of second-order work is explicitly calculated in three-dimensional and plane strain cases. The procedure leading to the damage value at localization in the plane strain case is also presented. Both criteria are then compared for some loading paths. The results obtained indicate the localization occurring before loss of positiveness of the second-order work for some loading paths for one of two models. The same loading paths were tested with the other isotropic elastic-damage model; it is shown that localization always occurs after the loss of positiveness of second-order work (i.e. in softening phase). To endow this result with more generality, we then consider the problem of localization through a spectral analysis which finally shows that localization cannot take place in the hardening phase.

Basic concepts and models in continuum damage mechanics

ABSTRACT In this paper, we present some basic elements of macroscopic modelling of damage. We then recall the general approach of continuum damage based on the thermodynamics of irreversible processes and its application to isotropic damage modelling. The study of damage-induced anisotropy is treated by considering a second order tensorial damage variable. Finally, we present an original macroscopic approach through which is addressed the question of unilateral effects due to the microcracks closure.