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International audience; In order to provide a physical interpretation of the variation of the mechanical properties of Callovo-Oxfordian argillite with mineral composition, we implement three linear homogenization schemes. The argillite is modeled as a three phase material composed of a clay matrix and inclusions of quartz and calcite. It is shown that, unlike the dilute scheme and the self-consistent scheme, the Mori-Tanaka model describes the in situ experimental data well. The determined properties are finally used in a finite element computation. The aim is to evaluate the effect of mineral composition on the elastic response of the excavation of a vertical shaft in the context of the underground laboratory of Meuse/Haute Marne.

International audience; The question of the nonlinear response of brittle materials undergoing elastic damage is investigated here. Owing to the specific nature of microcracking, the macroscopic behaviour of these materials is complex, generally anisotropic owing to the possible preferential orientation of defects and multilinear because of the unilateral effect due to the transition between open and closed state of microcracks. A new three-dimensional macroscopic model outlined by Welemane and Cormery [1] has been proposed to account simultaneously for these both aspects. This paper intends to present in details the principles of such approach and to demonstrate its applicability to a stress-based framework. Based on a fabric tensor representation of the damage density distribution, the model provides a continuum and rigorous description of the contribution of defaults which avoids classical spectral decompositions and related inconsistencies. The model is also strongly micromechanically motivated, especially to handle the elastic moduli recovery that occurs at the closure of microcracks. The macroscopic theoretical framework proposed constitutes a general approach that leads in particular to predictions of a class of micromechanical models. The capacities of the approach are illustrated and discussed on various cases of damage configurations and opening–closure states, with a special attention to the differences with the strain-based framework and to the influence of the damage variables order.

International audience; This paper presents an application of a micromechanical model to the analysis of cavity excavation in heterogeneous rocks by taking into account influences of mineralogical compositions. The Callovo-Oxfordian argillite is considered here in the context of feasibility studies for geological storage of nuclear waste storage. Based on the microstructural analysis, a micromechanical model is first proposed using nonlinear homogenization techniques for heterogeneous materials. The argillite is seen as a three phase composite with elastoplastic clay matrix, elastic damaged calcite grains and elastic quartz grains. Using the proposed model, the variations of elastic and plastic properties of material with mineralogical compositions at different depths are systematically taken into account. Comparisons between experimental data and model's predictions are presented. The proposed model, implemented into a finite element computation code, is finally applied to the analysis of excavation of a vertical shaft.

The present study is devoted to the development and validation of a nonlinear homogenization approach of the mechanical behavior of Callovo-Oxfordian argillites. The material is modeled as an heterogeneous composite composed of an elastoplastic clay matrix and of linear elastic or elastic damage inclusions. The macroscopic constitutive law is obtained by adapting the incremental method proposed by Hill [Hill, R., 1965. Continuum micro-mechanics of elastoplastic polycrystals. J. Mech. Phys. Solids 13, 89–101]. The approach consists in formulating the macroscopic tangent operator of the material by considering the nonlinear local behavior of each phase. Due to the matrix/inclusion morphology of the microstructure of the argillite, a Mori–Tanaka scheme is considered for the localization step. The developed model is first compared to Finite Element calculations and then validated and applied for the prediction of the macroscopic stress–strain responses of argillites.

International audience; A Hill type incremental homogenization method was recently proposed by Abou-Chakra Guéry et al. [Abou-Chakra Guéry, et al., 2008. A micromechanical model of elasto-plastic and damage behavior of a cohesive geomaterial. Int. J. Solid. Struct., 45(5), 1406–1429] for the elasto-plastic damage behavior of a cohesive geomaterial, the Callovo–Oxfordian argillite. The aim of this paper is then to extend the homogenization method to its time-dependent behavior. The argillite is now seen as a three phase composite with an elasto-viscoplasticity matrix and elastic damaged calcite grains and elastic quartz grains. Considering that the incremental formulation of Hill cannot rigorously be used, we proposed a new modified incremental method. A validation of its predictions against experimental data is then conducted.

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.