A micromechanical model of elastoplastic and damage behavior of a cohesive geomaterial

AbstractThe 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

Incremental variational approach for time dependent deformation in clayey rock

International audienceAn extension of Lahellec (2007) incremental variational approach to geomaterials is proposed. By using an implicit time-discretization scheme, the evolution equations describing the small strains constitutive behavior of the phases can be reduced to the minimization of an incremental energy function. This minimization problem is rigorously equivalent to a nonlinear thermoelastic problem with a transformation strain that is a heterogeneous field. The new approach proposed is for Callovo-Oxfordian argillites and considers the specific properties of geomaterials such as compressibility-dilatancy transition and influence of confining pressure. An isotropic, kinematic hardening effect is also considered for the more general cases. The accuracy of the model is assessed by comparison with FE and experimental results

A comparative micromechanical analysis of the effective properties of a geomaterial: Effect of mineralogical compositions

International audienceIn 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

Micromechanics based modeling of the Callovo-Oxfordian argillite mechanical behavior

The present study is devoted to the development and validation of a non-linear homogenization approach of the mechanical behavior of Callovo-Oxfordian argillites. The material is modelled as an heterogeneous one composed of an elastoplastic clay matrix and of linear elastic or elastic damage inclusions. The macroscopic constitutive law is obtained by adapting the Hill-type incremental method [1]. The approach consists in formulating the macroscopic tangent operator of the material from the non-linear local behavior of its phases. Due to the matrix/inclusion morphology of the microstructure of the argillites, a Mori-Tanaka scheme is considered for the localization step. The developed model is first compared to Finite-Elements calculations and then validated and applied for the prediction of the macroscopic stress-strain responses of argillites

Multi-scale modeling of time-dependent behavior of claystones with a viscoplastic compressible porous matrix

International audienceThis paper is devoted to multi-scale modeling of time-dependent behavior of claystones using a two-step homogenization procedure. Two materials scales are considered. At the mesoscopic scale, the material is constituted by a clay matrix and embedded mineral grains. At the microscopic scale, the clay matrix is a porous medium composed of a solid phase and spherical pores. The macroscopic plastic criterion of the clay matrix is first determined by a modified secant method (Maghous et al., 2009) considering a pressure sensitive yield function for the solid phase. This criterion is then used as the loading function for the description of viscoplastic deformation of the clay matrix, together with a non-associated viscoplastic potential. At the second step of homogenization, the macroscopic behavior of the claystone is determined by taking into account the effect of mineral grains (quartz and calcite). For this purpose, we propose an extension of the incremental approach initially proposed by (Hill, 1965) to modeling of time-dependent behavior. Therefore, the micromechanical model is able to explicitly account for the effects of pores and mineral grains at two different scales. The numerical algorithm for numerical implementation of the micromechanical model is also presented. The proposed model is finally verified through comparisons between numerical results and experimental data in triaxial compression tests with constant strain rate and in triaxial creep tests

Multi-scale modeling of time-dependent behavior of claystones with a viscoplastic compressible porous matrix

International audienceThis paper is devoted to multi-scale modeling of time-dependent behavior of claystones using a two-step homogenization procedure. Two materials scales are considered. At the mesoscopic scale, the material is constituted by a clay matrix and embedded mineral grains. At the microscopic scale, the clay matrix is a porous medium composed of a solid phase and spherical pores. The macroscopic plastic criterion of the clay matrix is first determined by a modified secant method (Maghous et al., 2009) considering a pressure sensitive yield function for the solid phase. This criterion is then used as the loading function for the description of viscoplastic deformation of the clay matrix, together with a non-associated viscoplastic potential. At the second step of homogenization, the macroscopic behavior of the claystone is determined by taking into account the effect of mineral grains (quartz and calcite). For this purpose, we propose an extension of the incremental approach initially proposed by (Hill, 1965) to modeling of time-dependent behavior. Therefore, the micromechanical model is able to explicitly account for the effects of pores and mineral grains at two different scales. The numerical algorithm for numerical implementation of the micromechanical model is also presented. The proposed model is finally verified through comparisons between numerical results and experimental data in triaxial compression tests with constant strain rate and in triaxial creep tests