Tensile damage response from discrete element virtual testing

Depending on the loading conditions on brittle materials, damage can generally not be reduced to a simple scalar. Microcrack orientation affects the stiffness in a preferential direction perpendicular to the crack lips. Taking into account the damage anisotropy in phenomenological models is a possible option, but the identification of the corresponding models with respect to damage anisotropy is not an easy task, usually because of the limited number of experimental results. Handling and performing tensile experiments on damaged samples made of quasi-brittle heterogeneous material is quite delicate. Then, one can consider virtual testing for the identification of specific properties. We propose in the present work such a protocol, based on the use of discrete element models and codes as a virtual testing machine. Discrete models are based on a material description at the microscopic scale by an assembly of particles. Cracks (and cracks orientations) are naturally described by broken connections between particles. After a brief description of the chosen model, a cross-identification procedure is proposed for the determination of a hydrostatic sensitivity parameter of an anisotropic damage model. A second application deals with the description of the evolution of the strength envelope under different isotropic and anisotropic damage states. These examples show the interest of virtual testing by discrete modelling for material behaviour characterisation at fine scale.