A coupled elastoplastic damage model for semi-brittle materials and extension to unsaturated conditions

In this paper, a coupled elastoplastic damage model is proposed for semi-brittle materials. This model is applied to a specific semi-brittle sedimentary rock material. A brief account of experimental investigations is presented in the first part. The data obtained show an important plastic deformation coupled with stress-induced damage corresponding to initiation and growth of microcracks. Influences of mineral compositions and water content on the mechanical behaviour are also investigated. Based on these experimental evidences, the general formulation of the model is presented in the second part of the paper. The effective elastic properties of isotropic damaged material are determined based on relevant considerations from micromechanics. Damage evolution law and plastic damage coupling are described by using the framework of irreversible thermodynamics. A non-associated plastic flow rule is used. The model is extended to partially saturated conditions in order to study coupled hydromechanical behaviours in drying–wetting processes. Comparisons between numerical simulations and test data are performed for various loading paths. It is shown that the proposed model is able to describe the main features of mechanical behaviour observed in this class of materials.