Using internal state variables for modeling the viscoplastic behavior of rocksalt in the semi-brittle regime

In the semi-brittle regime, the time-dependent behavior of rocksalt results from two types of inelastic deformation mechanisms, which involve dislocations motion producing hardening and microcracks propagation leading to fracturing. In constitutive models, the former type of mechanisms can be expressed from empirical functions using external variables or introduced through the use of the internal state variables (ISV). The latter type of mechanisms, on the other hand, is often neglected or expressed from usual failure criteria. However, because these two types of mechanisms act simultaneously, a ∞upled approach should be considered. In this paper, the authors present a general ISV model that is used to describe in a unified manner the semi-brittle behavior of rocksalt for a variety of loading conditions. As specific examples, constant strain rate and creep test results under triaxial compression are presented and compared to model predictions.