A unified representation of the plasticity, creep and relaxation behavior of rocksalt

Abstract

This paper shows how a unified model with a single set of equations and material constants can be used for describing inelastic flow of rocksalt submitted to a variety of loading conditions associated with plasticity, creep and relaxation. After introducing the complete model in its full expanded version, the authors demonstrate that these different observed material responses are specific manifestations of a unique (unified) inelastic behavior, each corresponding to an imposed load path. The unified model relies on the use of internal state variables (ISV) attached to specific phenomena, including isotropic and kinematic hardening. Each ISV appears in the kinetic (flow) law and evolves according to a growth rule as a function of the inelastic strain tensor until it reaches saturation. The flow law, which relates the deviatoric stress to the inelastic strain rate, takes into account the evolution of these ISV as well as the external (observable) variables. Together, they represent a complete description of inelastic flow. These concepts are illustrated by results obtained on rocksalt samples submitted to different loading conditions, including constant strain rate (CSR) tests, creep (constant stress) tests, and relaxation (constant strain) tests.