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

This paper shows how a unified model with a single set of equations and mat erial constants can be used for describing inelastic flow of rocksalt submi tted to a variety of loading conditions associated with plasticity, creep a nd relaxation. After introducing the complete model in its full expanded ve rsion, the authors demonstrate that these different observed material respo nses 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, incl uding isotropic and kinematic hardening. Each ISV appears in the kinetic (f low) law and evolves according to a growth rule as a function of the inelas tic 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. Toge ther, they represent a complete description of inelastic flow. These concep ts are illustrated by results obtained on rocksalt samples submitted to dif ferent loading conditions, including constant strain rate (CSR) tests, cree p (constant stress) tests, and relaxation (constant strain) tests. (C) 2000 Elsevier Science Ltd. All rights reserved.