Denis E. Gill

A unified viscoplastic model for the inelastic flow of alkali halides

Abstract The present paper proposes a novel viscoplastic model to describe the inelastic behaviour of polycrystalline alkali halides. This model is of the unified type. It consists of a kinetic law and three evolution laws associated with three state variables, B, R and K. Variables B and R are internal stresses, which usually oppose the applied stress, and which induce kinematic and isotropic hardening respectively. The variable K is a scalar used to normalize the active stress, thus contributing to the isotropic hardening of the material. The proposed unified model is physically based, and allows a correct representation of both transient and steady-state flow under diverse loading conditions. It is valid for both instantaneous (plastic) and delayed (creep) components of the inelastic strains. Various phenomenological attributes of the model are discussed and compared to the theoretical and experimental behavior of polycrystalline alkali halides.

An internal variable model for the creep of rocksalt

SummaryThe creep strain rate

Stress measurements in soft rocks

\dot \varepsilon

Constitutive Equations With Internal State Variables for the Inelastic Behavior of Soft Rocks

of rocksalt, like that of other ductile crystalline materials, can be described by a power law equation of the type

Elastoplastic modeling for the ductile behavior of polycrystalline sodium chloride with SUVIC

\dot \varepsilon

Experimental and numerical evaluation of stress redistribution in thick-walled rocksalt cylinders

α(σα)n, where the active stressσα is the difference between the total deviatoric applied stress σ and an internal stressσi. In this paper, the origin and the nature of this internal stress, which develops during inelastic deformation of the material, are discussed. It is shown that this internal stress can serve as an internal (or state) variable in the constitutive model of rocksalt, which reflects the microstructure evolution of the material under the competitive action of hardening and recovery mechanisms.An analysis of experimental data, both our own and those taken from the literature, demonstrates that such a law is able to correctly reproduce rocksalt creep test results in the steady-state domain. The proposed model is in accordance with the macroscopic and microscopic behavior of salt, and with direct measurements of the internal stresses made by others on this material.