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.

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