Extended Overstress Model with Overstress Tensor

Introduction The elastoplastic stress is first defined as the stress which evolves as the actual strain rate is induced in an imaginary quasi-static process of elastoplastic deformation, while internal variables evolve with the viscoplastic strain rate calculated by the viscoplastic constitutive equation. Further, the novel variable “overstress tensor” reaching the current stress from the elastoplastic stress is defined. Thus, the overstress model [1] is extended so as to describe also the tangential viscoplastic strain rate induced by the overstress tensor component tangential to the yield surface, extending the tangential inelastic strain rate [2]. Further, the viscoplastic strain rate due to the change of stress inside the yield surface is incorporated by adopting the concept of the subloading surface [3].