On stress controlled thermoviscoplastic shearing and higher order strain gradients

We give a brief discussion on the stability and non-uniformity of shear in a slab of finite width and infinite extent made from a non-hardening, non-conducting, anisothermal viscoplastic material with stress controlled boundary conditions. The new ingredient in our analysis is the inclusion of higher-order strain gradients in the expression for the flow stress. It is shown that this inclusion allows for the development of non-uniformities for a certain condition between the thermomechanical parameters for which the classical model (absence of strain gradients) imposes a uniformly evolving stable solution