Finite element modelling of plastic instability during ECAP processing of flow-softening materials

A finite element analysis of the equal channel angular pressing (ECAP) of flow-softening materials is presented in this paper. A very fine mesh was used in the simulations, allowing a detailed analysis of the development of localized shear phenomena. Two different flow curves were used in the simulations; one displayed an initial flow-softening followed by perfect plastic behavior, whereas the other followed a constant flow-softening behavior. The flow-softening rate affects the intensity of shear localization. The deformation zone, that is usually concentrated around a fixed shear plane during processing of perfect plastic or strain hardening materials, splits into two parts and its position varies cyclically during the process, leading to oscillations in the punch load during processing. A comparison of the finite element predictions with those from the slip line field theory is also presented.