Modelling and simulation of the Portevin-Le Chatelier effect

Abstract

During deformations of an Al-Mg alloy (AA5754) dynamic strain aging occurs in a certain range of temperatures and strain-rates. A manifestation of this phenomenon, usually referred to as the Portevin-Le Chatelier (PLC) effect, consists of the occurrence of strain localisation bands accompanied by discontinuous yielding. The PLC effect is due to dynamic dislocation-solute interactions and results in negative strain-rate sensitivity of the flow stress. The PLC effect is detrimental to the surface quality of sheet metals and also affects the ductility of the material. Since the appearance of the PLC effect strongly depends on the tri-axiality of the stress state, three-dimensional finite element simulations are necessary in order to optimise metal forming operations. We present a geometrically non-linear material model which reproduces the main features of the PLC effect. The material parameters are identified by experimental data from tensile tests. Special emphasis is put on the prediction of the critical strain for the onset of the PLC effect and the statistical characteristics of the stress drop distribution. © Springer Berlin Heidelberg 2008.