Effect of deformation geometry on the intermittent plastic flow associated with the Portevin-Le Chatelier effect

The unstable plastic flow Caused by the Portevin-Le Chatelier effect is studied experimentally. Non-local effects due to strain heterogeneity are addressed by comparing the statistical and multifractal properties of tension and compression deformation curves ofan AlMg alloy. Power-law statistical distributions and multifractal scaling are found in certain experimental conditions, and provide a quantitative characterization of the plastic-flow intermittency. The analysis reveals distinct temporal patterns associated with stress serrations in tension and compression, reflecting distinct modes of the collective dislocation dynamics. In contrast, the onset of instability follows similar relationships in both loading conditions. This similarity justifies the conventional approach to modeling the loss of stability of a uniform plastic flow as a local property, governed by the homogenized behavior of the dislocation ensemble. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.