Use of abrupt strain path change for determining subsequent yield surface: Illustrations of basic idea

For elastic-plastic materials, a new method is proposed for determining the shape of the subsequent yield surface in the Vicinity of a current loading point. A proportional strain path is prescribed until the loading point of interest has been reached, then an abrupt strain path change is prescribed, which makes the stress point move quickly along the yield surface. It is assumed that a closed-loop testing machine is used for the experiment, so that the strain path can be prescribed according to strain gauge measurements. Relative to the standard method of determining yield surface shapes by probing in many different stress directions from the elastic region, using some chosen plastic strain offset, the main advantage of the proposed method is that elastic unloading is not needed prior to tracing the yield surface. The method is illustrated here by a few analyses, first for the simplest how theory of plasticity, and subsequently for crystal plasticity, using the Taylor model to represent a polycrystal. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.