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 t hat the strain path can be prescribed according to strain gauge measurement s. Relative to the standard method of determining yield surface shapes by p robing in many different stress directions from the elastic region, using s ome 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 th e Taylor model to represent a polycrystal. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.