Plasticity theory strength-differential(SD) phenomenon, and volume expansion in metals and plastics

Abstract

Appreciable differences have been reported recently between tensile and compressive yield strengths (SD or strength-differential effect) in martensitic steels and other alloys, as well as in plastics. Data on plastic volume changes are not yet available for the steels, but a volumeexpansion in both tensile and compressive deformation accompanies the SD effect in plastics and in granular media. In this paper, the coupled SD-volume expansion predictions of elementary perfect plasticity and more complex forms of work-hardening plasticity theory, including a possible key role of the theoretical strength under triaxial tension, are described briefly and pictorially. They then are compared with available data to provide some estimates of the likely successes and failures of the approach. An attempt is made to sharpen the distinction between true and apparent SD, and to suggest several critical experiments.