Effect of Pre-Strain on Yield Surfaces in Copper

Abstract

An investigation into the effect of both tensile and torsion pre-strain is reported. A thin-walled tube was pre-strained in either tension or torsion, unloaded, and then subjected to a combination of tension and torsion to establish the yield locus in the tensile-stress-shear-stress plane corresponding to the particular pre-strain. The results for torsion pre-strain in particular support a hardening theory, proposed by Hodge, that an inflation of the yield surface is accompanied by a translation. It is shown that the method of defining yield is of prime importance. Different conclusions can be drawn about the general behaviour of the yield surfaces for a work-hardening material, depending on the definition of yield used.