Formulation of stress-strain relation for plastic deformation of mild steel for strain trajectory consisting of two straight branches

A relation between the stress and incremental strain deviators, which are not coaxial, is derived by considering the characteristics in tensor space. On the bases of this relation and of precise experimental results for mild steel, a specific plastic stress-strain relation is formulated for a strain trajectory with a comer in a 3D-vector space corresponding to the strain deviator, as a typical example of plastic behaviour under complex loading. It may be confirmed that the effects of plastic anisotropy and of the third invariant of the strain deviator on the plastic behaviour of mild steel under complex loading are expressed precisely by means of the above formulation.