Evolution equations for distortional plastic hardening
In an earlier paper the authors proposed a geometrical description of distortional plastic hardening. The parameters of this model describe, in turn, all the elements of transformation of the initial yield surface, namely proportional expansion, translation, affine deformation, rotation, and distortion. The present paper is devoted to evolution equations for individual parameters: after a general discussion and analysis of existing experimental data, some effective equations are proposed. In particular, they are adjusted to describe Bui's experiment on subsequent yield surfaces under combined compression and torsion of a thin-walled tube.