Work softening and instability during torsion of predeformed non-homogeneous copper rods

Work softening occurs at ambient temperature when copper rods of circular cross-section - predeformed by methods where elongation is the dominating deformation - are subsequently subjected to torsion. A range of work softening appears on torque/shear-strain curves preceding the strain-hardening: range. Its magnitude depends on the characteristics of the distribution of hardness of the rods in the initial state. These ranges are associated with transient instability and subsequent stability of plastic flow and they may be accurately defined on the basis of the Stuwe-Asbeck criterion. This criterion takes also account of the microcracks which are generated and grow due to the change of the deformation mode.