WORK SOFTENING AND INSTABILITY DURING TORSION OF PREDEFORMED NONHOMOGENEOUS COPPER RODS

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