Shear instabilities in blanking and related processes

Abstract

To explain the peak in the load-displacement diagram observed in blanking and related processes, three modes of shear instability are introduced: two modes of geometrical instability concerned with the process and the microstructure, and thermoplastic instability which is dependent on the physical parameters of the material. Except for materials of low density and specific heat, in which thermoplastic instability is quite likely to occur, the peak in the load corresponds to the activation of geometrical instability owing to the combined effects of the process and the microstructure. It is proposed that fracture is preceded by the activation of thermoplastic shear instability.