Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands

Abstract

Experiments were conducted to determine the shear strains and strain rates in adiabatic shear bands in a Ni-Cr steel. An explosively driven punch was used to shear plugs from steel plates and, thereby, create adiabatic shear bands for investigation. There were originally planes of chemical inhomogeneity (reference bands) in the plane of the steel samples. The slopes of the reference bands were altered by the plastic shear, and they were, therefore, a measure of the plastic shear strain. From measurements of the slopes of the reference bands, it was found that the plastic shear was approximately an exponential function of distance through an adiabatic shear band. Shear strains of at least 572 developed after the onset of adiabatic shear, and with measured rates of punching, it was estimated that shear strain rates as great as 9.4 x 10⁷ sec⁻¹ were attained within the adiabatic shear bands. The results suggest how heating occurs within the shear bands and that there is a plastic instability due to carbide and lath morphology changes and, possibly, a magnetic transformation associated with the deformation and heating.