The relation between adiabatic shear instability strain and material properties

Abstract

Adiabatic shear bands were nucleated in hollow right circular cylinders of AISI 4340 steel which were explosively expanded in a quick-stop containment apparatus. Groups of cylinders were heat treated differently, before expansion, producing a variation in material properties among the groups. True shear strain was measured for annular sections taken from the cylinders and these complete annular sections were metallographically examined for the presence of adiabatic shear bands. The onset of adiabatic shear instability was found experimentally to take place at a true shear strain γ c = -Cn/( δτ δT ) , where C is the volume specific heat, n is the strain hardening exponent and δτ/δT is the slope of the temperature dependence of flow stress. This experimental result agrees with an analytical prediction from first principles given here. This relation is expected to have wide application: to apply to any alloy whose initial portion of the stress-strain curve is parabolic This suggests that the relation could be as important to adiabatic shear deformation as the Considère condition is to tensile deformation. The significance in adiabatic shear of each of the material properties appearing in the relation is discussed.