Plastic deformation and fracture response of 304 stainless steel subjected to dynamic shear loading

This paper describes an experimental investigation into the effect of strain rate on the plastic and fracture response of 304 stainless steel subjected,to dynamic shear deformation by a torsional split Hopkinson bar in the strain rate range 10(2) s(-1) to 3 x 10(3) s(-1). Results indicate that dynamic shear response and fracture characteristics of 304 stainless steel depend strongly on applied strain rate. The yield and failure strength as well as the fracture strain increase with strain rate. It is also found that increasing strain rate increases work hardening, strain rate sensitivity, and deformation heat. However, the inverse tendency is observed for activation volume. The observed shear response can be described by the Kobayashi-Dodd constitutive relation. Good agreement is found between predicted and measured data. Fractographic analysis shows that localised shearing failure is predominant under all deformation conditions. The fracture surface consists of dimples, typical of ductile materials. Increasing the strain rate increases both density and depth of dimples, verifying that the fracture strain increases with strain rate. The presence of deformed shear bands confirms the existence of instability in the form of unstable flow due to flow localisation. Within the deformed shear bands, the deformation is not homogeneous and the grains are heavily distorted, resulting in enhancement of microhardness. (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.