Compact SHPB System for Intermediate and High Strain Rate Plasticity and Fracture Testing of Sheet Metal

Abstract

A new set-up is proposed to perform high strain rate tension experiments on sheet metal using a compression Hopkinson bar system on the input side. With the help of a custom-made load inversion device, the compression loading pulse is converted into tensile loading of the specimen boundary. A tensile output bar is used to measure the tensile force acting on the specimen boundaries. A high speed camera system is employed to measure the displacement history at the specimen level through planar digital image correlation. The output bar is positioned on top of the input bar. As a result, the valid experiment duration of the proposed system is twice as long as that of conventional Kolsky systems. It therefore facilitates the execution of intermediate strain rate (~100/s) experiments without increasing total system length. Numerical simulations are carried out to assess the effect of spurious bending effects that are introduced through the eccentricity of the input and output bar axes. In addition, experiments are performed on straight and notched specimens to demonstrate the characterization of the rate dependent plasticity and fracture properties of a 1.06 mm thick DP780 steel.