Dislocation density and mechanical threshold stress in OFHC copper subjected to SHPB loading and plate impact

Abstract

The dislocation density and mechanical threshold stress (MTS) of oxygen-free high-thermal-conductivity (OFHC) copper loaded at strain rates in the range of 102 to 106s−1 were measured. Moderate-strain-rate (102 to 104s−1) experiments were performed using a Split Hopkinson Pressure Bar (SHPB). A steel collar was placed around each specimen to control the maximum loading strain. High-strain-rate (105 to 106s−1) experiments were carried out using a 57-mm-bore single-stage gas gun. The radial release effect was eliminated using the momentum trapping technique. The loaded samples were recovered, and the dislocation characteristics and dislocation density were determined by X-ray diffraction profile analysis. The fraction of the screw dislocation was found to decrease with increasing loading strain and strain rate. The dislocation density was found to lie between 1.8×1014 and 2.2×1015m−2. Quasi-static reload compression tests were performed on the recovered samples at room temperature. The mechanical threshold stress (or the flow stress at 0K) was obtained by fitting the reload stress–strain data to the MTS model. The results of analysis of the equivalent strain, mechanical threshold stress, and dislocation density measurements suggest that the relation between the mechanical threshold stress and the dislocation density can be described well by the Taylor relationship.