Work hardening and rate sensitivity material coefficients for OFHC Cu and 99.99% A1

Abstract

Large strain tensile tests were carried out on OFHC Cu and 99.9% A1 with the aim of determining the first and second order work hardening and rate sensitivity coefficients. The tests were performed at room temperature and 473 K and at constant true strain rate in the range 5 x 10 -4 to 10 −1s −1. The use of a diameter transducer to measure and control the rate of reduction of the neck diameter of the tensile specimens is described. In this way, the strain rate at the minimum cross-section was held constant well beyond the point of maximum load. A second diameter sensor for use at 473 K is also described. In order to determine the coefficients for Cu at 698 K, constant strain rate compression tests were performed. The detailed dependence of the material coefficients on stress, strain rate and temperature is characterized. It is shown that the values of the rate sensitivity of the work hardening rate B σ beyond the maximum load are less than one, but are not negligible. As a result, the rate sensitivity] at constant work hardening rate N is not the material coefficient that controls the growth of strain rate gradients at large strains. It is also shown that the actual value of the coefficient B σ is substantially higher than the one obtained from the single state parameter approach.