Dynamic materials testing, texture, and yield-surface calculation of an automotive sheet steel

Abstract

The relationships between the stress state and anisotropic mechanical response for a drawing-quality, special-killed (DQSK) mild sheet steel has been analyzed. The strain rate and temperature sensitivity of the flow stress and the insensitivity of the strain hardening to strain rate are shown to be consistent with thermal activation over a Peierls barrier as the rate-controlling mechanism for deformation in DQSK. A calculated yield surface, using the quadratic Hill criterion, is shown to produce an accurate correlation with the experimental results as a function of stress state. Annealing of the DQSK sheet steel at 773 K for 1 hour reduced some of the residual stresses developed during the forming process, but had little effect on the texture. The R values derived from computed yield surfaces suggested very little difference between in-plane (IP) and transverse tensile tests, consistent with the experimental results. A comparison of the stress-strain response with the calculated yield-surface and texture measurements correlates well with the relationships between the IP and through-thickness (TT) deformation.

High Strain Rate Properties of DQSK GI Steel Spot Welds

“…The stress-strain plots were analyzed to obtain the yield strength of the materials under various strain rates. As shown in Figures 6a through 6d, a fall-off (drop) region is observed which is believed to be a result of adiabatic heating effects [23].…”

“…Effect of increasing strain rate from low to high strain rates at room temperature on DQSK GI steel was presented by Cady et al [23]. They tested DQSK GI steel at different strain rates ranging from low strain rates (0.1 s -1 ) to high strain rates up to 3500 s -1 .…”