Effect of hydrostatic stress on the strength differential effect in low-carbon steel sheet

Abstract

The effect of hydrostatic stress on the strength differential effect (SDE) in a 0.8-mm-thick low-carbon steel sheet is experimentally investigated. The in-plane compressive stress-strain curve is approximately 10% higher than the uniaxial tensile stress-strain curve at a strain of 0.15, confirming that the test sample exhibited the SDE. A stack compression test in the thickness direction of the test sample is also performed. The measured through-thickness uniaxial compressive stress-strain curve is found to be higher than the equibiaxial tensile stress–thickness plastic strain curves measured using a cruciform equibiaxial tension test (ISO 16842) and a hydraulic bulge test (ISO 16808), indicating a positive correlation between hydrostatic pressure and flow stress. From these experiments, we conclude that the SDE in a low-carbon steel sheet is caused by the effect of hydrostatic pressure on flow stress. However, the pressure coefficient of the test sample, 50−150 TPa−1, is found to be significantly higher than those for high-strength steel alloys and Fe single crystals (13−23 TPa−1) reported by Richmond and Spitzig (1980).