Determination of strain rate dependent stress-strain curve up to fracture for mild steel

The post-yield plastic flow of mild steel is affected by strain rate. Thus, for numerical modeling purposes, it will be helpful if the true stress-true strain relationship of the material up to fracture is known for different strain rates. A procedure that allows the strain rate dependent true stress-true strain curve up to fracture to be determined from the tension test has been developed. Tension specimens of mild steel were tested at a constant strain rate ranging from 10 -5 s -1 to 10 0 s -1. Non-standard round specimens with a tapered profile were used to permit the diameter at the minimum cross-section to be measured continuously during the test. Due to necking of the tension coupon, an equation has been established to correct for the effect of the non-uniaxial hydrostatic stress on the measured stress. This stress correction allows the true stress-true plastic strain curve of the material at various strain rates to be determined directly from the measured load and cross-section dimension. The procedure and correction equation are validated against the test results through numerical simulations