An experimental and numerical study of the strain rate effects on mild steel for cyclic loading

A combined experimental and numerical study has been carried out to determine the effects of strain rate on mild steel under mainly cyclic loading. In addition, effects of loading history and cyclic mean strain on the flow stress were also investigated.;A procedure has been developed to generate strain rate dependent input data for a numerical simulation under a general loading condition for moderate strain rate using the mixed-mode hardening model by Lemaitre and Chaboche. Finite element analyses using the input data generated from this procedure has been found to be able to simulate the strain rate effect on the load-deformation behaviour of the tests. However, the numerical simulations have been less accurate on tests performed at a strain range other than the one used in the calibration to generate the input data.;Tapered and notched round specimens of CAN/CSA 040.20/21 Grade 300W and ASTM A572 Grade 50 steels were tested under a variety of cyclic loading conditions at a strain rate ranging from 10-4 s-1 and 10 -1 s-1. A positive rate sensitivity on flow stress has been found for both these materials during initial cyclic loading. However, with continual loading, tests performed at the strain rates of 10-2 and 104 s-1 can be seen to show negative flow stress rate sensitivity due to adiabatic heating. The rupture strain has been found to decrease with strain rate for the strain rate range considered in this study. On the other hand, findings on the effect of strain rate on the fatigue life are inconclusive. The loading history and mean strain effects on the final cyclic stress-strain curve at a strain range have also been found to be small if a sufficient number of loading cycles have been performed at that particular strain range.