Studies on the experimental and simulated cyclic-plastic response of structural mild steels

Abstract

Experimental investigations have been conducted on the cyclic-plastic response of a structural mild steel (Grade YST210) under varying strain amplitudes (εa) under symmetric strain-controlled cycling. The results on the investigated YST210 steel and the reported results on four similar grades of steels (E250A, Q235, SS400, and GR345 steel) under symmetric strain-controlled cyclic loading are analyzed using a suggested approach based on Chaboche isotopic-kinematic hardening (CIKH) model. The parameters of the CIKH model are estimated from the stabilized hysteresis loops, and the obtained parameters are subsequently optimized using genetic algorithm to obtain closer predictions for the experimental cyclic-plastic response. The experimental fatigue response of YST210 steel reveals cyclic softening, and the estimated softening factor (SF) varies from 10% to 22% when εa alters from 0.25% to 2%; the magnitude of SF at εa = 2% decreases from 22% to 17.5% as the strain rate increases from 5 × 10−4 s−1 to 5 × 10−2 s−1. The efficacy of the suggested approach was estimated using the maximum root mean square error (Ferror) between predictions and experimental results. For the YST210 steel at different εa, the magnitude of Ferror is <4.5%, while for the other steels it is <3%. The suggested approach inherits the merit that it considers only a single set of parameters for different test conditions unlike multiple set of parameters often being used in the reported simulations. But still the results of simulations for E250A and SS400 steels depict an improvement of more than 40% over the available reports of simulations for the same steels.