Time-dependent ratcheting assessment of steel samples undergoing multi-step loading cycles through use of hardening rules

Abstract

The present study evaluates ratcheting of U71Mn rail and 316 L stainless steel samples subjected to various multi-step loading cycles by means of kinematic hardening rules of Ohno-Wang (O-W), Abdel Karim-Ohno (AK-O) and Ahmadzdeh-Varvani (A-V). Chaboche’s isotropic hardening and visco-plastic description was introduced into the kinematic hardening models to further address yield surface expansion/contraction and time-dependency of steel samples. Over Low-High-High loading sequence, ratcheting was increased continuously, while as loading steps changed to subsequent steps of High-Low-Low, ratcheting slightly dropped at the transition of steps. Ratcheting over High-Low steps was preserved since ratcheting over the prior step was largely promoted. Predicted ratcheting strains and hysteresis loops were compared with those of measured values under multi-step loading conditions. Both the O-W and AK-O models under-predicted ratcheting strains over loading cycles particularly over the last loading steps. The A-V model predicted ratcheting over Low-High and High-Low sequences and closely agreed with experimental data. Evolution in size and width of loops as stress levels altered with loading steps was evident from predicted hysteresis loops. While the O-W and AK-O models were yet to generate loops along axial direction comparable with measured data, the A-V model predicted hysteresis loops in close agreement with those of experimental values.