The concurrent ratcheting and stiffness degradation-based damage variable in SA508 steel samples undergoing stress cycles at room and elevated temperatures

Abstract This study evaluates the interaction between ratcheting and stiffness degradation in SA508 steel samples at various operating temperatures using a combined isotropic-kinematic hardening framework. The Ahmadzadeh-Varvani (A-V) kinematic hardening rule, along with the isotropic hardening description by Lee-Zavrel, was employed to respectively translate and expand yield surfaces as the loading level exceeded the yield limit. To address the accumulation of plastic strain at elevated temperatures, the dynamic strain aging phenomenon was introduced through an exponential function into the dynamic recovery term of the A-V model. The evolution of the yield surfaces and materials yield strength was found substantial within a temperature range of 500–778 K where the DSA effect was dominant. A damage variable was defined through stiffness degradation as stress cycles proceeded. The continuum damage mechanics variable was then adapted into the constitutive equations and the hardening framework. The A-V kinematic hardening rule held the damage term in two distinct methods (i) as a multiplier to the linear hardening portion of the A-V model, and (ii) as a multiplier to both linear hardening and dynamic recovery terms. The former adaptation of the damage term verified that the foremost influence of damage was achieved when both linear and non-linear portions of the hardening framework were involved. This resulted in closer agreement of the predicted ratcheting values with those measured. The deviation of the predicted and measured values dropped to 11%. For the latter adaptation, the deviation of predicted ratcheting from experimental was found twice.