A unified hardening and damage characterization of Q960 steel under reverse loading

High-strength steels have received widespread attention in the research community owing to superior strengthto-weight ratio. Limited by lower ductility compared to mild steels, high-strength steels might have faster damage initiation and worse damage accumulation. The phenomena of cyclic softening within multiple cycles and monotonic hardening in single cycles have been reported regarding cyclic plasticity research. However, the damage softening might dominate in single cycles, especially for high-strength steels, which has not been focused on and studied yet. To characterize the potential and complex damage property of high-strength steels, this has led to the need for a unified use of kinematic hardening model and continuum damage mechanics model. Accordingly, three progressive tests undergoing large deformation involving monotonic tension, compression followed by tension, and cyclic loading were carried out for Q960 high-strength steel. Aiming at the Bauschinger effect and nonlinear hardening behavior, three hardening models including the Voce isotropic hardening model, Voce-Chaboche hardening model and updated Voce-Chaboche hardening model, were numerically compared. Regarding the following damage softening property, a modified continuum damage mechanics model considering cut-off value under compressive stress state was then developed. Compared to the three aforesaid hardening models used alone, the updated Voce-Chaboche hardening model, in conjunction with the cut-off value dependent modified continuum damage mechanics model, was verified to accurately characterize the hardening and damage behavior of Q960 high-strength steel under reverse loading within a large strain range.