Vershinin–Bai–Wierzbicki plastic model for mild steel and accurate prediction of structural plastic response and failure behavior

The isotropic plastic hardening behavior of ductile metals is commonly characterized by the accumulated equivalent plastic strain. Advanced plasticity models further incorporate dependencies on hydrostatic pressure and Lode angle to more accurately represent material behavior under complex stress states. However, such models have rarely been applied to mild steels or structural failure analyses. This study evaluates the applicability of the Vershinin–Bai–Wierzbicki (VBW) model to mild steel, such as Q235 in China. Constitutive parameters are calibrated using a parameter identification approach that integrates inverse modeling with multi-objective optimization. Computational results of the VBW and Mises models are compared, with particular attention to differences in the large-deformation plastic stage. In addition, the VBW model incorporating the Lode angle-modified void growth model (LMVGM) is evaluated for its capability to predict fracture behavior and structural failure responses. Simulation results indicate that plastic deformation and fracture behavior of mild steel under large strains are highly sensitive to stress triaxiality and Lode angle. The conventional Mises model fails to accurately capture plastic evolution influenced by these stress-state parameters, whereas the VBW model, coupled with LMVGM, provides accurate predictions of both large-strain plasticity and fracture responses in mild steel materials and structures.