A new yield surface model considering non-uniform strain rate hardening behavior

Uniaxial tensile tests using specimens of different geometries and stress states were performed on H340 steel sheets with various specimen orientations to rolling direction (RD) under strain rates ranging from 10−4 to 103s−1. Such uniaxial tensile tests, especially simple shear tests, show clear differences in work hardening that are significantly dependent on strain rate. This phenomenon, referred to as non-uniform strain rate hardening, has not been considered in existing yield surface models. Thus, a new yield surface model, termed the YldSRH model, based on Tsai-Wu strength criterion was proposed in this study to describe the non-uniform strain rate-dependent expansion of the yield surface. All parameters in the YldSRH model are independent of each other and can be directly determined using experimental results from tensile tests conducted in different directions and stress states at various strain rates. Moreover, the YldSRH model was coupled with a rate- and temperature-dependent damage mechanics (e2MBW) model for a combined YldSRH+e2MBW model. The predictive capability of the YldSRH+e2MBW model was validated by comparing the experimental and simulated force-displacement responses of different fracture specimens (SH, CH-R3, NDB-R8 and PS-R4) corresponding to different stress states at the three material orientations and at loading speeds of up to 10000 mm/s. In this study, the new model exhibited improved predictability for the dynamic anisotropic plasticity and fracture behavior of H340 compared with the existing model.