Coupling effect of stress triaxiality and Lode angle over a wide range on the ductile fracture behavior and mechanism of high-strength steel 30CrMnSiNi2MoVE

This research systematically investigates the mechanical and fracture behavior of 30CrMnSiNi2MoVE (30VE) high-strength steel through experimental, numerical, and microscopic approaches over wide ranges of stress states. First, the experiment of fourteen different type specimens is carried out. Then, the newly proposed stress state-dependent yield function is applied to simulate the plasticity behavior of all fracture experiments. The hybrid experiment-simulation method is carried out to obtain its fracture parameters. And the DF2016 and newly proposed fracture model are used to model the fracture parameters. The results showed that the proposed fracture model has higher prediction accuracy than DF2016, especially under the middle and low stress triaxiality range. Following the fracture experiments of V-notched three-point bending with different widths are carried out to evaluate the performance of the newly proposed models for predicting the structure's mechanical behavior. The results indicated that the newly proposed yield function and fracture model can accurately predict the experiment results. Finally, scanning electron microscopy (SEM) is utilized to characterize the microscopic morphology of the fracture surfaces to investigate the fracture mechanism effected by the stress states on the fracture specimens and on the crack initiation and propagation of the V-notched three-point bending specimens. The results showed that the stress triaxiality and Lode angle parameters have significant effects on fracture mode. The high stress triaxiality and Lode angle parameters result in the localization of the plastic flow, then resulting in the fracture mode dominated by elongated dimples; on the contrary, the fracture mode is dominated by equiaxed dimples. For V-notched three-point bending fracture tests, the crack initiation is controlled by the middle and high stress triaxiality range, which leads to the equiaxed dimples dominating the fracture mode; the crack propagation is controlled by the ultra-high stress triaxiality range and the elongated dimples dominate the fracture mode.