Fracture prediction of high-strength steel sheet during in-plane compression-shear forming under negative stress triaxiality

Predicting fracture failure of metals at negative stress triaxiality has been challenging, particularly for the in-plane compression-shear fracture failure of sheet metals. In this study, the in-plane compression-shear experiment and finite element stress analysis of a high-strength TRIP800 steel sheet were conducted. The fracture behavior of the TRIP800 sheet under different stress states was analyzed. The results showed that the stress triaxiality of the fracture zone was all less than 0, and the fracture surface was mainly characterized by micro-shear band defects. The decrease in stress triaxiality tends to accelerate the closure of voids, which is significantly different from the micro-voids-dominated fracture behavior at positive stress triaxiality. This indicates including more stress states in the negative stress triaxiality range when calibrating the Modified Mohr–Coulomb (MMC) fracture criterion helps improve the prediction accuracy of compression-shear fracture. Moreover, it was found that the in-plane compression-shear fracture could initiate at a stress triaxiality of − 0.48. This finding extends the cutoff value of stress triaxiality for ductile fracture and further expands the research scope for high-strength steel fracture.