Shear-sensitive failure prediction for ultra-thin steel sheets: A combined necking and fracture framework incorporating through-thickness anisotropy

Failure prediction of ultra-thin deep drawing steel under shear-related forming paths requires the combined assessment of localized necking and ductile fracture. In this study, 0.3 mm BDCK ultra-thin deep drawing steel was characterized by uniaxial tensile and Nakajima tests. The material exhibited weak in-plane anisotropy but pronounced through-thickness anisotropy, with an average r -value of 1.720. A hybrid experimental strategy was used to determine the necking forming limit curve and fracture forming limit curve from near-pure shear to balanced biaxial tension. The results show that localized necking and fracture act as competing failure limits, indicating that both limits should be evaluated within a unified framework. For necking prediction, an updated modified maximum force criterion model accounting for through-thickness anisotropy and shear-sensitive strain-path evolution was employed. For fracture prediction, the Hu-DFC criterion incorporating through-thickness anisotropy was adopted after comparison with DF2012. The framework was applied to a box-shaped deep drawing process. The predicted localized necking and fracture displacements showed relative errors of approximately 8.8% and 7.0%, respectively. The predicted critical region agreed with the experimental fracture location near the die shoulder radius.