Identification of strain localization-induced failure in hot-rolled steel sheets: A hybrid numerical-experimental approach to the virtual forming limit test

A coupled numerical-experimental inverse calibration approach was implemented and systematically validated to evaluate the formability of high-strength, hot-rolled, hyper-burring (HB780) steel sheets and dual-phase (DP780) steel sheets. The proposed methodology featured the determination of hardening behavior beyond the uniform elongation limit at large strain and shapes of 3-D, non-quadratic yield functions: Hosford and Yoshida models. To accurately identify the 3-D yield functions and directly monitor the strain localizations of hemispherical domes for the virtual numerical forming limit analyses, stretching tests were recommended for the investigated hot-rolled sheets. The modeling procedure was evaluated by comparing the forming limits of the stretching tests' various sample widths to those of the experiments, which confirmed the validity of the identified constitutive model parameters by predicting the localized failure strains and punch force-displacement curves under different deformation modes. For the purpose of validation, simulations and experiments of cylindrical circular cup drawing tests were performed. The proposed numerical procedure could predict the profiles of eared cups, locations of fracture, and drawing limit ratios of the two hot-rolled sheets without the input of the forming limit diagram when proper calibrations of the 3-D, non-quadratic, anisotropic yield function and strain hardening at large strains were guaranteed.

Automated summary

A coupled numerical-experimental inverse calibration approach was applied to evaluate the formability of high-strength steel sheets, with stretching tests used to determine hardening behavior and shape. The study successfully validated the proposed methodology through comparisons of forming limits and confirmed the effectiveness of the modeling procedure.