Forming Limit Prediction of DP780 Dual Phase Steel Based on Different Instability Theories

Limit strain test of DP780 dual phase steel was carried out with a comprehensive sheet forming test machine. Based on C-H instability theory and M-K groove instability theory, the forming limit curve of DP780 dual phase steel was predicted by using Yld2000 yield criterion and power exponent hardening model, and compared with the test results. The results show that the prediction accuracy of forming limit curve based on M-K groove instability theory and C-H instability theory for the forming limit was 97.97% and 95.82%, respectively. The larger the initial thickness non-homogeneity, the smoother the steel plate surface, which was more conducive to forming. When the initial thickness non-homogeneity was 0.992, the M-K groove instability theory had the highest accuracy in predicting the forming limit of DP780 dual phase steel,with a relative error of 0.66%. The theoretical model can be used as a reliable method to obtain forming limit curve of DP780 dual phase steel in actual stamping production when the initial thickness non-homogeneity was 0.992.