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The formability and failure behavior of transformation-induced plasticity (TRIP) steel blanks were investigated through various stress states. The forming limit diagram (FLD) at fracture was constructed both experimentally and numerically. Numerical studies were performed to evaluate the applicability of different damage criteria in predicting the FLD as well as complex cross-die deep drawing process. The fracture surface and numerical results reveal that the material failed in a different mode for different strain path. Therefore, the Tresca model, which is based on shear stress, accurately predicted the conditions where shear had a profound effect on the damage initiation, whereas Situ localized necking criterion could calculate the conditions in which localization was dominant.

Dual phase steels offer good combination of mechanical properties which is attractive for automotive industry. However, some challenges still remain and suppress using them widely. One of these challenges is the formation of premature cracks at shear-cut edges during the subsequent forming processes, which cannot be predicted by the conventional finite element methods. Therefore, the present study aims to propose a numerical tool to predict edge cracks in DP steel components. In this regard, the hole expansion method was applied as an edge crack detection technique on DP1000 steel sheets. To elaborate the study, parallel finite element simulations were performed as well. The simulation method considered the whole hole piercing process and the following hole expansion test as a one-stroke two-step strategy. The hole piercing process was applied in the first step on the sheet and a hole was cut. The results reveal that this process forms some surface irregularities and applies a special amount of damage at the cut edge, which both could have effects on the edge crack sensitivity. To study these effects, the subsequent hole expansion test was simulated on the manufactured hole. Thus, the effects of both surface irregularities and residual damage from hole piercing process were investigated in different case studies with all possible combinations of these effects. This strategy provides possibilities to numerically separate effects of surface quality and residual damage. The contribution shows on the one hand the experimental investigations and on the other hand deals with the numerical influence analyses.