Material Characterization and Validation Studies for Modeling Ductile Damage during Deep Drawing

Modern high strength steels can exhibit ductile damage evolution till fracture which drops ductility for certain loading conditions. This complex formability characteristic as well as shear induced fracture cannot be described by standard methods like forming limit curves. As a remedy, the continuum damage models (CDM) can be applied. In this study, a variant of Lemaitre CDM was investigated to model ductile fracture of an advanced high strength steel, DP1000 in deep drawing processes. This model variant scales the effect of maximum shear stress on damage evolution to predict especially the shear cracks under low stress triaxialities. A decelerated damage evolution due to compressive stress components is taken into account. The material characterization for the damage model requires several tests such as tensile tests with notch, shear test and biaxial cupping tests to capture some characteristic stress states that can occur during deep drawing and further sheet forming processes. An inverse parameter identification methodology using the finite element modeling of whole samples is applied. From the experimental data, force displacement curves and optical strain measurements were used. Test parts were simulated for the validation of the model integrated in the commercial software LS-Dyna. The identified model parameters were finally validated on a cross die cup of high strength steel. The model predictions show good agreement with experimental observations.