Forming Limit of Dual Phase Steel: An Experimental and Numerical Investigation

Forming limit diagrams and forming limit curves are used to determine the failure limits of sheet metal materials by conducting a forming limit analysis. The aim is to enable the selection of suitable materials, geometries and process parameters at an early stage in the component development. In this way, engineering time and costs can be reduced. In addition to experimental forming limit analyses, different models and model approaches exist to numerically predict damage and failure. All have in common that calibration is necessary based on experimental investigations. The correspondingly determined parameters specify when ductile damage initiation begins, how it evolves, and how the material finally fails. Thus, the calibration and the parameters determined have a significant impact on the models’ accuracy. The present work focuses on the numerical prediction of DP 800 dual phase steel in a Nakajima test using a modified Bai-Wierzbicki model. Besides the calibration influence of the damage model coming from a non-unique parameter selection is investigated. A sensitivity analysis of the experimentally determined parameters of the damage model is carried out with the aim of predicting the crack initiation with high accuracy and to determine the influence of the calibrated parameters, especially the range between the damage initiation locus, the failure locus and the damage evolution rate. The objective is to determine which damage model parameters possess a high influence on the failure prediction, in order to be able to make a risk assessment with regard to the prediction accuracy for later applications.