Strain Path Change Influence on Residual Stress after Deep Drawing

摘要

Automotive manufacturers have shown a growing interest in an integrated design approach, considering the coupling and interactions of different design phases, as it saves time and increases part reliability. In particular, the residual stresses induced by the forming process of metallic sheets affect the service life. Therefore, the accuracy of the service life prediction is closely related to the reliability of the forming process simulation. As complex strain path changes can occur during forming and affect the mechanical behavior of the sheets, there is a growing interest for models that take their influence into account, e.g. the recently developed Homogeneous Anisotropic Hardening (HAH) model. In a first step, this study focuses on the influence of the mechanical model on the residual stresses after the direct redrawing of cylindrical cups. First, a cup is stamped from a circular dual phase steel DP600 sheet of thickness 1.2 mm. Then, the cup is stamped a second time in the same direction to obtain a cup with a smaller diameter. These two stages involve complex strain path changes. To estimate their influence on the residual stress field, the numerical simulation of the two step process is performed with three models of the material behavior, i.e. isotropic hardening associated with either an isotropic or an anisotropic yield criterion and the enhanced HAH model with material parameters taken from the literature. The residual stress field is then analyzed and correlated with strain path changes, evaluated by the indicator included in the HAH model.