Formability prediction of high-strength steel sheet using experimental, analytical and theoretical analysis based on strain and stress forming limit curves and its application to automotive forming parts

In this work, the high-strength steel (HSS) sheet dual-phase 440 (DP440) were conducted to establish the forming limit curve (FLC) and analytical forming limit stress curve (FLSC) obtained from experimental forming limit curve. First, the Nakajima stretch forming examination was carried out to obtain forming limit curve of investigated sheet. Afterwards, the theoretical Marciniak-Kuczinsky (M-K) model was developed and calculated to evaluate localized necking limits both in strain and stress spaces combination with anisotropic yield criteria. Then, the analytical forming limit stress curves were plastically calculated by using experimental forming limit curve data combination with Swift hardening model and anisotropic yield criteria namely, Hill'48 and Yld2000-2d for representing anisotropic plastic deformation behavior on examined steel sheet. Finally, automotive stamping parts were performed in order to verify an applicability of all developed curves. It was observed that the analytical forming limit stress curves could more precisely predict the formability of automotive parts better than the forming limit curve based on strain. Particularly, the one based on Yld2000-2d predict better than the one based on Hill'48. Simultaneously, the experimental forming limit curve and analytical forming limit stress curve were also evaluated comparing with the theoretical calculated forming limit curve and forming limit stress curve using the Marciniak-Kuczinsky model. It should be noted again that the experimental forming limit curve and analytical forming limit stress curve are the best one. Therefore, the Yld2000-2d yield function better represented the anisotropic behavior of the high-strength steel sheet dual-phase 440 than Hill & PRIME; 48 yield function, and can suitable be used for the analysis prediction and design of bumper automotive parts under forming processes. The formability prediction of bumper-deep-drawing part is experimentally and numerically evaluated using the experimental forming limit curve, analytical forming limit stress curve and theoretically developed Marciniak-Kuczinsky model based on strain and stress spaces. At failure state, the developed analytical forming limit stress curve can realistically predict the fracture formation.image