Effect of complicated deformation behaviors during cold stamping on springback prediction of DP980 steel

High-strength DP980 steel has been used on the automobile to improve the crash safety and lightweight, but serious springback is unavoidable during stamping. In this paper, complicated deformation behaviors during cold stamping of DP980 steel are investigated by combining experiment and simulation in order to promote the accuracy of springback prediction. Deformation behaviors including varied elasticity, anisotropic yield, and cyclic hardening are studied by testing, modelling, and model-programming. Firstly, uniaxial tension, biaxial tension, and in-plane cyclic tension–compression tests are carried out by a self-developed platform to test the mechanical behaviors of DP980 steel in the complicated deformation process. Secondly, elastic, yield, and hardening behaviors are modelled and evaluated. A modified elastic attenuation model by establishing a relation between chord elastic modulus and plastic strain is proposed to describe the elastic behavior. Three yield models, such as BBC2005, Hill-1948, and von-Mises, are presented to compare the description ability to the yield locus and anisotropy. A coupled isotropic and nonlinear kinematic (CINK) hardening model is proposed to accurately describe the hardening behaviors (Bauschinger effect, transient effect and permanent softening) by cyclic tension and compression loads. Finally, U-shaped part is stamped and simulated by using models that can describe actual deformation behaviors. The springback prediction with modified elastic attenuation, anisotropic yield, and CINK hardening models obtains an optimal result, and the overall relative error is only 1.803%. Among three factors, the effect of elastic attenuation on springback is the greatest. The results show that the accurate testing, modelling, and implementing of complicated deformation behaviors of DP980 steel contribute to high-precision simulation results.