Experimental and numerical investigation of springback effect for advanced high strength dual phase steel

In sheet metal forming process of automotive components, the springback effect is crucial, in particular for Advanced High Strength Steels (AHSS), like the dual phase (DP) steel. Most construction parts in modern vehicles having very complex shapes require multi-step forming procedures. In this work, the influences of pre-deformation on the springback of steel AHSS sheets were investigated under consideration of the elastic modulus change. The sheet strips were firstly pre-stretched to a uniaxial engineering strain of 4% and 6%. The steel sheets prepared parallel, transverse, and 45° to the rolling direction were taken into account. A modified S-rail forming test was used to verify the degree of springback of the steel sheets after pre-straining. In parallel, Finite Element (FE) simulations of the S-rail forming test were performed, in which the planar anisotropic Hill’s 1948 material model, Barlat–Lian’s 1989 model, and Yoshida–Uemori kinematic hardening material model were applied. Experimental and numerical results were compared with regard to the final angles between the sample flanges. The effect of the elastic modulus change as a function of plastic strain was examined. It was found that higher pre-deformation state led to a noticeable increasing in springback effect. Considering the variable elastic modulus improved the accuracy of the springback prediction. The Yoshida–Uemori model showed better predictions of the final shape for the investigated steel parts in comparison with other models.