Advanced constitutive modeling of advanced high strength steel sheets for springback prediction after double stage U-draw bending

In this study, a U-shaped channel formed using a double drawing process (double stage U-draw bending) was proposed to reduce the amount of springback in the AHSS sheets. The performance of the double stage U-draw bending process in reducing the amount of springback was compared with that of the conventional U-draw bending process. The process was simulated using a finite element (FE) analysis with two different types of anisotropic hardening models, namely, isotropic-kinematic and distortional models, to describe the Bauschinger effect and associated anisotropic hardening transients during the strain-path changes. Moreover, plastic anisotropy, captured by different yield functions, and the degradation of the elastic modulus were taken into account. In addition to the basic mechanical characterization tests conducted to identify the material coefficients, in-plane compression-tension experiments were conducted. The experimental and FE simulated results of the double stage U-draw bending process were compared and analyzed to understand the effect of anisotropic hardening on the springback under non-proportional loading.