Numerical Modeling for Springback Predictions by Considering the Variations of Elastic Modulus in Stamping Advanced High-Strength Steels (AHSS)

Abstract

This paper presents a numerical modeling approach for predicting springback by considering the variations of elastic modulus on springback in stamping AHSS. Various stamping tests and finite‐element method (FEM) simulation codes were used in this study. The cyclic loading‐unloading tensile tests were conducted to determine the variations of elastic modulus for dual‐phase (DP) 780 sheet steel. The biaxial bulge test was used to obtain plastic flow stress data. The non‐linear reduction of elastic modulus for increasing the plastic strain was formulated by using the Yoshida model that was implemented in FEM simulations for springback. To understand the effects of material properties on springback, experiments were conducted with a simple geometry such as U‐shape bending and the more complex geometry such as the curved flanging and S‐rail stamping. Different measurement methods were used to confirm the final part geometry. Two different commercial FEM codes, LS‐DYNA and DEFORM, were used to compare the experiments. The variable elastic modulus improved springback predictions in U‐shape bending and curved flanging tests compared to FEM with the constant elastic modulus. However, in S‐rail stamping tests, both FEM models with the isotropic hardening model showed limitations in predicting the sidewall curl of the S‐rail part after springback. To consider the kinematic hardening and Bauschinger effects that result from material bending‐unbending in S‐rail stamping, the Yoshida model was used for FEM simulation of S‐rail stamping and springback. The FEM predictions showed good improvement in correlating with experiments.