Evaluation of Constitutive Models for Springback Prediction in U-draw/bending of DP and TRIP Steel Sheets

Abstract

U-draw/bending experiment and simulation have been employed to investigate the characteristics of springback in sheet metals, because they can represent the deformation of material in forming processes with simple but robust manner. Finite element method is frequently used for the simulation of springback, but the prediction is strongly influenced by the constitutive models such as yield criteria and hardening laws. In the present study, springback of DP and TRIP steel sheets in U-draw/bending was predicted with a finite element analysis. Various constitutive models were considered: the von Mises isotropic and Hill’s anisotropic yield models for the yield criteria

isotropic and non-linear kinematic hardening models for the hardening laws. Especially, to characterize the hardening behavior, both uniaxial tensile test and balanced biaxial tensile test (by hydraulic bulge test) were carried out. The prediction was greatly influenced by the choice of hardening model, while slightly affected by the choice of yield criterion. It was found that the kinematic hardening model provides better prediction than the isotropic hardening model for the particular model materials. The use of flow curve from hydraulic bulge test seems to be more reliable than the use of uniaxial tensile flow curve owing to extended measurable strain range.