Spring-back prediction based on a rate-dependent isotropic-kinematic hardening model and its experimental verification

This paper deals with spring-back prediction with a rate-dependent isotropic-kinematic hardening model with tension/compression in high speed U-draw-bending tests. In order to verify the validity of the present model, spring-back simulation is carried out and its results are compared with experimental results. A rate-dependent isotropic-kinematic hardening model has been proposed by combining the rate-dependent function of material parameters and the Chaboche type model for the TWIP980 steel sheet under tension and compression. The proposed model can accommodate the strain rate effect on the material properties by providing rate-dependent hardening curves under loading and reverse loading condition. This change of the rate-dependent material properties is important to predict spring-back under high speed deformation in practical sheet metal forming undergoing tension and compression during the deep-drawing forming. High speed U-draw-bending tests have been performed to investigate the strain rate effect on spring-back of the TWIP980 steel sheet after draw-bending at intermediate strain rates of up to a hundred per second. The experimental results have been compared with simulation results of high speed U-draw-bending and spring-back analysis with four hardening cases: isotropic; isotropic-kinematic; rate-dependent isotropic; rate-dependent isotropic-kinematic hardening models. It is demonstrated with the comparison that the rate-dependent isotropic-kinematic hardening model proposed provides the best prediction of spring-back after U-draw-bending at intermediate strain rates among the four hardening cases.