Enhancement of Accuracy of Springback Simulation Using the Material Model Considering the Strength Differential Effect

Abstract

The strength differential (SD) effect, i.e., the difference in flow stress between tension and compression, of a high-strength cold-rolled steel sheet with a tensile strength of 980 MPa is measured using an in-plane tension-compression test apparatus. Biaxial tensile stress tests are also performed to measure the contours of plastic work of the test material. From the experimental results, a material model that can reproduce the SD effect is determined. Furthermore, this material model is implemented into the commercial FEM code LS-DYNA using a user-subroutine function. To validate the accuracy of this material model, curved hat panel forming without a blank holder is carried out. By comparing the experimental and forming simulation results, we validated the influence of the SD effect on the enhancement of the predictive accuracy of springback.