Effects of pre-strain and bake-hardening on the crash properties of a top-hat section

The effects of pre-strain on the crushing properties of a crash-box structure are reported for two Advanced High Strength Steels produced by ArcelorMittal (Dual-Phase DP600 and Transformation Induced by Plasticity TRIP780 steels). In addition, the effect of a bake-hardening treatment is studied on the TRIP780 steel. The material's behaviors have been determined in tensile loading in a wide range of strain-rates (8×10−3 s−1≤ε˙≤103 s−1) including strain-rate jump tests from quasi-static to dynamic loading. These interrupted tests allow us to characterize the effect of the (quasi-static) forming process on the subsequent dynamic behavior associated to the crash event. A phenomenological visco-plastic model, based on the evolution of an internal variable, has been implemented in PAMCRASH using a user-defined subroutine in order to simulate the crushing of the crash-boxes. A simple approach is proposed to account for the bake-hardening treatment in numerical simulations. A good correlation between experimental and predicted mean crush forces is obtained.