Material Characterization of the Newly Developed Advanced High Strength Steels for Prediction of Crash Performance

New highly ductile AHSS steel grades with tensile strength greater than 980 MPa have been developed with the aim of combining high strength and excellent formability. The new jetQ[TM]-Family offers high local and global ductility which is expected to contribute to the improvement of vehicle crash performance. For reliable design and management of vehicle crash performance, material modeling including work hardening behavior, strain rate dependence and material failure strain plays an important role in numerical simulation. Especially, the accuracy of material failure prediction is important for the development of crash performance. In this study, the fracture behaviors of both the 980jetQ[TM] and conventional Dual-Phase (DP) are investigated through simple tensile and V-bending fracture tests incorporating experiment-numerical hybrid ductile fracture analysis. Based on the experimental results, the material parameters in Hosford-Coulomb fracture model are determined for the numerical crash simulation. And dynamic tensile tests with Split-Hopkinson pressure bar method are carried out to characterize the strain rate dependence of the high strength steels. Effect of strain rate on the fracture strain is investigated for the material fracture modeling in the crash deformation. In order to investigate the impact characteristics of the steels, axial crash tests of hat square columns are performed. Numerical simulations of axial impact are also performed by LS-DYNA under the same conditions as the axial crash test. The validity of the material models is verified by comparing the numerical simulation results and the experimental results on the absorbed energy and material fracture behavior. The developed material model can express the excellent local elongation performance of jetQ material. The crash simulation with the material model shows good crash performance with low risk of fracture during the crash deformation.