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

<div class="section abstract"><div class="htmlview paragraph">New highly ductile advanced high strength steel (AHSS) grades with tensile strength greater than 980 MPa have been developed with the aim of achieving a combination of high strength and excellent formability. The new jetQ<sup>TM</sup>-Family [<span class="xref">1</span>, <span class="xref">2</span>] offers high local and global ductility, which is expected to contribute to the improvement of vehicle crash performance.</div><div class="htmlview paragraph">For the reliable design and management of vehicle crash performance, material modeling, including work hardening behavior 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.</div><div class="htmlview paragraph">In this study, the fracture behaviors of 980jetQ<sup>TM</sup>, 1180jetQ<sup>TM</sup>, and conventional Dual-Phase (DP) steels are investigated through simple tensile and V-bending fracture tests incorporating experimental-numerical hybrid ductile fracture analysis. Based on the experimental results, the ductile fracture parameters in the Hosford-Coulomb fracture model [<span class="xref">3</span>] are determined for numerical crash simulation.</div><div class="htmlview paragraph">To investigate the validity of the calibrated ductile fracture model, axial crushing tests of hat-shaped square columns are performed for the 980 MPa grade. Numerical simulations of axial impact are also performed by ANSYS LS-DYNA [<span class="xref">4</span>] under the same conditions as in the experimental tests, and three-point bending tests are carried out for the 1180 MPa grade to simulate side crash deformation. Both the numerical simulations of the axial crash and the three-point bending crash show good agreement with the experimental results.</div><div class="htmlview paragraph">The developed material model can express the excellent local elongation performance of the jetQ materials. The crash simulation with the material model shows good crash performance with a low risk of fracture during crash deformation.</div></div>