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The simulation of a crash event in the design stage of a vehicle facilitates the optimization of crashworthiness and significantly reduces the design cost and time. The development of a fracture material card used in crash simulation is heavily dependent on laboratory testing data. In this paper, the experimental characterization process to generate fracture data for fracture model calibration is discussed. A third-generation advanced high strength steel (AHSS), namely the XG3TM steel, is selected as the example material. For fracture model calibration, fracture locus and load-displacement data are obtained using mechanical testing coupled with digital image correlation (DIC) technique. Test coupons with designed geometries are deformed under different deformation modes including shear, uniaxial tension, plane strain and biaxial stretch conditions. Mini-shear, sub-sized tensile, and Marciniak cup tests are employed to achieve these strain conditions.

For the past decades, the adoption of empirical equations in the forming limit curve (FLC) calculation for conventional steels has greatly simplified the forming severity assessment in both forming simulations and on the stamping shop floor. Keeler’s equation based on the n-value and sheet thickness is the most popular one used in North America. However, challenges have been encountered on the validity of the equation for advanced high strength steels (AHSS) since Keeler’s equation was developed based on the FLC data mostly from mild steels and conventional high strength steels. In this study, forming limits of various AHSS grades under different strain conditions are experimentally determined using digital image correlation technique. Both Marciniak cup and Nakazima dome tests are exercised to demonstrate the differences in the resultant forming limits determined with different test methods.

To improve the energy absorption capacity of front-end structures during a vehicle crash, a novel 12-sided cross-section was developed and tested. Computer-aided engineering (CAE) studies showed superior axial crash performance of the 12-sided component over more conventional cross-sections. When produced from advanced high strength steels (AHSS), the 12-sided cross-section offers opportunities for significant mass-savings for crash energy absorbing components such as front or rear rails and crush tips. In this study, physical crash tests and CAE modeling were conducted on tapered 12-sided samples fabricated from AHSS. The effects of crash trigger holes, different steel grades and bake hardening on crash behavior were examined. Crash sensitivity was also studied by using two different part fabrication methods and two crash test methods. The 12-sided components showed regular folding mode and excellent energy absorption capacity in axial crash tests.