Impact testing of a hot-formed B-pillar with tailored properties - experiments and simulation

This paper presents the numerical validation of the impact response of a hot formed B-pillar component with tailored properties. A laboratory-scale B-pillar tool is considered with integral heating and cooling sections in an effort to locally control the cooling rate of an austenitized blank, thereby producing a part with tailored microstructures to potentially improve the impact response of these components. An instrumented falling-weight drop tower was used to impact the labscale B-pillars in a modified 3-point bend configuration to assess the difference between a component in the fully hardened (martensitic) state and a component with a tailored region (consisting of bainite and ferrite). Numerical models were developed using LS-DYNA to simulate the forming and thermal history of the part to estimate the final thickness and strain distributions as well as the predicted microstructures. A strain-rate-sensitive constitutive model is used to model the as-quenched behavior of the hot-formed components with tailored microstructures. With an impact mass of 300 kg and total energy of 1.7 kJ, the measured maximum impactor displacement of the tailored components was approximately 9% (7.6 mm) greater than the fully hardened components. The measured peak impact load of the tailored components was approximately 24% (9.3 kN) lower than the fully hardened components. The numerical impact models are able to capture the force-displacement and deformation trends observed in the experiments. © 2013 SAE International.