Numerical assessment of stiffness and dent properties of automotive exterior panels

The use of thinner sheets and the introduction of new materials have lead to greater focus on the stiffness and dent resistance of exterior panels in the automotive industry during the last years. This paper describes an investigation of the suitability of FE analysis as a means to determine the stiffness and dent properties of panels. The investigation covers two parts, experiments and simulations. The results are then compared in order to assess the accuracy of the simulation technique. The study is based on an automotive side-door. Two sets of simulations were carried out. In the first set stamping effects were neglected. In the second set stamping effects were taken into account in terms of thickness changes and work-hardening effects. When dealing with the stiffness properties, the simulations show great accuracy in results. It is shown that simulating dent resistance using nominal material values leads to an underestimation of the dent resistance. The extent of this underestimation depends highly on the post-stamping strain level. At low strain levels, nominal values give satisfactory accuracy whereas in regions with high strain levels the accuracy of the simulations becomes slightly worse. When work-hardening effects are taken into account, the dent resistance is overestimated. Again the deviation from experimental results becomes more obvious in regions with high strain levels. This may be related to the assumption of isotropic-hardening, which most likely overestimates the yield stress after stamping.