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Body panel performance properties such as denting force, oil canning/critical buckling load, initial and secondary stiffnesses under dynamic loading (drop weight test) were measured for different strength steels and two aluminum alloys using both flat and curved sheets. It was found that all these properties varied with the drop velocity. For the steels, the denting force steadily increased with the increase in drop velocity. For the aluminum alloys, the denting force increased with the drop velocity at lower velocities and decreased or remained unchanged at higher velocities. The oil canning/critical buckling load increased with the increase in drop velocity and initial and secondary stiffnesses decreased with the increase in drop velocity for both steel and aluminum. The dent resistance performance for some aluminum alloys with thicker gauge is comparable to steels dent tested at lower velocities.

In previous investigations, it has been shown that the dent resistance of an auto body panel depends upon the yield strength of the material. However, it is known that the yield strength of steel increases with prestrain due to strain hardening. Panel design and material selection based on the material properties obtained from unstrained sheet steels may lead to inaccurate prediction of the dent resistance of the formed panel. In this study, the effect of prestrain on the static dent resistance of auto body panels was investigated. Using existing empirical relationships between dent resistance and panel properties, it was found that the static dent resistance of an auto panel depends not only on the part geometry and material properties but also on the strain level in the panel. The improvement in dent resistance resulting from a material change from an AKDQ steel to a bake hardenable steel or a high strength steel was determined at different strain levels.

The effects of sheet thickness, yield strength, strain aging and prestrain on the dynamic dent resistance of sheet steel are investigated using an instrumented drop-weight test. It is found that the dynamic dent resistance is less dependent on the sheet thickness and the yield strength of the material than the static dent resistance. The dent resistance of automotive steels under dynamic loading conditions increases with prestrain in a manner similar to static denting. The relative ranking of different strength steels in the performance of dynamic denting is provided at various strain levels. An empirical relation of dynamic denting force and energy with the sheet thickness and the yield strength of the material is derived for a flat panel. Data confirm that dynamic dent resistance is improved using high strength steels including bake hardenable steels and rephosphorized steels.