Dynamic Dent Resistance Performance of Steels and Aluminum 930786

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. At higher velocities, however, the dent resistance performance of the steels was significantly better than the aluminum alloys, although the aluminum alloys were thicker. At any given velocity, the aluminum alloys had significantly lower oil canning/critical buckling load and initial/secondary stiffness values than the steels. This study also showed that the initial stiffness and the oil canning/critical load were independent of boundary conditions while the secondary stiffness and the denting force depended on the type of boundary condition used.

The availability of high strength steels for automotive body panel applications has offered the potential to make further vehicle weight reductions through downgauging. Of concern are panel performance properties such as stiffness, dent resistance and oil canning load after downgauging. In the past two decades, a significant amount research work in the area of dent resistance, stiffness and oil canning load of a panel has been done [ 1] *. Great attention has been paid to the static denting behavior of body panels. In the real world, however, most denting phenomena are dynamic. Understanding of the dynamic denting behavior of automotive body panels is of equal or even greater important than that of the static denting behavior.

One of the available dynamic denting tests is the drop-weight test. It was used to study the effect of sheet thickness and material yield strength on dynamic dent resistance using a flat panel with various prestrains [ 2]. It was found that the dynamic dent resistance increased with the increase in sheet thickness and yield strength of the material as in static dent resistance but its dependence on sheet thickness and material yield strength is less than in static denting.

As a continuation of the work in [ 2], four different geometries/shapes of specimens, including one with curvature, were used in this study using the drop weight test. Five drop heights (drop velocities) were used to examine the drop velocity effect. Panel performance properties such as denting force, oil canning/critical buckling load, initial and secondary stiffness were measured for all four types of specimens. Effects of boundary conditions and specimen geometries on these panel performance properties were also investigated. Significant effects of the panel geometries on these properties are demonstrated. These properties are then compared among different strength steels and between steels and aluminum alloys. The dependence of these properties on yield strength, sheet thickness, Young's modulus and drop velocity are also discussed.