The Use of Increased Curvature to Reduce the Weight of Body Panels

Current trends in the automotive industry seem to be to use the minimum panel curvature that is possible, on the theory that a box provides the most space at the least weight. The purpose of this paper is to investigate the premise that increased curvature of body panels results in a net weight reduction, since the contribution of the increase in surface area is less than the reduced thickness resulting from the increased overall stiffness of panels with increased curvature. In assessing this concept, an expression has been developed for calculating the surface area as a function of panel curvature and panel size in two perpendicular directions. Using this relationship and previously published Chrysler work on the effect of these same two curvature and panel size variables on panel stiffness, an expression is developed for percent weight change at constant stiffness.

In the paper, the percent weight change at constant stiffness is described in terms of the relevant curvatures and panel spans for conditions of interest to the automotive industry. It is shown that the basic premise is correct and that increased curvature can, in fact, result in lighter body panels at constant stiffness. These results are not linear, and considerable attention is devoted to assessing the magnitude of the weight savings for a range of geometrical conditions. Other factors to be covered include illustrations of the effect of curvature on appearance and some comments on where high strength steel is important to prevent denting when panel thickness is reduced. Formability is also covered briefly. These latter comments will also be based essentially on the published literature and personal experience.