Prestrain Effects on Static Dent Resistance of Automotive Steels

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. It is shown that the dent resistance of a panel can be significantly improved by a small increase in the strain level of the panel. It is believed that the information provided in this investigation can be used to help optimize the design and to assist in material selection relative to the dent resistance of auto body panels.