Effects of Patches on Dent Resistance 2004-01-0162
Dent resistance has become one of the key performance criteria of automotive outer body panels due to the increased use of lightweight sheet steels for vehicle weight reduction. In order to sustain or improve the dent resistance of body panels with reduced metal thickness, commercial patches have been attached to the inner surface of exposed panels. The actual patch effects on dent resistance are not evident. Hence, the understanding of benefits of using a patch to improve dent resistance is also limited.
In this study, the effects of a patch on dent resistance are investigated. A special fiberglass patch is developed to compare with commercial patches. Fixed load  and fixed speed, single loading conditions are carefully designed and incorporated into the quasi-static and dynamic dent test. For comparison purposes, the incremental quasi-static loading condition is also examined. Experiments are conducted on a servo-hydraulic dent tester incorporating a laboratory produced stretch dome test panel with 2% biaxial strain. Three different patches are attached to the inner surfaces of separate panels. Five different steel grades are used: a mild steel, two bake-hardenable steels and two dual phase steels.
The results show the commercial patches do not always improve dent resistance. A fiberglass patch developed in the study significantly improves dent resistance. By attaching this fiberglass patch, the bake-hardenable steels perform as well as the dual phase steels in dent resistance. The use of fiberglass cloth enables automotive companies to use light-thickness sheet metal for weight reduction while still maintaining excellent dent resistance.