Experimental and numerical investigation on the dent resistance of a dual phase steel originated from the yield-point phenomenon

The yield-point phenomenon (YPP) is generally eliminated or reduced in aged sheet metals to avoid defects during metal forming applications; however, it may be beneficial in specific applications and could be induced to enhance certain properties. For example, bake hardening (BH), peculiarized by a sharply elevated yield stress after baking of pre-strained low carbon steel, can be used to improve the dent resistance in automotive sheet metal forming applications. However, many previous investigations about the bake hardenability concentrate primarily on the hardening response under uniaxial tension and related influence factors. Additionally, various numerical studies on dent resistance rarely consider the BH effect in their model. In this study, the BH behavior of a dual phase (DP) steel is comprehensively investigated under uniaxial loading cases, and the static dent experiments are conducted in pre-strained and bake-hardened conditions to study their effects on dent resistance. We develop a constitutive model considering both BH and YPP implemented using a robust implicit stress-integration algorithm for finite element analysis. Numerical simulations corresponding to the experiments are conducted to further investigate the dent resistance of the DP steel. The proposed numerical procedure is shown to be able to capture the BH behavior of the DP steel reasonably well and appropriately assess its enhanced dent resistance.