A hybrid method for prediction of damage initiation and fracture and its application to forming limit analysis of advanced high strength steel sheet

In this work, damage locus for predicting both ductile damage initiation and fracture of the advanced high strength steel grade JAC780Y was developed. Tensile tests of sheet samples with various geometries were performed and occurred damage was identified by the direct current potential drop method. Then, FE simulations of the corresponding tests were carried out, in which local stress triaxiality and plastic strain values of the critical areas were evaluated. As a result, damage loci for the states of damage onset and fracture could be obtained. Effects of different yield criteria on the resulted limiting curves were also investigated. Furthermore, the damage loci were transformed to strain based forming limit curves. To verify applicability of the determined damage loci and forming limit curves, stretch-forming tests and forming of an industrial part were conducted. The damage loci and transformed forming limit curves could fairly describe both occurred damage initiations and fracture of the steel.