A novel uncoupled ductile fracture criterion for prediction of failure in sheet metal forming

The ductile fracture behavior of anisotropic materials was modeled by the uncoupled ductile fracture criterion. The ductile fracture model was concerned with the micro mechanisms of void nucleation, void growth, and evolution of void coalescence. The advance plastic model of Hill'48 non-associated flow rule is considered in proposed ductile fracture criterion. A series of basic fracture testing covering a wide range of stress state for aluminum alloy 6016-AC200 are carried out. Strain field on the surface of specimens is captured by the non-contact measurement DIC system. The fracture locus constructed using the proposed criterion is close to the experimental data points over a wide stress triaxiality range from negative to intermediate and high stress triaxiality. Then, a square cup drawing test is conducted in order to verify efficiency of the proposed fracture criterion in predicting fracture behavior of metal sheet. The results indicate that the proposed ductile fracture criterion can be utilized for predicting initial fracture in sheet metal forming.