Evaluation of Facture Criteria Considering Complex Loading Paths in Cobalt Alloy Tube Hydroforming

Abstract

In this study, a free bulge test simulation was performed with conditions corresponding to experiments for a cobalt-alloy tube hydroforming. A 3D strain measurement scheme was introduced to obtain strain data after free bulge tests, and the measured strain values were used in the evaluation of ductile fracture criteria. Cockcroft ductile fracture criterion, Oyane ductile fracture criterion and the modified Cockcroft criterion were adopted for establishing the material constants by simple tensile test and notched tensile test. Experimental data from free bulge tests were used for fracture prediction with these criteria. The results revealed that for the purpose of tube hydrofoming, the modified Cockcroft criterion with strain paths is more accurate than either the Cockcroft ductile fracture criterion or the Oyane ductile fracture criterion.