A calculating method of tube constants of ductile fracture criteria in tube free bulging process based on M-K theory

The purpose of this work was to obtain the accurate constants in ductile fracture criteria based on the M-K theory, which determined the condition of convergence in numerical simulations and predicted the ductile fracture during the tube free bulging process. In this paper, the equivalent stress was analyzed based on the M-K theory, and the constitutive equation of the tube free bulging was established. The ductile fracture criterion constants were obtained by the integral on the basis of the Freudenthal, Normalized C&L and Oyane theories. The comparison between the experimental and the simulation results regarding the free bulging, indicated that the Oyane ductile fracture criterion was more precise than the other criteria by the perimeter increase trend, the burst locations of the risky area and the crack length. The burst defects prediction became significantly accurate by the Oyane ductile fracture criterion utilization based on the M-K theory.