Prediction of the forming limit in hydroforming processes using the finiteelement method and a ductile fracture criterion

Using the finite element method, Oyane's ductile fracture integral I was ca lculated from the histories of stress and strain according to every element and then the forming limit of the hydroforming process was evaluated. The fracture initiation site and the forming limit for two typical hydroforming processes, a bumper rail and a subframe, under different forming condition s are predicted in this study. For these products, the ductile fracture int egral I is not only affected by the process parameters, but also by the sha pe of the pre-forming blank. Due to no axial feeding at the end of the blan k, the possibility of cracking in hydroforming of these products is influen ced by the friction condition more strongly than for the axial feeding of p roducts such as a the tee extrusion. All the simulation results show reason able plastic deformation and the applications of the method could be extend ed to a wide range of hydroforming processes. (C) 2001 Elsevier Science B.V . All rights reserved.