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

Abstract

Using the finite element method, Oyane’s ductile fracture integral I was calculated 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 conditions are predicted in this study. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by the shape of the pre-forming blank. Due to no axial feeding at the end of the blank, the possibility of cracking in hydroforming of these products is influenced by the friction condition more strongly than for the axial feeding of products such as a the tee extrusion. All the simulation results show reasonable plastic deformation and the applications of the method could be extended to a wide range of hydroforming processes.