Numerical approach to prediction of forming limit in hydroforming of X-joints

In this paper, to predict the hydroforming limit for X-joints, two different criteria for ductile fracture are introduced into the finite element simulation and their values are calculated from the histories of stress and strain in each element. The initiation of fracture is predicted by means of these two fracture criteria. The obtained results are checked with those in the literatures using forming limit curve (FLC) method and experimental data.Very good agreements exist between our results and the reported experimental data.However, it seems that the predicted results for the onset of strain localization and bursting failure using FLC method gives a considerable underestimation of hydroforming limit for X-joints. Hence, it is believed that the present approach using the ductile fracture criteria give better prediction and could be used in hydroforming process planning specifically in X-joints.