Forming Limit Curve at Neck and Forming Limit Curve at Fracture in Hydroforming of Aluminum Tubes

Bursting is the most important defect in tube hydroforming. Prediction of bursting can help to design the process. Aim of this paper is the application of ductile fracture criteria for prediction of bursting, forming limit curve at neck and forming limit curve at fracture in tube hydroforming process. Different ductile fracture criteria have been calibrated and applied in simulation to identify the best criterion for prediction of fracture zone. A free bulge setup has been manufactured to verify the simulation results. This setup has fixed bulging length and the ability of applying axial feed. To bulge the tube under fixed strain ratio, different loading curves (internal pressure versus axial feed) have been created. Using loading curves and prediction of ductile fracture criteria, FLCN and FLCF have been obtained and compared with experimental ones. Predicted FLCN using ductile fracture criteria have been compared with M-K Model too. Results show that the criteria which consider the effect of stress triaxiality on the prediction of fracture are more appropriate for tube hydroforming. Prediction of Ayada' s criterion and Rice' s criterion have the best conformity with the experimental results.