Prediction of Bursting in Warm Tub Hydroforming using Modified Ductile Fracture Criteria

Prediction of critical process parameters which causes bursting and its location in warm tube hydroforming is a key factor in hydroforming parts design. In this paper, ductile fracture criteria have been modified so that effect of variation of temperature and strain rate on fracture is considered in forming of aluminum AA6063 tubes. Calibration of modified ductile fracture criteria has been performed using uniaxial tension tests at different temperatures and strain rates. Also, fracture strain and fracture work have been obtained as functions of Zener-Holloman parameter. Tube hydroforming process of a square part has been simulated at high temperatures in Abaqus software and loading curves with various axial feeds have been used to deform the tube. Then, the formed corner radius before bursting has been predicted using modified fracture criteria. A subroutine has been written for using modified fracture criteria. A warm tube hydroforming setup has been fabricated and prediction of modified ductile fracture criteria is compared with experimental results at various temperatures. Results show that modified criteria determine the location of bursting well. Maximum of thinning occurs in transition zone which the tube loses its contact with die cavity. Also, modified Ayada criterion, rather than other criteria, predicts corner radius with little error at high temperatures. Thus, because of its precise prediction, modified Ayada criterion can be used to predict the bursting of aluminum tubes at elevated temperatures.