Plastic damage of T-shape hydroforming
(1. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology,
Harbin 150001, China;
2. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
3. Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada;
4. FAW Car Co., Ltd., Changchun 130011, China)
Harbin 150001, China;
2. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
3. Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada;
4. FAW Car Co., Ltd., Changchun 130011, China)
Abstract: The Gurson-Tvergaard-Needleman model (GTN model) was employed to analyze bursting behavior in the hydroforming of stainless steel T-shape. A free-bulging test combined with simulation was conducted to determine the critical porosity and the failure porosity in GTN model. The effects of the forming pressure and the axial feeding on damage development were investigated and the influences of stress triaxiality and the plastic strain on porosity variation were also studied. The results show that a higher forming pressure or a less axial feeding will lead to bursting failure. The stresses of the top of protrusion are in bi-axial tension state, while the stresses of the side wall of main tube are in hoop tension state and axial compression state, respectively. The plastic strain has a more significant influence on the porosity than the stress triaxiality under the lower internal pressure; however, the stress triaxiality will govern the growth of porosity under the higher internal pressure. The simulation results give a good agreement with the experimentally determined thickness, and the maximum thickness-thinning rate is about 36%.
Key words: T-shape; hydroforming; GTN model; damage; bursting fracture; porosity; internal pressure