Damage evolution mechanism of aluminum alloy stiffened cylinders during flow forming

Fracture is one of typical defects for complex stiffened cylinders during flow forming. The introduction of complex structures makes fracture prediction challenging. This study aims to assess the forming limits of stiffened cylinders during flow forming, alongside the selection of appropriate prediction models. Therefore, a spinnability method was proposed to evaluate the formability of stiffened cylinders and its corresponding finite element model was developed. The results show that cracks initiated at the stiffener downstream fillet in flow forming of AA6061-T6 stiffener cylinders, and then developed along the circumferential direction due to significant axial tensile stresses. Four typical uncoupled damage models were incorporated into the finite element model to simulate the damage evolution in spinnability tests of stiffened cylinders. The prediction results show that all selected models demonstrated an ability to correctly predict the location of cracking, but H-C model offers the most accurate predictions in spinnability tests of AA 6061-T6 stiffened cylinders. These approaches can provide an evaluation method for flow spinning process design of stiffened cylinders.