Prediction of fracture in press bend forming of aluminum alloy high-stiffener integral panels

Aluminum alloy high-stiffener integral panels are widely used on modern aircrafts to meet the demand of light weight and high stiffness. Press bend forming is an important method of producing this structure, of which fracture on stiffeners is a severe forming defect. In this study, a series of ductile fracture criteria that have been successfully applied in the metal forming field are adopted, the constants of which are obtained by tensile tests of different specimens and their corresponded FEM simulations. Then all the criteria are implemented into ABAQUS with user subroutine. A set of press bending dies is designed, with which bend to fracture experiments of single stiffener and multi-stiffener specimens are carried out. By comparative analysis of the experiments and the FEM simulations including many ductile fracture criteria, the most suitable ductile fracture criteria for predicting the fractures in this forming process are determined. The reasons of the usability are also explained based on the mechanics of the fracture.