Prediction of forming limit in bore-expanding of sheet metals using ductile fracture criterion

Abstract To predict the forming limit in sheet metal forming, a criterion for ductile fracture is introduced into the finite element simulation. From the histories of stress and strain in each element calculated by the finite element simulation, the initiation of fracture is predicted by means of the fracture criterion. Calculations are carried out for axisymmetric bore-expanding processes of mild steel and high strength steel sheets using flat-, hemispherical- and conical-headed punches. Comparison with experimental results shows that the fracture initiation site and the critical stroke are predicted successfully by the present approach.