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

To predict the forming limit in sheet metal forming, a criterion for ductil e fracture is introduced into the finite element simulation. From the histo ries of stress and strain in each element calculated by the finite element simulation, the initiation of fracture is predicted by means of the fractur e criterion. Calculations are carried out for axisymmetric bore-expanding p rocesses of mild steel and high strength steel sheets using flat-, hemisphe rical- and conical-headed punches. Comparison with experimental results sho ws that the fracture initiation site and the critical stroke are predicted successfully by the present approach. (C) 1999 Elsevier Science S.A. All ri ghts reserved.