1998 年 84 巻 3 号 p. 182-187
A criterion for ductile fracture is applied to the prediction of forming limit in bore-expanding processes of sheet steels. Axisymmetric bore-expanding tests of mild steel and high strength steel sheets using conical-, hemispherical-and flat-headed punches are simulated by the rigid-plastic finite element method. From the calculated distributions and histories of stress and strain in the sheets, the fracture initiation sites and the critical strokes are predicted by means of the ductile fracture criterion. The comparison with the experimental results show that the forming limits due to various types of fracture initiations in the bore-expanding processes are successfully predicted by the present approach.