FINITE-ELEMENT ANALYSIS OF BORE-EXPANDING PROCESSES WITH DUCTILE FRACTURE CRITERION

A criterion for ductile fracture is applied to the prediction of formi ng limit in bore-expanding processes of sheet steels. Axisymmetric bor e-expanding tests of mild steel and high strength steel sheets using c onical-, hemispherical- and flat-headed punches are simulated by the r igid-plastic finite element method. From the calculated distributions and histories of stress and strain in the sheets, the fracture initiat ion sites and the critical strokes are predicted by means of the ducti le fracture criterion. The comparison with the experimental results sh ow that the forming limits due to various types of fracture initiation s in the bore-expanding processes are successfully predicted by the pr esent approach.