Abstract
Upsetting of an aluminum alloy A6061-T6 is performed to investigate the effect of surface flaw on fracture. A prediction of surface cracking by means of three fracture criteria is attempted. A parameter for prediction of orientation of crack is proposed. The longitudinal flaw leads to earlier surface cracking, while circumferential flaw does not affect surface cracking. Ohyane's criterion, which is based on void growth under triaxial stress state, can well predict the surface cracking by using the stress and strain at flaw root by FEM. The crack orientations predicted by the parameter proposed are in good agreement with the experimental ones.
