Abstract
Upsetting of an aluminum alloy A6061-T6 was performed to investigate the effect of initial defect on fracture. A prediction of fracture initiation by means of three fracture criteria was attempted. The normal cylindrical specimen and the one with scratch were employed. Surface cracking on the specimen with longitudinal scratch occurred earlier than the specimens without scratch or with circumferential scratch. The Ohyane's criterion based on void growth under triaxial stress state, could well predict fracture initiation.
