On the cut-off value of negative triaxiality for fracture

Although yield condition of metals does not strongly depend on it, mean stress plays an important role in fracture of metals. A cut-off value of the stress triaxiality equal to −1/3, below which fracture never occurs, was derived analytically from the fracture locus in the principal strain space experimentally reported from upsetting tests. It was found that this result is consistent with tensile tests under hydrostatic pressure (Bridgman tests). Numerical simulations performed in this study with the cut-off value in fracture loci successfully captured the main features observed in tensile tests under hydrostatic pressure by Bridgman and others, and simulated the tests on 1045 steel performed by Kao et al.