Ductile Fracture of Carbon Steel under Cold Metal Forming Conditions : 3rd Report, Effects of Deformation Mode and Deformation History on Ductile Fracture Strain

Abstract

The criterion for ductile fracture strain of carbon steels proposed in the previous reports is applied to a few modes of deformation. In general, the fracture strain predicted by the criterion agrees fairly well with the experimentally obtained one. The result suggests that the fracture strain is affected to some extent by the mode of deformation which was not taken into account in the criterion. When the direction of deformation is reversed during torsion test, a sharp bend is observed in the relationship between the strain before reversal and the strain to fracture after reversal. The bend is related to the initiation strain of fracture-nuclei-growth. The fracture strain of a torsional specimen after intermediate annealing is also found to change sharply when the strain prior to intermediate annealing exceeds the initiation strain of fracture-nuclei-growth.