Abstract
Unstable ductile fracture criteria of a power hardening material have been investigated to derive the relation between a critical remote uniform strain at fractureεf and a crack length c of plate specimen under uniaxial plastic extension.
(1) The fracture criterion is given by the following equation based on the energy consevation law. εf c1/1+n1/1+n=const.
(2) The theory has been approved by the experiment on the saw cut notched plates of normalized 0.8 %C steel, 0.17%C steel and austenitic stainless steel. The results of numerical analyses by the finite element method also reasonably support the validity of the theory.
(3) The present criterion is identical with Griffith criterion in the brittle fracure when strain hardening exponent n=1. In view of this theory one can have better understanding about the reduction of area in, the conventional tensile test, and a whole physical interpretation of ductility of material is obtained throughout tensile test, unstable ductile fracture and brittle fracture.
