2018 Volume 36 Issue 4 Pages 285-292
Ductile crack initiation limit characteristic of metallic material, which is evaluated with stress triaxiality and equivalent plastic stain, shows material dependency. The main purpose of this study is to propose the evaluation approach of ductile crack initiation limit with the material dependency. Ductile crack initiation behaviors were experimentally and analytically comprehended using notched round bar specimens of aluminum alloy as non-ferrous metal in addition to two different steels. On the basis of analyses, the locus of stress triaxiality during loading was found to be dependent on strain hardening exponent which is one of the parameter characterizing stress-strain relationship of material, and the behavior was confirmed in the strain region after uniform elongation for smooth specimen. Focusing on Mohr-Coulomb fracture criteria, limit strain was derived using strain hardening exponent and stress triaxiality. In addition, considering ductility after uniform elongation, ductile crack initiation limit with material dependency could be evaluated and it was found that limit strain at ductile crack initiation could be predicted using basic material properties obtained from monotonic tensile test, which are strain hardening exponent and ductility after uniform elongation.