2017 Volume 58 Issue 678 Pages 617-623
In this study, the ductile fracture limit at low stress triaxiality was examined．Spheroidized medium-carbon steel JIS-S55C was adopted as the test material. Notched-bar combined torsion tests were carried out so as to control low stress triaxiality states. The stress triaxiality and equivalent plastic strain were calculated by the finite element method. The ductile fracture limit at low stress triaxiality could be expressed as a function of the stress triaxiality and equivalent plastic strain. It was not consistent with the ductile fracture limit at high stress triaxiality determined by notched-bar tensile tests. This result suggested that the ductile crack initiation mechanism differed between the tensile mode and the shear mode.
