The effects of stress triaxiality and temperature on the ductile fracture process have been investigated with particular reference to the micro-void formation and growth. The steels used were SM50A, SM50B and 21/4Cr-1Mo-steel. To develop triaxial stress of various acuity, round bar tensile specimens with circumferential notch of different acuity were chosen for the tests. From the metallographic observation on the sections of the specimens off-loaded on the way of loading, it was found that both the formation and the growth of voids were significantly influenced by stress triaxiality. Temeprature mainly affects the void formation process rather than its growth. The effect of temperature may be assumed to be caused by its effect on the flow stress of the material.
Fracture toughness tests on CT specimens have also been made in order to obtain the relation between the fracture toughness and the ductility under the axisymmetric condition with the high triaxiality.
