Abstract
The effect of stress triaxiality on ductile fracture was investigated on several structural steels. Round bar tensile specimens with circumferential notches of different acuity were used for the tests to develop the triaxial state of stress. The steels used were three mild steels, two medium strength steels and a 21/4Cr-1Mo low alloy steel.
For all the steels tested, the size of dimples increased and the strain at the ductile crack initiation sharply decreased with an increase of stress triaxiality of the specimen. The degree of this stress triaxiality effect differed largely with materials. This material dependence of triaxiality effect may, mainly, be due to the difference in size distribution of inclusions.
To investigate the effect of stress relief annealing on void formation and growth, the tests, in which annealing after 20% (or 40%) straining was repeated until fracture, were also carried out. The test results showed that, in the notched specimens, the voids grew to huge dimples by the repetition of annealing after 20% straining.
