EFFECT OF VOID GROWTH AND SHAPE ON THE INITIATION OF DUCTILE FAILURE OF STEELS

Notched tensile bars of a high strength structural steel were loaded t o first void coalescence. The results show that damage curves determin ed by using proportionally loaded specimens are not valid for specimen s under non-proportional loading. The results of the experiments with different load histories of notched tensile bars show, that a single p arameter criterion like reaching a critical void volume is not suffici ent to describe the initiation process of void coalescence. The stress -triaxiality at initiation and the shape of the voids exhibit a strong influence on the initiation values. Two ways to describe initiation a re shown: A simple one considers a critical combination of void volume , stress-triaxiality and plastic strain at initiation. The other one u ses a shape factor to describe the shape of the voids and calculates t he initiation values. Both models work with an accuracy in the order o f the experimental scatter. (C) 1997 Elsevier Science B.V.