Influence of strain history on ductile failure of steel

Notched tensile bars of a high strength structural steel were loaded to void coalescense. The results show that the damage curve determined using radially loaded specimens is not valid for specimens under non-radial loading. The results of the experiments with different load histories of notched tensile bars show, that a single parameter criterion like a damage parameter is not sufficient to describe the initiation process of void coalescense. The shape of the voids and the triaxiality at initiation exhibit a strong influence on the initation values. There are two ways to describe the initiation. A simple one considers a critical combination of void growth rate, triaxiality and plastic strain at initiation. The other one uses a shape factor to describe the shape of the voids and calculates the initiation values. Both models work with an accuracy in the order of the experimental scatter. (orig.)