Ductile failure as a result of a void-sheet instability: experiment and computational modeling

The ductile fracture of circumferentially notched HY-100 steel specimens tested at high stress triaxiality is characterized by a fracture surface with a zig-zag profile created by large elongated voids separated by inclined sheets of microvoids. The failure path suggests that a local deformation instability, triggered by the growth of MnS inclusion-nucleated voids, may be responsible for this form of fracture. Measurements show that the failure strains are small and decrease slowly with increasing stress triaxiality as compared to a more global void coalescence. Micro-mechanical modeling by finite element analysis of a geometry based on the observed metallurgical microstructure shows a distinct localization of plastic flow. The localization of plastic flow leads to a void-sheet failure prediction and the experimental results are correctly characterized by the computational model.