Influence of flow stress and specimen geometry on the fracture morphology of Nickel 270

The effects of flow stress and specimen geometry on the fracture morphology of Nickel 270 were studied experimentally and computationally. Tensile tests were performed on cold worked and annealed specimens with two gauge geometries. Fractographic observations revealed that all specimens failed by microvoid coalescence and shear. The relative proportions of the two failure modes were a function of stress - strain response. Microvoid density and aspect ratio were influenced by changes in microstructure and specimen geometry. Computational simulations were performed for both gauge geometries for both the cold worked and annealed specimens in order to determine the stress states that developed in these specimens during loading. It was found that the changes in fracture morphology observed in these specimens are directly attributable to the resulting stress state history in a given specimen. Differences in ductility before failure initiation are consistent with changes in fracture morphology and stress state history.