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We describe a computer model for predicting ductile-fracture initiation and propagation. The model is based on plastic strain. Fracture starts or a crack extends when the integrated product of the equivalent plastic-strain increment and a function of the mean stress exceeds a critical value over a critical length. This critical length is characteristic of the microstructure of the material. The computer fracture model is calibrated by computer simulation of simple and notched round-bar tension tests and a precracked compact tension test. The model is then used to predict fracture initiation and propagation is the standard Charpy V-notch specimen. The computed results are compared with experiments. The model predicts fracture toughness from tests of standard surveillance specimens from nuclear-reactor pressure vessels and can be applied to fracture calculations for these vessels.

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Static and dynamic pretest simulations of a degraded nuclear piping test are performed to investigate crack stability and piping integrity. The purpose of this study is to provide system design guidance for a large-diameter piping test and to gain insight on modeling dynamic crack behavior in austenitic and carbon steel base metal and weldments. Combined operating temperature and pressure plus an idealized seismic loading are applied until substantial crack growth, leakage, or pipe guillotining is predicted. The importance of modeling elbow deformation and plasticity is demonstrated.