Elevated-temperature failure of structural materials (e.g., austenitic stainless steels, low-alloy steels) used in energy-conversion systems can occur by fatigue, creep, or by interactive processes involving creep, fatigue, and environment. The fracture surfaces of these materials exhibit a variety of microstructural features depending upon the type of material, strain rate, temperature, environment, hold times, and sequence of waveshapes. These microstructural observations have been used as a guide in the formulation of generalized damage-rate equations that include interaction between a crack and cavities in a given environment. Crack-propagation rate as well as total life of a fatigue specimen have been calculated by integrating the damage-rate equations over the inelastic strain history of the specimen, and compared with experimental results.

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