Unified two-stage fatigue methodology based on a probabilistic damage model applied to structural details

Fatigue cracks are often a result of incremental stable crack growths that can be described by fracture mechanics. Fatigue crack initiation, however, has been most often described using empirical relationships between an alternating stress or strain and the number of cycles at those loads until either a specimen fails or a crack is observed. There are, however, modem views that consider fatigue crack growth and crack initiation directly related phenomena, the former being repeated instances of the latter, localized at an existing crack tip. Models of this newer class allow for an integrated initiation and crack growth calculation process which is advantageous when dealing with notched details in elastoplastic strain conditions. Recently, Huffman developed such a model which relates Walker-like stress-life relation and fatigue crack growth behaviour. This paper expands upon this new approach in order to account for the expected statistical variation using probabilistic S-N and e-N fields as per works of Castillo and Femandez-Canteli. A unified local approach proposed to treat fatigue crack initiation and growth is used on notched geometries with the predicted probabilistic variations being accounted. Notched details made of puddle iron from the Eiffel bridge and P355NL1 pressure vessel steel are considered in this study.