Fatigue-life prediction methodology using small-crack theory

This paper reviews the capabilities of a plasticity induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional State-of-stress effects, were selected to correlate large-crack growth rare data as a function of the effective-stress-intensity factor range (Delta K-eff) under constant-amplitude loading. Some modifications to the Delta K-eff rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well. (C) 1999 Elsevier Science Ltd. All rights reserved.