ANALYSES OF FATIGUE AND FATIGUE-CRACK GROWTH UNDER CONSTANT- AND VARIABLE-AMPLITUDE LOADING

J. C. Newman, Jr.        

Anales de la Mecánica de la Fractura, nº 16 . 1999 . Pág. 24 -35
Ver (.pdf): Anales16-003

Resumen: Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily 'crack growth' from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using 'small-crack theory' under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (L1Kerr) under constant-amplitude loading. Modifications to the L'1Kerrrate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. 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 under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and anal y ses agreed well.

LocalizaciónTorremolinos, Málaga

Mechanics of Materials Branch. NASA Langley Research Center. Hampton, Virginia USA 23681