Growth of Short Cracks During High Strain Fatigue and Thermal Cycling

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Abstract
Research in high-temperature fatigue usually concerns either crack initiation and endurance of smooth specimens in high strain fatigue (HSF) or the growth of long cracks in the nominally elastic regime described by linear elastic fracture mechanics. This review shows that the relatively unfamiliar growth rates in HSF can be linked to those in stress-intensity controlled growth, and so can be used satisfactorily for predicting component failure. Either a strain-based intensity parameter or a J-integral method may be used, and several examples are given. Integrated HSF growth rates are also shown to be consistent with smooth specimen endurance from (1) striation measurements, (2) direct measurement, and (3) the predictions of the shear decohesion model.Empirical HSF growth relations are summarized and the effects of temperature, environment, tension dwells, and microstructural damage are assessed in several alloys. The greatest correction that has to be made to the experimental and theoretical growth relations arises from the accelerating effects of creep during dwell.