Prediction of Fatigue Crack Growth under Variable-Amplitude and Spectrum Loading Using a Closure Model

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Abstract
The present paper is concerned with the application of an analytical crack-closure model in the study of crack growth under various load histories. The model was based on a concept like the Dugdale model, but modified to leave plastically deformed material in the wake of the advancing crack tip. The model was used to correlate crack growth rates under constant-amplitude loading, and to predict crack growth under variable-amplitude and aircraft-spectrum loading on 2219-T851 aluminum alloy sheet material. Predicted crack-growth lives agreed well with experimental data. For 80 crack growth tests subjected to various load histories, the ratio of predicted-to-experimental lives, NP/NT, ranged from 0.5 to 1.8. The mean value of NP/NT was 0.97 and the standard deviation was 0.27.