Critical Appraisal of the McDonnell Douglas Closure Model for Predicting Fatigue Crack Growth
AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA)
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The McDonnell Douglas fatigue crack growth model CNTKM8 has been used to predict crack growth in CCT-specimens with through cracks under four different load sequences, including a flight by flight sequence, and two stress levels. The predictions were compared against experimental data. The results ranged from fairly good for the more-structured sequences, to rather poor for the more-random sequences. Furthermore, the experimental trend of the structured sequences giving longer crack growth lives than the random sequences was not predicted correctly. An enhanced model was proposed, which was also tested. The predictions of this model were more consistent with the experimental data, and the above-mentioned experimental trend was also predicted correctly. This report contains a detailed description of both models, including the equations that are relevant for the case of a CCT-specimen with a through crack, and of the tests that they were subjected to.