FATIGUE LIFE PREDICTION FROM INCLUSION INITIATED CRACKS

Fatigue cracks have often been observed to nucleate at inclusions or c onstituent particles in thin sheet 2024-T3 aluminum. Large amounts of scatter are commonly observed in the experimental fatigue lives and cr ack nucleation site data. This research attempts to address some of th e stochastic issues associated with the fatigue process. An experiment al program was conducted to investigate the influence of inclusions on fatigue crack formation. Inclusions were found to be the dominant cra ck nucleation site and the inclusion sizes that nucleated fatigue crac ks were from the large particle tail of the overall inclusion size dis tribution. A probabilistic model has been developed to predict the obs erved variability in the experimental fatigue lives from the measured distribution of inclusion sizes. In order to model crack growth from a microstructurally sized defect (such as an inclusion), a total fatigu e life prediction model accounting for the small crack effect must be utilized. The probabilistic model uses a Monte Carlo simulation and Ne wman's FASTRAN II model to predict fatigue life. The fatigue life dist ributions, that were generated with the probabilistic model, predicted the critical, lower experimental fatigue lives and the overall variab ility in fatigue lives under several loading conditions. (C) 1998 Else vier Science Ltd.