A method for evaluation of in-service fatigue cracks

This paper examines the case of unexpected fatigue crack detection in a fleet of military aircraft and proposes a technique to determine the mean life of the failures and/or appropriate inspection intervals. Use is made of the Frost and Dugdale relation, that suggest that as a first approximation a linear relationship exists between the natural log of the crack length or depth and the service history (number of cycles) for a large number of practical cases.