| Damage tolerance analysis, based on fracture mechanics, is an important tool for ensuring the safety of flight of airframes. Traditionally, these analyses are deterministic in nature, but probabilistic methods have been applied to damage tolerance analysis in limited cases. The purpose of this dissertation is to formulate probabilistic damage tolerance analyses for metallic structural components, based on U.S. Air Force damage tolerance philosophy for slow crack growth and fail safe components. A survey of the literature was conducted on probabilistic durability and damage tolerance methods. The important elements of the methods are covered; including the initial fatigue quality, the variability in crack growth rate, and the probability of crack detection.;A probabilistic damage tolerance analysis was performed with a deterministic crack growth rate and then a stochastic crack growth rate, based on a probabilistic durability method. Examples of slow crack growth and fail safe structures are presented. As an example of a slow crack growth component, a lug from an aircraft subjected to an 80-flight fighter/trainer wing lower surface spectrum was selected. A stiffened panel from a lower wing skin of a tanker was selected as an example of a fail-safe component. Crack arrest in the panel, followed by catastrophic failure of the stiffener was considered as the failure mechanism.;The model formulated here can be used to decide on the frequency and quality of the inspection of a component needed to keep the probability of failure at acceptable levels. Results of this study can serve as bases for decision making for inspection maintenance and fleet management. |
