On the development of statistical knock-down factors for WFD assessment

icaf2023 Tracking Number 115

icaf2023 presentation

The nucleation of multiple fatigue cracks over large areas, how they interact, and whether they can lead to a catastrophic event has been for a long time a concern, not only for the OEMs and the Regulatory Agencies, but also for the entire community involved in aircraft fleet management, as long as the fleets age. The phenomenon of Widespread Fatigue Damage (WFD) has been investigated for decades, and to demonstrate freedom of WFD up to the LOV for large transport aircraft structures became mandatory in the latest amendments of the regulations. During the ICAF Symposium in 2013, Safarian [1] has proposed an approach to assess WFD based on fatigue life estimation and the application of a set of knock-down factors. The present work provides an in-depth investigation for each of these factors, bringing a deduction or an explanation for them based on statistical approaches, together with some examples of application. By understanding each and every factor’s origin and eventual built-in conservativeness, the engineer in charge can propose alternative approaches and come out with more realistic results, eventually saving weight and resources, without compromising safety. [1] P. Safarian, (2013), Widespread Fatigue Damage Evaluation Method, Proceedings of the 27th ICAF Symposium, Jerusalem.