Probabilistic Fatigue Methodology for Safe Retirement Lives

Author： Everett Richard A. Bartlett Felton D. Elber Wolf

ISSN： 2161-6027

Source： Journal of the American Helicopter Society, Vol.37, Iss.2, 1992-04, pp. : 41-53

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Abstract

Fleet readiness and flight safety strongly depend on the degree of reliability and maintainability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification far new rotorcraft is the so-called “six nines” reliability, or a probability of failure of one in a million. This report reviews the progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance to investigate reliability-based fatigue methodology. The participants in this cooperative effort are the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliabilily calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic for including both fatigue strength and spectrum loading variability to develop a consistent reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study.