Damage tolerance issues as related to metallic rotorcraft dynamic components

Tn this paper issues related to the use of damage tolerance in life managin g rotorcraft dynamic components are reviewed. In the past, rotorcraft fatig ue design has combined constant amplitude tests of full-scale parts with fl ight loads and usage data in a conservative manner to provide "safe-life" c omponent replacement times, In contrast to the safe-life approach over the past twenty Sears the United States Air Force and several other NATO nation s have used damage-tolerance design philosophies for fixed wing aircraft to improve safety and reliability, The reliability of the safe-life approach being used in rotorcraft started to be questioned shortly after presentatio ns at an American Helicopter Society's specialist meeting in 1980 showed pr edicted fatigue lives for a hypothetical pitch-link problem to vary from a low of 9 hours to a high in excess of 2594 hours. This presented serious co st, weight, and reliability implications, Somewhat after the U.S. Army intr oduced its six nines reliability on fatigue life, attention shifted towards using a possible damage-tolerance approach to the life management of rotor craft dynamic components, The use of damage tolerance in life management of dynamic rotorcraft parts will be the subject of this paper, This review wi ll start with past studies on using damage-tolerance life management with e xisting helicopter parts that were safe-life designed. Also covered will be a successful attempt at certifying a tail rotor pitch rod using damage tol erance, which was designed using the safe-life approach. The FAA review of rotorcraft fatigue design and their recommendations along with some on-goin g U.S. industry research in damage tolerance on rotorcraft will be reviewed , Finally, possible problems and future needs for research will be highligh ted.