Spectrum Loading Fatigue-Crack-Growth Predictions and Safety-Factor Analysis.

摘要

The adequacy of fatigue-crack-growth predictions was investigated. Various possibilities of applying safety factors were examined. The work was confined to service-load histories as experienced by fighter aircraft. Crack-growth analyses were made for basic fighter spectrum and for numerous variations of that spectrum. The analyses were based on existing crack-growth retardation models, using the CRACKS computer program. Also, a simpler computational technique was developed. Crack-growth experiments were carried out on a 7075-T73 aluminum alloy and a Ti-6Al-4V titanium alloy. Adequate crack-growth predictions can be made consistently with some of the techniques, however, some experiments will always be necessary. The only satisfactory way to apply a safety factor to crack-growth predictions is to apply a factor to crack-growth life. Safety factors on initial crack size or baseline data are unacceptable because they result in varying degrees of conservatism. (Author)