Fatigue Life Estimate of Centre-Box Lug in Seahawk's Stabilator

摘要

The fatigue failure of a center-box lug found in the Seahawk's stabilator, highlighted deficiencies in the fatigue life assessment of helicopter airframe structure. Thus a methodology for fatigue life assessment was developed using this cracked lug as a demonstrator. Indirect measurements from the Flight Loads Survey on the Black Hawk although not ideal allowed the estimation of the amplitude and frequency of the lug's loading. Of the sixteen assumptions made in this fatigue analysis the most restrictive was that a high amplitude and high frequency loading acts for the entire flying time. Three different fatigue lives were obtained based on different levels of conservatism in the loading estimates. These three loadings were: the worst-case scenario, a high loading scenario, and a best-case scenario. The worst-case and high-loading scenarios resulted in low fatigue lives. while the best-case scenario resulted in an unlimited life for the cracked lug. It was surprising to find such low fatigue lives for the of these scenarios but these low lives may be due to the conservative assumptions used in the analysis.