Study of Statistical Variations of Load Spectra and Material Properties onAircraft Fatigue Life

摘要

NAVAIR utilizes the fatigue spectrum of an existing Navy aircraft to set thestructural design requirements for a new Navy aircraft. The current design requirement is for the new aircraft to withstand a fatigue spectrum at least as severe as the spectrum experienced by 99.73% (3 standard deviations) of the aircraft from which the design requirement originated. Two years of A-6 data were used in the study, which contained the number of g exceedences at the four g, five g, six g, and seven g levels. Trade off studies were completed to analytically examine the variation in the fatigue life of an aircraft while varying the reference stress at the notch of a crack, re-ordering of the load sequences within the spectrum, varying the 3 sigma design requirement, and changing the material properties of the metal. The results indicated that NAVAIR's current requirement for a new aircraft to withstand a three o spectrum may be too severe. This conclusion is only valid for a three o spectrum based on the A-6 load history.