Predicting Flight by Flight Fatigue Crack Growth Rates

Several crack growth prediction approaches are examined for their ability to predict both the magnitude and trend of fatigue crack growth rate data generated under transport wing flight simulation loading. Three cycle-bycycle accounting approaches, one with no load interaction and two which incorporate high-to-low load interaction, are studied. Two stress-stress intensity factor characterization approaches are also examined. These two characterization approaches isolate principal variables from the input stress spectrum and then utilize the no-load interaction, cycle-by-cycle approach to obtain estimates of crack growth rates. The results indicate that load interaction cycle-by-cycle accounting procedures lead to more accurate crack growth predictions principally because they incorporate the influence of the high-to-low load interaction phenemonon. a da/dN da/dF C, p F KR Kth N NF N50 R S

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