Fatigue-Crack Propagation in D6AC Steel Plate for Several Flight Loading Profiles in Dry Air and JP-4 Fuel Environments

摘要

The objective of this experimental program was to obtain an independent evaluation of the fatigue-crack propagation characteristics of D6AC steel for the F-111 aircraft under specific flight loading spectra. The program also included selected studies of constant amplitude fatigue-crack propagation and crack growth retardation under the influence of single overloads. It was determined that fatigue crack propagation specimens evaluated under spectra with peak loads exceeding one-half of the tensile yield strength of the material sustained significantly longer lifetime than under spectra wherein the peak loads were significantly below this stress level. Although the observations were limited, an effect of maximum cyclic stress on constant amplitude crack growth rates was apparent. In the crack growth retardation studies, it was observed that the overload ratio plays a direct role, and the maximum cyclic stress level an inverse role, in delaying crack growth. (Author)