Use of General Fatigue Data in the Interpretation of Full-Scale Fatigue Tests,
ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT PARIS (FRANCE)
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The fatigue behaviour of notched specimens depends on two elasticity parameters, namely the stress concentration factor and the relative stress gradient or the radius of curvature at the notch root. Laboratory fatigue test results are not always representative of the environmental conditions within aircraft structural assemblies, particularly because of water condensation in gaps and recesses. The frequency effect is mainly ascribable to humidity, and therefore to corrosion, owing to hydrogen penetration. In assemblies, stress concentrations due to load transfer through fasteners are investigated for the case of asymmetric single shear. The breakdown of the applied loadings must include the peak-to-peak, ground-air-ground variation. In load transfer by fastener bearing stresses, the low compressive loads may be neglected, the local highest stresses varying from zero to the maximum. Interpretation of full-scale fatigue test results, either for a different loading or for a slightly modified local design of the structure, is essentially comparative.
- Properties of Metals and Alloys