Generation of Spectra and Stress Histories for Fatigue and Damage Tolerance Analysis of Fuselage Repairs
BATTELLE MEMORIAL INST COLUMBUS OH COLUMBUS LABS
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This report describes a simplified procedure for the development of stress histories for use in the analysis of aircraft repairs. This report concentrates on stress histories for fuselage skin repairs. A description of typical fuselage loadings is provided, and basic fuselage stress histories are described. A method for development of an exceedance diagram for analysis of fuselage skin repairs is detailed. Subsequently, a methodology for generating detailed stress histories is reviewed. Some of the key features are 1 the inclusion of a range of flights of different severities, 2 the inclusion of deterministic loads where they occur, e.g., ground-air-ground cycles, 3 the use of a near-optimum number of stress levels 10-16 positive and negative, 4 the combination of positive and negative excursions of equal frequency, and 5 matching of the total number of flights and cycles with the total exceedance diagram. Two methods of estimating fuselage skin stresses are presented, the first based on static equilibrium requirements and the second based on a limit load analysis. A comparison of the proposed history generation scheme with that of an airframe manufacturer for the KC-135 is also presented. The predicted fatigue crack growth patterns for a hypothetical through crack at a fastener hole are compared for the two history generation schemes at three areas within a fuselage.
- Civilian Aircraft