AN ENGINEERING EVALUATION OF METHODS FOR THE PREDICTION OF FATIGUE LIFE IN AIRFRAME STRUCTURES
LOCKHEED AIRCRAFT CORP BURBANK CA
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Comparison and verification was studied for methods of fatigue life prediction suitable for handling the complex problems encountered in the design and operation of modern aircraft. The problems of airframe fatigue analysis are reviewed from the viewpoint of design, development testing, and interpretation of fleet service history to maintain a necessary comparative basis for relating a practical fatigue life prediction method to operational results. From a study of 20 proposed fatigue life prediction methods 10 procedures were chosen for evaluation numerically with a group of 78 complex spectral test results representing approximately 266 individual specimens. An experimental program generated constant amplitude axial load S-N type data on simple notched coupons of 7075-T6 aluminum alloy sheet for use in the analysis procedures. New magnetic tape controlled fatigue test machines were utilized to apply simple spectra of gust, maneuver, ground, composite spectra of flight gust, ground taxi, and ground-air-ground transitions and composite spectra of flight maneuver, ground taxi, and ground-air-ground transitions. A series of specimens of a complex joint were also fatigue tested.