Multi-Site Fatigue Testing and Characterization of Fuselage Panels from Aging Aircraft Structure
United States Air Force Academy Air Force Academy United States
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Multi-site fatigue damage is a common problem in the riveted lap joint structure of aging aircraft. Modeling and characterization of such damage is an especially daunting task. In this effort we present the results from fatigue tests which were performed on fuselage lap joints extracted from various retired USAF military aircraft. The test specimens were extracted from a variety of fuselage locations of these aircraft and subjected to spectrum loading simulating fuselage pressurization cycles. The test panels varied in width from 15 to 22 inches and typically had three 3 rows of fasteners in the lap joint. Some spot welded lap joint panels were also tested during the larger program however, only the results from mechanically fastened joints are presented here. The results from approximately 25 panels from two different aircraft are presented here. Also presented is the process used to prepare the panel test specimens. Instrumentation consisting of strain gages on either side of the lap joint was used to verify symmetric load introduction across the width of the specimen. All tests were run to lap joint failure. Post failure, the fatigue damage at each fastener location of the lap joint was characterized in detail. Wherever possible the first fastener hole to exhibit fatigue cracking was identified. The data are presented in graphical as well as tabular format for easy incorporation into validation and development testing for modeling software platforms such as AFGROW and NASGRO. These data also provide an excellent map for damage initiation and propagation, which could be used to validate modeling and simulation efforts aimed at predicting the life and reliability of similar aircraft structure.