Abstract Aircraft are subjected to unpredictable variable amplitude loadings (operational loads, varying widely according to the missions flown by the aircraft). For safety reasons, it is necessary to estimate each aircraft’s actual fatigue “consumption” relative to its potential. For this purpose, most French military aircraft are equipped with load monitoring systems, giving direct or indirect access to the in-service loads. The cumulative fatigue damage is calculated at various points of the structure pointed out as being critical. Thus, for fleet life-extension purposes and usage predictions, the use of more precise damage and crack growth prediction models is a major concern. The initiation models are yet insufficient to cover the entire aircraft lifetime. In order to maintain the design safety margin, the airworthiness authority introduced the damage tolerance philosophy: cracks are allowed below a given size provided that the propagation process is well known. Systems currently in operation on the French Air Force enable the acquisition of large number of flight parameters. This data associated with crack growth models provide information about the propagation phase. The fatigue potential consumption during the operational life can thus be estimated by combining initiation and propagation models. Initiation model are based either on real load sequence combined with unit damage matrix or on rebuilt load sequence (from g-counters output) combined with cumulative damage laws. Different propagation models are investigated. At this stage, experiments have been carried out on CT samples and are ongoing on a geometry close to the spar one (thick holed aluminum alloy part). Further investigations will be carried out to extend the conclusions made on aircraft equipped with load monitoring systems to aircrafts only equipped with g-counters. It means build a temporal spectrum using g-counters output in order to take load history into account in the propagation process (mostly retardation effect due to variable amplitude loading).
Fatigue Crack Growth Approach for Fleet Monitoring
2019-07-03
16 pages
Article/Chapter (Book)
Electronic Resource
English
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