Abstract
Acoustic Emission (AE) is a passive form of non-destructive testing that relies on the detection and analysis of stress waves released during crack propagation. AE techniques are successfully employed number of industries there remains some scepticism in aerospace engineering. The reported investigation details a single four point bend test specimen undergoing fatigue loading. This test is part of a much larger programme designed to demonstrate a technology readiness level (TRL) of five of the use of AE to detect crack initiation and growth in landing gear structures. The completed test required that crack growth had to be monitored to allow a comparison with the detected and located AE signals. The method of crack monitoring had to be non-contact so as not to produce frictional sources of AE in the crack region, preventing the use of crack mouth opening displacement gauges. Furthermore adhesives on the specimen surface had to be avoided to eliminate the possibility that the detected AE was from adhesive cracking, thus the use of strain gauges or foil crack gauges was not possible. A method using Digital Image Correlation (DIC) to monitor crack growth was investigated. The test was stopped during fatigue loading at 1000 cycle intervals and a DIC image captured at peak load. The displacement due to crack growth was observed throughout the investigation and the results compared with the detected AE signals. Results showed a clear correlation between AE and crack growth and added further evidence of TRL5 for detecting fractures in landing gears using AE.
Highlights
Messier-Dowty are world leaders in the design and manufacture of aircraft landing gear systems, structures and components
It is proposed that Acoustic Emission (AE) can be used to monitor the landing gear during the certification test in order to reduce the down time associated with conventional nondestructive testing (NDT) inspections
Acoustic Emission (AE) is a passive NDT technique that relies on the detection of the stress waves that are released during crack propagation
Summary
Messier-Dowty are world leaders in the design and manufacture of aircraft landing gear systems, structures and components. Nondestructive testing (NDT) is used to confirm the integrity of the landing gear structure at key stages in the fatigue test regime. It is proposed that Acoustic Emission (AE) can be used to monitor the landing gear during the certification test in order to reduce the down time associated with conventional NDT inspections. Acoustic Emission (AE) is a passive NDT technique that relies on the detection of the stress waves that are released during crack propagation. A major aspect of implementing an AE solution for monitoring landing gears is that Messier-Dowty requires an automated system capable of identifying fractures at an early stage in what is a high-noise environment and in specimens that have complex geometry. The reported investigation details a single specimen test that is part of a much larger programme that includes tests on real landing gears in a high noise environment, designed to demonstrate a technology readiness level (TRL) of five of using AE to detect crack initiation and growth in landing gear structures undergoing certification tests
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