Pulsed eddy current detection of cracks in F/A-18 inner wing spar without wing skin removal using Modified Principal Component Analysis |
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| Affiliation: | 1. Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, #08-03, 138634, Singapore;2. Institute of High Performance Computing, A*STAR (Agency for Science, Technology and Research), 1 Fusionopolis Way, Connexis North, #16-16, 138632, Singapore;1. Instituto Superior Técnico, Universidade de Lisboa, Portugal;2. Instituto de Telecomunicações, Portugal;3. Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento, Portugal;1. IST Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal;2. INESC-ID Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento, 1000-029 Lisbon, Portugal;3. IT Instituto de Telecomunicações, 1049-001 Lisbon, Portugal;4. INESC-MN Instituto de Engenharia de Sistemas e Computadores Microsistemas e Nanotecnologias, 1000-029 Lisbon, Portugal;1. Dipartimento di Ingegneria, Polo Scientifico Didattico di Terni, Università di Perugia, Strada di Pentima 4, 05100 Terni, Italy;2. Dipartimento di Ingegneria Elettrica e dell’Informazione, Università degli Studi di Cassino e del Lazio Meridionale, Via G. Di Biasio 43, 03043 Cassino, FR, Italy;3. School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne NE1 7 RU, UK;1. School of Mechanical, Electronic and Industrial Engineering, University of Electronic Science and Technology of China, No.2006, Xiyuan Road, Hi-Tech Industrial Development Zone, Chengdu, Sichuan 611731, PR China;2. Shanghai Spaceflight Precision Machinery Research Institute, Shanghai, PR China |
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| Abstract: | Stress corrosion cracks may develop between fasteners in the aluminum inner wing spars of F/A-18 Hornet aircraft. These fasteners secure carbon-fibre/epoxy composite wing skin, of nominal 13 mm thickness, to the spar. Inspection of the spar through the wing skin is required in order to avoid wing disassembly. Pulsed eddy currents, generated by a probe design that utilizes the ferrous fastener as a flux conduit, are demonstrated as having the capability of detecting simulated cracks within the spar with the wing skin present. Differentially connected pickup coils are used to sense differences in response due to asymmetries in induced eddy current fields arising in the presence of cracks. To overcome variability in PEC signal response due to variability in magnetic coupling to the fastener, a large measurement set was analyzed using Modified Principal Component Analysis (PCA). The modified PCA minimizes residual sum of squares to extract eigenfunction scores, which are used to detect the presence of cracks ending on one side of the fastener hole. The ability of the method to sense simulated cracks independent of confounding measurement parameters was demonstrated. |
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