14 November 1996 Eddy current inspection of bonded composite crack repair
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The aging of the US aircraft fleet poses serious economic and safety challenges. Fatigue cracks in the 7079-T6 aluminum fuselage skin of aging transports have presented zn opportunity to test a prototype repair. GLARE, a fiber metal laminate, has been applied to repair fuselage cracks in the fuselage skin of a US transport aircraft. This affordable prototype solution to extend the life of aging aircraft requires an inspection method to track crack growth and monitor the effectiveness of the patch on repaired fuselage skin. The fiber metal laminate patch is opaque and the fuselage skin at the damage location generally can only be accessed from the outside surface requiring the use of a non-destructive means to monitor crack length. Advances in eddy current inspection technology have provided a means to detect and track crack growth beneath patches on fuselage skins. This paper describes the development of low-frequency eddy current techniques to monitor cracks under bonded composite repair patches applied to stiffened fuselage structures. The development involved the use of a rugged portable eddy current inspection unit. The results show crack growth can be monitored to ensure the continued structural integrity of repaired flawed structures; however, the influence of substructure present a challenge to the inspector in detecting crack growth.
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Thomas K. Smith, Cornelius Guijt, Robert Fredell, "Eddy current inspection of bonded composite crack repair", Proc. SPIE 2945, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware, (14 November 1996); doi: 10.1117/12.259104; https://doi.org/10.1117/12.259104

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