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14 November 1997 Monitoring of crack growth beneath a bonded repair using Bragg gratings
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In the aircraft industry the use of externally bonded composite repairs has become an accepted way of repairing fatigue, or corrosion, damaged metallic structural components. Optical fibers offer a means of monitoring the load transfer process in these repairs, and can therefore be used to provide an indication of the integrity of the repair. This paper describes the use of an array of fiber Bragg grating strain sensors (FBGs) for the in-situ monitoring of bonded repairs to aircraft structures and, in particular, the monitoring of crack propagation beneath a repair. In this work the FBGs have been multiplexed using a combination of wavelength and spatial techniques employing a tunable Fabry-Perot filer to track individual gratings. The multiplexed FBGs were then surface mounted on a Boron-Epoxy unidirectional composite patch bonded to an aluminium component. The sensors were located so as to monitor the changing stress field associated with the propagation of a crack beneath the patch. The ability of relating experimental results to sensor readings is then confirmed using both a thermo-elastic scan of the patch and 3D finite element analysis. Additionally, the relative merits of surface bonding verses embedding sensors are discussed, and a standardized embedding procedure for fiber optic sensor in Boron-Epoxy patches is described.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Iain A. McKenzie, Rhys Jones, W. K. Chiu, D. Booth, and S. Galea "Monitoring of crack growth beneath a bonded repair using Bragg gratings", Proc. SPIE 3242, Smart Electronics and MEMS, (14 November 1997);

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