Volume 14, Issue 5, 2005

Structural Health Monitoring of Bonded Composite Joints Using Embedded Chirped Fibre Bragg Gratings

J Palaniappan¹, H Wang¹, S L Ogin¹,*, A Thorne¹, G T Reed², A D Crocombe¹ and S C Tjin<sup>3

1</sup>School of Engineering, University of Surrey, GU2 7XH, UK
²Advanced Technology Institute, School of Electronics and Physical Sciences, University of Surrey, GU2 7XH, UK
³School of Electrical and Electronic Engineering, Photonics Research Centre, Nanyang Technological University, Singapore

*Author to whom correspondence should be addressed:                            E-mail: S.Ogin@surrey.ac.uk

(Received 2/2006; accepted 3/2006)

Abstract
Chirped fibre Bragg gratings (CFBGs) have been used to monitor disbond initiation and disbond growth in composite bonded joints. The CFBGs have been embedded within, but near the surface of, a transparent GFRP composite adherend that has been bonded to a second transparent adherend. The low wavelength end of the CFBGs has been arranged to be adjacent to the end of the first adherend. Disbond initiation is readily detected as a modification to the reflected spectrum of the CFBG, consisting of the low wavelength part of the reflected spectrum being shifted to lower wavelengths; this is due to the unloading of the adherend resulting from the disbond. Disbond growth is detected by the movement of a dip in the reflected spectrum of the CFBG (as a consequence of the load redistribution at the disbond front); this dip moves to higher wavelengths as the disbond propagates. The relationship between the shift of the dip in the reflected spectrum with the position of the disbond front has been determined directly through the use of transparent GFRP joints.