NDE detection of manufacturing defects in composite bonded joints using CFBG sensors

This paper reports the use of chirped fibre Bragg grating (CFBG) sensors to detect defects introduced during the bonding of composite joints. The single-lap joints were made from transparent GFRP cross-ply composites which had a CFBG sensor embedded within one of the two adherends during the manufacturing stage. Joints with defects simulated using PTFE or introduced real air-gaps have been investigated. The sensors were interrogated with no load on the joints and also under a moderate quasi-static load. For the joints with PTFE “defects”, the perturbations observed in the reflected spectra provided a clear indication of the location of the defects and were in very good agreement with modelling predictions. Changes in the reflected spectra for the air-gap defects also provided an indication of the location of the defects and the spectrum changes were in reasonable agreement with modelling predictions. However, further work is required to establish the limitations of the technique for air-gap defects