Monitoring of Disbonding in Bonded Composite Joints Using Cfbg Sensors Embedded within the Adhesive Bondline

Chirped fibre Bragg grating (CFBG) sensors have been embedded within the adhesive bondline of single-lap bonded composite joints, fabricated using a transparent glass fibre reinforced plastic (GFRP) adherend bonded to a carbon fibre reinforced plastic (CFRP) adherend. During fatigue cycling, disbonds initiated adjacent to the cut ends of one, or both, of the adherends and the disbonds propagated with continued fatigue cycling. The results show that the CFBG sensor within the bondline can detect the initiation of the disbond and can also monitor the position of the disbond front as it propagates during fatigue cycling. As the disbond front propagated, there was reasonable agreement between the measurements of the position of the disbond front using the CFBG sensor spectra and photographic measurements of the location of the disbond front taken through the transparent GFRP adherend. This method of monitoring disbonding (with the sensor embedded in the adhesive bondline) could be used to monitor bonded composite structures when it is difficult to embed the sensors within the adherends themselves.