The use of a CFBG fibre optical sensor to detect disbond development in composite/composite and metal/composite adhesively bonded joints

Abstract

This paper describes a novel technique to monitor disbond initiation and propagation in both composite-composite and metal-composite adhesively bonded joints using chirped fibre Bragg grating (CFBG) sensors embedded within fibre-reinforced composite adherends. Characteristic changes in the reflected spectra from the sensors indicate both (a) disbond initiation (due, for example, to fatigue loading) and (b) the current position of the disbond front (to within about 2 mm). For composite-composite bonded joints, the reflected spectra are recorded with the joint under a small load (in practice, this could be the self-weight of the structure). In the case of a metal-composite joint, the difference in the coefficient of thermal expansion between the adherends is sufficient to enable disbond propagation to be monitored when the joint is unloaded. The experimental results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra, with very good agreement between the experimental observations of the reflected spectra and the predicted spectra, for disbonds of different lengths