The use of chirped fibre Bragg grating sensors to monitor delaminations in composite materials and structures

Abstract

Chirped fibre Bragg grating (CFBG) sensors embedded within composite materials have been shown to be able to monitor delamination growth in adhesively bonded single-lap joints, whether the sensors are embedded within a composite adherend or within the adhesive bondline itself. The relative ease of interpretation of CFBG reflected spectra with regard to delamination growth is a consequence of the relationship between the spectral bandwidth of the reflected spectrum (typically 20 nm) and physical locations along the sensor length (typically 60 mm). When the sensor is embedded in, or bonded to, a composite material subjected to a tensile uniform strain, all the grating spacings are increased and the entire spectrum shifts to higher wavelengths-just as for a uniform FBG sensor. However, if the strain field is perturbed by damage in the composite (such as a matrix crack or a delamination), so that the smooth linear increase in the grating spacing is disrupted, then a perturbation appears in the reflected spectrum that can be used to determine the physical location of the damage. In this paper, results on monitoring delamination/disbond growth will be discussed with regard to sensor location, together with the possibility of using the sensors to monitor repaired composite structures. © 2012 Taylor & Francis Group, London.

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