Fibre grating refractometer sensors for composite process monitoring

摘要

Optimum performance from advanced composites requires careful control of theresin matrix during cure. This is to ensure there are no cure induced voids andto minimise the build up of internal stresses. Careful control of the process isalso necessary to reduce wastage. Traditional resin inspection techniques arebulk or sample oriented and thus cannot provide data about critical componentparts. Optical fibre based sensors however, allow for in-situ monitoringtechniques to be deployed in components without effecting their structuralintegrity. In this work, two fibre optic grating techniques are demonstrated asprocess monitoring sensors and are compared with a Fresnel refractometricmethod. The change in refractive index of a resin has previously been used as ameans for assessing the degree of cure. The central wavelength of an attenuationband of a long period grating (LPG) was monitored during the cure of a resin. Inparallel the spectral resonances of a tilted fibre Bragg grating (FBG) are alsomonitored. The two techniques are shown to correlate well with the Fresnel basedmethod in both detecting the resin and monitoring the state of cure, indicatingthe potential of the techniques for online production monitoring