In-situ internal strain development and cure monitoring in a curing composite using in-fibre Bragg gratings and dielectric sensors

In-fibre Bragg gratings (IFBGs) and dielectric sensors have been embedded in the same carbon fibre epoxy composite and have been used together during the curing process to make in-situ measurements of two cure parameters, namely internal strain and conductivity. This was performed using an automated acquisition system, part of which could use real-time measurements to estimate and predict cure parameters. The IFBGs were demodulated using a scanning fibre Fabry-Perot interferometer. The results obtained using this combined cure monitoring system demonstrate that it is possible to monitor the strain levels in the optical fibre resulting from the onset of liquification, gelation, and vitrification within the surrounding resin matrix.