Thermal sensitivity and relaxation of carbon fibre-foam sandwich composites with fibre optic sensors

The increasing use of sandwich composites for structural applications brings with it a need to establish a reliable inspection and monitoring method to ensure structural integrity and safe operation throughout the service life. Since optical fibre-based photonic sensing technologies are increasingly common for structural health monitoring of composite structures, selection of optical fibre Bragg grating sensors could be one possible choice for this purpose. In this paper, performance characterisation of sandwich composite with embedded silica fibre Bragg grating sensor is reported. Experimental tests were performed on a carbon fibre foam core sandwich composite embedded with a silica fibre Bragg grating sensor to extract the structural health monitoring parameters such as strain and temperature. The current study found that sandwich composite exhibits foam relaxation; however, its impact on strain measurement is negligible. Another important finding from the theoretical and the experimental thermal modelling was that although the constituent components of the sandwich composite have entirely different thermal expansion coefficients, its effect on the embedded fibre sensor can be minimal if the sensors are embedded between the face sheets. These results can initiate further research in this area and can lead to the development of state-of-the art structural health monitoring techniques for sandwich composite structures.