Carbon fibre-foam sandwich composite laminate embedded with fiber Bragg grating sensors

Carbon fibre-foam sandwich composite with embedded FBGs are fabricated and dynamic load testing and temperature studies were carried out. It was found from the tests that, the embedded FBG can measure the strain inside a sandwich composite, but a gauge factor is required to measure the absolute strain experienced inside the composite. The temperature sensitivity of the embedded FBG is found to be close to that of the free space sensitivity of the FBG, concluding that the thermal expansion of the carbon fibre-foam composite is minimal and has negligible effect on the embedded grating. The effect of the foam relaxation is also studied and it is found that foam relaxation can contribute to a strain error of ±16 με in strain measurements during the observed time period in this study. The results presented in this paper points to a direction that, embedded FBGs can be reliably used for strain measurement in sandwich composites and is less impacted by the thermal expansion of the composite laminate which is an advantage compared to other types of composite laminates. Further studies are required to estimate the FBG gauge factor for strain measurements and also to quantify the foam relaxation error based on an applied load.