Fatigue monitoring of flax fibre reinforced epoxy composites using integrated fibre-optical FBG sensors

We demonstrated the applicability of integrated Fibre Bragg Grating (FBG) sensors in the case of flax fabric reinforced epoxy matrix composites produced by resin transfer moulding (RTM). FBG sensors were integrated between the reinforcing layers of the composites. We verified the robustness of FBG-based strain measurement by comparing it to strain gauge strain measurement, optical fine strain measurement and deflection measurement from crosshead displacement during four-point flexural tests. After the extensive characterization of the static properties of the composite material, fatigue tests were performed in the same setup on the specimens with integrated FBG sensors. We demonstrated that with the integrated optical fibres, the cyclic creep strain of the composites could be monitored, which could be used as a criterion to predict the fatigue failure of the composites. The proposed technique can provide an effective and robust way for periodic condition monitoring of composite structures, especially in natural fibre reinforced composites, where creep is more pronounced than in the case of synthetic fibre reinforced composites.