Composite materials are most often made by association of reinforcing fibers with a matrix (thermoplastic or heat-hardening resin). Reinforcing fibers allow enhancing mechanical properties (mechanical resistance, rigidity, hardness, ��) and physical properties (thermal resistance, fire resistance, electric properties, ��). They have a low density and are easy to handle. There exist different forms (short or continuous fibers) as well as different types. The most often encountered are glass fibers and carbon fibers. The matrix is present to guarantee a proper transfer of the strain to the reinforcing fibers, to protect them against external perturbations and to ensure, after molding, the geometrical form of the structures. The matrix has to be compatible to the reinforcing fibers while ensuring some deformability.

It is generally a thermoplastic or thermoset resin.Composite materials can be built by different techniques. Of course, the most straightforward is molding, which can be performed simply through contact (reinforcing fibers placed in the mold are manually impregnated with the resin), under vacuum or with the more advanced resin transfer molding (RTM) process. Exhaustive details on the manufacturing techniques can be found in [2].Nowadays, newly produced materials are more and more smart in the sense that they embed sensors and/or metrological tools able to provide real time information about the internal stress state. As such, they intrinsically ensure predictive maintenance.

This feature is highly appreciated as it can mitigate the risk of failure due to a sudden breakage, on the one hand, and decrease the maintenance costs, on the other hand. Of course, smart composite materials are also envisioned. Anacetrapib Considering the composition and geometry of composite materials, optical fiber sensors are very well suited to be embedded into composite materials without altering their mechanical performances.Optical fibers are cylindrical silica waveguides made of two concentric layers, the core and the cladding, which guide light thanks to a slight refractive index difference between both layers [3]. Fibered sensors most often exploit telecommunication-grade single-mode optical fibers made of a ~8 microns thick core in silica doped with germanium oxide surrounded by a 125 microns thick cladding in pure silica. The attenuation is minimum at the wavelength 1,550 nm and is equal to 0.2 dB/km. Naturally, this wavelength range is also exploited for sensing purposes. Optical fiber sensors present decisive benefits [4]. In terms of reliability, they are passive devices and are characterized by a long life time (more than 20 years).