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Fibre reinforced plastics offer high specific mechanical properties (performance vs. weight ratio). Thus during the last decade, they have been increasingly used as components in engineering structures and particularly for aeronautical applications. Ageing, load-transfer, and off-axes behaviour of composites are directly dominated by the viscoelastic matrix properties linked to cure process. So, there is a growing need for sensors, which provide real-time, in-situ monitoring of the manufacturing process. This study proposes to follow the cure mechanism of an epoxy-amine resin using simultaneously three sensors embedded in the material: The fibre-optic sensor is based on the measurement of angular distribution of light transmitted through an optical fibre inside the cured polymer. The original siloxane cladding is removed from the central part of the fibre. Then a sample of curing epoxy is placed around the stripped region. It is thus possible to monitor the refractive index variation of the polymer. Frequency dependant dielectric measurements provide a sensitive in situ sensor able to access to the electrical conductivity and complex permittivity of the surrounding medium. The conductivity parameter related to the ionic mobility is linked to the polymerisation advancement. The ultrasonic waves are generally used for global characterisation of mechanical properties. For in situ applications, a piezoelectric implant is embedded in the structure during its processing and the rheological properties of such a material-system can be monitored. The parameters, determined simultaneously with these three techniques, allow to understand the different steps of the epoxy cure regarding molecular motion, viscosity, density and their consequences on the mechanical properties of the material.
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