We report below about the control of processing of composite materials in particular carbon fibre dyed into epoxy
resin. In the aeronautic industry, structures made of such composite materials have a very high "mechanical property to
weight" ratio and can for this reason successfully compete with metallic ones. Their utilisation is constantly increasing
in this industry and this growth is leading to the development of RTM processes. In order to optimize these process nonintrusive
and multi-parameter sensors are required to measure and track the internal evolution for the continuous control.
We study and describe a fibre optic sensor which detects the optical refractive index variations of its environment
during the fabrication of a composite part. The major innovative part of our approach is the mould which has been
designed and instrumented to simultaneously provide the polymerisation degree and the refractive index analysis of the
resin. From these data, we have been able to determine the thermo-optic coefficient of the resin when it is not
polymerised and the evolution of the polymerisation degree versus the resin refractive index. So this result is using as
calibration to determine a polymerization degree of the resin in an industrial mould.