Potentiality of Optical Fibre Bragg Grating Sensors for Resin Transfer Moulding Process Monitoring

Resin transfer moulding (RTM) is a widely used process for manufacturing composite parts. It is currently gaining market shares compared to autoclave process in particular for high performance applications, such as aerospace, thanks to its higher versatility permitting the manufacturing of complex and high quality composite parts in fairly short cycle times. The major disadvantage of RTM remains its lack of repeatability in particular for complex shape parts manufacturing. For these, it is not rare to observe dry spots and partially impregnated zones. In RTM process, fibre preforms are placed in a closed mould. Resin is injected to saturate the empty pores in the preform. Resin flow conditions are affected by the resin viscosity, the preform permeability, the applied pressure, the temperature, the reinforcement stacking sequence and the resin infusion strategy. The monitoring of resin flow and its control, from inlets at different position, has been shown to lead to an improvement of the process [1]. Several types of sensors (e.g. dielectric [2], temperature [3] and optical fibre [4]) have been successfully applied to resin flow monitoring, in laboratory applications, for parts with simple geometries. However, their application in a control strategy for the manufacturing of complex shape parts often requires a selective placing of the sensors at previously identified disturbance locations. In parallel, optical fibre Bragg grating (FBG) sensors are now increasingly embedded in composite parts to design a health monitoring system that will be used during service. We evaluate in the present work the potentialities to use FBG sensor arrays, placed for health monitoring and not a priori at disturbance locations, during the RTM process as a monitoring tool. The degree of reliability of the FBG sensors information on flow front progression and internal strains during cure is discussed.