Development of an Integrated Fibre Bragg Grating Contact Pressure and Temperature Sensor for Composite Smart Manufacturing

Polymer matrix composites are widely used as structural materials due to their low weight and high strength vs. metallic ones. However, some issues concern their durability, the possibility of damage detection and prediction, the characterization of residual stresses, and the identification of their global mechanical properties. A better knowledge would help to understand the material's structural integrity and the inevitable variability of properties induced by manufacturing processes. In this way, the monitoring of composite material manufacturing is a key feature for better process understanding and quality improvement. Today, measurements are often limited to global or indirect sensing, but very few are routinely performed locally or in the vicinity of the composite parts during the process. Therefore, controlling curing parameters in such areas where resin flows are complex appears relevant for process optimization [1-3]. In such a context, the research project ELICo-CP devoted to the development of a small and weakly intrusive optical Fibre Bragg Gratings (FBG)-based sensor for both contact pressure and temperature variation measurements has been initiated. Such a sensor will allow the measurement of contact pressures up to 10 bar with surrounding temperatures greater than 200 C in small curvature areas (down to 4 mm radius) inside manufacturing tools (autoclave and moulding processes based on a liquid resin injection). This sensor could be multiplexed and interrogated thanks to a high resolution and fast speed analyser similar to the BraggFIT (R) FBG measurement system already developed by the CEA LIST [4-5]. Experimental results of the sensor prototype, tested in a dedicated Resin Transfer Moulding (RTM) tool equipped with commercial reference sensors, demonstrate that the contact pressure variation information inside the mould can be measured with 0.1 bar resolution over the 10 bar range with such small sensors. However, for these first contact-pressure sensorprototypes, both hysteresis (10% full scale) and temperature cross-sensitivity shouldbe improved.