A Fresnel's reflection optical fiber sensor for thermoset polymer cure monitoring

The paper presents a novel optical sensor that can perform real-time measurements of the degree of cure of an epoxy resin used as a matrix in fiber reinforced polymer composites. This sensor is based on the Fresnel's reflection at the end of an optical fiber. An increase in the degree of cure induces a corresponding increase in the density of the resin and therefore an increase in the measured reflected light intensity. The response of this optical sensor is shown to be in agreement with a well-established method, namely the Differential Scanning Calorimetry (DSC). In addition, a calibration method for the optical sensor in service is proposed. This calibration takes advantage of the heating phase of the epoxy resin at the beginning of the process. Due to its low intrusivity, this sensor can be easily embedded into a composite material to monitor the resin cure in-situ.