An optoelectronic sensor for cure monitoring in thermoset-based composites

In this paper, we present the design and the experimental results of an optoelectronic fiber optic sensor able to monitor the polymerization reactions of thermoset polymer-matrix composite processing. These kinds of materials are now widely used in large industrial areas: aeronautical, aerospace, automotive and civil due to their low cost/low weight features. Unfortunately, their final properties are strongly dependent on the processing stage. In order to ensure the setting of correct processing parameters (i.e. temperature and pressure), it is crucial to monitor, during the reaction, the process variables such as degree of cure (DOC) and viscosity. In this work, we point out our attention upon the use of a fiber optic sensor, which can be embedded into the composite component, to monitor the cross-linking formation, occurring during the curing process. Based on the Fresnel refraction principles, the proposed sensor scheme is sensitive to refractive index variation. Experimental results are shown on sensor capability to monitor the cure kinetics, and a novel calibration method is proposed in order to link the optoelectronic response directly to the DOC of the reacting resin. (C) 2000 Elsevier Science S.A. All rights reserved.