Thermal sensitivity of fiber optic Rayleigh sensors embedded in the consolidation roller for future application in the process monitoring of Automated Fiber Placement

Abstract This research paper presents a study that investigates the thermal sensitivity of fiber optic Rayleigh strain sensors embedded in an elastic silicone material. The results form the basis for a novel measurement concept for temperature measurement in in-situ Automated Fiber Placement. For the study, individual glass fibers were embedded in grooves in the silicone coating of simplified consolidation rollers. In this context, the geometry of the groove was varied, which changed the embedding characteristics. As part of an experimental study, the previously produced sensors were statically pressed against a heating plate at a constant temperature. The aim of the study was to evaluate the dynamic response behavior as well as the thermal sensitivity at different times after contact with the heating plate. The present empirical investigations have shown that the thermal sensitivity in the analyzed temperature range of 150 °C to 350 °C is independent of this temperature and increases with decreasing depth of the groove. In addition, a steady increase in thermal sensitivity was observed within the investigated contact time of 3 s. In this study, final theoretical considerations were made regarding Automated Fiber Placement. It was found that, assuming typical contact times from the process and taking into account the signal noise of the measurement system, a theoretical measurement accuracy of ± 9 °C is possible with the most sensitive sensor configuration. However, the experiments carried out have also shown that thermal disturbance variables due to convective and radiation-based heat transfer can influence the accuracy of the measurement.