Chirped fiber-Bragg grating as self-temperature referenced strain sensor in nonisothermal thermoset processing

A partially embedded chirped fiber-Bragg grating (FBG) has been used to monitor the strain build up during nonisothermal curing of a model thermoset resin. The particular feature of the spectrum of a linearly chirped and strongly apodized FBG to encode position along the sensor has been used to simultaneously measure temperature and strain during the cure cycle of an epoxy-based polymer. In particular, the embedded part of the grating allows the monitoring of temperature and processing strain while the rest of the sensor is sensible to temperature variation only. A new self-temperature referenced sensor system has been successfully tested in an operative condition where usually thermomechanical loading are simultaneously active. The onset and progression of gelification, as well as the residual processing strain, have been experimentally measured.