Monitoring of Thermal Ageing Cycles of a Silicone Adhesive in a Simulated Space Environment Using Embedded TFBG Sensors

This research demonstrates the promising abilities of a tilted Fibre Bragg Grating (TFBG) sensor for monitoring the status of a silicone adhesive during a simulated space environment exposure. The silicone is used as adhesive between two thin cover glasses and the TFBG is embedded into the polymer such that it is fully enclosed. Then, the sample is exposed to standard space environment conditions in a vacuum chamber simulated by creating a high vacuum (1.3×10^-6 mbar) and thermal cycles between -120 ℃ to 190 ℃. The TFBG spectra recorded during the exposure were demodulated to obtain the wavelength shifts of the Bragg and Ghost peaks and the envelope area of the upper and lower cladding modes resonances peaks. This will allow the thermomechanical and the refractive index (RI) variations of the silicone to be measured during the testing. In particular, the silicone RI depends on the material chemical and physical state and its thermal history, and the TFBG envelope area is sensitive to these RI changes. Hence, the envelope area of the TFBG spectrum can be used to obtain information on the evolution of the silicone adhesive during the test. The resulting trend of the selected peak wavelengths variation and envelope area were used to detect a variation of the degradation state of the material.