Effect of multilayered coating of single-mode optical fibers on distributed temperature and strain measurement in mortar specimens

Abstract

This study aims to characterize the effects of multilayered coatings on the performance of distributed fiber optic sensors (DFOS) when the coatings experience softening and melting at high temperatures. Two strain sensors (B-DFOS and W-DFOS) and one temperature sensor (Y-DFOS) were calibrated. They were either embedded along the centerline of a mortar bar or bonded on the surface of the specimen. The Y-DFOS was found to be no longer strain-free at high temperature since the softened sheath, aramid yarns, buffer, and polymer coatings became viscous and adhered to their surrounding mortar above softening temperatures 263–320 °C. Both the B-DFOS and W-DFOS captured uneven strain distributions along the mortar specimen due to non-uniform temperature distribution, mortar heterogeneity, and temperature-dependent strain transfer efficiency. The W-DFOS showed higher measured strains than the calculated thermal-induced strains at 100 °C - 300 °C due to the high thermal expansion coefficient of the additional buffer layer. The B-DFOS gave smaller measured strains than the thermal-induced strains at 300 °C - 500 °C. The displacement calculated by integrating the measured strains along the length of each mortar specimen was related to the applied temperature by parabolic regression equations.