Abstract
Optical fiber sensors have been extensively adapted as structural health monitoring devices. Due to the existence of the adhesive layer, a portion of the strain is absorbed by the adhesive. As a result, the structural strain sensed by the optical fiber is underestimated and required to be corrected. An analytical solution is presented through which it is possible to establish the relationship between the strains in the host structure and the surface bonded optical fiber sensor. Experimental measurements based on the Mach–Zehnder interferometric technique were performed to validate the theoretical prediction and reveal the differential strains between the optical fiber strain sensor and test specimen. Parametric studies show that the percentage of the strain in the test specimen actually transferred to the optical fiber is dependent on the bonding length of the optical fiber and the adhesive. The strain transfer is increasing from 56% to 82% as the bonding length increases from 5 cm to 12 cm with the epoxy adhesive. The general trend of the strain transfer obtained from both experimental tests and theoretical predictions shows that the longer the bonding length and the stiffer the adhesive, the more strain is transferred to the optical fiber.
Highlights
Optical fibers are widely applied in various sensing systems, owing to the excellent properties, such as small dimensions, flexibility, embeddability, high temperature endurance, dielectric nature, immunity to corrosion, as compared with traditional sensors, and being light weight [1]
A number of optical fiber-based sensor systems have been proposed for structural health monitoring; two sensor designs tend to predominate, namely fiber Bragg gratings (FBGs) and interferometric sensors
A series of experimental tests is performed to evaluate the influences of the adhesive and the bonding length on the strain transferred from the host structure to the optical fiber
Summary
Optical fibers are widely applied in various sensing systems, owing to the excellent properties, such as small dimensions, flexibility, embeddability, high temperature endurance, dielectric nature, immunity to corrosion, as compared with traditional sensors, and being light weight [1]. The capability of an optical fiber sensor to monitor the strain in a structure depends on the bonding characteristics which includes the bonding length, cladding diameter, adhesive and protective coating. Lau et al [15] developed a simple model to calculate the percentage of strain applied to the host structure transferred to the embedded fiber optic sensor. Previous work [18] developed a theoretical model to predict the strain transfer between the host structure and surface bonded optical fiber. Present work employed the theoretical model to study the effects of the adhesive and bonding length on the optical fiber strain sensor. A series of experimental tests is performed to evaluate the influences of the adhesive and the bonding length on the strain transferred from the host structure to the optical fiber
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