Strain measurement of fiber optic sensor surface bonding on host material

Fiber optic sensor has been widely used as a structural health monitoring device by either embedding into or surface bonding onto the structures. The strain of optic fiber induced by the host material is strongly dependent on the bonding characteristics which include the protective coating, adhesive layer and the length of bonding. The strains between the fiber optics and host structure are not exact the same. The existence of the protective coating and adhesive layer would affect the strain measured by the surface bonding optic sensor. The analytical expression of the strain in the optic fiber induced by the host material was presented. The results were validated by the finite element method. The theoretical predictions reveal that the strain in the optical fiber is lower than the strain of host material. Parametric study shows that a long bonding length and high modulus of protective coating would increase the percentage of strain transferring into the optical fiber. Experiments were conducted by using Mach-Zehnder interferometer to measure the strain of the surface bonding optic fiber induced by the host structure. Good agreements were observed in comparison with the experimental results and theoretical predictions.