Strain transfer mechanism in surface-bonded distributed fiber-optic sensors subjected to linear strain gradients: Theoretical modeling and experimental validation

Abstract

Strain transfer analysis is an important means of assessing the measurement accuracy of embedded or surface-bonded fiber-optic sensors; however, the effect of complex strain fields in substrates has not been well elucidated. Here, a theoretical model was proposed for the analysis of strain transfer mechanisms in surface-bonded distributed fiber-optic sensors due to linear strain gradients. Closed-form solutions were obtained for both single linear and bilinear strain distributions, which were validated through controlled laboratory testing. High-resolution strain profiles acquired with optical frequency-domain reflectometry allowed also the establishment of a simple approach for determining the strain transfer coefficient at the turning point of a bilinear-type strain. Moreover, parametric analyses were conducted to investigate the influences of geometric and mechanical properties of protective and adhesive layers on the strain transfer efficiency, shedding light on the design, installation, and measurement accuracy improvement of fiber-optic sensors after accounting for the effect of substrate strain patterns.