Strain Transfer in Surface-Bonded Optical Fiber Sensors

Abstract

Fiber optic sensors represent one of the most promising technologies for the monitoring of various engineering structures. A major challenge in the field is to analyze and predict the strain transfer to the fiber core reliably. Many authors developed analytical models of a coated optical fiber, assuming null strain at the ends of the bonding length. However, this configuration only partially reflects real experimental setups in which the cable structure can be more complex and the strains do not drastically reduce to zero. In this study, a novel strain transfer model for surface-bonded sensing cables with multilayered structure was developed. The analytical model was validated both experimentally and numerically, considering two surface-mounted cable prototypes with three different bonding lengths and five load cases. The results demonstrated the capability of the model to predict the strain profile and, differently from the available strain transfer models, that the strain values at the extremities of the bonded fiber length are not null.

Experimental and Numerical Investigation on the Strain Response of Distributed Optical Fiber Sensors Bonded to Concrete: Influence of the Adhesive Stiffness on Crack Monitoring Performance

“…Although these sensing cables are more robust, strain measured by the core fiber may be different from the actual strain in the host structure, due to shear deformation of the coating of the cable. To overcome this bias and produce quantitative strain measurements, a general methodology was introduced in a previous work [ 22 ] and has proven to be efficient for both DOFS cables embedded in concrete [ 21 , 23 ] and cables bonded to the surface of existing concrete structures [ 24 , 25 ]. This methodology is based on a modelling of the strain transfer mechanism through the coating of the cable (and also through the adhesive layer in the case of bonded cables), and allows to determine a mechanical transfer function (MTF) that relates the measured strain to the actual strain in the host structure.…”

Strain Transfer Function of Distributed Optical Fiber Sensors and Back-Calculation of the Base Strain Field

“…It is noted that here we use a simplified model for the validation of the spatial period dependent strain transfer function and the strain back-calculation method proposed. However, for practical applications of the proposed methods, one can use other OFS models [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 43 ] depending on the test model to derive the strain transfer function. Additionally, we can consider using empirical approaches [ 42 ] together for a better fit to the test model.…”

“…This has been well summarized in a recent review paper [ 41 ]. A few studies have considered more complex geometry for more realistic analysis, such as side width, top and bottom thickness of the adhesive layer [ 42 ], and many-layered structure (7 layers) with extended boundary conditions [ 43 ].…”

Measurement error analysis of surface-bonded distributed fiber-optic strain sensor subjected to linear gradient strain: Theory and experimental validation

“…Recently, thanks to the development of the high-performance distributed FO sensing technology -optical frequency-domain reflectometry (OFDR), Zhang et al systematically investigated the effect of mechanical parameters and bonding method of FO cable on the strain transfer efficiency from both theoretical and experimental sights [29]. Falceteli et al developed a strain transfer model of multi-layered FO cable and derived the distribution of strain transfer coefficient for a non-zero boundary condition; the theoretical analyses were more consistent with actual observations [30].…”

“…The deformation or temperature of the structure can be monitored by bonding the sensor on the structure surface or directly embedding it into the structure. Extending the research of Falcetelli et al [30], a strain transfer model of surface-bonded distributed FO sensor with an nlayered structure subjected to a non-uniform host strain is established (Fig. 1).…”