Effects of bonding on the performance of optical fiber strain sensors

Abstract

Summary The structural health monitoring (SHM) of existing buildings, structures, and infrastructures has become increasingly important in recent years, while the interest of the scientific community is focused on the use of new high‐performance technologies. Fiber optic sensors have become particularly attractive, thanks to their potential for monitoring strain in smart structures. The performance of this new technology depends to a large extent on the bonding technique used for its manufacture. Although the related literature has identified a correlation between some efficiency issues and the geometrical parameters of the bonding and mechanical properties of the materials adopted, the phenomenon is still not completely understood. This paper describes an in‐depth study of the geometrical and mechanical parameters that influence the efficiency of optical fiber point sensors' surface bonding by synergistically related techniques such as computational simulation, experimental tests, sensor manufacturing, and data analysis. The paper's novelty is fourfold: (1) the investigation of the strain transfer mechanism of surface‐bonded fiber optic sensors by considering, for the first time, all the parameters influencing the phenomenon through a considerable number of finite element (FE) analyses (117 three‐dimensional FE models); (2) the development of a series of bonding efficiency predictive models; (3) the design of a specific laboratory test to validate the computational outcomes; and (4) the definition of useful guidelines for effective bonding manufacturing in order to maximize the performance of these sensors when acquiring monitoring data.

Compliant Mechanism-Based Sensor for Large Strain Measurements Employing Fiber Optics

“…In practice, if bonding is performed manually, it is difficult to control the bonding thickness and other parameters with very tight accuracy. According to studies, the strain transfer rate can be about 70–80% [ 18 , 40 , 41 ]. However, determination of the exact value of the strain transfer rate is not important for this sensor design.…”

Numerical and experimental analysis of the reliability of strain measured by surface‐mounted fiber‐optic sensors based on Bragg gratings

“…The problem of obtaining the values of measured strains in a complex stress state in the FBG zone is most fully covered in works where sensors embedded into the material are considered. The results of these works are also quite applicable to sensors mounted on the material surface and hence located in the volume of the adhesive joint 12 . In review paper, 13 it was noted that an embedded FBG is subjected not only to longitudinal strains but also to the total strain field occurring in the structure.…”

“…For the proposed three‐layer model of optical fiber‐to‐substrate bonding, quantitative estimates are given of the influence of the shear modulus of the adhesive material, the thickness of the adhesive layer between the optical fiber and the substrate, and the length of the optical fiber section glued to the substrate on the strain transfer coefficient from the substrate to the FBG written in polyimide coated optical fiber. Analytical and experimental studies of the strain transfer coefficient for point sensors glued to the surface of the controlled material are given in previous works 12,27 . Based on the finite element method, a multiparametric analysis of the influence of the length and width of bonding, the lower and upper thickness of the adhesive, the presence of an optical fiber protective coating, and the mechanical properties of the material was performed.…”

“…The results of these works are also quite applicable to sensors mounted on the material surface and hence located in the volume of the adhesive joint. 12 In review paper, 13 it was noted that an embedded FBG is subjected not only to longitudinal strains but also to the total strain field occurring in the structure. This implies that the FBG must be calibrated with respect to these strains.…”

“…Analytical and experimental studies of the strain transfer coefficient for point sensors glued to the surface of the controlled material are given in previous works. 12,27 Based on the finite element method, a multiparametric analysis of the influence of the length and width of bonding, the lower and upper thickness of the adhesive, the presence of an optical fiber protective coating, and the mechanical properties of the material was performed. The calculation results are confirmed by quasi-static tensile tests.…”