Fiber-Reinforced Polymer-Packaged Optical Fiber Bragg Grating Strain Sensors for Infrastructures under Harsh Environment

Optical fiber Bragg grating (FBG) has been recognized as an outstanding high-performance local monitoring sensor and is largely applied in structural health monitoring (SHM). This paper proposes a series of fiber-reinforced polymer- (FRP-) packaged optical fiber Bragg grating strain sensors to completely meet the requirements of rough civil engineering infrastructures, and their sensing performance under normal environment and harsh environment is experimentally investigated. It is experimentally and theoretically proved that FRP-packaged FBG strain sensors maintain excellent sensing performance as the bare FBG sensor under a harsh environment, and their durability is significantly enhanced due to the FRP materials. These FRP-packaged FBG strain sensors are successfully applied in the SHM system of Aizhai Bridge

Spatially Continuous Strain Monitoring using Distributed Fiber Optic Sensors Embedded in Carbon Fiber Composites

A distributed fiber optic strain sensor based on Rayleigh backscattering, embedded in a fiber-reinforced polymer composite, has been demonstrated. The optical frequency domain reflectometry technique is used to analyze the backscattered signal. The shift in the Rayleigh backscattered spectrum is observed to be linearly related to the change in strain of the composite material. The sensor (standard single-mode fiber) is embedded between the layers of the composite laminate. A series of tensile loads is applied to the laminate using an Instron testing machine, and the corresponding strain distribution of the laminate is measured. The results show a linear response indicating a seamless integration of the optical fiber in the composite material and a good correlation with the electrical-resistance strain gauge results. The sensor is also used to evaluate the strain response of a composite-laminate-based cantilever beam. Distributed strain measurements in a composite laminate are successfully obtained using an embedded fiber optic sensor

A Uniform Strain Transfer Scheme for Accurate Distributed Optical Fiber Strain Measurements in Civil Structures

We report a screw-like package design for an embeddable distributed optical fiber strain sensor for civil engineering applications. The screw-like structure is the exterior support for an optical fiber sensor. The bare optical fiber is embedded and secured in a longitudinal groove of the screw-like package using a rigid adhesive. Our packaging scheme prevents damage to the bare optical fiber and ensures that the packaged sensor is accurately and optimally sensing strain fields in civil structures. Moreover, our screw-like design has an equal area in a cross-section perpendicular to and along the screw axis, so strain field distributions are metered faithfully along the length of the embedded optical fiber. Our novel screw-like package optical fiber sensor, interfaced to a Rayleigh scattering-based optical frequency domain reflectometer system enables undistorted, accurate, robust, and spatially-distributed strain measurements in bridges, tunnels, pipelines, buildings, etc. along structural dimensions extending from centimeters to kilometers

Distributed fiber optic sensors for monitoring spatially continuous strain and quasi-distributed refractive index using optical frequency domain reflectometry

This thesis is comprised of two papers and they describe distributed fiber optic sensing using an optical frequency domain reflectometry (OFDR) instrumentation system. The first paper presents about distributed fiber optic sensor embedded within the layers of a composite laminates to monitor the continuous profile of strain using the optical frequency domain reflectometry (OFDR) system. The OFDR system was used to analyze the Rayleigh backscattered signal. The shift in the Rayleigh backscattered spectrum (RBS) was observed to be linearly related to the change in strain of the composite material. The continuous strain sensing using OFDR was demonstrated by an INSTRON tensile testing system and cantilever beam experiment. The results shows a good strain transfer between the composite laminate and the optical fiber with no slipping or hysteresis issues. The second paper of the thesis proposes and demonstrates the distributed refractive index sensing by a macrobending single mode fiber (SMF) and the OFDR system. The macro-bending fiber is fabricated by bending a piece of SMF to a particular radius of curvature in several millimeters. The refractive index (RI) of the external medium surrounding the macrobending fiber is measured by the RBS shift using OFDR system. RI is measured from the range of 1.3348 to 1.3557 using the proposed method in our experiment. This sensor can also be used to detect multipoint RIs simultaneously verifying the capability of distributed sensing --Abstract, page iv

Detection and Measurement of Matrix Discontinuities in UHPFRC by Means of Distributed Fiber Optics Sensing

International audienceFollowing the significant improvement in their properties during the last decade, Distributed Fiber Optics sensing (DFOs) techniques are nowadays implemented for industrial use in the context of Structural Health Monitoring (SHM). While these techniques have formed an undeniable asset for the health monitoring of concrete structures, their performance should be validated for novel structural materials including Ultra High Performance Fiber Reinforced Cementitious composites (UHPFRC). In this study, a full scale UHPFRC beam was instrumented with DFOs, Digital Image Correlation (DIC) and extensometers. The performances of these three measurement techniques in terms of strain measurement as well as crack detection and localization are compared. A method for the measurement of opening and closing of localized fictitious cracks in UHPFRC using the Optical Backscattering Reflectometry (OBR) technique is verified. Moreover, the use of correct combination of DFO sensors allows precise detection of microcracks as well as monitoring of fictitious cracks' opening. The recommendations regarding use of various SHM methods for UHPFRC structures are given