Research Of Fiber Bragg Grating Sensing Technology And Engineering Application

Based on the research of FBG's sensing properties, the packaged FBG sensors have been developed for the sake of long-term health monitoring of large civil infrastructure. Also the strain and temperature properties of packaged FBG sensors well as their temperature compensation technique were studied. Then, after fully analyzing the strain transmitting process of the strain sensors and calculating the strain response time and operation frequency of the packaged FBG sensors, the factors influencing the strain transfer ratio of the packaged FBG sensors and the problems of the strain transfer when the packaged FBG sensors are embedded in the host matrix have been studied. And in series of experiments and practical projects, homemade FBG sensors have been used to monitor strain, temperature and crack of the structures. The main contents include:Firstly, based on the principle of light travel in FBG, the strain and temperature sensing properties of the FBG sensors as well as the coupling problems of them have been analyzed. Then, the principle and technique for the temperature compensation of FBG sensors are given when using as strain sensor. The results indicate that the temperature influence cannot be neglected when using FBG to monitor the strain of the real structures.Secondly, considering the need of long-term monitoring for civil engineering, the mental tube packaged FBG strain sensor and temperature sensor are developed and their sensing properties are investigated experimentally. The calibration errors of FBG strain sensor using the usually equal-strength beam method are analyzed and modified from the standpoint of mechanics. And the strain sensitivity coefficients are studied in detail when sticking the mental tube packaged FBG sensors on two materials.Thirdly, by analyzing the strain transmitting process in host matrix, the strain response time and maximum frequency of FBG strain sensor under dynamic work conditions when glued on different materials have been computed. The results show that strain response speed of the FBG strain sensors developed by us is fast and the lag problem of strain response of FBG strain sensor needn't be considered. The operation frequency of FBG strain sensor fulfills the frequency request in low frequency vibration system.Fourthly, factors influencing strain transfer ratio of FBG strain sensor are analyzed by FEM (finite element method) and several methods calculating strain transfer ratio of FBG strain sensor embedded in host matrix are compared.Fifthly, homemade FBG strain sensors and FBG temperature sensors have been used in a series of experiments. The technique of FBG sensor installation in these experiments, and the method that the curing of concrete is monitored by use of FBG sensors in brought forward has been studied, and the technique of simultaneous strain and temperature monitoring, the dynamic strain measurement of offshore platform model and submarine pipeline model in seismic load have been realized. In shaking table test of frame structure, FBG strain sensor has been successfully monitored dynamic strain of "key parts" of structure and "remnant strain " of rebar in several tests. By analyzing of test data, the growing state of the crack could be find from elastic state to plastic state of structure. "Original strain" of structure also can be monitored. The experimental results show that FBG's superior ability of explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment.Sixthly, the FBG temperature sensors have been embedded in a pipe underground of ground-source heat pump system. The sensors are used to measure the temperature distribution of the soil and thermal energy of the underground soil to heat or cool a building. The FBG sensors were designed and packaged delicately to eliminate the influence of strain as well as to improve the thermal sensitivity. The measurement temperature is consistent with associated theories on the temperature distribution of underground soils. The technique of FBG sensor spot installation has been explored, and FBG strain sensors and FBG temperature sensors have been successfully installed in a building of Dalian University of Technology. The FBG sensors have monitored the strain course and temperature change under construction of building.