Smart Bolt Based On Optical Fiber And Its Application In Power Grid

For many years,with the continuous development of economy,more and more large tools,buildings and civil engineering structures have been put into use.Bolts,as the most widely used connectors in various structures,are often overlooked by people.However,in real life,many major accidents with different manifestations are caused by the failure of bolts.Among them,bolt loosening is the most common failure mode.In order to ensure the structural safety of various large-scale instruments,engineering and appliances,and reduce the incidence of accidents,it has become an inevitable requirement and means to master the loosening state of bolts by means of structural health monitoring.In recent years,smart bolts have become an important research branch and hotspot in the field of structural health monitoring due to their high integration and monitoring effectiveness.Because of the superior performance of optical fiber,more and more researchers focus on smart bolts based on optical fiber sensing technology.Based on the analysis and research of the current smart bolt technology,this thesis presents a kind of smart bolt based on optical fiber sensing technology.The smart bolt is systematically introduced from the aspects of design,fabrication,testing and application.It is installed as one of the intelligent units in the optical fiber smart grid system for monitoring and testing,and many cases of practical application conditions are simulated by the transmission line galloping simulation test machine.The effective monitoring performance of the smart bolt is verified by the application condition.The research contents of this thesis are as listed below.1.Structural health monitoring and its application in bolt loosening monitoring are introduced.The research status of bolt loosening monitoring in China and abroad is analyzed.The research progress of smart bolts,especially smart bolts based on optical fiber sensing technology,is introduced in detail.2.The sensing principle and characteristics of fiber Bragg grating are introduced.A kind of smart bolt based on fiber sensing technology is proposed and designed.The internal structure design of the smart bolt is introduced in detail.The corresponding design of optimizing the mechanical strength,the mechanical transmission characteristics,the influence of external nonuniform force,temperature compensation and transmission loss of the smart bolt are introduced.3.Based on the design scheme of the smart bolt proposed in this study,the smart bolt for practical monitoring is manufactured,and the structural stability,temperature response characteristics and loosening characteristics of the smart bolt are tested respectively.The test results show that the smart bolt made according to the design scheme has good structural stability and can effectively realize temperature compensation.The calibration curve of the bolt loosening is established through the calibration experiment of the state of the bolt loosening and the strain monitoring.On this basis,the failure threshold is set.This method realizes the reliability and accuracy of smart bolt monitoring.4.In order to verify the actual monitoring performance of smart bolts,smart bolts are installed in the optical fiber smart grid system as one of the smart units,so that they can carry out long-term loosening monitoring and testing.In this process,in order to understand the working status of smart bolts in the monitoring process as soon as possible,the transmission line galloping simulation test machine is used to test the loosening monitoring performance of smart bolts,and at the same time,simulate various practical application conditions to test the monitoring performance of smart bolts.The test results show that the smart bolt can effectively monitor its loosening state in the power grid environment,based on the loosening calibration curve.In addition,the test results of smart bolts under transmission line galloping conditions show that the characteristic frequencies in low frequency region can effectively reflect the galloping frequencies of transmission lines,and different characteristic frequencies can characterize the different influencing factors leading to transmission line galloping.