Theoretical And Experimental Studies On Strain Transfer Based On Distributed Optical Fiber

With the development of structural health monitoring system,the optical fiber sensor plays an important role in sensing subsystem because of its superior performance.Optical fiber is of poor shear resistance,easy to break.In the actual application process,the optical fiber needs to be protected or encapsulated,which courses transmission loss between the measured strain and the strain measured by the optical fiber sensor.In order to improve the measurement accuracy of optical fiber sensors and the packaging process,it is necessary to study the optical fiber strain transfer mechanism.Based on the existing theories,this paper presents an experimental study of the strain transfer mechanism.The main contents of this paper are as follows:(1)The chapter 1 is the introduction.The composition of the structural health monitoring system,the type and development of the optical fiber strain sensor,the development status of the buried optical fiber strain transfer mechanism and the surface bonded optical fiber strain transfer mechanism theory,and the development of the distributed optical fiber sensing technology are mainly introduced.(2)The chapter 2 introduces the basic structure of optical fiber,sensing principle of fiber Bragg grating(FBG)and distributed optical fiber,establishes the theoretical model of surface-attached optical fiber sensor,and deduces its average strain transfer rate,and obtains formula of the average strain transfer rate of surface-attached optical fiber.(3)In the chapter 3,we use the distributed optical fiber based on optical frequency domain reflectometry to design the experiment on the three main factors affecting the average strain transfer rate of the optical fiber.The strain distribution is obtained and the strain transfer rule of the optical fiber is summarized.The distributed optical fiber was used instead of the fiber grating to package two different clamped optical fiber sensors.Several experiments were carried out.The internal strain distribution of the optical fiber sensor was measured and its performance was verified.(4)The chapter 4 is the application of FBG sensors and distributed optical fiber sensors in spiral case model test and pull-out test of anchor cables.The fiber grating sensor is installed inside the spiral case model to monitor the internal strain of the model,and the distributed fiber sensor is attached to the surface of the model to capture the cracking time and cracking position of the concrete.In the pull-out test of anchor cables,a protection method was successfully used to deploy a distributed optical fiber sensor inside the model to obtain the continuous strain distribution of the internal space of the model.