Research On Applying Distributed Optical Fiber Sensing Technology In Rail Strain Monitoring

Rail is the railway system operation of the railway infrastructure. Through rail strain detection can get the wheel rail force and temperature force. The measure of wheel/rail loads has great significance on vehicle dynamics, derailment mechanism, the theory of wheel/rail on test and the vehicle security monitor. Great rail internal temperature force could make rail expansion rail or broken rail. The traditional electrical sensors in the monitoring results of reliability will influence the harsh environment.Fiber grating sensing technology is a kind of distributed optical fiber sensing technology.Fiber grating has the advantages of simple method of making, high reliability, small size,immune of electromagnetic interference, flexibility, and it is apt to integrate with optical fiber.Its mature encapsulation technology makes fiber grating sensor can provide stable and reliable in bad conditions of test information.The problem of fiber Bragg grating sensor technology in rail strain monitoring is studied in this thesis. From the sensing principle of fiber grating, the location of the fiber Bragg grating on the rail is proposed. This thesis describes the calculation model of the tunable Fabry-Perot(F-P) filter demodulation method and designed the system of fiber Bragg grating strain monitoring.The main research contents and conclusions are as following:(1) Analysis of spectrum characteristics of fiber Bragg grating, the reflection spectrum of fiber Prague grating is easy to identify. Through the analysis of fiber Bragg grating sensing characteristic, the result is that the fiber Bragg grating center reflective wavelength shift and strain and temperature are linear. Analysis results showed that strain and temperature can be achieved by wavelength shift detection of fiber Bragg grating. Fiber Bragg grating strain sensor package is designed, the package can be improved simulation strain sensitivity.(2) The location of fiber grating sensor is put forward and the strain field of rail under train load and temperature load is analyzed by finite element analysis. Analysis shows that the train load strain monitoring location for rail track near the top of the waist position,temperature load strain monitoring location waist rail centerline. By ANSYS analysis to verify the correctness of detection principle. Find the position of the train load strain monitoring analysis results for rail waist position near the rail top, the location of the temperature load and strain monitoring for rail waist centerline. The effect of temperature on Fiber Bragg grating strain sensor is solved, and the fiber grating sensor is designed.(3) F-P tunable filter method can achieve distributed sensing demodulation techniques and has the advantages of small volume, low price, high light energy utilization rate, simple operation and other advantages. This paper proposed computational model F-P filter method.The simulation results showed that the computational model can achieve an effective measure corresponding variables. Multiplexing technology of fiber grating sensor is the realization of distributed fiber Bragg grating sensing technology. According to the requirements of the steel strain monitoring, the paper using wavelength division multiplexing and space division multiplexing technology. According to the fiber Bragg grating strain monitoring application in rail technology analysis, a fiber Bragg grating rail strain monitoring system is designed.