Rail Longitudinal Additional Force Monitoring Technology Based On Hetero-cladding FBG Sensors

Continuous welded rail?CWR?has become one of the most important choices in the field of transportation because of its unique advantages.At the same time,the health status of CWR has become the focus of research.Fiber Bragg grating sensing technology is becoming a new application to railway safety monitoring because of its lots of advantages,such as high measurement accuracy,small size and so on.It is possible to calculate the running state of the track by measuring the wavelength information reflected from the FBG,and it can provide theoretical analysis for the safety operation to the line.In this paper,the fiber grating sensing technology is applied to track the health monitoring system,different grating sensing characteristics are deduced according to different railway conditions,and then a set of additional force measurement scheme is proposed.Firstly,this paper introduces the background and purpose of the research on CWR,and the research methods of the longitudinal additional forces both at home and abroad are summarized,then the main work and structure arrangement of this paper are pointed out subsequently.Secondly,the temperature and strain sensing characteristics of Fiber Bragg Grating are introduced.Furthermore,the common problems of temperature and strain of FBG are summarized in application.Finally,in order to apply the FBG in the harsh environment,we do some research on the grating packaging technology.To explore FBG sensing principle under two kinds of railway condition,namely the rail vertical and axial force state is in constrained and free status respectively,and FBG sensing principle verified by experiment.The experimental results show that the error between theoretical and actual values of FBG₁ and FBG₂ is 1.6%and 3.2%in the range of 60?,respectively.Through the verification on the transmission characteristics of different constraints can not only calibrate the grating strain and temperature sensitivity coefficient at the same time,but provide more theoretical basis for measuring the longitudinal forces.At last,a new method has been proposed to accurately determine longitudinal additional force in?CWR?on bridges via hetero-cladding fiber Bragg grating?HC-FBG?sensors.And the principle to measure longitudinal additional force of CWR is deduced by using HC-FBG.As shown by the test results,the linearity between the relative wavelength difference and the longitudinal additional force is greater than 0.999.Compared to the theoretical results,the accumulated error is controlled within 5.0%.It can solve temperature compensation and difficult of strain monitoring by HC-FBG through experiment validated.And then combined with the previously designed packaging process,HC-FBG is encapsulated.The accuracy of longitudinal additional force which is measured by encapsulated HC-FBG can be achieved 92.5%.