Study On The Method Of Clamp Force Measurement Of Railway Elastic Strip Fastener Based On Modal Analysis And Ultrasonic Testing

As one of the common railway fastenings nowadays,the railway elastic strip fastening system is widely used in the laying of jointless track.The clamp force of the elastic strip fastener is a significant part of railway safety inspection,which is related to whether the railway system can maintain a safe and stable running state.Based on the vibration state of the elastic strip fastener and the pre-tightening state of the screw spike,this thesis proposes two measurement methods for the clamp force of the elastic strip type II fastener,and carries out research from three aspects: theoretical research,simulation analysis and test verification.Firstly,the working principle and possible failure causes of the elastic strip type II fastener system are analyzed.The reason for the deviation of the vibration characteristic frequency of the elastic strip fastener in service is studied from the theoretical level,and the modal analysis and measurement method of the clamp force of the elastic strip fastener is proposed based on the modal analysis theory.By studying the acoustic elastic effect of solid structure and the working principle of elastic fastener,combined with the transverse and longitudinal wave detection method,the ultrasonic measurement method of the clamp force of the elastic strip fastener is extended from the ultrasonic detection theory of bolt stress.The influencing factors of two measurement methods at a theoretical level are studied.Secondly,the COMSOL Multiphysics finite element simulation software is used to simulate and analyze 6 modes of the elastic strip type II fastener in the free state and2 modes in the service state.On this basis,the relationship between the characteristic frequency of the elastic strip fastener and the clamp force is further studied.The influence of the shape-size,and material parameters of the elastic strip on the characteristic frequency are simulated and analyzed.The acoustic elastic effect is simulated by the parameter equivalent substitution method,and the relationship between the pre-tightening of the screw spike and the ultrasonic transit time is predicted.The influence of material parameters and operating temperature of road studs on characteristic frequencies are simulated and analyzed.The displacement,deformation law and stress distribution law of the elastic strip fastener in service are simulated.Finally,a test device for measuring the clamp force of elastic strip fastener is designed.Conduct indoor and on-site experiments using modal analysis method to study the relationship between the clamp force of the elastic strip fastener and the characteristic frequency of the elastic strip fastener.The acoustic vibration response test is set up to study the influence of the mass of the vibration sensor on the characteristic frequency of the elastic strip fastener.The axial force acoustic elastic coefficients are defined and the numerical solution are calculated based on experimental data.Conduct ultrasonic measurement method test bench tests and tensile tests,and improved the relationship formula for measuring the buckle pressure of the elastic strip through transverse and longitudinal wave acoustic time difference.