Key Technologies Research On Ultrasonic Guided Wave Flaw Detection Of Railway Turnout Rail Bottom

At present,the combination of manual inspection and visual inspection is used to detect the bottom of the switch rail,which has low efficiency,large possibility of missing inspection,and low detection accuracy.And the non-destructive detection of the whole section of the rail bottom with instruments is not realized.The propagation process and modal characteristics detection technology of ultrasonic guided wave in waveguide medium have been studied,and the Lamb wave dispersion curve has been drawn.The modal analysis method and analogy method have been combined to carry out the analogy research on the vertical bending mode of switch rail bottom and the antisymmetric mode A0 in the plates with different thickness.The results show that the vertical bending mode of the switch rail bottom at the frequency of60 k Hz is equivalent to the anti-symmetric mode A0 in the plates with thickness of20 mm and 25 mm,and Mode I is selected as the excitation mode.Based on this,COMSOL Multiphysics is used to simulate the dynamics of the three-dimensional sharp rail model,analyze the propagation process of the obtained modes,calculate the simulated damage location,and perform error analysis.At the same time,a guided wave detection test system is established to study the propagation characteristics of guided waves in the switch rail bottom by using different detection forms.Combined with time domain method,frequency domain method and time-frequency domain method,the existence of damage in the bottom of switch rail is distinguished and the damage is located,which verifies the feasibility of 60 k Hz frequency ultrasonic probe for simulation and test.The main works of this thesis are as follows:(1)Selection of the best excitation mode of switch rail bottomThe modal analysis method is used to conduct modal analysis on the section with obvious changes in the 60AT1 switch rail,look for the mode whose energy is mainly concentrated at the bottom of the switch rail,count the wave number and frequency of the section at different positions,draw the dispersion curve of the modes.At the same time,combined with the analogy method,the switch rail bottom is compared with the plates of 20 mm and 25 mm thickness for comparative study and analysis,to determine the best excitation mode.(2)Application research of ultrasonic guided wave damage detectionThe finite element software COMSOL Multiphysics is used to simulate the non-damage and damage of the three-dimensional turnout switch rail.The frequency dispersion relationship and propagation characteristics of the guided wave are studied in the form of spontaneous self-receiving detection.The change of the displacement amplitude and spectrum amplitude of the ultrasonic guided wave signal at different distances with and without damage are analyzed to determine whether there is damage,locate the damage and analyze the error.(3)Ultrasonic guided wave test system construction and experimental research analysisTwo sets of test systems are set up,and high-frequency probes and low-frequency probes are respectively used to study the propagation mechanism of guided waves and the identification method of structural damage in switch rail bottom.Different detection methods are used to compare and analyze the amplitude changes of ultrasonic guided wave signals at the switch rail bottom with and without damage at different distances,and signal processing methods(time domain method,frequency domain method,time-frequency domain method)are used to process and analyze the guided wave signals to determine whether there is damage,locate the damage,and verify the correctness of theory and simulation.