| In recent years,high-speed railway construction in China has been rapidly developed,basically forming a transport network of “four vertical and four horizontal” high-speed railways.To ensure the safety of railway transport,maintenance to the railway tracks in operation becomes especially important.Traditional rail detection methods have slow speed and low efficiency,and are unable to fully satisfy the needs of long distance,wide coverage and high precision in existing railway detection.Ultrasonic guided waves possess the features of long propagation distance and high detection efficiency,distinguishing itself in rail detection.The application of ultrasonic guided waves in non-destructive rail detection was studied in this paper and the main research contents were as follows:(1)The features of the modal analysis method and the two-dimensional Fourier transform method were analyzed and compared in the calculation of the wave guide dispersion curves.A finite element model was established for the plate and the modal analysis method and the two-dimensional Fourier transform method were used for calculation respectively.The calculated results were then compared with that of the analytical method.The results show that it was possible to calculate the propagation characteristics of ultrasonic guided waves either by conducting modal analysis of the structure or performing two-dimensional Fourier transform of the time-domain signal of the guide wave.Besides,the wave structure information of modes could be obtained in the modal analysis result and the energy distribution of guided waves with different modes could be attained in the two-dimensional Fourier transform result.(2)The propagation characteristics of ultrasonic guided waves with different modes were studied when the steel rail was excited at different positions.The modal analysis method was used to calculate the dispersion curve of the rail and analyze the wave structure for guided waves with different modes.Excitation and receiving positions were set at the rail head,the rail web and the rail base,respectively,and the two-dimensional Fourier transform method was used to calculate the dispersion feature and energy distribution of the generated guided waves.Through the comparison of the results from the two methods,the propagation characteristics of ultrasonic guided waves with different modes could be obtained in the cases of excitation at the rail head,web or base.And their propagation characteristics were evaluated according to the proposed modality evaluation factor.(3)A lead zirconate titanate piezoelectric ceramics(PZT)element was utilized to experimentally study the propagation characteristics of ultrasonic guided waves in rails.The amplitude,the group velocity and the phase velocity of ultrasonic guided waves when excited at the rail head,web and base were mainly researched and compared to simulation results.The GT-S1,GY-A1 and GD-A2 guided wave modes were respectively selected as the targets for detection.(4)Straight transverse cracks were prefabricated at the rail head and the rail base,and ultrasonic guided waves with the targeted modes were selected for detection according to the specific damage location.The research results show that the cracks would cause the amplitude of the targeted modal waves to be smaller when detected with the penetrating method.Specifically,when the detectors were set at 0.3m and 0.6m for both ends of the rail head crack(Translucent,10 mm vertical depth,2mm longitudinal width,damage area accounts for about 20% of rail head),the detection sensitivity was 33.5% and 23.1%,respectively.While when the detectors were set at 0.3m and 0.6m for both ends of the rail base crack(The lateral depth is about 23 mm,the vertical depth is about 10 mm,and the longitudinal width is about 2mm.The damage area accounts for about 15% of the rail base.),the detection sensitivity was 69.7% and 58.6%,respectively.It was shown that ultrasonic guided waves could be used to effectively detect structural damages of rails. |
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