Study On The Measurement Method Of Ultrasonic Guided Wave Phase Velocity In Seamless Rail

Ultrasonic guided waves have many advantages such as wide detection range,electromagnetism isolation,propagate long distance,etc.It can be used for long distance nondestructive testing especially in the seamless rail.Currently,Seamless rail crack detection based on guided wave,locating a crack in the rail by measuring the velocity of ultrasonic guided wave group,due to the multi modes and dispersion nature of ultrasonic guided wave,can't measure the group velocity accurately in time domain,the location of the crack position can't be located accurately.The ultrasonic guided wave detection based on phase velocity,measuring the phase velocity of ultrasonic guided wave by 2D-FFT algorithm,could improve the accuracy of ultrasonic guided wave velocity detection effectively,could accurately locate crack in the rail,it is beneficial to grasp the working state of the seamless line accurately,have great significance to ensure the safety of high speed railway.The paper studies of the measurement method of wave phase velocity of ultrasonic guided in seamless rail based on 2D-FFT algorithm,the ultrasonic guided wave signal transmitting module,synchronous acquisition of multi-channel ultrasonic signal module and linear array probe are designed,and then,established the phase velocity measurement system,the main work are as follows:1.Studied the propagation characteristics of ultrasonic guided wave,selecting 2D-FFT method for measuring the phase velocity of ultrasonic guide wave,the overall research program of the paper is designed.2.The 32-channel linear array receiving transducer is designed,it working at 150KHz,the excitation probe was selected through experiment and simulation,and installed in the rail waist.3.Using STM32 microprocessor and FPGA as hardware frame,the ultrasonic guided wave emission module and the 32 channel ultrasonic signal synchronous acquisition module are designed respectively,the voltage amplitude,time interval,and signal cycle of the transmitting module can be changed,meet the incentive requirements,signal acquisition module implements synchronous acquisition 32 channel ultrasound signal,sampling rate is 2.4MHz,Data can be transmitted to the host computer to display,save and data processing.4.In the laboratory,we set up a phase velocity measurement system,we could get the relationship between the frequency and wave number of the guided wave by 2D-FFT method,extraction the wave number at the excitation frequency,calculate the phase velocity of the guided wave at this frequency,comparison and analysis of theoretical values with the semi analytical calculation,the experimental data are in good agreement with the theoretical values.The paper completed the overall program of ultrasonic guided wave phase velocity measurement based on 2D-FFT algorithm,set up a phase velocity measurement system,could measure the phase velocity of ultrasonic guided wave in a seamless,it lays a good foundation for the research on ultrasonic guided wave defect detection and guided wave mode recognition.