Method For Detecting R Angle Defects Of Rail By Laser Line Scanning Stimulated Ultrasound

Laser ultrasonic defect detection technology uses laser pulse to irradiate the measured object,and realizes defect detection by detecting the changes of ultrasonic signal generated inside or on the surface of the object.Laser ultrasonic detection is noncontact detection,can eliminate the additional influence caused by coupling agent,suitable for harsh environment application;It has the advantages of rich mode,wide band,high signal-to-noise ratio and many application scenarios,which can be used for nondestructive testing of objects with different shapes conveniently and flexibly.In this paper,a simulation model for detecting metal surface defects by laser line scanning is constructed by using laser line scanning to excite ultrasonic waves.The characteristics of surface waves excited by laser line scanning in the far and near fields are studied,and a method for determining the location of defects is proposed.Through simulation and experiment,the metal surface is detected by laser line scanning,and the defects in R Angle of rail are detected.The main research contents of this paper are as follows:The finite element simulation software COMSOL was used to model the laser line source excited ultrasound under the thermal elastic mechanism,and the propagation principle of the laser line source excited ultrasonic surface wave on metal was studied.The reflection and transmission effects of the excited ultrasonic wave on surface defects were analyzed to verify the correctness of the model.The scanning process of laser line source is simulated by changing the position of laser line source,and the characteristics of surface wave in time domain and frequency domain at different excitation positions are analyzed.The width of defect can be accurately judged by the maximum reflection echo and transmission echo detected at the defect boundary from line source scanning.The interaction between surface defects and surface waves of metallic objects is explored,and the effect of laser line source on surface waves in the far and near fields is analyzed.The influence of laser line source on surface waves is studied by changing the detection position,excitation position and defect size.According to the change of peakto-peak value of surface wave signal,a method to judge the defect size is proposed.A line source probe double moving mode is proposed to excite the metal surface to improve the measurement accuracy.An experimental system of laser line scanning ultrasonic detection of metal surface cracks was established.The non-contact detection system of interference detection and the contact detection system of ultrasonic probe detection were used to collect ultrasonic signals at the same time,and the defects on the surface of test blocks were located by the defect echo.The results show that the calculated defect positions are basically consistent with the actual ones,and the experimental data are consistent with the simulation results,which verifies the effectiveness of the experimental system in detecting surface defects of objects.By moving the test block,the scanning mode in which the detection point and the excitation point move simultaneously is simulated,which has higher accuracy in measuring the position of defects.Based on the surface defect detection of aluminum test block,it is applied to the surface of rail for detection.Laser line source is used to excite the rail tread to detect defects at R Angle of rail,and the possibility of practical application is verified.