Method For Detecting Rail Tread Defect By Laser Line Scanning Excitation Ultrasonic

Laser ultrasonic detection is a method that a laser is used to excite ultrasonic and the ultrasonic is detected to get the defect of the sample.It not only has the advantages of conventional ultrasound,but also has the advantages of non-contact,high precision,wide band,rich waveform,etc.Laser ultrasonic is very suitable for nondestructive testing of objects.In this paper,laser line source was used to excite ultrasonic wave,and the mechanism of laser line scanning to detect metal surface defects is studied through the finite element simulation and experiment.A set of experimental system was built to detect the defects of rail tread crack.The main research contents are as follows:Based on the basic theory of laser ultrasound and the finite element method,the simulation models of laser line source excitation and surface defect detection was built,the propagation properties of ultrasonic was analyzed,and the correctness of the simulation models were verified.The interaction between ultrasonic wave and defect is studied,and the effectiveness of surface wave detection was verified.By changing the size of the defect,the influence of the defect on the surface wave was studied,and a method for calculating the defect depth was proposed.A simulation model for detecting metal surface defects by laser line scanning was built,and the characteristics of surface waves excited by laser line source in far and near fields were studied.According to the changes of the peak-to-peak values of surface waves in the process of laser line scanning,a method to judge the location of defects was proposed.By changing the size of the defect,the influence of the defect on the laser line scanning excited ultrasound was studied,and the method to judge the defect width was put forward.An experimental system for the detection of metal surface defects by laser line scanning excitation ultrasonic was established.Through the detection of metal surface defects of different sizes and the judgment of defect information,the experimental results were consistent with the actual,which verifies the effectiveness of laser line scanning excited ultrasonic detection of surface defects.The established experimental system was used to detect the rail tread defects,and the more accurate defect information is obtained,which provides a basis for further research on the detection of rail tread defects by laser line scanning.