Research Of Rail Flaw Detection Based On Ultrasonic Guided Waves

Rail as the basis for the train operation,its security play a crucial role in operational safety.How to timely find the rail damage and ensure the safety of rail traffic,has become the focus of nondestructive testing in rail.Considering ultrasonic guided wave with the advantages of longer propagation distance and highly detection efficiency,it has some advantages for rail flaw detection.Therefore,this paper studies on rail flaw detection based on ultrasonic guided waves.(1)Based on semi-analytical finite element method,the dispersion of ultrasonic guided wave in rail is analyzed.By consulting a large amount of references,and based on the principle of dispersion curve in arbitrary cross-section waveguide media by using SAFE.The semi-analytical finite element algorithm has been self-designed with MATLAB.According to the result,guided wave modal shape,dispersion characteristics under the stress condition,forced responces are also analyzed,and propagation characteristics of each guided wave mode in rail has been obtained,which provideds a theretical reference basis for rail flaw detection.(2)Excitation signal parameters,guided wave mode,excitation position have been optimal selected.Based on the dispersion characteristics of ultrasonic guided wave,the detection frequency band and the excitation signal cycle are determined by the dispersion coefficient and the duration time of wave packet.Then mode shape coefficient and mode shape sensitive factor are introduced to selected guided modes.And excitation position for selected guided mode can be rapid located by using excitation location algorithm.Finally,3D-finite element model has been built for simulation.This method can rapid obtain the detection frequency,excitation cycle,detection mode and the excitation position of selected guided mode,which improve the efficiency of engineering applications.(3)The finite element analysis software ANSYS is used to establish the 3D-detection model of rail head and rail web.The relationship between the longitudinal length,the inclination angle,the depth,the cross-sectional area of the defect and the reflection coefficient or the transmission coefficient has been studied.Meanwhile,considering the development of air-coupled ultrasonic guided wave detection technology,a 3D-air coupled model of rail detection which based on ultrasonic guided wave has been established,and the propagation characteristics of the surface wave in the rail head is simulated.By using the wave transmission detection method,the characteristics of the defect signal is analyzed by simulating different defects,which provide the theoretical basis for the quantitative evaluation of the defect.