Research On Guided Waves Inspection For The Oblique Crack And Welding In The Rail Bottom

Rail is an important part of the railway track, along with the train speed increase and overloading Trains, it accelerated the damage to the track, thus affecting the traffic safety. Currently, Railway repair process is used longitudinal and transverse waves rail flaw detection method based on vehicle technology only rail head and rail web and the rail extension for testing, because of the surface of the rail was "workers" shape,bottom rail on both sides of the region can not be detected. Rail bottom cross-sectional shape of the structure is irregular, discontinuity, Once there is a defect will cause the rail foot rupture,thus threat traffic safety, it is necessary to work out a new method of nondestructive testing for defects Rail Base. In recent years, Guided Wave technology has been widely used in long-range detection of pipes and piece, Compared with conventional ultrasonic inspection method, the new ultrasonic guided wave technique has along the propagation path attenuation, propagation distance, test speed and other advantages. In this paper, ultrasonic guided wave propagation characteristics of the rail bottom and bottom containing wave scattering characteristics of the defect state are researched, providing the basic theory and method of detection for the rail bottom of guided wave testing technique on the actual rail line.In this paper, using the finite element software to establish three-dimensional numerical model to simulate ultrasonic guided wave propagation in the bottom of the rail, analysis the guided wave propagation characteristics and model dispersion characteristics. Compared with the experimental testing, research propagation and scattering properties exist bugs orbit when its bottom. From the end of the rail waveguide dispersion curve showed the rail bottom existed lateral vibration mode,vertical vibration mode, longitudinal vibration mode. the lateral vibration mode and vertical vibration mode are consist of many sub-waveguide mode, but exhibit good propagation characteristics, dispersion characteristics is small, thy are suitable for detecting the end of the rail, while the dispersion characteristics of longitudinal vibration mode is big, it is not conducive to a detection mode wave.Secondly, by using the finite element software ABAQUS on the rail simulation and experimental tests, It was studied the influence of different excitation frequencies and the number of different pulse cycle for lateral and vertical vibration mode waveguide propagation, through anysis echo amplitude and wave packet width of the echo waveform confirmed the basis of selecting for proper excitation frequency andthe number of pulse cycles.Thirdly, experimental study the influences of flaw echoes on different defects and different depth on rail bottom, the results show that the defect echo amplitude is affected by the impact of the defect angle, therefore, conduct the numerical simulation of guided wave detection to oblique crack on rail bottom at different angles, through different angles of reflection and transmission coefficient of oblique crack to analysis the effect of the frequency and number of pulses cycle to oblique crack defect echo amplitude and transmission amplitude. In order to verify the correctness of finite element numerical simulation, designe and worke a set of sample,through guided wave detection experiments researche on different angles oblique cracks on rail bottom, the results show that the bottom rail of the oblique angle oblique crack echo amplitude Influence is the same as numerical simulation, lateral vibration mode more fit than vertical vibration mode.Finally, through guided wave detection experiments to analysis the feasibility of acoustic guided waves detective the defects in the rail bottom, the experiment result of the guided waves of thermite welding on rail bottom shows, though the reinforcement of thermite welding will cause echo, but when it exists defects, the echo waveguide having a different spectral characteristics of the signal compared with reinforcement,and using lateral vibration mode detect the defect of welding is easily than vertical vibration mode. These jobs provided meaningful reference for the thermite welding on the rail bottom of guided wave testing technique on the actual rail line.