Research On Railhead Flaw Inspection Method Based On Electromagnetic Ultrasonic Surface Wave

In recent years, as the acceleration of the high-speed rail construction and the density of the railway transport, various flaws arise in the rail especially in the railhead, which causes increasingly serious threats to the railway transport safety. The conventional inspection methods, such as piezoelectric ultrasound, eddy current, magnetic flux leakage, machine vision, are unable to inspect the railhead completely and effectively for a series of shortcomings. With the advantages of couplant-free, high efficiency, high inspection speed and wide inspection area, the electromagnetic ultrasonic surface wave is perfect for the railhead inspection which will make a significant contribution to the railway safe all to nothing.After researching on the theory of flaw detection and identification based on ultrasonic surface wave deeply and comparing the electromagnetic ultrasound with the piezoelectric ultrasonic technology, a technical target about the railhead inspection method based on the electromagnetic ultrasonic surface wave was proposed and the overall scheme was put forward.In order to realize the inspection of the railhead, a railhead flaw inspection device based on the electromagnetic ultrasounic surface wave was accomplished. The transmitting and receiving circuit, data acquisition circuit were designed to generate, receive and acquire the surface wave. Synchronously, the electromagnetic ultrasound acqisition and analysis platform was used to complete the design of software, realizing the control of hardware.The electromagnetic ultrasonic narrowband coils were designed and the narrowband surface waves of three different frequencies were excited by the coils to detect the railhead flaws of different positions and types. The electromagnetic ultrasonic wideband coil was achieved to excited the wideband surface wave which was used to detect the slots and holes in the railhead.The railhead flaw inspection and identification algorithms based on electromagnetic ultrasonic surface wave were also achieved. The wavelet transform method was used to denoise the received signal. Then the FFT and wavelet packet transform were adopted to analyze the time-frequency properties of the echo, and extract the features such as echo center frequency, the energy of the central frequency and the wavelet packet energy spectrum. Finally, the flaw classifier based on support vector machine was designed and implemented. According to experimental results, the classifier could accurately carry out the identification and classficaion of the slots and holes in the railhead.