| With the construction of China's high-speed railway, rail flaw detection is more and more important. At present, piezoelectric ultrasonic testing is the major technique of rail flaw detection, but it needs couplant. Without using couplant, electromagnetic ultrasonic testing has higher detection speed. This paper researched the application of internal rail flaw detection using electromagnetic acoustic angled shear vertical wave, which made the detection of rail flaw with Electromagnetic Acoustic Transducer (EMAT) more comprehensive.Firstly, an equivalent circuit of EMAT based on the coil's characteristic was introduced, the EMAT's circuit parameter was extracted by Ansoft Q3D Extractor, the influence of wire parameter and lift off on coil inductance was analyzed,Γ-matching circuit and transformer matching circuit were given, the transmit efficiency of EMAT was improved with the transmit matching circuit.Secondly, the sound field of angled shear vertical wave was simulated. The simulation result showed that it was very hard to excite 70°shear vertical wave. A line focused coil was designed in order to solve the bidirectional transmission problem and the sound filed characteristic was also simulated. The probe of 37°shear vertical wave in pitch-catch mode was used in rail flaw detection. Different turns of transmit coil and receive coil were designed to find the optimal coil shape. The flaw detection experiment was done with GTS-60 standard rail block, the experiment result showed that electromagnetic angled shear vertical wave could detect rail web and rail bottom crack effectively.Finally, an equipment of rail flaw detection using electromagnetic acoustic angled shear vertical wave was designed. A quick startup method of DSP was introduced based on QDMA, and the startup speed was improved remarkably. To solve the problem of low work repetition frequency, three optimizing ways of DSP algorithm were given and used, the repetition frequency was improved to 40Hz. |
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