The Research Of Rail Stress Detection Based On Electromagnetic Acoustic Transducer

Seamless rail stress caused by temperature changes has been the outstanding problem of the railway industry. Because traditional detection methods are time-consuming, slow and affect the normal use of rail, this paper studies the electromagnetic acoustic (EMA) testing of rail stress as a way to solve this problem. This method is fast, non-contact and has no damage to the material. At present, the default of this method is that the conversion efficiency of electromagnetic to ultrasound is very low, which causes the signal to noise ratio is not high enough. And acoustoelasticity is a weak effect, so the difference between the speeds is hard to detect.At first, this paper describes the various non-destructive stress measurement methods. Because of the advantages of EMAT, we choose the Rayleigh wave method based on acoustoelasticity to detect the stress of seamless rail. At first, we analyze the coupling mechanism of the EMAT, especially the principle of Lorentz force and magnetostriction . Based on that theory, we have optimized the structure of the probe, analyzed the probe's impedance matching, and designed the low noise amplifier and filter circuit. The results show that it works very well.Accord to the acoustoelasticity, the speed of surface wave changes only a little because of stress. So it requires appropriate algorithm to calculate the ultrasound's speed. First, we use high-speed data acquisition card to sample the incentive and receive signal. And then we use appropriate filtering and correlation algorithm to calculate the propagation time of ultrasound, this method can achieve a very high time resolution.Based on the above software and hardware, this article does some stress detection experiments, fits the time-stress relationship and does the error analysis.Finally, we compare EMAT with MBN to detect stress and discuss the advantages and disadvantages of both.