Research on laser-EMA ultrasonic detection system for the defects of rail screw hole

With the increase of the railway load and running speed, the probability of the rail screw hole defects increases and can cause serious damage to the rail operation safety. The traditional nondestructive testing (NDT) is not suitable for the rail development of testing needs nowadays, so we need to develop a new method to test the defects of the rail screw holes. The laser-electro magnetic acoustic (EMA) testing system of rail is designed based on the basic principles of the laser-EMA ultrasonic technique and the characteristics of the rail nondestructive testing. The comparison experiments are conducted by using the laser-EMA to test the screw hole, and the results show that the method can precisely find the upward tilted cracks. From the laser-EMA signal processed based on wavelet threshold denoising, it could be seen that the signal to noise ratio is greatly improved and all characteristics of the original signal are remained, thus the signal processed by the wavelet threshold denoising will be convenient for the damage identification and features extraction. Experimental results show that this method doesn't need coupling medium and good surface conditions, and could realize non-contact, rapid scanning and precise inspection to the rail screw holes.