Automatic in-motion inspection of the tread of railway wheels by e.m.a. excited Rayleigh waves
A technique is presented to detect surface and subsurface cracks in the tread of railway wheels. An ultrasonic surface wave pulse (Rayleigh wave) of 400 kHz is excited by an e.m.a. transducer inserted in the rail when the wheel contacts the transducer. This pulse propagates along the wheel surface in both directions making several round trips and is partially reflected by defects. An e.m.a. receiver unit inserted in the same rail assembly directly besides the transmitter, detects in two channels simultaneously echoes from the clockwise and counterclockwise direction. The inspection can be done at wheels in motion until now up to 10 km/h. The system is described. Furthermore, investigations of the defect detectability and the wave propagation on the wheel surface are presented. Results of a field test in a railway station are shown.