Transverse and longitudinal crack detection in the head of rail tracks using Rayleigh wave-like wideband guided ultrasonic waves

We have developed a 'pitch-catch' low frequency-wideband Rayleigh wave EMAT system with a centre frequency of approximately 200kHz, extending to around 500kHz and study here its applicability to crack detection in the head of rail tracks. On the head of a rail, the generated waves are strictly speaking a type of guided wave mode as the propagation surface is not a flat halfspace. They propagate along the surface of the rail penetrating down to a depth of several millimetres. We have used this approach to demonstrate detection of gauge corner and longitudinal cracking in the rail head. On samples containing machined slots we have shown that crack depth can be estimated by measuring the proportion of the ultrasonic wave at a particular frequency that passes underneath the crack. The approach that we have used is fundamentally different to and has several advantages over conventional ultrasonic contact methods and should ultimately facilitate testing the rail head more thoroughly at higher speeds.