An ultrasonic sensor for monitoring wheel flange/rail gauge corner contact

Wheel/rail contact is critical to the successful operation of a railway network. Contact occurs at the wheel tread/rail head and wheel flange/rail gauge corner. Contact conditions are more severe in the latter, which occurs mainly at curves. The contact is small and supports large loads; therefore, high contact stresses are generated. These, combined with the slip in the contact, are primarily responsible for driving the processes that lead to wheel and rail damage, whether by deformation, wear or a fatigue process. Multi-body dynamics software is useful for predicting the wheel/rail contact characteristics; however, there is a shortage of experimental tools available. In this study, the feasibility of an approach based on an ultrasonic sensor mounted on the wheel is investigated. The sensor emits an ultrasonic pulse which is designed to impinge on the wheel flange. If there is no contact the pulse is fully reflected back at the flange and picked up by the same sensor. If flange contact takes place, a proportion of the pulse amplitude will be transmitted into the rail. The signal reflected back to the sensor is therefore reduced. The amount by which this signal reduces indicates how much flange contact has occurred. This work had two aspects. First, a standard ultrasonic ray-tracing software package was used to establish what it is possible to measure with sensors mounted in the wheel and to determine the best location and orientation. The second aspect was an experimental study to determine whether such measurements are feasible. Test specimens were cut from sections of wheel and rail, and a 2 MHz ultrasonic contact transducer was bonded onto the wheel in a position best suited to detect the flange contact. The specimens were pressed together in a bi-axial loading frame to generate differing degrees of rail head and flange contact. The reflected signal was monitored as the normal and lateral loads were varied. It proved possible not only to detect the onset of flanging, but also to record a signal that varied monotonically with both normal and lateral applied load. A map of reflected ultrasound against the applied loading is presented. The technology, while not currently suitable for full field implementation could be very useful in laboratory studies on, for example, a full-scale wheel/rail rig.