Feasability study for an ultrasonic sensor for monitoring wheel flange contact

If the contact between the wheel and rail occurs at the flange, a high degree of slip is inherent. This can result in excessive wear and the potential for rolling contact fatigue cracking. Multi-body dynamics software is useful for predicting the bogie and track characteristics that may lead to flange contact occuring. However, there is a shortage of experimental tools available to validate such models or to assist in vehicle and track condition monitoring. In this study, the feasibility of a new approach is investigated. The method is based on an ultrasonic sensor mounted on the wheel. The concept is that 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 occurs. Test specimens were cut from sections of wheel and rail, and a 2MHz ultrasonic contact transducer was bonded onto the wheel in a position best suited to detect the flange contact. The specimens were pressed to together in a bi-axial loading frame to generate differing degrees of 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.