Ultrasonic measurements of nominal contact area and contact pressure in a wheel-rail system

Abstract

For more than a century, the contact between wheel and rail has been the subject of careful investigation by scientists and railway technicians. Many efforts have been made to understand a series of phenomena (wear, pitting, fatigue, failures, etc.) that are closely related to processes occurring in such a small contact patch. A huge amount of numerical and theoretical research work (starting from Hertz's theory) has been carried out, but there is a noteworthy lack of experimental tests, which is probably due mainly to difficulties in accessing the contact area with conventional techniques. In the present paper, an experimental investigation dealing with the evaluation of the contact area and stresses transmitted across it is proposed: the technique employed is based on a non-invasive ultrasonic method that analyses the reflection of ultrasonic waves by the contact interface. By using a set-up commonly employed in many non-destructive testing (NDT) analyses it was possible to obtain graphic maps of static contact conditions, and several tests were carried out to evaluate changes with increases in external load. Results show reasonable agreement with Hertz's theoretical predictions and suggest a possible future use of the ultrasonic method to investigate contact during motion.