Estimation of real contact area in a wheel-rail system by means of ultrasonic waves

The application of an ultrasonic technique to estimate the Real Contact Area (RCA) in a wheel-rail system is proposed. The method is based on the analysis of the reflection of ultrasonic waves which are sent over the contact region and reflected by it according to the state of contact. The interaction of the experimental data with a theoretical model formulated in the early 1990s by Krolikowski allows us to calculate the RCA for the area illuminated by the ultrasonic beam. By varying the external load and the surface conditions of the contacting elements, it is possible to obtain the trend of the RCA with increasing load (for a certain roughness) as well to explore changes in RCA for different roughness while the load is kept fixed. Results showed that RCA grows almost linearly with the applied load and that an increase of one order of magnitude in combined roughness of the wheel-rail system leads to a roughly sevenfold reduction in RCA under a given load.