Ultrasonic measurement of railway wheel hub–axle press-fit contact pressures

Abstract

Railway wheels are secured onto the axle by means of an interference fit. The wheel is either shrink fitted or press fitted onto a pre-lubricated axle, and the resulting interference fit induces a contact pressure at the interface. Occasionally railway axles fail by fatigue, with the initiation point for the failure frequently traced to the interference fit. In this study, the reflection of ultrasound was used to determine contact conditions in the interference fit. It is a non-intrusive technique preserving the mechanics of the contact. The concept is simple; an acoustic wave bounces back from an incomplete interface. The higher the contact load, the more conformal the contact and hence more of the wave will be transmitted. A spring model is used to determine maps of contact stiffness from ultrasonic reflection data. A calibration procedure is then used to determine the pressure. Two types of wheelsets were used for the measurements, both with a hollow axle that was used as an access point for the ultrasonic transducer. The wheels differed in the design of their web sections. Variations were detected in the determined interface pressure profiles, due to both surface roughness effects and discontinuities in the fit geometry. When comparing the two fits, it was found that material removal from the web of the wheel in the second fit reduced the interface pressure distribution.