The interaction of machine components under loading is an integral part of railway engineering design. It results in a mechanical contact and associated stress distribution, which may be an initiation point for failure modes such as fatigue, fretting or wear. In this study the reflection of ultrasound is used to investigate how real engineering components contact. 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 will be the contact and hence more of the wave will be transmitted. A spring model is used to determine maps of contact stiffness from contact ultrasonic reflection data. A calibration procedure is then used to determine the pressure. The technique has been used to study two railway engineering applications. The first was a wheel/rail contact. Measurements were taken using specimens cut from sections of wheel and rail. Both the tread/railhead and flange/gauge corner contacts were studied. The second was a wheel hub/axle interference fit. An actual wheelset was used, with a hollow axle to allow access for the ultrasonic transducer.

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