The Real-Time Characterisation of Dry Machine Element Contacts Using Ultrasonic Reflectometry

For two components to be in contact, they must be physically touching. If two solids are touching, the contact is by definition inaccessible. How do engineers develop an understanding about a contact if the interface is inaccessible? Load, geometry and material properties govern the contact pressures of touching components. As they move against one another, the result is often wear and this inherently changes the contact behaviour. By understanding how interfaces interact in terms of contact pressure, contact area and wear, components can be optimised to reduce cost and maximise efficiency.

Ultrasonic reflectometry has been widely used in medical imaging and non-destructive testing. It is a non-invasive technique that has the ability to probe deep into solid structures and extract information regarding the material and the interface. Two methods have been developed to measure wear in real-time based on ultrasonic time-of-flight and the resonant frequency model. The ultrasonic technique has also been applied to learn more about the contacting parts of machine elements. By analogising the interface asperities as springs, ultrasonic reflectometry can be used to calculate the interfacial stiffness and from this, contact pressure of a tribosystem. Previous work has been limited to laboratory based static measurements. This work builds on this technology to characterise dynamic machine elements with the hopes of developing industrial condition monitoring tools.

This thesis is aimed to be a guide for those who wish to use ultrasound as a tool to measure and monitor a dry dynamic tribosystem. More specifically, this work highlights a series of recommendations and pitfalls for ultrasonic measurements of contact pressure and wear in industrial applications.