Tribo-Acoustic Sensors for In-Situ Measurement of Machine Element Contacts

PI Poster Presentation

R S Dwyer-Joyce

The Leonardo Centre of Tribology, University of Sheffield, UK

The critical part of any machine element is the interface; the rubbing surface where two parts contact. It is at these surfaces where friction is manifested, where wear takes place, fatigue cracks initiate, or where lubricant films or tribo-layers form. Measuring what happens at these interfaces is challenging because they are usually inaccessible - buried within a machine. One approach is to use ultrasound. Sound waves can penetrate through many engineering materials and reflect back from an interface.  If we can understand the response of the interface to an incident wave we can use this as a measurement tool.

There are a number of kinds of acoustic wave, and the interface will respond to them differently. The reflection of longitudinal bulk waves depends on the stiffness of an interface and this can be used to measure oil film thickness in components like journal bearings, thrust pads, and piston rings.  The reflection of shear polarised sound waves at a solid–liquid interface depends on the viscosity of the liquid. This can be used as a non-contact viscometer for analysing oil inside pressure vessels, pipes, and bearing lubricating films. In addition changes in the time of flight of a wave can be used to deduce deflection, distortion, or wear.