A method to determine acoustic properties of solids and its application to measuring oil film thickness in bearing shells of unknown composition. (31st May 2022) - Beamish, S.
Highlights: A new method to determine acoustic impedance of solid materials in layered systems is presented. The technique is applied to a range of materials under static conditions and compared against the conventional mass-volume method to demonstrate its effectiveness. The technique is also applied to a journal bearing test rig to demonstrate its capability to measure acoustic impedance in more complex dynamic systems. Abstract: Acoustic impedance is an important property used to interpret acoustic reflection measurements in tests to determine oil film thickness, a critical parameter dictating efficiency and wear rates of lubricated components. A new method to measure acoustic impedance of solid media, based on the well-established spring model, is described. The advantage of this method over existing techniques is that it can be applied to thin, multi-layered materials where individual reflections cannot be distinguished, common in many tribological systems such as bearings, piston rings and piston liners. The method is demonstrated experimentally for a range of materials. Results compare well with values calculated independently from acoustic velocity and density. The method has been applied to a bearing test rig to determine acoustic impedance of a thin-walled bearing. This study demonstrates that the technique is capable of measurements in dynamic systems and where traditional methods of calculating acoustic impedance are not feasible.