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Title: The acoustic emission from mixed elastohydrodynamic lubrication
Author: Hutt, Simon
ISNI:       0000 0004 7962 1271
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2018
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This thesis presents an investigation of the Acoustic Emission (AE) from mixed Elastohydrodynamic Lubrication (EHL). In mixed EHL the contact surfaces are partially separated by an oil film, and partially by direct contact between opposing roughness asperities. The proportion of each can vary and excessive amounts of asperity contact can precipitate surface damage. Researchers have recently shown that, in mixed EHL, asperity contacts are a source of AE (a class of mechanical wave) and the aim of this thesis was to characterise the relationship between the AE and the amount / severity of the asperity contacts. Two experiments were conducted on a disk machine which simulates the lubrication conditions of heavily loaded transmission gears. The rig was instrumented with two AE sensors placed on the test disk, one interfaced using a novel oil-coupling. In the first experiment the thickness of the lubricating film was varied using speed and temperature control. The AE measurements were found to be susceptible to noise but after frequency filtering a clear and precise exponential relationship between the amount of AE and the amount of direct asperity contact was identified and modelled. The oil-coupling was found to be noisy but fundamentally feasible. In the second experiment two previously unused disks were tested. All operating parameters were kept constant and the test disks were allowed to wear naturally. Surface measurements confirmed a rapid and large initial reduction in asperity height caused by running-in, and then a much slower and more limited reduction caused by further wear, which included some micro-pitting. The wear affected the amount of AE which was found to correlate well with changes in the Rq (RMS roughness) of the contact surfaces. The AE measurements revealed that running-in of asperities occurs immediately, i.e. within the start-up of a new contact.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available