No description available.

No description available.

No description available.

No description available.

The friction and wear behaviour in the sliding four-ball contact system has been investigated, using a non-additive base oil, SAE 10, as the test lubricant. Load, speed, and test duration were each varied and the friction behaviour was measured and then related to the flash temperature calculation in the contact. The results of flash temperature calculation indicate that the temperature locally in the contact approaches the melting point of the EN31 steel as the state of the wear in the contact increased markedly in the transition wear region. A controlled micro-etching technique was devised to permit analysis of the sub-surface region. There were clear indications that intense heating had occurred in the sub-surface layers of the worn contact region. Hardness measurements confirmed that the surface hardness increased as a function of the applied load and that embrittlement of the surface layers occurred, notably at the higher loads. The wear particles have been studied using Ferrography in conjunction with the optical and electron microscope, the X-ray probe analyser, and the image analysing system, Quantimet. Important information relating to the wear behaviour was obtained from examination of free metal, oxide, and polymeric particles. From the results of measurement and analysis, a new hypothesis concerning the thermally-activated wear process was proposed in which thermal decomposition of the lubricant is postulated. This activity releases the products of hydrogen and carbon. The former causes embrittlement, and hence, a tendency to fail in a fracture mode, while the latter causes an increase in the hardness of the surface layers. The hypothesis was tested by adding a small quantity of hydrogen scavenger into the test lubricant. By thus nullifying the effect of hydrogen, the friction and wear were reduced and there was about a threefold increase in hardness, with no indication of brittle fracture occurring in the surface. The implications concerning the nature of the wear and the associated controlling mechanisms are discussed.

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Wear of machine elements is the inevitable and anticipated consequence of surface contact between interacting machine parts such as shafts, bearings and gears, etc., which occurs even in properly lubricated systems. As component loading system investments and maintenance costs have risen, so the need for highly reliable and long-lasting systems has become very important. Wear particle morphology, allied to composition, can be used to monitor machine health conditions. Techniques used to determine morphological features of wear particles in indicating mode/mechanism of wear are mostly subjective ones. With the increasing "power" of computers and the use of image analysis, it is opportune to find some relationships between the quantitative morphological characteristics of wear particles found in circulating oil and the physical processes involved in generating them. The principal contribution arising from the results presented in this thesis is the underlying unique development of analysis methods, based on image processing and analysis, in conjunction with other physical means, to monitor the wear of rubbing contacts. Based on multi-variate statistical analysis, several different approaches were used to establish systematic wear particle identification processes. The combined use of shape factors, edge detail and size parameters was found to be superior to other previously proposed methods. This new approach was then used to differentiate wear particles quantitatively in terms of different wear situations, using an optical microscope-camera-image analysis system.

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No description available.