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The increasing demands made on operational availability and reliability of machinery requires the adoption of innovative methods to assess the machine’s current condition and predict its condition in future. Rapid advances in the design and working condition of mechanical systems in industrial, aerospace and military equipment over the years have resulted in the ever-increasing complexity of problems encountered in the management of their maintenance. The ability to monitor the performance of machinery components in terms of wear and durability is extremely invaluable. Thus, it is essential to monitor wear occurrences and severity so prediction of any forthcoming failure can be made and hence accurate maintenance schedules can be planned. Acoustic emission (AE) is widely used in industry for detecting: cracking in a bridge structures; cavitation in pumps, piping and turbines; leak detection; welded joint defect; creep cracking; fatigue cracking; stress corrosion cracking; hydrogen embrittlement cracking; fracture and crack propagation; corrosion detection, etc. Electrostatic (ES) monitoring was originally developed for condition monitoring of the gas path of jet engines and turbines but has recently been adopted for studying lubricated systems at the University of Southampton. Both AE and ES are relatively new condition monitoring techniques that provide real-time outputs. The purpose of this project is to combine these two technologies together to examine whether they are sensitive to different aspects of the physics of contact degradation and elucidated the potential of the systems to detect precursors to severe wear. The project involved two experimental series: the first examined dry sliding and the second investigated lubricated sliding. Both employed steel-on-steel, ball-on-flat configurations using a pin-on-disc tribometer. During dry sliding test, the two condition monitoring techniques indicated three periods of activity identified by differences in magnitude and signal characteristics. Post-test analysis by SEM and EDX identification these three regions/wear regimes as running-in, delamination and delamination/oxidation. Experimental data showed that the AE RMS signal was very sensitive to the variation of the friction and good correlation was seen throughout testing. AE energy, counts and amplitude distribution are shown to be particularly sensitive to different wear mechanisms under dry sliding test conditions. The physical mechanisms behind the wear mechanisms were deeply investigated and the results showed that the intensity of AE signal was related to the scale of the de-bonding of material during severe adhesive, material transfer and severe delamination. Cracking and plastic deformation of the material, which occur during ratchetting, mild delamination and oxidation, generate lower level AE signal compared with the de-bonding of material. The bandwidth of the power spectrum of AE signals can be used to distinguish different wear mechanisms. Lubricated tests indicated again that AE and ES where sensitive to wear mechanisms in both loading and steady-state periods: plastic deformation, filmy wear, mild wear and scuffing (identified by post-test analysis). Transitions from mild to severe wear modes, detected by AE and ES sensors, were linked to intermittent white layer (phased transformed) regions and/or to incomplete oxide layers formed in the wear track. Overall the research project has shown that AE and ES exhibited the potential to become a powerful suite in condition monitoring.

In modern automotive engines, especially in diesel engines, consumer demand for ever increasing service intervals for vehicles has led to longer oil drain periods. Consequently this has increased contamination levels in lubricating oils that will in turn reduce engine efficiency and increase the possibility of system failure due to increases in viscosity and the potential of oil starvation leading to scuffing and catastrophic failure of the engine. Therefore it is necessary to investigate the effects of diesel engine oil contaminants on the tribological performance of tribocontacts and also the possible interaction between the contaminants. The thesis aims to investigate the influence of contaminants and their interactions on diesel engine oil using Electro sensing (ES) monitoring. ES monitoring suggest sensitivity to tribocharging, triboemission, surface charging, and wear debris generated in the tribocontact. However, ES monitoring is still in its initial stages of development but the relationships between the ES charge signal and corresponding wear mechanisms are established. Initial experiments showed the sensitivities between charge and wear to changes in additive chemistry, as well as contamination (specifically a soot stimulant). The results indicated some interesting findings which were difficult to elucidate but paved the way for a parametric study. The parametric matrix examined the effect of contaminants and it was observed that wear rate was mainly influenced by acid and soot additions. The best correlation of steady state charge with the other measured tribological parameters of wear rate, friction and temperature is seen for the series of oxidised oils. The multi-contaminated oil (L4×4) shows remarkably little degradation in tribological performance with a reduced friction level compared with the uncontaminated oil and only a modest increase in wear rate, slight increase in charge levels. This clearly showed that there were interactions between the contaminants. The factorial matrix studied interactions between the diesel engine oil contaminants on various tribo-couple materials, including silicon nitride, using ES monitoring. For charge, pin material – sulphuric acid and oxidation –sulphuric acid, interactions were statistically identified as having significant influence on performance. For friction, both pin and disc materials were identified as main influences along with pin material – sulphuric acid interactions. For wear, the presence of soot and the influence of pin material were identified statistically as the main effects. To conclude, the ES monitoring was sensitive to the presence and levels of contaminants in diesel lubricating oil, particularly diesel soot. The change in charge levels indicated the concentration of soot level present in the contact, which was directly related to wear. ES monitoring also detected interactions between the contaminants through statistical analysis. ES monitoring has shown that monitoring lubricant performance and the effects of contamination are feasible under laboratory conditions.

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The key focus of this research was to investigate the bearing options most suited to operation in a novel direct drive linear generator. This was done through bearing comparisons, modelling and testing. It is fundamental that the linear generator is designed to suit the marine environment. Key design constraints include reliability, survivability, maintenance intervals and cost. Resilient mechanical structural components, such as bearings, will prolong the time a device can operate without maintenance hence prolonging the operating period. Effective lifespan predictions for bearings will feed into the structural design of the generator which forms part of an overall objective to combine each generator design stage into one integrated design process. This promises to provide a cost effective, light weight generator design. This thesis covers the initial investigations into effective, long life and low-wear bearings to meet the operating demands of WEC. It includes an assessment of conventional bearing technology, designs of water-fed hydrostatic bearings and testing of novel polymer bearings. The development of an experimental test rig from a prototype linear generator is described. The rig was built in order to validate and fully explore the potential of self-lubricating, submersible polymer bearings with the ultimate aim of identifying wear constants and frictional properties of the bearings in the low-speed, mid to high-load, oscillating operation of a WEC in order to more accurately predict a bearing lifespan. The outcome of this research served to underpin the need for the design of application specific bearing systems to be based on empirically determined data and observations from test data taken from application specific tests. For inclusion in the design of these linear generators, sizing a bearing requires knowledge of the electrical loading in addition to the expected operating conditions of a WEC. Choosing bearing materials and hence lubricant regimes is dependant on the thermal operating characteristics. Then bearing knowledge in terms of size, load capacity and lifespan can be put directly into the structural model. This iterative process of design can then be merged into a fully integrated generator design tool hence this research was part of the development of an integrated design tool for direct drive generators.

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The influence of the horizontal magnetic field has not been sufficiently studied in contrast to study activity on the influence of the vertical magnetic field by researchers. The reason was that the influence of horizontal magnetic field to change the wear mass loss of ferromagnetic materials is smaller compared to the vertical magnetic field. However, the influence of horizontal magnetic field on rolling contact changes the subsurface crack initiation point toward surface is postulated by a researcher. Therefore, it is significance finding out how the horizontal magnetic field influences the tribological characteristics. This thesis presents a study on the influence of the horizontal magnetic field on wear in sliding contacts contributes for ascertainment the effect and mechanism of horizontal magnetic field on tribological characteristics of sliding contacts, through the experimental approach.The static magnetic field with densities of 0 and 1.1 Tesla and different orientations was applied to different contact conditions, different surface modifications and two sliding frequencies, using a ball-on-plate contact configuration. In conclusion, the presence of magnetic field enhances the chemical adsorption between iron or oxide iron and oxygen, and causes the transition of adhesive wear to oxidative wear. Besides, the presence of magnetic field combined with low sliding frequency forms the bulging on the wear surface and weakens the prevailing wear mechanism due to the low frictional temperature. On the other hand, the presence of magnetic field combined with high sliding frequency induces the transition to the oxidative wear mechanism and reduces the wear. Also, distinctly different appearances of wear surface are created by different magnetic field orientations. In the lubricated sliding contact, the magnetic field causes the reduction of wear and induction of oxide. It is postulated that the presence of magnetic field enhances the oxygen adsorption on the wear track by iron wear particles and hence varies the tribological behaviour. The influence of magnetic field on carbon steel coating consists in changes of oxide iron layer and steel layer, alterations of mechanical properties of the coating, and decrease in the mass loss and the surface roughness on the dry sliding contact. All these could be suggested the influence of adhesive strength of the interface between the base material and coating.

The objective of this Ph.D work is to establish an affective engineering system for general surface tactile evaluation, which fits in the current knowledge gap between the micro-surface physical properties and the customers’ peceptual responses to surface tactile senses as well as their affective preferences. Drawing upon a broad multidisciplinary review, this research identifies the value of such affective system for tactile evaluation in both academic research and industry application. A concept framework of surface tactile evaluation system is specified, including three substructs: instrumentation, sensory evaluation and database construction & mining. The framework is implemented to investigate how surface tribological factors such as topography, hardness and friction against skin affect the tactile attributes and general preference, with regard to 'soft-touch' polymer coatings and patterns. Works were done in three major folds: Firstly, two instrumentation features for tribological test and surface characterisation have been developed. The works include (1) a novel tribometer with flexible configurations of in-vivo friction test by finger touch and dry sliding Roller-on-Block test and (2) a Hot-tip Tribological Probe Microscope (hot-tip TPM) with localized surface thermal measurement. Their novelty in design and performance are presented and discussed in detail. Some preliminary tactile studies on car interior materials and regular machined surfaces are also performed on tribolgical aspects. To help interpreting the data acquired from TPM and to improve the understanding of the limitation of surface characterization at micro/nano scale, fidelity issues are considered on two aspects: (a) finite tip size effect on topography measurement and (b) probe misalignment effect on nanoindentation test. Secondly, a database of ‘soft-touch’ polymer surfaces has been constructed at both physical level and psychophysical level. On one hand, the surface microstrutures are physically characterized by the home-made instruments and other commercial ones, in terms of topography, surface nanohardness and friction coefficient. Internal correlations among the measured surface properties are observed. Attempts have been made to explain these correlations by the aforementioned fidelity issues and classical tribology theory. On the other hand, the tactile perception towards the polymer samples are evaluated and quantified in the four major tactile sensory modes (Smooth-rough , soft-hard , slippery-grippy , cool-warm) and the general preference (Like-dislike). Nonparametric statistical tests such as Kendall’s W test and Wilcoxon test are applied to study the evaluation effectiveness among the subjects and the perceptual difference among the samples. Gender difference is identified in the tactile evaluation effectiveness of polymer coatings. Last but not least, this research further explored the complex relationships among the perceived attributes and measured surface properties by using a range of classical data mining techniques such as cross correlation analysis, factor analysis and regression methods. It was noted that the perceived attributes such as smooth/rough and grippy/slippy are influenced by surface topography with parameters of roughness and average spacing while the perceived softness largely depends on the ratio of hardness to modulus H/E. A regression model is established to describe the psychophysical relationships in relation to surface tactile design of the ‘soft-touch’ polymers.