Even though research into aluminium-silicon alloys is becoming increasingly fashionable, very little is known regarding the tribochemistry of these substrates when lubricated with conventional engine oil additives, especially when compared against ferrous surfaces. In this thesis, many advancements and thus contributions have been made in the field of aluminium-silicon lubrication. Firstly, using a Cameron Plint TE77 tribometer, the tribological performance of overbased calcium sulfonate, zinc dialkyldithiophosphate and an organic antiwear additive on aluminium-silicon surfaces were evaluated. Secondly, contact conditions on silicon grains within the AI-Si alloy were replicated using a silicon crystal substrate, as the silicon regions were vital in the effective lubrication of the aluminium-silicon alloy. Simulation was validated through tribological testing. Thirdly, the role of the aluminium matrix under boundary lubricated wear was evaluated using a replicate aluminium alloy. Tribofilm formation and morphology on the three substrates was analysed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Tribofilms were generated on silicon surfaces more effectively than on the aluminium alloy. Wear levels were lower on the non-conductive substrate compared to the aluminium substrate. The mechanical properties of tribofilms on silicon crystal surfaces were analysed using AFM and nanoindentation, and related to observed wear levels. Fourier transform infrared (FTIR) and secondary ion mass spectrometry (SIMS) determined the tribochemistry of generated tribofilms on all three tribosystems to be very similar to those on ferrous substrates. The addition of the organic antiwear additive to lubricants containing detergent, ZOOP or a combination of the two, consistently improved film formation and wear levels in the three tribosystems. The mechanisms by which this occurred were identified using labelling techniques. This research has provided great insight into the effective lubrication of aluminium-silicon substrates, with the results compiled to provide a definitive mechanism by which the boundary lubrication of aluminium-silicon alloys occurs.

The objective of the overall project is to assess the effect of water on the performance of lubricants and related tribochemistry in boundary lubricated steel/steel contacts. The effect of water on the bulk properties of the lubricant, the tribological performance of lubricants and the mechanism of tribofilm formulation are the focus of this project. The tribological performance of different lubricants is evaluated by a ball-on-disc test rig as well as a micropitting rig under boundary lubrication and with different levels of humidity. Selected post test samples are analysed to study the reactions occurring during the test and the composition of the tribofilm. The surface analysis techniques used are Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The results of this thesis show that water can change the bulk properties (viscosity and TAN) of some lubricants in specific conditions dependent on the water level in the lubricants. The increase of relative humidity always increases wear of the components no matter whether under pure sliding or rolling-sliding conditions, but addition of water in the oil before the tribological test will not always increase wear. It is also observed from XPS results that there is a direct relationship between the oxygen concentration as oxide on the contact surfaces, the layer thickness on the wear scar of post test ball/roller and relative humidity. Also, it is revealed from the results that not only physical parameters but also chemistry must be considered to evaluate the micropitting behaviour, which is found by XPS analysis to be related to the chain length of the phosphate as well as the oxygen concentration as oxide on the wear scar of the surfaces.

The wear rate and the magnitude of friction of commercially available graphites in air have been shown to be dependent on the corrosion resistance of the graphite. In air the wear rate of graphite was observed to increase with increasing temperature up to 6000 C. A very rapid type of wear was found to occur when graphite rubbed against austenitic stainless steel over a certain temperature range. The occurrence of this rapid wear was shown to be dependent on the surface finish of the steel, the composition of the steel, the state of oxidation of the metal, the corrosion resistance of the graphite and on the speed of sliding. It is concluded that this rapid wear is a result of oxidation of the graphite at the rubbing surface which leads to a rapid deformation and work-hardening of the normally soft austenite. Both the wear rate and friction of electrographites have been shown to decrease with increasing temperature in the inert environments of argon, helium and vacuum, though an exception to this general trend was found in one case. The general downward trend with temperature is ascribed to the increased activity of incident reactive species, particularly oxygen, towards the rubbing graphite. The importance of metal oxides in determining the magnitude of graphite wear rate in inert environments was investigated and it was shown that pre-grown oxide films could, in certain Circumstances, reduce wear rate by several orders of magnitude. It was also noticed that when low wear was induced by the presence of a metal oxide no transfer of a graphite film to the metal journal took place. The efficacy of a run-in film in allowing low wear to obtain under normally adverse conditions was investigated and it was shown that the substrate against which the graphite was rubbing was important. Only against copper could a low wear rate be sustained in vacuum after prior running-in in air had taken place. The topography of several rubbed graphite surfaces was investigated using a scanning electron microscope but no firm conclusions could be drawn with regard to particular mechanisms of wear, though agglomerates of very fine particles of graphite were often observed and it appeared, therefore, that a gradual attrition of the ends of firmly bonded crystals had taken place to produce these. X-ray diffraction confirmed that wear debris was amorphous in circumstances of both low and high graphite wear.

The conventional ion plating technique is described and the physical mechanism and energies involved in the technique reviewed. The triode (assisted discharge) ion plating is studied and it is shown to increase the ionization several times. Ion plating with a hollow cathode discharge is studied. The characteristics of the deposited film under these conditions are presented including thickness, adhesion and structure, and a comparison is made with ion plating in abnormal glow discharge. Carbon films have been deposited by both chemical vapour deposition and ion plating using methane cracking and arc and electron beam gun evaporation sources. Triode ion plating has also been used. It is found that the best way for depositing thick carbon films is the electron beam gun method. The optimum plating conditions are determined. The characteristics of the ion plated carbon films are studied. Diffraction studies indicate that the deposited carbon films are graphitic. Full structural details including graphiticity index, lattice parameters, grain size measurements are presented. Triode ion plating produces a more dense structure for carbon films. A pin-on-disc friction and wear rig has been designed and constructed. The friction and wear characteristics of ion plated carbon films have been studied in normal atmosphere and at higher temperature. It is concluded that the friction of ion plated carbon films is slightly higher than that reported for graphites, however, the film exhibits good-wear resistance. A numerical investigation of the relationship between surface topography and friction of ion plated carbon films is presented.

Friction tests were carried out to assess the friction between a human finger and contacting surface, in different conditions. Tests examined the effect of normal force, the area of contact, the effect of triangular and rectangular cross-section ridges and the effect of moisture. The tests found that when a finger is contacting a nominally flat surface, the friction force increases with normal force, following a two part linear relationship. This is associated with a large initial deformation of the finger, followed by a smaller scale deformation, after a certain load. The introduction of water to the contact results in an initial increase, which is followed by a decrease, in friction. There are two principal mechanisms responsible for this increase; water absorption to the stratum corneum, and capillary adhesion. These mechanisms increase friction by increasing the area of contact, and therefore the amount of adhesion. When the finger is contacting a ridged surface, triangular ridges display a higher friction force than rectangular ridges. This is thought to be due to the larger penetration depth that is possible with triangular ridges. The main mechanisms of friction for the triangular ridges are adhesion and interlocking friction. The main mechanisms of friction for the larger, rectangular ridged surfaces are adhesion, ploughing friction and a reduction in friction force due to an energy return from the finger forming back to its original shape. These tests showed that for a large friction force, surfaces should have high, narrow and widely spaced ridges. This, however, is at the expense of consistent friction across the surface. The understanding gained was then applied to the area of rugby ball design. Tests showed that the existing rugby ball surface designs with the highest friction were ones with pyramid pimples. However, rounded pimpled surfaces performed more consistently across all test conditions.

Friction and wear are experienced both in terms of machine operation and finance. They impact, amongst other things, energy consumption and material loss, product manufacture and component maintenance. Liquid lubrication is widely used on machinery interfaces to separate the loaded surfaces, with the ultimate aim of reducing friction and wear from direct metallic contacts. However, in most engineering applications, the lubricant film thickness is not thick enough to fully separate matching surfaces because of too high loads or low speeds. Therefore, the interface contains isolated asperity contacts with the surrounding gaps filled by liquid, which is known as mixed lubrication. The aim of this project is to investigate engineering interfaces using both theoretical and experimental approaches. A statistical mixed lubrication model has been built in this study. The friction force, load sharing proportions, film formation and normal contact stiffness can be simulated for engineering interfaces under varying operating conditions. The model was applied to a greased contact of a landing gear articulating pin joint and an oil lubricated contact of a ball-on-disc. Friction forces, load sharing ratios, contact stiffness, and mean film thickness from asperity contact and lubricant layer have been predicted and compared with experimental measurements. The ultrasonic method was applied to the greased pin joint contact and the oil lubricated ball-on-disc contact. Reflection measurements have been linked to the interface characteristics, including contact pressure, lubricating film thickness and contact stiffness. A start-up process of a ball sliding on disc was studied to extract contributions from asperity interaction and trapped lubricant on the interface. Finally, a shear study on a dry Perspex contact was carried out using the ultrasonic technique. The shear stiffness in the stationary and stick-slip process was studied which presents the shear performance of contacting asperities under normal pressure. Results of these investigations show that the mixed lubrication model and the ultrasonic technique could be used to accurately determine the interfacial characteristics for real engineering contacts. Agreement between analytical model and ultrasonic measurement is found to be good, indicating the applicability of the technique for analysis of contact size, contact pressure and interfacial stiffness.

Scale formation is recognized as one of the major problems affecting production in the oil and gas sector. There are many approaches to remove and prevent scaling with chemical inhibition, chemical scale removers and mechanical methods being the most prevalent ones. Recently the focus has shifted onto more environmentally friendly inhibitors that are less toxic to the environment, thus the development of green inhibitors. Another way forward is to turn to surface engineering - this is a very popular approach in the control of biofouling but only a few attempts have been made to use it for the purpose of scale inhibition. It is fair to say that there is a potential for more widespread study and exploitation of such systems. Biomimetics in surface engineering is receiving more attention as nature provides surfaces with a whole range of functionality. In the present work, microand nano-structured polymers surfaces with the self-cleaning Lotus and antireflective Moth-eye effects have been assessed as potential surfaces able to reduce mineral scale deposition. Calcium carbonate (CaCO3) was deposited onto them and their performance compared with reference stainless steel surfaces. In addition, the anti-scaling performance of three commercially available coatings – DLC, Tech 100 and Tech 23 was also investigated. The surfaces were tested in a rotating cylinder electrode (RCE) under different fluid hydrodynamic conditions i.e. both laminar to turbulent flow. Last but not least, micro-adhesion tests under water were conducted in an attempt to relate deposition tests to the adhesion properties of a single CaCO3 crystal against a surface as a measure of anti-scaling performance.

In this thesis, a high-order finite element scheme, based upon the Discontinuous Galerkin (DG) method, is introduced to solve one- and two-dimensional Elastohydrodynamic Lubrication (EHL) problems (line contact and point contact). This thesis provides an introduction to elastohydrodynamic lubrication, including some history, and a description of the underlying mathematical model which is based upon a thin film approximation and a linear elastic model. Following this, typical nondimensionalizations of the equations are discussed, along with boundary conditions. Two families of problems are considered: line and point contacts. Following a review of existing numerical methods for EHL problems, a different numerical technique, known as the Discontinuous Galerkin method is described. This is motivated by the high accuracy requirement for the numerical simulation of EHL problems. This method is successfully applied to steady-state line contact problems. The free boundary is captured accurately using the moving-grid method and the penalty method respectively. Highly accurate numerical results are obtained at a low expense through the use of h-adaptivity methods based on discontinuity and high-order components respectively. Combined with the Crank-Nicolson method and other implicit schemes for the temporal discretization, highly accurate solutions are also obtained for transient line contact problems using the high order DG method for the spatial discretization. In particular, an extra pressure spike is captured, which is difficult to resolve when using low order schemes for spatial discretization. The extension of this high order DG method to the two-dimensional case (point contact) is straightforward. However, the computation in the two-dimensional case is more expensive due to the extra dimension. Hence p-multigrid is employed to improve the efficiency. Since the free boundary in the two-dimensional case is more complicated, only the penalty method is used to handle the cavitation condition. This thesis is ended with the conclusions and a discussion of future work.

In this thesis, adjoint error estimation techniques are applied to complex elastohydrodynamic lubrication (EHL) problems. A functional is introduced, namely the friction, and justification is provided as to why this quantity, and hence its accuracy, is important. An iterative approach has been taken to develop understanding of the mechanisms at work. A series of successively complex cases are proposed, each with adjoint error estimation techniques applied to them. The first step is built up from a model free boundary problem, where the cavitation condition is captured correctly using a sliding mesh. The next problem tackled is a hydrodynamic problem, where non-linear viscosity and density are introduced. Finally, a full EHL line contact problem is introduced, where the surface deforms elastically under pressure. For each case presented, an estimate of a finer mesh friction, calculated from solutions obtained only on a coarse mesh, is corrected according to the adjoint error estimation technique. At each stage, care is taken to ensure that the error estimate is computed accurately when compared against the measured error in the friction. Non-uniform meshes are introduced for the model free boundary problem. These nonuniform meshes are shown to give the same excellent predictions of the error as uniform meshes. Adaptive refinement is undertaken, with the mesh being refined using the adjoint error estimate. Results for this are presented for both the model free-boundary problem and the full EHL problem. This is shown to enable the accurate calculation of friction values using an order of magnitude fewer mesh points than with a uniform mesh. Throughout this thesis, standard numerical techniques for calculating EHL solutions have been used. That is, regular mesh finite difference approximations have been used to discretise the problem, with multigrid used to efficiently solve the equations, and spatial adaptivity added through multigrid patches. The adjoint problems have been solved using standard linear algebra packages.

This thesis is concerned with an investigation of the vibrational characteristics of oil lubricated journal bearings and, in particular, the instability known as oil whirl, which is a self-excited oscillation induced by the hydrodynamic forces generated in the bearing. The thesis is divided into two parts. In Part 1, linear stability theory is used to determine the critical parameter values at which oil whirl is initiated. This information is conveniently expressed on a two dimensional stability chart, separating regions of stability from those of instability. The vibrational characteristics of a variety of bearing models are contrasted with particular emphasis on the effect of adopting different cavitation boundary conditions at film rupture and the effect of oil film behaviour during journal vibration. An analysis of the single axial groove journal bearing is presented and the effects of groove location and oil supply pressure on the vibrational characteristics of the bearing are examined. In Part 2, attention is focused on the nonlinear aspects of oil whirl, one objective being to determine the motion of the journal beyond its stability threshold. Several nonlinear techniques are employed to analyse the nonlinear equations of motion and to identify different features (bifurcation theory, multiple scaling, the method of averaging and numerical integration). Particular emphasis is placed on examining the structure of periodic solutions of the equations of motion at and close to the position of neutral stability. It is shown that the onset of oil whirl is a bifurcation phenomenon in which the equilibrium position gives way to a small amplitude whirl orbit (limit cycle). Two different types of bifurcation behaviour are possible, depending on the operating parameters of the bearing. Results obtained from the different nonlinear techniques are contrasted and an assessment is made of how suitable these methods are for examining the phenomenon of oil whirl.