Achieving sustainable lubrication by using environmentally friendly formulated lubricants has became an essential component of the transition process from fossil-powered vehicles to electrified transportation. Mixtures, or aqueous solutions of molecules such as polyhydroxy alcohols, and glycols usually known as green lubricants make it possible to achieve low friction coefficients under different lubrication conditions, which constitutes a potential alternative to improve the tribological performance of moving parts in automotive systems, at the same time that the environmental requirements are satisfied. There is a need to improve the protection against mild-wear and micropitting offered by green-lubricants before consider using them in the transmission gear box of battery electric vehicles BEVs, where their low shear-stress resistance can potentially help to improve the vehicle efficiency. Therefore, this research work aims to gain understanding of the tribological behaviour of rolling-sliding elements under glycerol-based lubrication, with focus on assessing the influence of different glycerol-based lubricant formulations on the wear modes associated to rolling contact fatigue such as micropitting, and macropitting.  Micropitting tests were carried out by using a micropitting rig, with a roller on ring planetary configuration. The evolution of microcracks, and micropitting was studied for several glycerol-based lubricants at different slide-to-roll ratios (SRRs) 5-30%, and different load contact conditions 1.5-2.5 GPa. A comparison against a fully formulated transmission oil has been performed. A relationship between the surface damage morphology and the operating conditions has been established. The lubrication regimes of DLC coated contacts and uncoated contacts in presence of glycerol-based lubricants were investigated through the construction of 3D friction maps, and Stribeck curves in a wide range of rolling speeds, and SRR testing conditions. The capability of two different DLC coating systems to prevent micropitting onset due to rolling contact fatigue in presence of glycerol-based lubricants was studied: Cr/a-WC:H/a-C:H and a-C:Cr.  Under mixed-lubrication regime it was found that a reduction up to 51% of friction can be achieved by using glycerol-based lubricants compared to a commercial transmission oil. The initial low friction coefficients at low contact cycles was attributed to the low pressure-viscosity coefficient of the glycerol-based lubricants. Friction was even further reduced with the increasing contact cycles since glycerol aqueous solutions were found to promote mild-wear, causing a smoothing of the surface asperities and therefore an enhancement of the hydrodynamic effect due a higher lambda ratio (Λ), making possible to trigger superlubricity in the contact. Surface micro-cracking was found to decrease at low SRR values under glycerol-based lubrication contrasted to the contacts lubricated with a fully formulated transmission oil. Once microcracks were nucleated, micropitting progressed faster in the contacts lubricated with glycerol-based lubricants, while micropitting was null or significantly delayed in presence of transmission oil. With the increasing SRR surface microcracks density and micropitting was found to became higher. The reduction of microcracks density with a glycerol-glycol based lubricant was attributed to the adsorption of long glycol molecules on the steel surface that avoid the direct interaction between asperities. The faster micropitting progression was attributed to the presence of dissolved water in the contact. Thin DLC a-C:Cr coatings were shown to significantly mitigate the penetration of surface initiated pits into the steel substrate, which was translated in a lower volume loss. Local micro-delamination was found to be the main reason behind coating failure in presence of glycerol-based lubricants, as a result, pitting took place on the steel exposed areas.

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Thesis (PhD (Mathematical Sciences. Applied Mathematics))--University of Stellenbosch, 2008. / This dissertation contains a detailed report on the results of a research project on the behaviour of a dynamical system consisting of a hoop to which a heavy particle is fixed at the rim. This loaded hoop rolls on a rough surface while remaining in the vertical plane. The motion of the hoop consists of various, possibly alternating, phases consisting of rolling without slipping, spinning or skidding motion and in some cases ends by hopping off the surface. A general mathematical model is developed, consisting of a system of second order ordinary differential equations, one for each of the three degrees of freedom. Analytic solutions are obtained in some cases; otherwise numerical solutions are used. Three specific applications of the general model are dealt with. In the first application the problem of massless hoops is investigated. The main emphasis is on the somewhat controversial question of what happens after the normal reaction becomes zero in a position where the particle is still moving downwards. A new result shows that the hoop can continue to move horizontally in a motion defined as skimming. The second application deals with rigid hoops and a large number of detailed results are presented. Classification schemes for the different types of behaviour are introduced and summarised in the form of phase diagrams. Some emphasis is placed on the rather amazing number of different patterns of motion that can be obtained by varying the parameters. In the third application two elastic models are analysed, with the primary purpose of explaining one aspect of the reported behaviour of experimental hoops, namely hopping while the particle is moving downwards. A chapter on experimental models rounds off the project.

Simulations are powerful and important tools for gaining insight into powder processes. Ultimately, simulations have the potential to replace experiments. Thus, accurate models and insight into the essential factors for descriptions of powder behaviour are required. In this thesis, discrete element method (DEM) simulations of granule flow and compression were evaluated to deduce parameters and potential models essential for the experimental and numerical correspondence. In addition, the evolution in tablet microstructure during compression was studied using mercury porosimetry. Granule flow was measured using angle of repose, discharge rate, and shear. The granular flow depended primarily on particle shape and surface texture due to the mutual influence of these two parameters on the inter-particle forces. Rolling friction stabilised both the heap formation and promoted shear in the elastic quasi-static flow regime. Thus, rolling friction was established to be an essential simulation parameter for the correspondence to experiments. Current compression models often neglect the elastic compact deformation during particle loading. In this thesis, two fundamentally different models were evaluated with focus of including the elastic deformation. The first model comprised a maximal particle overlap, where elastic deformation commences. The second model accounted for the contact dependence and impingement at high relative densities. This model was based on a truncated-sphere followed by a Voronoi extension. The validity of the models was demonstrated by the elastic qualitative correspondence to experimental compressions for ductile materials. In tablets, the void (inter-granular pore) diameter was dependent on the degree of compression. Thus, the degree of compression provides an indication of the tablet microstructure. The microstructure was subsequently observed to be related to the tablet tensile strength as inferred from a percolation threshold required for formation of coherent tablets. In summary, this thesis has shed light onto the potential of simulating flow and compression of granulated pharmaceutical powders using DEM. Continuous work in the area are required to further improve the models to increase the experimental and numerical correspondence.

Improved diagnosis, prognosis and disease follow-up is a fundamental procedure and a constant challenge in medicine.  Among the different molecular biomarkers, proteins are the essential regulatory component in blood; hence, by developing enhanced specific and sensitive molecular tools will gives great insight into the different processes in disease treatment.  In this thesis, we build on the proximity ligation assay to develop and apply new adaptable methods to facilitate protein detection. In paper I, I present a variant of the proximity ligation assay (we call PLARCA) using micro titer plate for detection and quantification of protein using optical density as readout in the fluorometer. PLARCA detected femtomolar levels of these proteins in patient samples, which was considerably below the detection threshold for ELISA. In paper II, we developed and adapted a new method into the in situ PLA methods for detection and identification of extracellular vesicles (EVs) using flow cytometry as readout (a method we call ExoPLA).  We identified five target proteins on the surface of the Evs and using three colors, we identified the EV using flow cytometer. In paper III, we aim to improve the efficiency of in situ PLA by creating and developing new designs and versions of the assay we called Unfold probes Through comparison of detection of protein using in situ PLA versus Unfold probes, we observed considerable decrease in non-specific signals, and also a lower detection threshold. In paper IV, we describe the development of a solid phase proximity extension (sp-PEA) assay for protein detection and quantification. We compared detection of IL-8, TNF-alpha, IL-10 and IL-6 using spPEA and PEA; spPEA demonstrations over 2 orders of magnitudes in the lower detection concentrations by decreased in background noise.

High-temperature, high-pressure (HTHP) conditions are exemplified in ultra-deep petroleum reservoirs and can be exhibited within diesel engines. Accurate pure component hydrocarbon data is essential in understanding the overall behavior of petroleum and diesel fuel at these conditions. The present study focuses on the HTHP properties of toluene since this hydrocarbon is frequently used to increase the octane rating of gasoline and toluene occurs naturally in crude oil. In this thesis experimental densities and viscosity are presented to 535 K and 300 MPa extending the database of toluene viscosity data to higher temperature than previous studies. The data is correlated to a Tait-like equation and a Padѐ approximate in conjunction with a single mapping of the isotherms. Free-volume theory and a superposition of the viscosity in relation to the Leonnard-Jones repulsive force are both used to model the toluene viscosity data. It was found that the data are in good agreement with the available literature data.

Modern automotive applications such as transmission clutch plates, combustion chambers, diesel fuel injector tips, and axle gears and friction plates operate at temperatures that can exceed 250°C and pressures of 40,000 psia. Industrial practice is to add homopolymers and copolymers to base oils to modify bulk fluid viscosity and frictional properties for these demanding applications. However, designing polymeric additives for lubricants and predicting their performance is limited by the lack of available high-temperature high-pressure (HTHP) viscosity and density data needed to test contemporary lubricity models. Thus, a major objective of this thesis is the design, development, and commissioning of a rolling ball viscometer/densitometer (RBVD) capable of simultaneously determining fluid densities and viscosities at temperatures in excess of 250°C and pressures of 40,000 psia. Resulting data may then be generated to directly address the fundamental need for lubricant property data at these HTHP conditions. The design and development of the RBVD is described in detail to highlight the design iterations and modifications utilized to ensure robust operation at extreme conditions. Three significant and novel features of this RBVD apparatus that distinguish and differentiate it from other apparatus of this type are: (1) specially designed metal-to-metal and sapphire-to-metal seated surfaces capable of eliminating temperature- and chemically-sensitive elastomeric seals; (2) use of a bellows piston to eliminate significant temperature and operational constraints; and (3) incorporation of a linear variable differential transducer (LVDT) to simultaneously permit determination of solution density and viscosity. A detailed analysis of initial accumulated uncertainty for the experimental viscosity and density techniques revealed the need for key RBVD modifications. Final data are presented showing that the RBVD is capable of measuring viscosities with an accuracy of ± 2 to 3 percent and densities to ± 0.7 percent, including at the extreme operating conditions targeted. A second objective of this thesis is the measurement of HTHP viscosities of star polymer-solvent mixtures to determine the impact of star polymer architecture on solution viscosity at extreme conditions similar to those that might be experienced in automotive applications. This objective is motivated by current challenges facing industry to identify polymeric additives that can be added to base oils to improve fuel economy and allow for the implementation of novel hardware technology that relies on enhanced lubricant properties. Relative to linear polymers, the unique architecture of star polymers enhances polymer solubility in base oils while having a more favorable impact on viscosity and density properties over a wide range of temperatures and pressures. Data are presented for an industrially-relevant star polymer in octane to assess the impact of the star configuration on solvent viscosity at extreme conditions. The star polymer used in this instance consists of an ethylene glycol dimethacrylate (EGDMA) core with poly(lauryl methacrylate-co-methyl methacrylate) (LMA-MMA) arms. The star polymer has a total weight averaged molecular weight (Mw) and Mw of each arm of 575,000, and 45,000, respectively. The copolymer arms of the star polymer have an LMA-to-MMA mole ratio of 0.6. The results of further viscosity studies are presented for a model system of well-characterized commercially available narrow polydispersity index (PDI) star polystyrenes (PS) in toluene. Each PS is evaluated at a two percent by weight concentration in toluene to evaluate the effect of arm molecular weigh on viscosity. Each three-arm star polymer has arm and total molecular weights ([arm Mw] total star Mw) of ([15,400] 41,200), ([36,000] 97,600), and ([108,000] 305,000). In this instance, the viscosity of toluene increased by more than a factor of three for the star with the highest Mw arms.

During life of railway vehicles, shape irregularities develop on wheels and rails because of wear. The shape irregularities then affect forces in wheel-rail contact and cause further damage of contact surfaces, vibrations and noise and increase risk of derailment. A numerical simulation of railway vehicle motion with more details on contact surfaces geometry was created to investigate dynamic contact loads in wheel-rail contact. A variety of methods can be used to evaluate forces in rolling contact, the method chosen for this study was algorithm CONTACT based on boundary element method. Four studies are presented in this papers: contact loads from a wheel with a flat and with a wavy tread pattern, loads on wavy rail and load in a curve. The first three studies investigated effects of existing wear patterns, the last one looked for cause of common wear pattern developing on rails. Results of the studies with worn components used showed that the worst kind of shape irregularities is a flat present on wheel. This type of shape cause loss of contact and following impacts. The study of ride in curve showed that cause of high wear in curves, especially those with small radii, is caused by vibration of wheelset. This vibration is then caused by different length of inner and outer rail and wheels travelling along a different path.

Multi-pass fusion welding by a filler wire (welding electrode) is normally carried out to join thick steel sections used in most engineering applications. Welded joints in an installation, is the area of critical importance, since they are likely to contain a higher density of defects than the parent metal and their physical properties can differ significantly from the parent metal. Fusion arc welding process relies on intense local heating at a joint where a certain amount of the parent metal is melted and fused with additional metal from the filler wire. The intense local heating causes severe transient thermal gradients in the welded component and the resulting uneven cooling that follows produces a variably distributed residual stress field. In multi-pass welds, multiple thermal cycles resulted in a variably distribution of residual stress field across the weld and through the thickness. These complex thermal stresses generated in welds are undesirable but inevitable during fusion welding. Presence of such tensile residual stresses can be detrimental to the service integrity of a welded structure. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements would result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements.

A recently developed approach, in the area of nonlinear oscillations, is used to analyze the single degree of freedom equation of motion of a oating unit (such as a ship) about a critical axis (such as roll). This method makes use of a closed form analytic solution, exact upto the rst order, and takes into account the the complete unperturbed (no damping or forcing) dynamics. Using this method very-large-amplitude nonlinear vessel motion in a random seaway can be analysed with techniques similar to those used to analyse nonlinear vessel motions in a regular (periodic) or random seaway. The practical result being that dynamic capsizing studies can be undertaken considering the shortterm irregularity of the design seaway. The capsize risk associated with operation in a given sea state can be evaluated during the design stage or when an operating area change is being considered. Moreover, this technique can also be used to guide physical model tests or computer simulation studies to focus on critical vessel and environmental conditions which may result in dangerously large motion amplitudes. Extensive comparitive results are included to demonstrate the practical usefulness of this approach. The results are in the form of solution orbits which lie in the stable or unstable manifolds and are then projected onto the phase plane.