AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today. / AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

This thesis presents a series of studies pertaining to tribological, thermal, kinetic and slurry utilization aspects of chemical mechanical planaraization processes. The purpose of this work is to both develop a better method of characterizing the tribological mechanisms during polishing, as well as propose methods by which slurry utilization efficiency can be increased in order to minimize environmental hazards and operational costs associated with polishing without compromising the desired polish outcomes. The first study was conducted using a modified version of the generic Stribeck curve using real-time shear and down force data collection at 1,000 Hz. This investigation served to provide a better understanding of the tribological and thermal mechanisms associated with polishing copper and tungsten blanket wafers on an industrially relevant soft pad. A multitude of gradual yet continuous changes in sliding velocity and polishing pressure were applied during polishing. Results indicated that polishing on the soft pad produced stable coefficient of friction (COF) values entirely within the "boundary lubrication" regime, while copper polishing on a hard pads produced a tremendous spread of data and resulted in both “boundary lubrication” and "mixed lubrication" regimes. In addition, the average pad surface temperature showed a linear relationship with the product of the COF, sliding velocity, and downward pressure for all copper and tungsten polishes on both soft and hard pads. Another study in this thesis investigated slurry availability and the extent of slurry mixing for three different slurry injection schemes. An ultraviolet enhanced fluorescence technique was employed to qualitatively measure slurry film thicknesses atop the pad surface during polishing. This study investigated standard pad-center point slurry dispensing and a slurry injection system (SIS) that covered only the outer half of the wafer track. Results indicated that the radial position of slurry injection and fluid interactions with the SIS greatly influenced slurry mixing and availability atop the pad. Silicon dioxide removal rates were also found to increase as slurry availability increased. Using a combination of standard pad-center slurry dispensing and a half-wafer track SIS resulted in similar silicon dioxide removal rates as standard pad-center slurry dispensing but at a 40% lower slurry flowrate. The final study in this thesis investigated the effects of ultrapure (UPW) water dilution of a ceria-based slurry on silicon dioxide removal rates. Results showed that pre-mixing the slurry and UPW increased the removal rate with dilution up to a slurry to UPW ratio of 1:7.5 due to the increasing presence of Ce3+ via the reduction of Ce4+ by UPW. Further dilution yielded a plateau in the removal rate trend as additional UPW reduced the coefficient of friction (COF) and the temperature during polishing, causing the benefits of increased ceria-silica binding to be offset by mechanical limitations. Mixing the slurry directly at point-of-use at the dispense nozzle resulted in a removal rate trend that was highly similar to pre-mixing, however, removal rates were higher at every dilution ratio. A novel slurry injection system (SIS) was employed at various rotation angles as measured from the leading edge. The SIS angles produced different retaining ring bow wave thicknesses, which led to varying extents of dilution and, by extension, removal rates. The SIS at -8° produced the highest removal rates of all angles. A third dilution ratio test was performed using point-of-use mixing through the SIS at the optimum angle of -8°, which resulted in a similar removal rate trend as pre-mixing and pad-center dispense point-of use mixing, but with dramatically higher removal rates at each dilution ratio. The ability to attain higher removal rates could potentially allow integrated circuit (IC) manufacturers to either reduce polishing times or reduce slurry consumption, subsequently reducing slurry waste and creating a more environmentally benign semiconductor manufacturing process.

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.

A thesis submitted to the Faculty of engineering. University of Witwatersrand. Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy Pretoria, 1995 / This thesis describes a study of the friction and wear characteristics of a range of oxide and silicon-based ceramics sliding against AlSI 440C stainless steel, as well as various sliding combinations of two types of De Beers polycrystalline diamond (PCD), namely Syndite and Syndax, To facilitate the former work, a high-speed reciprocating sliding test machine with computerized data acquisition and control was developed. It was confirmed that under water-lubricated sliding, the oxide ceramics (alumina, PSZ, 3YTZP, and Ce-TZP) showed higher friction coefficients and Weal' rates than the silicon-based ceramics (Sialon and silicon nitride). This was related to different levels of adhesion and the formation of metallic transfer films. For the zirconia ceramics, increased transformation toughening was associated with increased surface fracture damage and metallic film formation. In general, the metallic transfer films were beneficial, protecting the underlying ceramic and dominating the friction and wear behaviour. The superior performance of the silicon-based ceramics was related to the formation of lubricious tribofilms containing silicon oxides and hydroxides. Experiments with synthetic mine water as lubricant demonstrated that the presence of significant amounts of chloride and sulphate in the water generally reduced friction and wear. This was tentatively explained in terms of reduced adhesion and the promotion of iron oxide and hydroxide formation. It is suggested that the influence of sulphate may be more important in thi'3 regard than that of chloride. The tribological behaviour of self-mated Syndite PCD sliding couples is dominated by the formation of Co-rich trlbofilms, which nrc associated with increased friction coefficients and reduced load carrying capacity (LCC). Syndax, which employs silicon as the binder phase, shows lower friction coefficients anti higher LCe under both dry and water-lubricated sliding conditions. Mixed Syndax/Syndite couples show superior performance to self-mated Synditc tinder dry sliding conditions, but 110 improvements in the presence of water. The former effect is related to the preferential removal of Co 11'0111 the Syndite surface to the Syndax / GR 2017

L’oxygène liquide est utilisé principalement dans le domaine de la propulsion spatiale et la connaissance des mécanismes d’usure dans cet environnement est donc indispensable pour le développement des différents moteurs. Ce domaine est mal connu car l’oxygène liquide est un des rares fluides à associer trois propriétés spécifiques pouvant influencer les mécanismes du contact. Ces trois propriétés tribologiques spécifiques sont l’état liquide, la réactivité et la température cryogénique. Une campagne d’essais a été réalisée dans le cadre du projet européen In Space Propulsion-1 (ISP-1) afin d’identifier l’influence de chacune de ces propriétés sur un contact PCTFE/métal. Plusieurs comportements ont ainsi été explicités. D’abord, la présence de lubrification limite a été mise en évidence dans le cas d’un contact en azote liquide. Ensuite,la rugosité de la piste s’est révélé un paramètre fortement influent sur l’usure, les frottements ainsi que sur la formation d’un film de transfert de PCTFE sur le disque. Ce transfert de PCTFE a une grande influence sur le contact. Son épaisseur ainsi que sa régularité influencent directement les mécanismes du contact et plus particulièrement l’usure. Enfin, ces films de transfert se forment rapidement et leur épaisseur augmente avec la distance de glissement, changeant ainsi la vitesse d’usure. Tous ces mécanismes sont très dépendants de la température de surface au niveau du contact qui peut modifier les paramètres des matériaux. L’étude a donc été complétée en comparant une évaluation théorique de la température de surface avec une extrapolation de cette même température à partir des données mesurées dans le pion pendant la réalisation des essais. / Liquid oxygen is mainly used for space propulsion. The knowledge of the wear mechanisms in this environment is therefore essential for the development of the engines. Wear mechanisms in liquid oxygen are not well known because liquid oxygen is one of the few fluids combining three tribological properties that can influence contact mechanisms. These three specific tribological properties are the liquid state, the reactivity and the cryogenic temperature. A test campaign was performed in the frame of the European project In Space Propulsion-1 (ISP-1) to identify the influence of each one of these properties on the PCTFE/metal contact. Several behaviors have been explained. First, boundary lubrication has been demonstrated for contactin liquid nitrogen. Then, we confirmed that disk roughness was greatly affecting wear, friction and PCTFE transfer film formation on the disk. This PCTFE transfer film has a great influence on the contact properties. Its thickness and its regularity directly influence contact mechanisms, especially wear. Finally, the transfer film is easily formed and the thickness increases with the sliding distance, thereby changing the wear rate. All these mechanisms are highly dependent on the surface temperature at the contact interface, which can modify the materials parameters.The study was completed by comparing a theoretical evaluation of the surface temperature with an extrapolation of this same temperature from the measured data in the pin during the experiments.

O presente trabalho aborda a modelagem unidimensional do regime misto de lubrificação para problemas caracterizados por condições genéricas de carga, velocidade e geometria. Tal modelagem foi desenvolvida a partir de modelos clássicos, tais como a equação de Reynolds relacionada com os fenômenos hidrodinâmicos, e as formulações de Greenwood & Williamson e Greenwood & Tripp utilizadas na descrição do contato de asperezas entre superfícies rugosas. A cavitação do fluido lubrificante foi considerada através dos modelos tradicionais de half-Sommerfeld e Swift-Steiber (Reynolds). Com relação à reologia do lubrificante, as possíveis variações de viscosidade devidas ao próprio campo de pressões hidrodinâmicas e às altas taxas de cisalhamento do fluido (\"shear-thinning\") foram também contempladas na modelagem proposta. Adicionalmente, quatro filtros não convencionais de rugosidade foram propostos e implementados com o objetivo de eliminar as distorções verificadas na definição do plano (ou linha) médio(a) de referência em topografias caracterizadas pela presença de vales profundos, tais como as obtidas após a aplicação da técnica de texturização a laser (LST). A definição adequada desse plano (ou linha) médio(a) de referência é imprescindível para a correta determinação dos parâmetros necessários para a utilização dos modelos de contato de Greenwood a partir das metodologias consideradas neste trabalho. Toda a modelagem unidimensional foi implementada em um programa computacional denominado VTL (\"Virtual Tribology Laboratory\"), cujo código fonte está disponível para qualquer usuário interessado em realizar simulações envolvendo sistemas lubrificados caracterizados por perfis com geometrias genéricas. A validação da modelagem unidimensional proposta foi verificada utilizando os resultados experimentais de um teste de atrito com movimento alternado (\"reciprocating test\") publicado na literatura. Como resultado, a correlação experimental dos resultados calculados com o programa VTL foi excelente. O programa VTL foi também utilizado para verificar a possibilidade da redução de atrito em sistemas lubrificados envolvendo superfícies planas texturizadas, como as obtidas utilizando a técnica de texturização a laser (LST). Devido à limitação unidimensional da modelagem proposta, as fileiras ortogonais de 7 micro-cavidades foram aproximadas como sendo ranhuras (\"grooves\") de dimensões fixas. Para tais situações, apesar da limitação comentada acima, a modelagem unidimensional proposta pode ser utilizada para analisar qualitativamente o mecanismo de micro-mancais responsável pela geração de pressão hidrodinâmica entre superfícies paralelas caracterizadas por esse tipo de micro-texturas. / This dissertation focuses on one dimensional modelling of the mixed lubrication regime for problems with general conditions of load, velocity and geometry. Such modelling was based on classical models, such as the Reynolds equation related to the hydrodynamic phenomena, and the Greenwood & Williamson and Greenwood & Tripp formulations for the description of the asperity contact between rough surfaces. Cavitation of the lubricant was considered adopting the well-known half-Sommerfeld and Swift-Steiber (Reynolds) models. As for the lubricant rheology, the viscosity-pressure dependence and viscosity-shear-thinning effects were considered. Furthermore, four non-conventional roughness filters were conceived and implemented in order to eliminate the distortions observed on the definition of the reference mean plane (or line) of topographies (or profiles) with deep valleys, such as those obtained with the laser surface texturing (LST) technique. The proper definition of the reference plane (or line) is indispensable for the calculation of the Greenwood\'s contact parameters according to the methodologies used in this work. The complete one dimensional modelling proposed was implemented as a computational program named Virtual Tribology Laboratory (VTL), an open source code available for any user interested in performing simulations of lubricated systems with generic profiles. In order to validate the one dimensional model, experimental results of a frictional reciprocating test published in the literature were considered for comparison. The correlations between the experimental and simulated results calculated with VTL were excellent. Simulations using the VTL program were also performed in order to evaluate the friction reduction potentialities of textured surfaces (LST). Due to the one dimensional model limitations, grooves were considered instead of micro-cavities (dimples). In such scenery, regardless the above mentioned limitations, the one dimensional modelling proposed yielded good qualitative descriptions of the micro-bearing mechanism that generates hydrodynamic load carrying capacity between parallel textured surfaces.

A marcação por feixe laser em superfícies é utilizada para assegurar a identificação e a rastreabilidade em biomateriais. A texturização via feixe laser confere maior aderência às superfícies dos dispositivos médicos implantáveis. Este trabalho teve o objetivo de avaliar o comportamento da superfície do aço inoxidável austenítico ABNT NBR ISO 5832-1 submetido à marcação e texturização com feixe laser de fibra óptica, alterando-se a frequência dos pulsos; frente ao seu comportamento biomecânico, por meio de: ensaios de resistência à tração, fadiga e desgaste; verificar a susceptibilidade à corrosão localizada, por ensaios eletroquímicos em solução que simula os fluidos corpóreos; e caracterizar a sua microestrutura. Os tratamentos alteraram a rugosidade e a dureza dos biomateriais em função do aumento da frequência dos pulsos. A microestrutura e composição química das superfícies sofreram mudanças que afetaram diretamente a camada passiva dos aços inoxidáveis. Este efeito foi comprovado com o uso de SVET, XPS e caracterização de propriedades eletrônicas do filme passivo. Os dois tipos de tratamentos implicaram em aumento de susceptibilidade magnética das superfícies. Os parâmetros utilizados para as marcações e texturizações não causaram diminuição na viabilidade celular, de modo que não apresentou citotoxicidade mesmo após incubação prolongada. Este biomaterial mostrou-se adequado perante os ensaios biomecânicos, uma vez que os tratamentos a laser, nas condições utilizadas, não induziram a formação de tensões superficiais de magnitude capaz de levar à fratura por fadiga, indicando vida em fadiga infinita; tampouco se pôde relacionar a região de fratura por tração com as marcações a laser. O volume de desgaste diminuiu em função do aumento da dureza produzido pela elevação da frequência do pulso nas texturizações. O caráter visual das marcações e texturizações por feixe laser foi assegurado após a maioria dos ensaios realizados. / Laser beam marking is used to ensure biomaterials identification and traceability. The texturing imparts greater adhesion to the surfaces of implantable medical devices. The aim of this work was to evaluate the surface behaviour of the austenitic stainless steel ABNT NBR ISO 5832-1 marked and textured by optical fiber laser beam using selected parameters, changing the pulse frequency; in face of its biomechanical behaviour, through tests of tensile strength, fatigue and wear; verify the localized corrosion susceptibility by electrochemical tests in a solution that simulates the body fluids; and analyze microstructural changes. The treatments performed altered the biomaterials roughness and their micro hardness as a function of the increase of the pulse frequency. The microstructure and chemical composition of the surfaces underwent changes that directly affected the passive layer of the stainless steels, triggering the corrosion process. This effect was evidenced by SVET, XPS and characterization of electronic properties of the passive film by the Mott-Schottky technique. These two types of laser treatments increased the surfaces magnetic susceptibility. The parameters used for the marking and texturing did not induce a decrease in the cellular viability of the samples, as no cytotoxicity was showed even after prolonged incubation. This biomaterial was adequate on the biomechanical tests, since the laser treatments, under the conditions used, did not induce the formation of surface tensions of magnitude capable of leading the fatigue fracture, indicating infinite fatigue life; the region of fracture by tension could not be related to the laser marking. The wear volume decreased as a function of the increase in micro hardness produced by the increase of the pulse frequency in the texturings. The visual character of the markings and texturings was assured after the majority of the tests performed.

Embreagens de prensas mecânicas, principalmente as de forja a quente se caracterizam por um intenso regime de trabalho com espaços muito curtos entre acionamentos. Muitas das embreagens apresentam desgaste acentuado obrigando a paradas frequentes para manutenção. Neste trabalho são discutidos os princípios de funcionamento de prensas excêntricas e os parâmetros de projeto de embreagens e freios. Pontos importantes são: o balanço entre torque de operação, número de inserções por minuto e a dissipação de calor. É feita uma breve revisão da literatura sobre compósitos, lonas e seu comportamento. Discute-se a diferença das premissas de projeto de uma lona automotiva e a lona para uso industrial com alto número de aplicações por minuto. Apresenta-se um pressuposto quanto ao processo de transmissão de calor na embreagem e o que influência no desgaste da mesma, relacionando-o com a pressão de contato. Nas manutenções se verificam resíduos (debris) diferentes sugerindo regimes diferentes de desgaste. Há um resíduo preto que caracteriza um regime severo de desgaste. Pode-se associar esse resíduo ao fenômeno da degradação da base polimérica que compõe a lona. A degradação da base polimérica é causada pela alta temperatura de operação dessas embreagens. Em ensaios simples de pino e disco consegue-se reproduzir desgaste das lonas, que comprova o observado na prática e as condições que isso ocorre. Finalmente são apresentadas sugestões para o dimensionamento das embreagens e cuidados necessários no projeto de freios e embreagens. / Mechanical press clutches, especially clutches for hot forging presses have a hard working cycle with a little time between engagements. Many of those clutches present a severe lining wear, needing frequent maintenance stops. This work is discusse, the basics of eccentric presses and the clutch design parameters. Important points are: the balance between operation torque, engagements per minute and heat dissipation. This also presents a short literature review regarding composites and linings. It is discussed the design baselines differences between automotive linings and this specific case. It is presented a hypothesis about the heat transfer process in the clutch and how its related with wear, associating it with the contact pressure. In maintenance it is found different kinds of wear debris, suggesting more than one wear regime. The black debris indicates a severe wear regime. This debris can be associated to the lining polymeric matrix degradation. The polymeric matrix degradation is caused by the high op eration temperatures in these clutches. Based on simple pin-on-disc tests can be obtained results that show what is practical observed and the conditions this occurs, proving the hypothesis. Finally are presented suggestions for clutch dimensioning and necessary project cares.

O meio corporativo, principalmente quando se trata de montadoras automotivas, é carente de conhecimento dos fatores que podem influenciar o processo de união entre pares tribológicos. Quando há um fim específico, como o tema deste trabalho: assegurar níveis de controle capazes de eliminar os riscos de uma vedação deficiente na câmara de combustão com custo mínimo, tal carência é ainda maior. O estudo da tribologia inerente à união entre cabeçote e bloco do motor diesel é fundamental para se compreender a que ponto é possível garantir a melhor estanqueidade possível, especialmente no que esteja relacionado ao processo rotineiro de aperto na linha de produção. Nesse sentido, a investigação proposta neste trabalho tem o claro objetivo de propor melhores condições técnicas de vedação ao caso particular da união entre cabeçote e bloco do motor de forma a eliminar / minimizar qualquer influência externa durante o aparafusamento do par supracitado. Adicionalmente, o conhecimento aqui exposto poderá ser difundido a muitas outras aplicações similares nas quais a fixação aparafusada está atrelada a funções que não apenas de fixação, podendo estas estarem inclusive em outros universos do produto, tais como motores, cabinas, eixos e transmissão. / The automobile corporate field has a lack of knowledge when the subject is related to tightening specific issues, especially regarding tribological studies. When there is a specific goal as this thesis theme: ensure all the control levels to eliminate sealing deficiency risks inside combustion chamber in a low investment cost, the needs are even higher. The tribological study between diesel engine block and its cylinder heads assembly is essential to comprehend what is necessary to have the best possible sealing, mostly when it\'s related to the routine on the assembly tightening process. Thinking on that, this work has the goal to propose the best condition on fastening technique that guarantees the sealing to any superficial topography roughness. Additionally, the acquired knowledge will be spread to other similar applications that are not unequally associated to bolted joints, but also in other vehicle universes, such as engines, cabs, axles and transmissions.

Healthy articular joints exhibit remarkable lubrication due in large part to the complex rheological and tribological behavior of the synovial fluid (SF) that lubricates the joints. Current approaches that seek to elucidate such remarkable lubrication usually focus on the roles of high molecular weight SF components such as lubricin and hyaluronic acid but frequently overlook the role of serum albumin (SA), although it represents 90% of the protein content of SF. In this thesis, we used the Surface Forces Apparatus to investigate in detail the structural and tribological response of SA thin films when sheared between model surfaces and subjected to a large range of shearing parameters. Our data indicate that, under shear, SA films reproduce closely the shear response previously reported for SF, i.e., film thickening and formation of numerous long-lived aggregates accompanied by low friction and efficient surface protection against damage. More specifically, our detailed investigation of shear parameters reveals that (i) strong anchoring of SA to surfaces promotes the formation of large rod-like shaped aggregates that enable rolling friction and keep surfaces far apart, preventing damage, (ii) aggregation mechanism is irreversible, which makes aggregates long-lived (though mobile) in the contact, and (iii) aggregate formation only occur when SA was sheared above a ‘critical’ amplitude Ac and a critical shear velocity Vc. Collectively, our results provide experimental evidence of the role of globular proteins, such as SA, in lubrication and establish a correlation between shearing parameters, formation and stability of aggregates, low friction and wear protection. Although our findings are based on experiments involving rigid, nonporous surfaces hence can hardly be generalized to compliant and porous cartilage surfaces, they are applicable to other rigid tribosystems such as artificial joints and will certainly advance our understanding of joint implants’ lubrication in SF mediated by protein aggregation, with implications for future design of artificial joints and therapeutic interventions.