yes / Advanced engineering polymers of the Polyaryletherketone (PAEK) family with carbon fibre reinforcement are finding application in engineering systems as tribological bearing surfaces under severe operating conditions that cyclically move the polymer into and beyond the glass transition temperature region. To support such an application, the friction in high speed and low load PAEK-steel sliding contacts was investigated both unlubricated and lubricated with a trinonyl trimellitate ester, a base fluid for high temperature industrial lubricants. Four polymers in the PAEK family, PEEK, PEK, PEKEKK and PEKK, with 30%wt of carbon fibre whiskers were tested against an AISI 4140 steel disc. When unlubricated, low friction depended upon the formation of a PAEK transfer film on the steel disc and when this became unstable in the glass transition region the friction increased to much higher levels with associated polymer surface damage. Frictional heating due to the high sliding speed dominated the differences in glass transition behaviour between the four PAEKs. When lubricated, the lubricant film controlled friction and there was no significant effect of the glass transition of any of the PAEKs. The irreversible nature of the glass transition in PAEKs in such tribological applications, due to high surface damage at high temperature, means that it is essential to ensure effective lubrication in both fluid film and boundary lubrication. / Innovate UK, Knowledge Transfer Partnership

The flow properties of polydimethylsiloxane (PDMS) melts at room temperature were studied by measurement of lubrication forces using an Atomic Force Microscopy (AFM) colloidal force probe. A glass probe was driven toward a glass plate at piezo drive rates in the range of 12 – 120 μm/s, which produced shear rates up to ~10⁴ s⁻¹. The forces on the probe and the separation from the plate were measured. Two hypotheses were examined: (1) when a hydrophilic glass is immersed in a flow of polymer melt, does a thin layer of water form at the glass surface to lubricate the flow of polymer and (2) when a polymer melt is subject under a shear stress, do molecules within the melt spatially redistribute to form a lubrication layer of smaller molecules at the solid surface to enhance the flow? To examine the effect of a water lubrication layer, forces were compared in the presence and the absence of a thin water layer. The presence of the water layer was controlled by hydrophobization of the solid. In the second part, the possibility of forming a lubrication layer during shear was examined. Three polymer melts were compared: octamethyltrisiloxane (OMTS, n = 3), PDMS (n _avg = 322), and a mixture of 70 weight% PDMS and 30 weight% OMTS. We examined whether the spatial variation in the composition of the polymer melt would occur to relieve the shear stress. The prediction was that the trimer (OMTS) would become concentrated in the high shear stress region in the thin film, thereby decreasing the viscosity in that region, and mitigating the shear stress. / Master of Science

The journal bearing is a critical machine element typically used to support rotating motion in high speed machinery. Through the generation of a hydrodynamic pressure in its thin lubricant film,which is usually in the order of 10-100μmthick depending on the diameter of the journal itself, the bearing is able to withstand large loads, both statically and dynamically, while having a very low rate of wear. It is of course essential that these components provide for a safe operation with as little wear and frictional losses as possible and it is therefore of great interest to develop simulation models of constantly increasing accuracy. Typical relevant quantities when designing a bearing are the load carrying capacity, metal/oil temperature, minimum film thickness, stiffness, damping and power loss. Classical lubrication theory builds upon the Navier-Stokes equations which, with the thin film approximation, can be reduced to a single equation which governs the hydrodynamic pressure build up in the lubricant. Since the problem now has been reduced to solving a single non linear partial differential equation in 2 dimensions, a significant advantage in terms of simulation time compared to the full set of Navier-Stokes equations can be enjoyed with an, in most cases, insignificant error of approximation. However, with time, as the need for bearings capable of operating at higher loads,speeds and with new designs involving more complex geometries, such as, for example, textured surfaces, the applicability of classic thin film theory should not be taken for granted, especially not when there is an increasing amount of turbulence involved. The purpose of the work contained in this thesis is to develop and asses the performance of a state of the art 3D TEHD model using the commercial finite element multi physics software COMSOL Multiphysics. Of special interest is the assessment of the Menter Shear Stress Transport (SST) turbulence model, which is a widely used, standard, 2-equation RANS eddy viscosity model, in predicting characteristic values for a bearing operating in the transition range between laminar and turbulent flow. A comparative study is carried out where the present model is benchmarked against experimental data on a large 4 pad tilting pad journal bearing. The present model is also compared to one of the classic models based on thin film theory. The present model is also used to study the influence of the geometry that constitutes the leading edge groove in a tilting pad journal bearing on the turbulence levels. Finally the possibility of using a shear thinning lubricant for reducing the bearing power loss is investigated. The calculations were all performed using the resources of the super computer cluster at HPC2N at Ume ̊a University. The results clearly show the inadequacy of the SST turbulence model when performing calculations on a bearing operating in the transition range between laminar and turbulent flow. Moreover, the model predicts slightly higher average values of turbulence in a leading edge grooved bearing compared to a conventional one, yet a higher maximum value in the latter.

It is desirable to build a single one-cylinder testing engine capable of manipulation so that it can test lubricating oils for wear, corrosion and tendency to oxidation and detergency, and give reproducible results. The purpose of this investigation is three-fold: (1) To install the control accessories required for control of the engine test conditions, and assemble the one cylinder, two-stroke cycle engine as a unit to be used in conducting the tests, (2) To determine the breakdown characteristics of a solvent refined, asphalt base oil at varying conditions of temperature and load in the test engine, and (3) to correlate the breakdown characteristics of the oil with the performance of the test engine so as to rate the engine as a possible test unit for evaluation of lubricating oils. / Master of Science

La plupart des montres mécaniques sont composées d’un échappement à ancre Suisse. Cet organe se situe à la fin du rouage et sert à entretenir et à compter les oscillations du balancier-spiral. Par l’intermédiaire de l’interface ancre / roue d’échappement, il est soumis à des sollicitations parfois extrêmes induisant un rendement faible, d’environ 35%. En outre, le maintien du lubrifiant au contact est délicat et les frottements occasionnés peuvent provoquer une usure prématurée des éléments du système. La première partie de ce travail a consisté au développement d’une démarche d’investigation et de compréhension du fonctionnement du contact entre l’ancre et la roue d’échappement par l’intermédiaire des concepts du triplet et du circuit tribologique. Une visualisation en temps réel du contact, par caméra rapide, a ainsi permis d’obtenir l’évolution de la vitesse réelle des corps en contact. Parallèlement, l’analyse des composants à différents instants de fonctionnement ont conduit à la détermination des débits de 1er et 3ème corps. Par ailleurs, afin de mieux comprendre le comportement tribologique local du contact, un modèle dynamique par éléments finis de l’échappement à ancre Suisse a été développé. A la suite de cette étude, un scénario relatif à la vie du contact a été proposé afin de décrire les différentes phases de fonctionnement de l’échappement. Malgré le rôle clé de la couche de 3ème corps formée pendant le vieillissement par l’activation du débit source, elle génère un débit d’usure qui peut être néfaste pour le mécanisme de montre. Ce résultat amène, par conséquent, à la nécessité de formuler et de réaliser un troisième corps « optimisé ». Dans une seconde partie, une optimisation du comportement de ce 3ème corps a donc été recherchée afin d’atteindre (à terme) une fiabilité à 10 ans et une usure contrôlée. Pour ce faire, deux technologies de lubrification du contact, i.e. fluide et solide, ont été utilisées. La lubrification fluide a été améliorée par texturation des surfaces. La puissance et le nombre de tirs laser ont ainsi été fixés afin de respecter les formes et dimensions des textures imaginées pour le triplet tribologique étudié. Afin de s’affranchir de l’assèchement en lubrifiant fluide du contact au cours du temps, une lubrification solide a été introduite par imprégnation de solides lamellaires et dépôt d’un revêtement « dur » sur la roue d’échappement. Grâce au circuit tribologique et par l’intermédiaire de la création d’un débit source initial et d’un débit d’usure faible, une première optimisation de la couche de 3ème corps formée a été intuité. Une meilleure compréhension du contact entre l’ancre et la roue d’échappement a été apportée. Cette compréhension a permis de passer d’une démarche essais / erreurs existante à une démarche scientifique de proposition de solutions pour l’optimisation du triple / Most of mechanical watches are composed of a Swiss lever escapement. This mechanism is located at the end of the gear train and consist in counting and maintaining the oscillations of the balance wheel. It is subject to extreme solicitations, mostly located at the interface anchor / escapement wheel, inducing a low yield of about 35%. Besides, the difficulty of keeping lubricant within the contact can create wear and induce harmful consequences for the system. The first part of this work involved developing an investigation and understanding approach of the contact between the anchor and the escapement wheel through the concepts of Tribological triplet and circuit. A real-time visualization of the contact, through high-speed camera, succeeded in obtaining the evolution of the real speed of contact bodies. At the same time, components’ observations at different operating times resulted in the evaluation of 1st and 3rd bodies’ flows. Furthermore, in order to understand the local tribological behavior of the contact, a dynamic finite element model of the Swiss lever escapement was developed. Following this study, a scenario of the contact life was proposed in order to outline the different phases of the functioning of the escapement. Despite the key role of the 3rd body layer formed during aging by activating the source flow, it generates a wear rate that can be harmful to the watch mechanism. Therefore, it is necessary to formulate and realize an “optimized” third body. In a second part, an optimization of this 3rd body’s behavior was sought in order to reach a 10-years’ reliability and a stabilized wear. To do this, two lubrication technologies of the contact, i.e. fluid and solid, were used. Fluid lubrication has been improved by surface texturing. The power and the number of laser pulses were determined in order to respect the shapes and dimensions of the textures designed for the studied tribological triplet. To overcome the drying up of lubricant along time, the solid lubrication was investigated by impregnation of lamellar solids and deposition of a “hard” coating on the escapement wheel. Thanks to the Tribological circuit and through the creation of an initial source flow and a low wear flow, a first optimization of the 3rd body’s layer formed has been assumed. A better understanding of the contact between the anchor and the escapement wheel has been provide. This understanding made it possible to go from an existing trial / error approach to a scientific approach for the optimization of the Tribological triplet. A stabilization of the wear and an optimized’s third body were obtained by impregnating a MoS2 solid lubricant on the escapement wheel.t. Une stabilisation de l’usure et un troisième corps « optimisé » ont ainsi été obtenus.

With industries aiming at higher efficiencies, lightweight parts, and easier manufacturability there has been a recent trend of replacing the metallic materials with polymeric materials and its composites. Particularly in the automotive industry, there is a demand of replacing metallic material of bushes and bearings with polymer based materials (PBM). For these heavy performance requirements (as in automobiles), the commonly used industrial polymers like Acetal and Nylon fail to provide good mechanical and tribological performance. High-performance polymer like Polyphenylene Sulfide (PPS) is a relatively newer material and shows a potential of being a PBM alternative for metallic bearings in automobiles if their tribological performance can be improved.  One of the ways of improving the tribological performance of the polymer is by the addition of filler material, hence making a polymer composite. In this study, we used Short Carbon Fibre as micro-reinforcement material and Nano-diamonds and Graphene Oxide as nano-reinforcement material to make PPS composites. The varying mechanical and tribological behaviour of PPS composites with different weight percentage of reinforcement materials was investigated. The optimum composition of the reinforcement materials was identified, which resulted in significant improvement in mechanical and tribological properties of the base material.

De nombreuses hypothèses sont classiquement utilisées pour décrire le comportement du fluide dans un contact lubrifié : film continu, viscosité constante dans l’épaisseur, film mince, fluide newtonien… Or, certaines s’avèrent erronées dès lors que l’on s’intéresse aux contacts Elasto- HydroDynamiques fortement glissants ou à la répartition du lubrifiant en sortie de contact. Une approche numérique originale, basée sur un retour aux équations de la mécanique des fluides générale et prenant en compte le couplage fluide/solide et les effets thermiques sont proposés ici dans le but d’apporter des éléments physiques supplémentaires aux modélisations usuelles. Dans un premier temps, l’influence des effets thermiques sur l’évolution du frottement dans les contacts Thermo-EHD est mise en évidence. La présence d’un minimum de frottement pour le cas du glissement pur est expliquée par l’analyse des transferts thermiques entre le lubrifiant et les solides. L’origine des modifications locales d’épaisseur de film observées et l’existence même d’une épaisseur de film lubrifiant pour les cas de vitesse d’entraînement nulle sont alors reliées à la présence d’un fort gradient de viscosité dans l’épaisseur de film. Une comparaison qualitative avec des éléments expérimentaux de la littérature est réalisée, validant les tendances obtenues. Dans un second temps, l’écoulement à surface libre du lubrifiant en périphérie du contact est étudié expérimentalement puis numériquement par une méthode à interface diffuse. Le rôle des effets capillaires est analysé et les résultats numériques confrontés à des résultats issus de la littérature. Un bon accord est obtenu tant qualitativement que quantitativement. Validé par l’étude numérique diphasique (air/lubrifiant) réalisée, un modèle analytique simplifié est alors développé, prédisant une loi de répartition du lubrifiant en sortie de contact. La zone de sortie des contacts EHD est ensuite traitée par un modèle de cavitation vaporeuse et la prise en compte nécessaire de l’air environnant est discutée. Enfin, une première modélisation tridimensionnelle de l’écoulement à surface libre du lubrifiant autour d’un contact ponctuel est réalisée mettant en avant l’influence des effets capillaires et la faisabilité d’une telle approche. / Classically, many assumptions are used to model the fluid behaviour in a lubricated contact : continuous film, constant viscosity across the film thickness, film thickness is very thin compared to other contact dimensions, Newtonian lubricant... However, some of them are not well-founded for the study of Elasto-HydroDynamic contacts with high sliding or to estimate the liquid distribution at the exit of the contact. An original numerical approach, based on the general fluid mechanics equations and taking into account the fluid/solid coupling and thermal effects, is developed here in order to give more physical insights to the usual modelling. First of all, the thermal effects are shown on the friction coefficient evolution for Thermo- EHD contacts. A minimum value is found concerning the friction value for the pure sliding case. It is explained by analyzing the heat transfer between the solids and the lubricant. The origin of the resulting local modifications of the film thickness and the existence of a film thickness for zero entrainment velocity cases are related to the presence of a high viscosity gradient through the film. A qualitative comparison is performed with experimental data from literature, validating the results. Second, the free surface flow of the lubricant around the contact is experimentally and numerically studied with a diffuse interface method. The capillary effects on the air/lubricant meniscus position are analyzed and quantitatively compared with experimental data from literature. Good agreements are found. An analytical approach is then developed, based on the numerical study of the two-phase flow. An analytical law predicting the liquid distribution is obtained. The exit area of EHD contacts is then investigated with a vaporous cavitation model highlighting the necessity of taking into account the effects of surrounding air and surface wettabillity. Finally, a first approach of the tri-dimensional two-phase flow is performed, showing the capillary effects on the interface location.

The increasing worldwide demand for more eco-friendly materials with improved tribo- logical properties has expanded the interest in research on polymer as an alternative for conventional metal/metal contacts under dry lubrication. Specifically, UHMWPE, a semi-crystalline polymer, has shown interesting tribological properties for low demanding applications, allied with excellent recyclability, manufacturability and low cost. Though, its limited working temperature range and wear resistance claims reinforcements to modulate these drawbacks. Metal sulfides, such as MoS2 and SnS2 are well-known 2D materials with outstanding thermal, mechanical and tribological properties which have the potential to increase the range of applicability of UHMWPE. Therefore, this work aims to investigate the influence of metal sulfide-based micro-particles on UHMWPE-based composites properties under reciprocating movement and to determine further acknowledgements about the mechanisms involved. The results showed that the incorporation of fillers im- proved in hardness and wettability, whereas thermal properties were conserved. Though, it is noted that chemical degradation processes (oxidation and un-saturation reactions) that occurred during the manufacturing negatively influenced the composite’s tribological response. Higher reinforcement weight percentages (10%) promoted metal-sulfides agglomeration, increased degradation and ultimately diminished wear resistance. Overall, optimizing the amount of filler in the matrix at 5 wt% provided its homogeneous dispersion and a good interface with the matrix, leading to enhancement in wear resistance up to 62%. Indeed, the incorporation of metal-sulfide based materials in the UHMWPE matrix revealed an excellent solution where wear resistance improvements are needed.

This master thesis is focused to make education exercise on simulation equipment, tilting pad apparatus and air bearing apparatus. Exercise are, for better understanding problems, completed about exercise measurement viscosity. Were to be proposed three separate exercise for exercising, which were to be well – tried. Measured data from stations for sliding bearing will students confront with computed data. To every exercise are created instructions for exercising, educational presentation and poster to arrangement.

This diploma thesis deals with an application of the finite element method on elastohydrodynamic (EHD) lubrication simulations. Commercially available software COMSOL is used for the computation, while two different modules for modeling EHD lubrication are described in a detail. Firstly, a new approach using the module Thin-Film Flow is developed, considering and describing some limitations of this approach. This is the very first published work dealing complex with EHD simulation in Thin-Film Flow module. In the second part of the thesis, there was created a model of line contact using the module for the introduction of partial differential equations (PDE). The model is partially verified with available works for different values of the input parameters. Subsequently, the velocity effect of the contact surfaces on the pressure and the lubricant thickness in contact is analyzed. Finally, the last part is examines the influence of the values of some parameters on the final value of the contact pressure and the lubricant thickness, as well as on numerical stability of the entire model.