Este trabalho apresenta uma discussão sobre o estudo dos efeitos térmicos e elásticos decorrentes da pressão de sustentação presentes nos mancais. Para tanto, propõe-se um modelo matemático baseado nas equações para mancais curtos considerando a região de cavitação e utilizando o princípio da continuidade de massa. Com isto, deduzem-se as equações para o mancal a partir das equações de Reynolds e da energia, aplicando uma solução modificada para a solução de Ocvirk, sendo as equações resolvidas numericamente pelo Método das Diferenças Finitas. Somado o tratamento de mecânica dos fluidos, o trabalho discute dois modelos térmicos de previsão de temperatura média do fluido e sua influência no campo de pressão, apresentando gráficos representativos do campo de pressão e de temperatura, assim como as diferenças e implicações das diferenças. Para o cálculo de deformação da estrutura, utiliza-se um Modelo de Elementos Finitos para uma dada geometria, fazendo-se uma avaliação da variação do campo de pressão e o quanto essa diferença afeta as demais propriedades do fluido. Por fim, com o modelo completo, calcula-se o quanto esse modelamento para mancais curtos se aproxima de soluções para mancais finitos, com base em resultados da literatura, chegando a desvios quase oito vezes menores que os previstos pela literatura. Além disso, pode-se estabelecer a abrangência do modelo, ou seja, prever as condições em que suas propriedades são válidas e podem ser utilizadas para estudos iniciais. / This work presents a study on thermal and elastic effects resulting from support bearings. It proposes a mathematical model based on short bearing equations within the cavitation region, using the principle of mass continuity. Then, the used equations are deduced from Reynolds and energy equations applying a modified solution for the Ocvirks solution. All the equations are numerically solved by the Backward Finite Difference Method. In addition to the treatment of fluid mechanics, this work discusses two thermal models to predict the average temperature of the fluid and its influence on the pressure field; it also presents the representative charts for pressure and temperature fields, as well as the differences and implications of these ones. To calculate the deformation of the structure, a Finite Element Model is used, considering a specific geometry and an evaluation of the variation of the pressure field is conducted to determinate how this difference affects other properties of the fluid. Finally, the full model is applied to analyse how this modeling for short bearing solutions can be used as an approach for finite bearings. Analysis reaches deviations nearly eight times smaller than predicted by literature data. Furthermore, it was possible to establish the range of the model in which its properties are valid and can be used for initial studies.

Orientador: Katia Lucchesi Cavalca / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T19:28:08Z (GMT). No. of bitstreams: 1 Daniel_GregoryBregion_M.pdf: 2663262 bytes, checksum: f7c1b338ec3a0dad168c82dc8c8d2fc2 (MD5) Previous issue date: 2008 / Resumo: Este trabalho visa analisar o comportamento dinâmico do sistema pino pistão. Por esse motivo, foi desenvolvido um modelo matemático para o mecanismo biela-manivela, considerando a influência do mancal hidrodinâmico da junção biela-pistão. As análises dinâmicas desse sistema foram realizadas utilizando dois modelos distintos. O primeiro modelo foi usado para representar o sistema quando o pino pistão está em contato com a superfície do mancal, assumindo, nesta condição, um comportamento similar aos mancais rígidos (sem folga). O segundo modelo foi empregado para representar o sistema quando o pino pistão está em lubrificação hidrodinâmica. Nesta condição, o pino pistão tem um movimento relativo à biela, o que torna este sistema um problema de múltiplos graus de liberdade. Diante disso, o primeiro modelo foi desenvolvido através da Equação de Movimento de Eksergian, sendo o segundo modelo, desenvolvido a partir do método de Lagrange. O modelo matemático de lubrificação hidrodinâmica foi introduzido com o intuito de obter resultados mais realísticos sobre o comportamento dinâmico do sistema. Este modelo de lubrificação considera as mesmas suposições básicas da teoria de lubrificação de Reynolds. A partir do modelo desenvolvido neste trabalho foram obtidas as orbitas do pino pistão, as distribuições de pressão e as velocidades e acelerações do mecanismo biela-manivela, o que permitiu realizar uma análise preliminar do comportamento dinâmico desse sistema. / Abstract: This work aims to analyze the dynamic behavior of the piston pin system. For this reason, a mathematical model for the slider-crank mechanism was developed, considering the influence of the hydrodynamic bearing of the piston-connecting rod joint. The dynamic analyses of the system applied two distinct models. The first represented the system when the piston pin was in contact with the bearing surface, assuming, in this condition, a similar behavior of rigid bearings (without clearance). The second model represented the system when the piston pin was in hydrodynamic lubrication. Under this condition, the piston pin presented a relative motion to the conrod, what turns this system into a multidegrees of freedom problem. Therefore, the first model was developed by Eksergian's Equation of Motion and the second model was developed by Lagrange method. The mathematical model of hydrodynamic lubrication was introduced to obtain more realistic results under the system's dynamic behavior. This lubrication model considers one of the basic assumptions of the Reynolds lubrication theory. From the model developed in this work were obtained the orbits of the piston pin, the pressure distributions and the velocities and accelerations of the slider-crank mechanism, what allows a preliminary analysis of the dynamic behavior of this system. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

The ageing population has become more active and live longer, these patients require hip replacement surgery at a younger age. Artificial hip implants, consisting of the acetabular cup and femoral head, affect the lives of many people, and the longevity of these implants pose significant concerns (rarely longer than 17 years). To help understand the lubricating performance of such a system, a hip joint model was built based on the Reynolds equation; the model developed simulated hydrodynamic lubrication. A steady-state angular rotation model was built whereby it was concluded that such motion would not support any load due to the anti-symmetric nature of the resultant pressure distribution (anti-symmetric about the axis of rotation). The pressure distribution from the steady-state rotation simulation contained a pressure source and sink which converged to the centre of the cup and whose pressure value increased in magnitude, as the eccentricity ratio increased. Infeasible results were obtained when the intermediary pressure constraint, allowing only positive pressure values, was implemented. The results obtained were not representative of the problem and it is recommended that this constraint not be implemented. The transient walking cycle model showed that a fluid with viscosity of 0.0015Pa.s is not sufficient to support a load in the walking cycle under conditions representative of hydrodynamic lubrication. Increasing the fluid viscosity promoted better results in the hydrodynamic model. Increasing the femoral head radius and decreasing the radial clearance between the components also improves the possibility of hydrodynamic lubrication. It is recommended that the model should be extended to investigate elasto-hydrodynamic lubrication. If possible, the effects of a boundary lubrication model should be investigated, as it is believed to be a major contribution to the lubrication of hip joints. / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Increasing demands for lower emissions from heavy trucks and buses creates new demands on the components in the engine. One such component is the journal bearing which is used at many positions in the engine. Implementing a start-stop system in a truck engine leads to that the crankshaft journal bearing gets worn out too quickly. A journal bearing is a sliding bearing with a constant flow of oil. When the journal starts rotating an oil film is formed between the bearing and the journal, separating the journal from the bearing surface when the rotational speed is high enough. When this happens a hydrodynamic oil film is formed. During start and stop the bearing and journal passes through boundary and mixed lubrication regimes. The increase in starts and stops leads to a vast increase in the time that the bearing is experiencing boundary and mixed lubrication. During these regimes the journal comes in contact with the bearing surface and eventually leads to wear. This thesis has compared two new materials provided by Höganäs AB with an existing bearing as a reference material. The new materials were laser cladded onto bearing shells and sent to Scania for grinding and testing. The thought was to use a start-stop test rig at KTH that simulates start-stop cycles. The reference bearings were first run in the test rig, but when the shells with the new materials arrived it turned out that they would not fit in the test rig. This created the need for a new test method on a short notice and a reciprocating tribometer at Scania was chosen. The tribometer underwent a number of modifications to be able to fit the samples. Five tests with each new material and the reference material were carried out. The tests ran for 60 minutes except for a long term test that ran for 600 minutes. The results showed that the material designated “S”, which had a solid lubricant, had a coefficient of friction similar to the reference material, but produced less wear and could handle a higher load. The thesis has also proved that the start-stop test rig at KTH works well and can deliver reliable results. / På grund av skärpta miljökrav för tunga lastbilar och bussar ökar kraven på motorns komponenter. En av dessa komponenter är radialglidlager som används på många platser i motorn. Implementering av start-stoppsystem i en lastbilsmotor leder till att vevaxellagren slits ut i förtid. Ett radialglidlager är ett glidlager med ett kontant tillflöde av olja. När axeln börjar rotera skapas det en oljefilm mellan lagerytan och axeln. När rotationshastigheten är tillräckligt hög bär oljefilmen lasten och separerar axeln och lagerytan. Då har det bildats en fullfilm. Under start och stopp passerar lagret genom smörjregimerna gränsskiktssmörjning och blandsmörjning. Ökningen av start och stopp leder till en stor ökning av tiden som lagret upplever gränsskiktsoch blandsmörjning. Under dessa regimer är axeln och lagerytan i kontakt vilket leder till nötning. Detta examensarbete har jämfört två nya material från Höganäs AB med ett existerande lager som referens. De två nya materialen påsvetsades på lagerskålar och skickades till Scania för att slipas och testas. Tanken var att använda en start-stopprigg på KTH som simulerar startstoppcykler. Till att börja med kördes referenslagren i riggen, men när lagerskålarna med de nya materialen levererades visade det sig att de inte passade i testriggen. Detta innebar att en ny testmetod behövdes tas fram med kort varsel och valet föll på en reciprocerande tribometer på Scania. Tribometern var tvungen att modifieras för att proverna skulle passa. Fem test med varje material utfördes. Varje test tog 60 minuter, förutom ett långtidstest som kördes under 600 minuter. Resultaten visade att materialet kallat ”S”, vilket inkorporerade ett fast smörjmedel, hade en friktionskoefficient som liknade referensmaterialets, men producerade mindre nötning och klarade av en högre last. Examensarbetet har också kunnat påvisa att start-stoppriggen på KTH fungerar väl och kan leverera konsekventa resultat.

Oil feed grooves are implemented in reciprocating compressor piston applications to assure a constant supply of lubricating oil on bearing surfaces and decrease friction loss. In a hermetically sealed compressor, due to small clearances encountered, oil supply becomes critical in order not to operate in boundary lubrication regime. Due to the small size of the piston and small piston &ndash / cylinder clearance, a partial lubrication regime is present. In the current study, a model that solves Reynolds&rsquo / equation for piston-cylinder lubrication and the average Reynolds&rsquo / equation that considers the effect of roughness on partially lubricated bearing for a compressor piston with oil feed grooves is developed. A parametric study is carried out to investigate the effects of piston design parameters and then arrive at an improved piston performance by using alternative designs for oil feed groove and the other design parameters.

Machines operating in dusty environments, such as mining and civil works, are prone to premature failure, leading to production losses. To address this problem, this research project examines the interaction between solid contaminants and the bearing micro-geometry, in lubricated surface contacts. In particular, it seeks to identify anti-wear additives that are effective in reducing wear under abrasive conditions, making machine elements more dirt tolerant. In general, the influence of antiwear additive is so small that it is difficult to isolate it. Manufactures often make claims about their antiwear products, which are difficult to verify. Hence, there is a need to characterising the antiwear additives available with a well-defined parameter, making it easier for consumers to compare the efficacy of various additives, and be able to select the most suitable additive for a given environment. Effect of micro-geometry parameters such as radial clearance, out-of-roughness and surface roughness was examined and a Film Shape Factor (FSF) – also termed gamma ratio – has been proposed for ensuring adequate separation of journal bearings operating in hydrodynamic lubrication regime, where the out-of-roundness values are higher than the surface roughness values. In this research, an experimental study has been conducted on journal bearings, to examine the influence of five antiwear additives on the bearing wear and micro-geometry. The test additives were provided by the industry partner without revealing their chemical identity or composition; however, these included some of the most commonly used antiwear additives. The tests were performed under three conditions: pure base oil, base oil containing contaminants, and base oil containing contaminants treated with five different additives. The experiments were aimed at choosing one wear measuring technique that evaluates the performance of an individual additive reliably, and based on this technique the additives were characterised. To achieve these objectives, a multi-wear parameter approach (MWPA) was developed, which employed three main wear measurement methodologies, i.e. weight loss, micro-geometry and particle counts –to examine the effect of the antiwear additives. Minimum oil film thickness was also measured to study the lubrication status in the bearing contacts. The MWPA helped in comparing different wear measuring methods, and in selecting the most reliable one. This approach also helped in developing short duration wear tests, thereby saving time, while still getting reliable results without repeating these. Wear experiments were performed on seven sets of bronze bearings and steel sleeve shafts. The test contaminant was 16 micron Aluminium oxide Al2O3 powder mixed in oil with 4% concentration by weight. These solid contaminants were treated with five different antiwear additives to study their influence on the bearings. Bearings were operated such that the minimum oil film thickness in the bearing was equal to the size of the contaminants. These tests were run for a constant sliding distance of 7536m. The results showed that most of the wear measuring techniques do not suit heavily contaminated test conditions. However, the out-of-roundness technique proved to be the most reliable and practical. Based on this technique a methodology was developed which gave a wear characteristic number (N). A unique value of N can be derived for each additive, thereby ranking the additives for their efficacy. The finding of this research provides a better understanding of the methodologies used for measuring wear in journal bearings subjected to dusty environments, and examines the efficacy of each one of these. The wear characteristic number (N) can be used by manufacturers with support from international standards organisations, so that the users can confidently choose the most appropriate antiwear additive for their application. Machines operating in a dusty environment, such as mining industry and civil works are prone to premature failure with subsequent production losses. In response to this problem, this research project examines the interaction between solid contaminant particles and the lubricant film micro-geometry in lubricated surface contacts. In particular, it seeks to identify lubricant anti-wear additives, which are effective in reducing wear under abrasive conditions and thus making machine elements more dirt tolerant.

The internal combustion engine is still at the heart of the vast majority of vehicles manufactured worldwide today. For these applications reciprocating pistons are typically employed to convert the pressures generated by internal combustion into mechanical work required by the vehicle. Of the energy supplied to the engine as a whole approximately 17% is lost by means of mechanical friction. The piston ring - liner and piston skirt - liner conjunctions contribute approximately 30% of the overall friction losses in almost equal proportions. It is, therefore, important to note that reduction in piston assembly friction would have a significant effect on the fuel consumption and, therefore, performance of engines manufactured today. In order to reduce the effect of friction it is of critical importance that the model and predictions made alongside the design of engine components accurately represent the real incycle conditions encountered in practice. Much of the published research to date has excluded the effects of global thermo-elastic distortions on the lubrication of the piston skirt. In cases where this effect has been studied, it has been for relatively low engine speeds or loads on relatively stiff conjunctions. In motorsport applications the expected component lifespans are much shorter than in the usual OEM production vehicles. Reduction in component mass, particularly in reciprocating components has been at the centre of these recent gains. The effect of mass reduction coupled with the increased BMEP observed in high performance engines emphasises the importance of underlying mechanisms of lubrication. This thesis develops the modelling methodology for piston skirt-cylinder liner conjunction for the motorsport and high performance engine applications. It presents a multi-body, multiscale approach to the prediction of the lubrication conditions of the skirt-liner conjunction, incorporating realistic measured boundary conditions. It highlights the effect of inertial loading observed at high speeds in such applications. Using the methodology developed in this work, future improvements in friction may be accurately predicted though the use of the modular boundary and component contributions used throughout. Crucially though, the models created have been scrutinised and verified using instantaneous ultrasonic film thickness measurements non-invasively from the conjunction. One of the key findings of the thesis is that the component stiffness profiles have a significant effect on the dynamics of the piston assembly. The shape of the conjunction at a given instant, and thus the contact condition, is largely governed by the interaction between the themo-mechanical distortion of the contiguous solids, as well as changes in lubricant characteristic responses. The iso-viscous elastic mechanism of lubrication has been identified as being the dominant mechanism of lubrication.

La texturation de surface est une thématique récente qui suscite un certain engouement pour les contacts dynamiques. Pendant de nombreuses années, les tribologues ont privilégié les surfaces lisses aux faibles rugosités pour limiter le frottement. Inspiré des rugosités de surface organisées observées dans la nature, les topologies de surfaces sont désormais axées sur la texturation et la structuration des rugosités. Fort de ce potentiel, de nombreuses études traitent, par une approche numérique, la modélisation de ces surfaces et les études expérimentales sont rares, avec une instrumentation souvent insuffisante pour appréhender tous les phénomènes physiques. Par une approche expérimentale, nous analysons le comportement des butées hydrodynamiques à faces parallèles partiellement texturées. Les 80 capteurs équipant le dispositif d'essais permettent d'apprécier avec rigueur la phénoménologie à l'interface du patin et du film lubrifiant. L'analyse met l'accent sur la capabilité de ce composant à être intégré dans un environnement industriel. Afin d'objectiver les résultats, les campagnes d'essais sont menées sur dix butées hydrodynamiques dont quatre sont munies de texturation. Une comparaison de ces butées facilite leur classement en termes de capacité de charge, de réduction de frottement ou encore de risque d'usure dans les phases de démarrage. Pour les configurations étudiées, les butées texturées ne peuvent concurrencer les butées à poches ou à plans inclinés du point de vue de la capacité de charge. En se référant à une butée à faces parallèles, les butées texturées permettent une réduction du frottement de 30% à faibles charges tandis que pour de fortes charges, les / Surface texturing is a recent topic which has raised a great interest in contact dynamics. For many years, engineers have favored smooth surfaces with low roughness in order to minimize friction losses. Inspired by textured surfaces which can be commonly found in nature, the research in surface topography is now focused on texturing and roughness characterization. Considering the great potential of surface texturing, many research studies analyze this subject, most commonly theoretically, while experimental works are often performed with inadequate equipment which does not allow a proper evaluation of the involved physical phenomena. This study uses an experimental approach in order to analyze the behavior of hydrodynamic thrust bearings with parallel textured pads. The experimental device is equipped with 80 sensors which allow a proper assessment of the phenomenology at the film/pad interface. This analysis focuses on the capability of this textured component to be integrated in an industrial environment. To objectify the results, the tests are conducted on ten hydrodynamic thrust bearings, among which four are textured. The comparison between the performances of these bearings facilitates their classification in terms of load-carrying capacity, friction loss and wears resistance during the start-up period. Results show that for the studied configurations, the textured thrust bearings cannot compete with pocketed or tapered land thrust bearings in terms of load-carrying capacity. In the case of parallel thrust bearings, surface texturing can help to reduce friction up to 30% at low loads while for heavy loads, their performance is equivalent or even lower than that of

Lors de diverses opérations de maintenance, des dégradations au niveau des rotors et des organes de supportage du groupe turbo-alternateur ont pu être constatées. Celles-ci se traduisent souvent par la présence de rayures au niveau des paliers hydrodynamiques, synonymes de fortes discontinuités dans le film d'huile. C'est dans ce contexte que s'inscrivent ces travaux de thèse. L'objectif est d'avoir une meilleure compréhension et prédiction de leur impact sur le fonctionnement du palier. Pour cela, les paliers à géométrie fixe sont étudiés théoriquement et expérimentalement. L'étude théorique présente un modèle de résolution en régime thermoélastohydrodynamique (TEHD) permettant de prendre en compte les déformations introduites par les champs de pression et de température. Le développement d'un code capable de faire des calculs en régime hydrodynamique (HD) pour des paliers à géométrie fixe a été réalisé. L'étude expérimentale permet d'étudier le comportement d'un palier à deux lobes symétriques pour diverses positions et profondeurs de rayure placée sur l'arbre. Pour tous les cas, différentes configurations de charge et de vitesses sont testées, 25 au total. Les résultats obtenus pour les cas rayés permettent de mettre en avant l'importance de la profondeur de la rayure sur le comportement du palier. Pour les cas de fonctionnement réalisés, il apparaît que les champs de pression sont plus fortement impactés par la présence d'une rayure que les champs de température. Ces résultats sont comparés à ceux obtenus par le calcul avec l'utilisation d'un code interne à EDF qui permet la résolution de problèmes en régime TEHD. / During various maintenance operations in power plants, some new issues have come to light. One of these issues is the degradation of the supporting and guiding components for the rotating shafts. The degradation has resulted in scratches on bearings which leads to discontinuities of the oil film. The operator of the plant should provide a fast diagnosis of the influence of these scratches. The aim of the work is to examine these issues, to acquire a better understanding of physical phenomenon and to improve numerical predictions. Theoretical and experimental studies have been done for plain journal bearings. The numerical model is based on a thermoelastohydrodynamic (TEHD) resolution that allows to take into account solid deformations induced by the pressure and temperature fields. A computer code has been developed to solve the hydrodynamic (HD) problem. An experimental study has been performed on a two lobe journal bearing with a scratch on the rotating shaft at two scratch locations and for several scratch depth. For all of these configurations, local pressures and temperatures have been measured for different rotational speeds and applied loads. The scratch depth is one parameter that affects the most the journal bearing behavior. It influences more significantly the pressure field, with a drop of pressure near the scratch, than the temperature field. Those results have been compared to the numerical results obtained with an internal EDF software that can provide TEHD solutions.

This master’s thesis describes the influence of conformity on friction in rolling bearings. The coefficient of friction is measured on an experimental machine - Mini Traction Machine 2 – using ball-on-disc method. The results are plotted in graphs which showing the dependence of the coefficient of friction at spin-to-roll ratio for specific conformity, normal load and speed in the contact area. The influence of load, speed or different lubricant viscosity is verified for a given value of conformity. Experimentally obtained data are compared with the mathematical model developed in MatLab, within this thesis.