Dans les grands systèmes de réfrigération, l’utilisation de réfrigérants comme lubrifiants, à la place des huiles, simplifie la conception du système, l’allège et réduit son impact environnemental. La très faible viscosité du réfrigérant conduit à une épaisseur de film séparant les deux surfaces comparable à leur rugosité. Néanmoins, des travaux expérimentaux avec le réfrigérant R1233zd suggèrent que la lubrification est possible dans ces conditions grâce à la formation d’une couche adsorbée sur la surface d’oxyde de fer. Les analyses expérimentales in situ dans le contact sont très difficiles à cause des conditions de fort confinement et haute pression. C’est pourquoi une approche numérique multi-échelles est développée, afin d’étudier l’impact des réactions physico-chimiques à l’interface réfrigérant-surface sur les propriétés de lubrification. La théorie de la fonctionnelle de la densité est utilisée pour quantifier au niveau quantique, l’adsorption d’une molécule de réfrigérant sur une surface d’oxyde de fer. Des énergies de liaison allant de -0.92 eV à -0.22 eV sont observées et reliées à différents cas d’adsorption. Ces résultats sont exploités pour paramétrer un champ de forces interfacial, qui prédit des structures moléculaires à l’interface, différentes de celles obtenues avec des potentiels basés sur les règles de mélange classiques. Des simulations de dynamique moléculaire utilisant ce champ de forces paramétré confirment l’existence d’une couche fortement adsorbée de R1233zd sur une surface d’oxyde de fer. Avec des surfaces atomiques lisses et seulement 2 nm d’épaisseur de film de réfrigérant, les couches adsorbées résistent à des pressions allant jusqu’à 4 GPa et des vitesses de cisaillement atteignant 100 m/s. Une valeur minimale de 5 molécules de réfrigérant par nm² est nécessaire à la formation de deux couches adsorbées à 0.5 GPa. De plus, des simulations en cisaillement avec une surface rugueuse prédisent une rupture totale du film à environ 13 GPa. / In large refrigeration systems, using the refrigerant as lubricant instead of oil can help to simplify the design, lighten the systems, and reduce their environmental impact. However, the very low viscosity of refrigerants leads to ultra-thin films separating the surfaces, with a thickness comparable to surface roughness. Nevertheless, experiments with the R1233zd refrigerant suggests that lubrication is still possible in that situation thanks to an adsorbed layer formed on iron oxide surfaces. Experimental in situ analysis area is very difficult because of high confinement and high pressure. That is why a multiscale numerical approach is developed here, to explore the impact of chemical reactions and physical processes at the refrigerant-surface interface on large-scale lubrication properties. Density functional theory is used to quantify the adsorption of a refrigerant molecule on an iron oxide surface at the quantum level. Binding energies ranging from -0.92 eV to -0.22 eV are measured and related to different adsorption cases. These results are then used to parametrize an interfacial force field, whose predictions of interfacial molecular structure differs from those obtained using potentials based on standard mixing rules. Large-scale molecular dynamics simulations involving this parametrized force field confirm the existence of a strongly adsorbed layer of R1233zd molecules on iron oxide surface. With atomically smooth surfaces, and a refrigerant film thickness as small as 2 nm, the adsorbed refrigerant layers resists pressures as high as 4 GPa and sliding velocities as high as 100 m/s. A minimum value of 5 refrigerant molecules per nm² is necessary to the formation of two adsorbed layers at 0.5 GPa. Moreover, sliding simulations with a rough surface reveal total film breakdown for ca. 13 GPa.

Cette thèse est consacrée è la modélisation et a la simulation de l’ensemble PISTON /SEGMENT/ CHEMISE, d’un moteur thermique. Dans un moteur, le piston muni de segments est en mouvement relatif dans la chemise. Ce système est lubrifié par projection d’huile, les segments et la surface de la chemise “contrôlent” la quantité de lubrifiant restant sur la paroi. Pour modéliser ce phénomène, le modèle conservatif parabolique-hyperbolique d’Elrod-Adams (P − θ), prenant en compte la cavitation (présence de gaz dans le fluide, aspect multiphasique de l’écoulement), est couplé a un modèle de contact, celui de Greenwood-Tripp (basé sur une approche statistique de la surface). En se restreignant a l’écoulement et au contact, nous négligeons beaucoup de phénomènes physiques pouvant intervenir comme le grippage ou les effets thermiques. Dans une première partie, les phénomènes mécaniques sont étudiés, de la réalisation de la surface des chemises è la modélisation de la physique de la lubrification du contact segment/chemise. Cette étude expose les simplifications effectuées et le choix des conditions aux limites pour la prise en compte de la cavitation en tant que problème a frontière libre, notamment au niveau du débit d’entrée pour simuler un fonctionnement “normal”. Dans une deuxième partie, la mise en oeuvre et la modification de l’algorithme “classique” pour des surfaces mesurées sont décrites en détail. Nous présentons les performances simulées de différentes surfaces, et nous les comparons è des essais effectués par Renault. Dans une troisième partie, des modifications sont introduites au modèle (P − θ) utilisé précédemment afin de rendre l’écoulement cohérent avec le modèle de Navier-Stokes. Bien que ce nouveau problème puisse être posé en dimension 2, l’étude mathématique ne concerne que la dimension 1. On se ramène a un système dynamique dont les inconnues sont les frontières libres. L’unicité de la solution impose l’introduction d’un paramètre artificiel. Le comportement local et/ou global en temps est déterminé par les paramètres géométriques et les conditions aux limites. L’introduction de deux paramètres supplémentaires permet de démontrer l’existence et l’unicité de la solution. Dans une dernière partie, nous comparons le modèle de cavitation proposé avec le modèle P − θ. / This work deals with the modeling and simulation of contact between piston rings and liner of an engine. In the engine, the piston-rings are in relative motion with respect to the liner. This mechanism is lubricated and the purpose of this piston-ring system is to control sealing between combustion chamber and lower part of engine, keeping under control lubricant quantity on the surfaces. We modeled this phenomenon using the Elrod-Adams models (P-θ), which are conservative parabolic-hyperbolic models, taking into account the cavitation phenomenon (the presence of gas bubbles in fluid, so that it can be understood a multiphased flow) coupled with the Greendwood-Tripp model, which models the elastic contact by a statistical approach. When we focus on the modeling of the oil flow and asperity contacts, we neglect many physical phenomena like scuffing and thermal effects. In the first part, we focus on the kinematics of the engine, from the design to the different models to describe a lubricated contact. We explain all the simplifications in the engine body and the boundary conditions we use in the cavitation model to solve it as a free boundary problem, in particular for the choice of the flow rate to simulate a ``normal functioning''. In the second part, we describe the algorithm implementation and the required modifications when using real surface topography. We compare several surfaces and study the influence of simulation parameters, then we compare the result with experimental data obtained by Renault company. In the third part, we modify the (P-θ) model, to have the same flow rate in the cavitation zone as in the Navier-Stokes model. It can be studied in 2-dimensions, however we only explain the mathematical study in 1D. We study this model as a dynamical system for which the unknown variables are the free boundaries. The uniqueness is imposed by the addition of an adjustable parameter. The local and global behavior in time are determined by geometrical parameters and boundary conditions. In the last part, we compare the new cavitation model with the P-θ model.

L'objectif principal de cette thèse est de conduire, à travers une étude théorique et expérimentale, vers une meilleure compréhension des différents effets induits par la texturation de surface dans un contact lubrifié. Le but ultime est de proposer un motif de texture qui permette de réduire le frottement et le niveau de fuite d'une garniture mécanique. L'étude bibliographique a permis d'identifier les différents travaux théoriques et expérimentaux réalisés sur la lubrification en présence de textures, les phénomènes physiques interagissant avec les textures et les différentes méthodes utilisées pour leur mise en forme. Une étude théorique utilisant un modèle conservatif basé sur l'équation de Reynolds est ensuite présentée. Dans la première partie de cette étude, les faces de frottement sont supposées parfaitement parallèles et les effets thermoélastiques sont négligés. Dans la seconde partie, les échanges de chaleur avec les anneaux et les déformations thermoélastiques sont pris en compte. Une étude paramétrique a permis de mieux comprendre l'influence des paramètres géométriques des textures, des défauts de formes et des déformations thermoélastiques des faces sur le fonctionnement de la garniture. En outre, cette étude a permis de définir une texture capable d'améliorer significativement les performances d'une garniture mécanique. Des essais expérimentaux ont ensuite été réalisés avec une garniture mécanique texturée et une garniture mécanique non texturée. Des mesures de couple de frottement et des relevés de température effectués par thermographie infrarouge ont montré que l'utilisation des textures permet de réduire de manière significative la température et le couple de frottement par rapport à une garniture à surfaces lisses. Enfin, une comparaison théorie/expérimentation a permis de valider le modèle développé qui prédit de façon correcte le comportement de la garniture texturée. / The main objective of this thesis is to lead, through a theoretical and experimental study, to a better understanding of the various effects induced by surface texturing in lubricated contacts. The ultimate goal is to provide a texture pattern that reduces friction and leakage of a mechanical seal. The literature review identified different theoretical and experimental works performed on lubrication in the presence of textures, physical phenomena interacting with textures and the different methods used for their manufacturing. A theoretical study using a conservative model based on Reynolds equation is then presented. In the first part of this study, the friction surfaces are assumed perfectly parallel and thermoelastic effects are neglected. ln the second part, heat transfer to the rings and thermoelastic deformations are taken into account. A parametric study then allows bettering our understanding of the influence of geometrical parameters of textures, defects and thermoelastic deformations of the faces on the performance of a mechanical seal. In addition, this study has identified a texture capable of significantly improving the performance of a mechanical seal. Experimental tests were then carried out with bath textured and untextured mechanical seals. Friction torque measurements and temperature measurements achieved by means of infrared thermography have shown that the use of textures allows to significantly reduce heat and friction torque compared with a seal with smooth surfaces. Finally, a comparison theory/experiment validated the developed model that predicts correctly the behavior of the textured mechanical seal.

Made available in DSpace on 2016-12-23T14:08:11Z (GMT). No. of bitstreams: 1 Roberto Balarini Junior - Parte 1.pdf: 4732272 bytes, checksum: 0c0798e2e5b19f7834c4ce1d56156d8f (MD5) Previous issue date: 2013-11-27 / Este trabalho é uma investigação tribológica envolvendo o par cerâmico composto por esferas de nitreto de silício (Si3N4) deslizando contra discos de óxido de alumínio (Al2O3) em água. No total, dez ensaios foram conduzidos com a intenção de reproduzir o fenômeno de Ultra Baixo Coeficiente de Atrito (UBCA) em laboratório, o qual é caracterizado pela obtenção de valores de coeficiente de atrito (&#956;) da ordem dos milésimos (&#956; < 0,01) no regime estacionário. Uma vez alcançado os valores de UBCA, o objetivo principal deste trabalho foi o de investigar o período de running-in, através de uma série de análises em relação ao comportamento do coeficiente de atrito durante o regime transitório, incluindo correlações com algumas variáveis, como rugosidade superficial, erros de batimento axial, íons formados durante o deslizamento e desgaste das cerâmicas. Para isto, as curvas de coeficiente de atrito por tempo foram expandidas para intervalos de tempos pré-determinados e o comportamento de &#956; em cada um destes intervalos foi investigado e comparado entre os ensaios realizados, sendo que o caráter oscilatório do coeficiente de atrito foi inserido nas análises do período transitório. Em geral, foi comprovado que maiores valores de rugosidade superficial resultaram em maiores períodos de running-in e que existe uma tendência de aumento de desgaste com o aumento do tempo de transição. Para todos os ensaios, a taxa de desgaste das esferas de Si3N4 foi superior à dos discos de Al2O3. Em adição, através de comparações entre a medida da soma das rugosidades das superfícies desgastadas com a espessura mínima do filme lubrificante, este trabalho confirma a hipótese de que é necessário um regime de lubrificação misto (hidrodinâmico e limítrofe) para a obtenção do regime de UBCA, sendo que, para a eficácia do modo de lubrificação esperado, estima-se que é necessário concentrações de íons de silício (Si) superiores a 1,3 mg/l, aproximadamente. Esta quantidade de íons Si é supostamente a mínima necessária para a formação de uma camada de sílica adequada para conferir a parcela de lubrificação limítrofe necessária para a obtenção do regime de UBCA / This work is a tribological investigation involving the ceramic pair composed by balls of silicon nitride (Si3N4) sliding against disks of aluminum oxide (Al2O3) under water. A total of ten tests were conducted in order to reproduce the phenomenon of Ultra Low Friction Coefficient (ULFC) in laboratory, which is characterized by obtaining values of friction coefficient (&#956;) below of 0,01 in the steady state. Once reached these values, the main objective of this study was to investigate the running-in period by a series of analyses in relation to the behavior of the friction coefficient during the running-in period, including correlations with some variables such as surface roughness, axial parallelism errors, ions formed during the sliding and wear of samples. For this reason, the curves of friction coefficient versus time were expanded for some predetermined intervals and the behavior of &#956; for each one of these intervals was investigated and compared between themselves, and the oscillatory behavior of the friction coefficient was inserted into the analysis of the running-in period. In general, it was concluded that higher values of surface roughness resulted in longer periods of running-in and that there is a trend of increasing wear with increasing time of transition. For all tests, the wear rate of the silicon nitride balls was higher than alumina disks. In addition, by comparing the measure of the sum of the roughness of the worn surfaces with minimum thickness of the lubricant film, the present work confirms the hypothesis that it is necessary a mixed lubrication (hydrodynamic combined with boundary) to obtain the regime of ULFC and for effective lubrication expected mode it is estimated that is required an ions concentration of silicon (Si) higher than 1.3 mg/l approximately. This amount of ions Si is supposed to be the minimum necessary for the formation of a silica layer enable to confer the boundary lubrication participation for obtaining the ULFC

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-10-19Bitstream added on 2014-06-13T18:41:35Z : No. of bitstreams: 1 alves_mcs_dr_bauru.pdf: 4541684 bytes, checksum: 03e1d27ea6b721a409bebc9862b0e67f (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / É analisada a influência das técnicas de mínima quantidade de lubrificante (MQL), refrigeração otimizada e refrigeração convencional, com diferentes vazões e velocidade de aplicação do fluido de corte, na qualidade das peças produzidas (acabamento, erros de forma, trincas, queima, perda da dureza) com aços endurecidos, no processo de retificação cilíndrica externa de mergulho com a utilização de rebolos superabrasivos com baixa concentração de CBN. Utilizou-se fluidos de corte de origem vegetal, que representam menos riscos à saúde e ao meio. A análise da qualidade das peças foi realizada através da avaliação das variáveis de saída do processo como o comportamento da força tangencial de corte, energia específica de retificação, rugosidade, desvio de circularidade, emissão acústica, tensão residual, análise de microscopias eletrônicas de varredura e microdureza. Com a análise das formas de aplicação e das várias vazões e velocidades do fluido de corte utilizadas encontraram-se condições de lubri-refrigeração que propiciam a diminuição do volume de fluido de corte, diminuição do tempo de usinagem sem prejudicar os parâmetros geométicos, dimensionais, o acabamento superficial e a integridade superficial dos componentes. Em relação as diferentes formas de aplicação do fluido de corte notou-se o melhor desempenho da aplicação otimizada para maiores velocidades mostrando a eficiência de um novo conceito de bocal utilizado. O processo otimizado e o processo MQL foram capazes de manter a dureza superficial e a integridade superficial das peças produzidas. Exceção somente para a condição MQL com vazão de fluido de corte de 40ml/h que produziu trincas e retêmpera superficial. O desvio de circularidade e a rugosidade proporcionada pelos métodos estão dentro de valores recomendados para a retificação sendo que a técnica otimizada... / The influences on surface integrity of the parts (finishing, geometrical errors, cracks, burn, microhardness) and grinding wheel (wear) have been analyzed in this research by employing the minimum quantity of lubrication (MQL), optimized and conventional cooling for hardened parts of steel and superabrasives grinding wheel in the cylindrical plunge grinding process. This study was carried out through the assessment of the process output variables such as the behavior of the tangential cutting force, specific energy, surface roughness, circularity errors, acoustic emission, residual stress, scanning electronic microscopy (SEM) and microhardness. The cutting fluid derived from vegetal oil has been utilized in order to comply with the environmental requirements and thus offering less risk to the health. It could be observed from the analysis on different ways of cutting fluid applications that there are cooling conditions which facilitate the decrease in cutting fluid volume, decrease in grinding time without impairing the geometrical and dimensional parameters, the surface finish and surface integrity of the parts. It could be noted the optimized application for higher velocities has presented the best performance regarding the different applications of cutting fluids. The optimized and MQL processes were able to maintain the hardness and surface integrity of the ground parts. Exception occurend only for MQL condition with flow rate of 40ml/h, which led to cracks and quench on the workpiece surface. Roundness errors and surface roughness are within recommended valus for grinding with the best results obtained for the optimized method (2'mü' for roundness error and 0.5'mü'm for surface roughness) compared with the MQL technique (6.8'mü'm for roundness error and 1.2'mü'm for surface roughness). The process of minimum quantity of lubrication, however, has showed possible... (Complete abstract click electronic access below)

Este trabalho trata de um estudo experimental das respostas de desgaste e de atrito encontradas em um sistema deslizante lubrificado. Para tanto, foram realizados ensaios de deslizamento em um equipamento para ensaios de desgaste, adotando-se o dispositivo pino-contra-disco, para ensaios com movimento relativo rotativo contínuo entre as amostras, e o dispositivo pino-contra-placa, para ensaios com movimento relativo alternado, ou oscilatório, entre as amostras. Os materiais metálicos ensaiados foram pinos de aço AISI 52100 e contra-corpos de aço AISI 8640. O óleo lubrificante foi o mineral de base parafínico, IV 100. Foram variadas as condições de aditivação e de contaminação do óleo lubrificante e foram utilizados dois níveis de carregamento mecânico, determinada pela relação velocidade/carga. O desgaste foi estudado por microscopia óptica e eletrônica de varredura, medição da área afetada pelo desgaste, perfilometria das superfícies desgastadas e análise de óleo. O atrito e o potencial de contato foram monitorados ao longo dos ensaios. Os resultados obtidos mostraram que o desgaste dos corpos metálicos foi sensível ao carregamento mecânico, à aditivação e à contaminação do óleo. Diferenças foram notadas nas morfologias superficiais entre os resultados de desgaste dos ensaios rotativos e oscilatórios. / This work concerns with experimental study of wear and friction responses of lubricated sliding system. Sliding tests were carried out using pin-on-disk wear testing machine for tests with continuous rotating movement, and the pin-on-plate device, for reciprocating tests between specimens. The metallic test coupons were AISI 52100 steel pins and AISI 8640 steel counter-faces. The used lubricant was paraffinic mineral oil, VI 100. The presence of additives and contamination in the lubricant oil were investigated under two mechanical loading levels, determined by the velocity/load relation. The wear was studied by means of optic and scanning electronic microscopes, perfilometry and dimensional analysis of the worn surfaces and oil analysis. The friction and the contact potential were monitored through out the sliding tests. The results showed that the wear of the metallic materials was susceptible to the mechanical loading, the additive and the contamination existence in the oil. It was observed differences among the wear results of the rotating and the reciprocating tests in terms of surface morphologies.

Les principaux mécanismes d'amortissement présents dans les transmissions par engrenages sont étudiés, en se basant sur une analyse transitoire du problème de lubrification élasto-hydrodynamique dans les contacts linéiques. Plusieurs modèles linéaires sont proposés suite à de nombreuses simulations numériques, permettant de prédire l’amortissement du lubrifiant dans les différentes conditions de contact, y compris les situations des pertes de contact momentanées suivies d’impact. Un modèle dynamique d’engrenage à un seul degré de liberté est présenté qui combine les contributions diverses du lubrifiant à l'amortissement structurel représentatif de la dissipation interne des engrenages. Un certain nombre de comparaisons avec des résultats expérimentaux est présenté pour une gamme de conditions de fonctionnement et de géométries d'engrenages, qui prouve la capacité du modèle à reproduire proprement le comportement dynamique des engrenages droits. On montre que l'amortissement associé au lubrifiant contribue essentiellement lors des pertes de contact et des chocs entre dentures se produisant au voisinage des vitesses critiques. Le cas des engrenages hélicoïdaux est analysé différemment du fait de l’absence de perte de contact pour ce type d’engrenage. Un modèle tridimensionnel simple est ainsi développé qui prend en compte la dissipation des différents éléments de la transmission. Un nombre de résultats est présenté qui, d'abord, confirme la contribution majeure de l'engrènement à l'amortissement global des engrenages droits, et, dans un second lieu, montre que les paliers constituent la principale source d'amortissement dans les transmissions par engrenages hélicoïdaux. / The primary damping mechanisms present in geared systems are investigated based on a transient analysis of the elasto-hydrodynamic lubrication problem for line contacts. Several linear models are derived from extensive numerical simulations, which make it possible to simulate the damping caused by the lubricant squeezing by the teeth with and without momentary contact losses and impacts. A one-degree-of-freedom gear dynamic model is set up which combines these lubricant damping sources along with structural damping that reproduces the internal dissipation in gear elements. A number of comparisons with benchmark experimental evidence are presented for a range of operating conditions and gear geometries, which prove that the proposed approach is sound in the case of spur gears. It is shown that the damping associated with lubricant squeezing contributes for the most part when contact losses and shocks between the teeth occur at critical speeds. The case of helical gears is analyzed differently since no contact loss occurs for such gears. A simple three-dimensional model is thus developed which accounts for the dissipation in the mechanical parts surrounding the gears. A number of results are presented which, first, confirm the primary contribution of the gear mesh to the overall damping in spur gears, and second, show that bearings constitute the main source of damping in helical gears transmissions.

De nombreux projets visant à réduire l’impact environnemental global des avions sont lancés au niveau européen. L’un des moteurs étudié pour les avions moyens et longs courriers est le moteur Ultra High Bypass Ratio (UHBR) : un moteur simple corps, double flux, à flux externe fortement augmenté. Le moteur UHBR doit être équipé d’un réducteur épicycloïdal, qui est un composant jamais utilisé dans un turboréacteur jusqu’à présent. L’optimisation d’un réducteur épicycloïdal a conduit à l’utilisation de paliers hydrodynamiques pour supporter les pignons satellites du porte-satellites.Pour une telle application, le palier hydrodynamique subit une déformation très élevée due aux charges de l’engrènement sur le pignon satellite et à l’effet centrifuge engendré par la rotation du porte-satellites. La géométrie optimisée des composants du palier varie avec le comportement thermique et mécanique des pièces, nécessitant la prise en compte d’une modélisation thermoélastohydrodynamique (TEHD).Afin de modéliser précisément ces phénomènes, un modèle conservatif dans la zone inactive en régime TEHD a été développé et validé à l’aide des résultats d’essais de la littérature et des bancs d’essais de Safran Transmission Systems. Les résultats obtenus montrent un double champ de pression dans le palier hydrodynamique du réducteur épicycloïdal, engendré par la forte déformation élastique du pignon agissant ainsi de façon significative sur le comportement dynamique du palier. De plus, l’influence de l’effet centrifuge sur l’huile dans le palier a été également examinée. / Several projects aimed at reducing the overall environmental impact of aircrafts are launched at European level. One of the engines studied for medium and long-haul aircraft is the Ultra High Bypass Ratio (UHBR) engine: a single-body, dual-flow gas turbine, with a greatly increased external flow rate. The UHBR engine must be equipped with an epicyclic reduction gearbox, which is a component never used before in a turbofan engine. The optimization of an epicyclic gearbox has resulted to the use of hydrodynamic bearings for supporting the satellite gears on the planet carrier.The hydrodynamic bearing of such application undergoes high deformations due to the gear contact loads on the satellite gear and to the centrifugal effect generated by the rotation of the planet carrier. The optimized geometry of the bearing components is influenced by the thermal and mechanical behavior of the bearing components, which requires a thermoelastohydrodynamic (TEHD) modeling taking into account the real film thickness under operation.In order to precisely simulate these phenomena, a conservative modeling in the inactive zone, under a TEHD regime has been developed and validated by comparing the predictions to the test results of the literature and of the test benches of Safran Transmission Systems. The results obtained show a double pressure field in the hydrodynamic bearing of the epicyclic reduction gearbox, due to the strongly deformed film thickness, which greatly affect the dynamic behavior of the bearing. In addition, the influence of the centrifugal force on the oil pressure in the oil film was also examined.

O esmalte dental é o tecido mineralizado mais duro do corpo humano; apesar disto, seu desgaste é um problema muito comum. Este pode estar associado aos processos de envelhecimento, ou ainda, ser encontrado em indivíduos jovens, como consequência de atividades parafuncionais, por exemplo, atrição dental. Este tipo de dano pode resultar em prejuízo da função mastigatória e em diminuição da qualidade de vida. Por isto, o desgaste do esmalte dental tem sido objeto de muitos estudos, embora poucos tenham utilizado conceitos tribológicos. Não foi encontrado nenhum estudo que explorasse o desgaste de esmalte e seus micromecanismos oriundos do deslizamento alternado de incisivo contra incisivo, configuração que mais se aproxima do tribossistema real de atrição. O presente estudo tem por objeto investigar o desgaste e seus mecanismos em pares deslizantes de esmalte incisal (configuração pino-plano), selecionados por seus similares valores de dureza e de tenacidade à fratura, submetidos a diferentes cargas normais e lubrificações do meio. Incisivos bovinos foram ensaiados em deslizamento alternado sob duas cargas normais (8 N e 16 N) e quatro modos de lubrificação: saliva natural; saliva artificial; gel lubrificante oral (Oralbalance!, Biotène); e grupo controle sem lubrificação (seco). Durante os ensaios, foram levantadas as curvas de atrito. O volume desgastado e a rugosidade da superfície foram mensurados via perfilometria 3D. Os micromecanismos de desgaste foram analisados ao microscópio eletrônico de varredura. O aumento da carga normal aplicada resultou em aumento do volume de desgaste para todas as condições. Comparando-se ao grupo sem lubrificação, as salivas (natural e artificial) não reduziram o desgaste, mas a lubrificação com o gel foi efetiva para reduzir tanto o volume de esmalte desgastado como o coeficiente de atrito. A relação entre o valor do parâmetro de rugosidade Sq e o coeficiente de atrito não foi linear, nem entre a rugosidade Sq e o coeficiente de desgaste, para todas as condições. Os micromecanismos de desgaste encontrados foram, em ordem crescente de severidade: desgaste da região interprismática (8 N - gel); propagação de trincas interprismáticas (8 N - seco); reações triboquímicas associadas à ação mecânica (8 N - saliva natural e artificial; 16 N - gel; 16 N - saliva natural e artificial); e desplacamento (16 N - seco). / Enamel is the hardest mineralized tissue in the human body; despite that, the enamel wear is a very common problem. The wear damage can be related to aging processes or also be found in young people as a result of parafunctional activities, for example, dental attrition. This type of damage can result in loss of masticatory function and decreased quality of life. Therefore, the wear of the enamel has been the subject of many studies, although few have used tribological concepts. The wear mechanisms of reciprocating sliding pairs from incisor against incisor have not been reported in the literature, this configuration is the one that is closest to the real tribosystem of attrition. The present study aims to investigate the wear behavior and the related mechanisms in reciprocating sliding pairs of incisal enamel (pin-on-flat configuration), selected for their similar hardness and fracture toughness values, with different applied normal loads and lubrication conditions. Bovine incisors were tested in reciprocating sliding with different applied normal loads (8 N and 16 N) and four lubrication conditions: natural saliva; artificial saliva; oral gel lubricant (Oralbalance!, Biotène); and control group (dry). During tests, the friction curves were recorded. The volume loss and the surface roughness Sq were investigated by 3D profilometry. Wear mechanisms were analyzed by scanning electron microscope. The increase of the normal load resulted in an increased volume loss for all conditions. Comparing to the group without lubrication, the saliva (natural and artificial) did not reduce the volume loss, but the lubricant gel was effective to reduce both the volume loss and the coefficient of friction. The relationship between the value of the roughness Sq and the friction coefficient was not linear, nor between the roughness Sq and the wear coefficient for all conditions. In increasing order of severity, the micromechanisms of wear were: wear at the interrod enamel (8 N - gel); crack propagation in the interrod enamel (8 N - dry); tribochemical reactions associated with mechanical wear (8 N - natural saliva and artificial saliva; 16 N - gel; 16 N - natural saliva and artificial saliva); and flake-like wear (16 N - dry).

Ce travail de thèse met en évidence deux phénomènes microscopiques dissipatifs au voisinage de la ligne de contact dans les phénomènes de capillarité et d'adhésion. L'étude s'appuie sur des expériences dynamiques et des modélisations théoriques. La mesure expérimentale de quantités macroscopiques et la théorie hydrodynamique permettent d'extraire les informations dynamiques localisées au voisinage la ligne de contact. Les différents phénomènes dissipatifs localisés au voisinage de la ligne de contact ont pour origines les propriétés des substrats sur lesquels se déplace la ligne de contact. Pour une surface rigide hétérogène, nous avons développé un modèle rhéologique de la ligne de contact fondé sur l'hydrodynamique, permettant d'établir théoriquement l'évolution temporelle de la ligne de contact et de ses déformations. Une décomposition modale fondée sur la réduction de l'énergie par la théorie du chemin de réaction fournit une prédiction quantitative de la dynamique thermiquement activée de la ligne de contact, en accord avec l'expérience réalisée. Pour un substrat déformable, à partir de l'analyse de deux expériences différentes de mouillage dynamique et de l'estimation de la dissipation dans le substrat, fondée sur sa viscoélasticité, nous avons développé une compréhension générale du comportement dynamique d'une ligne de contact sur un substrat viscoélastique. Pour finir, ce modèle de dissipation viscoélastique est appliqué au cas de l'adhésion réversible, où expérimentalement nous mesurons la dynamique de pelage et de recollement sur un substrat viscoélastique. Cette extension à l'adhésion permet de relier les phénomènes interfaciaux en une compréhension générale / This thesis reveals two dissipative microscopic phenomena close to the contact line in the fields of capillarity and adhesion. The study is based on dynamic experiments and theoretical predictions. Experimental measurement of macroscopic quantities and the hydrodynamic theory give access to dynamic information located close to the contact line. The different dissipative phenomena, located close to the contact line, originate from the properties of the substrates on which the contact line moves. For a heterogeneous rigid surface, we have developed a rheological model of the contact line based on hydrodynamics, in order to theoretically establish the temporal evolution of the contact line and its deformations. A modal decomposition based on the reduction of the energy by the reaction path theory allows a quantitative prediction of the thermally activated dynamics of the contact line, in agreements with the experiment carried out. For a deformable substrate, based on the analysis of two different experiments of wetting dynamics and on the estimation of the dissipation in the substrate founded on its viscoelasticity, a general understanding of the dynamical behavior of contact lines on viscoelastic substrates is achieve. Finally, this viscoelastic model is applied to the case of weak adhesion, where experimentally we measured the peeling dynamics from a viscoelastic substrate. This extension to adhesion bridge the gap between different interfacial phenomena into a general understanding