Dissertationen zum Thema „Couche de lubrification“
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Trifa, Mohamed. „Nanorhéologie du contact sphère-plan avec couche mince interfaciale“. Ecully, Ecole centrale de Lyon, 1999. http://bibli.ec-lyon.fr/exl-doc/TH_T1780_mtrifa.pdf.
Der volle Inhalt der QuelleThe surface force apparatus developed at E. C. L. By A. Tonck and J. M. Georges is frequently used in the characterisation of confined fluid (such as lubrification oil or polymer solution). The exploration of such experimental results requires a precise analysis of the contact problem between an elastic place and an elastic sphere separated by a thin interfacial layer which may be considered eleastic, viscous or viscoelastic. Previous works in this direction (F. Auslender) leads to a generalised Reynolds equation describing, under imposed harmonic vertical displacement, the sphere plane contact with an heterogeneous viscoelastic compressible interfacial layer. In this work we intend to account, in the context of the previous analysis, the deformation of the elastic substrate. In order to clarify the roles of the film compressibility and the substrate deflection, we have studied two simple configurations : the first one is the case of an homogeneous elastic solid as interfacial layer, the second one is the case of a compressible Newtonian viscous fluid as interfacial layer. By reffering to experimental results, we have identified the rheological characteristics for three types of lubricant oils. The interface heterogeneity has been represented by two parietal solid layers with the same characteristics, separated by a fluid bulk. In order to obtain more information on the parietal layers rheology, we have studied their contact, assuming them to obey to hyperelastic behaviour laws associated to compressible Mooney - Rivlin elastic energy
Damiens, Bruno. „Modélisation de la lubrification sous-alimentée dans les contacts élastohydrodynamiques elliptiques“. Lyon, INSA, 2003. http://theses.insa-lyon.fr/publication/2003ISAL0037/these.pdf.
Der volle Inhalt der QuelleThe life of lubricated mechanisms is a function of the lubricant film thickness separating the contacting solids. The degree of lubricant starvation affects this film thickness and the life of the mechanisms. A free boundary model has been adopted. The lubricant distribution in the inlet of the contact is used as a boundary condition. The "multigrid" and "Multi-Level Multi-Integral" techniques, used to solve the equations describing the problem, are briefly exposed. The pressure field and the deformed geometry of the surfaces are obtained on the computational domain. This solution allows the validation of an analytical model developed to study the ejection flow and to quantify this flow in the boundary layer surrounding the contact. The flow is governed by the width of the boundary layer. This width, determines the contact response to a lubricant starvation. The dimensionless width can also be used to predict the persistence of local lubricant starvation, in a particular mechanism
Damiens, Bruno Lubrecht Antonius A. „Modélisation de la lubrification sous-alimentée dans les contacts élastohydrodynamiques elliptiques“. Villeurbanne : Doc'INSA, 2004. http://docinsa.insa-lyon.fr/these/pont.php?id=damiens.
Der volle Inhalt der QuelleRmili, Yosra. „ÉTUDE DE LA DILATANCE DE REYNOLDS DU BÉTON ET DE SON EFFET SUR LA FORMATION DE LA COUCHE DE LUBRIFICATION DANS LES TUYAUX DE POMPAGE“. Electronic Thesis or Diss., CY Cergy Paris Université, 2024. http://www.theses.fr/2024CYUN1283.
Der volle Inhalt der QuelleConcrete pumping process is important in the construction sector, facilitating the transport of fresh concrete to the casting site, even in difficult-to-access areas. This technique enables the achievement of considerable heights and distances. However, this process presents challenges. Therefore, accurately predicting the pumpability of concrete appears to be essential. Indeed, concrete pumpability relies on its rheological properties and its ability to form a lubrication layer (LL) during its flow through pipes. Accordingly, it is worthy to mention that mastering the rheology of concrete and understanding the characteristics of the LL is important, especially considering that the mechanisms of LL formation remain not well understood.This project focuses on investigating Reynolds dilatancy (RD), a potential mechanism involved in LL formation, and aims to highlight the key parameters governing it. The first part of the study introduces the development of a new method to assess shear-induced variations (RD) at free-surface flow. This method, although more reliable for conventional vibrated concrete (CVC), it does not fully explore this mechanism. Consequently, a new empirical device, the CRD-Test, was designed to evaluate the RD of self-compacting concrete (SCC) subjected to various scenarios under free-surface and pressurized conditions, simulating real casting and pumping processes. In this second part of the study, SCC is considered as a biphasic mixture of coarser particles (> 1.25 mm) in a fluid matrix of fine mortar (< 1.25 mm). Moreover, the new experimental device, named CRD-Test, offers wide range of shear and pressure levels. It is based on a modified coaxial cylinder tribometer, with a rotational speed ranging from 0 to 3 rps, and an air pressure regulator from 0 to 300 kPa. The RD phenomenon is manifested by fluctuations in lateral pressure measured at the outer cylinder of this apparatus and it was investigated through new indices.Experimental results reveal that RD values were found to be in good agreement with the workability and design parameters of the investigated concrete mixtures. Concrete with low fluidity values exhibited high RD indices under both free-surface and pressurized shear conditions. Furthermore, a biphasic approach highlights correlations between RD and the characteristics of aggregates with a diameter greater than 1.25 mm, as well as the viscoplastic characteristics of the fine mortar (i.e., the suspending phase). Moreover, RD results are mainly affected by the relative packing density of coarse aggregate during pumping process. Finally, Reynold values were in good agreement with flow regime characteristics, particle dynamics, and shear-induced particle migration indices. According to established correlations, dynamic segregation can significantly influence the mechanisms of LL formation during concrete pumping at low shear rates, illustrating the importance of Reynolds dilatancy in this process. However, at higher shear rates, dynamic segregation has been observed to negatively impact RD values, thereby increasing the risk of blockage during concrete pumping
Maupas-Zarrad, Hanène. „Lubrification des micromécanismes“. Ecully, Ecole centrale de Lyon, 1995. http://www.theses.fr/1995ECDLA020.
Der volle Inhalt der QuelleThe silicon-made and nickel-made micromecanisms realized until now have all the major disadvantage to wear very fast. In order to lubricate such micromecanisms, the idea is to graft on the rubbing surfaces organic monolayers, that have a few nanometers of thickness. The objective of the study is the development and the optimization of this technique of lubrification
De, Feo Modestino. „Impact du vieillissement de l'additif MoDTC sur ses propriétés tribologiques pour les contacts acier-acier et DLC-acier“. Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0054/document.
Der volle Inhalt der QuelleEuropean legislation on vehicle emissions continues to become more severe to minimize the impact of Internal Combustion Engines (ICE) on the environment. One area of significant concern in this respect is the reduction of friction losses resulting in reduced emissions and as well as higher fuel efficiency and lower fuel consumption. To decrease these losses, several approaches have been made particularly at design of mechanical parts stage and at experimental level to optimize lubricant components. A great contribution to solve the problem can be given by the optimization of the additives package blended into the engine lubricants. The molybdenum dithiocarbamate (MoDTC) is the additive showing the best tribological performance by acting as friction modifier. It decomposes under high temperatures and pressure, forming layered structures on the engine surfaces. However, the use of effective friction reducing additives to achieve low boundary friction coefficient is not enough to have great engine fuel efficiency. In addition, in fact, it is needed also to maximize their durability, preventing premature consumption or depletion of these additives. It has been shown, in fact, that the friction reduction performance of MoDTC is sensitive to engine operating time and that is related to the degradation of MoDTC itself. In the first part of my thesis we tried to get a good comprehension of the chemical mechanisms of MoDTC ageing and to study the impact on the tribological properties. The chemical bulk oil characterization of MoDTC blended into the base oil when subjected to thermo-oxidative degradation allowed to propose a new hypothetical chemical pathway followed by the friction modifier molecules during the ageing process. At the same time, these findings were linked to the impact of the MoDTC degradation on its tribological properties. As reported in literature, another MoDTC drawback is its strong antagonism with DLC coating. In fact, when DLC-involving contacts are lubricated by MoDTC-containing base oil, a catastrophic DLC wear is produced. For this reason, in the second part of the project a multi-techniques approach has been adopted to get a better understanding of this wear mechanism. The combination of all the findings allowed to propose for the first time a new wear mechanism based on the formation of molybdenum carbide species inside the contact. A strong chemical interaction between the molybdenum-based species formed on the steel counter-body and the carbon of the DLC material has been supposed, leading to the formation of MoC species. All the results found are discussed to clarify the correlation between degradation time, tribological performance and tribofilm characterizations in both steel/steel and DLC/steel contact
Auslender, François. „Nanorhéologie des couches minces confinées application aux appareils à forces de surface“. Ecully, Ecole centrale de Lyon, 1996. http://www.theses.fr/1996ECDL0042.
Der volle Inhalt der QuelleDoki-Thonon, Thomas. „Thermal effects in elastohydrodynamic spinning circular contacts“. Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00749882.
Der volle Inhalt der QuelleMatta, Christine Martin Jean-Michel. „Lubrification des couches minces de carbone adamantin non hydrogéné Supraglissement avec les alcools /“. [S.l.] : [s.n.], 2009. http://bibli.ec-lyon.fr/exl-doc/cmatta.pdf.
Der volle Inhalt der QuelleSoullier, Jérémie. „Monocouches auto-assemblées d'acides phosphoniques comme revêtements lubrifiants“. Montpellier 2, 2007. http://www.theses.fr/2007MON20125.
Der volle Inhalt der QuelleMatta, Christine. „Lubrification des couches minces de carbone adamantin non hydrogéné : Supraglissement avec les alcools“. Ecully, Ecole centrale de Lyon, 2008. http://www.theses.fr/2008ECDL0006.
Der volle Inhalt der QuelleLang, Stéphane. „Multifunctional properties of nanostructured ZrO2-based coatings for tribological applications“. Université Louis Pasteur (Strasbourg) (1971-2008), 2005. http://www.theses.fr/2005STR13010.
Der volle Inhalt der QuelleThe loadings applied to engine components are increasing with the demand for more efficient, safer, and environmental friendlier cars. On the opposite to coatings for cutting applications, the future coatings should also protect the counterpart and reduce the friction between the bodies. In the past decade a new type of wear protective films -called nanocomposite coatings- showed promising results in terms of hardness and fracture toughness. Most of the investigations were performed with nitride or carbide-based materials. Oxides were less studied because of their brittleness, but these materials would offer the corrosion and temperature stability required in the future engines. In this work, we proposed an investigation of a nanocomposite coating based on oxides for tribological applications in various environments. We choose ZrO2 as oxide for high temperature applications and copper as surrounding. The properties of this coating were extended with the addition of carbon as solid lubricant material. First, we optimized the pulsed magnetron sputtering for the deposition of nanoparticles. This experience was applied to the deposition of ZrO2/Cu nanocomposite coatings. The Zr-Cu-O-C coatings were optimized for tribological applications under various environments. The film structure was correlated with the mechanical properties. The tribological behavior of this coating was investigated in various environments and wear conditions. The enhanced ion bombardment during the reactive sputtering was obtained by pulsing the cathodes, providing a high sputtering power to the targets, and applying a negative bias to substrate. Using these conditions, 10 nm-particles were captured. This experiment was verified in the ZrO2/Cu coatings with t-ZrO2 particles smaller than 20 nm. The insertion of 35 atomic percent carbon in the nanocomposite structure increased the hardness to 30 GPa and reduced the COF to 0. 15. The hardness of this coating was stable in annealing tests up to 500°C. The structure investigations showed the presence of ZrO2 and ZrC particles inserted in a matrix of copper and a-C:H. This coating presented a low COF independent of the humidity in sliding tests without lubricants. The impact resistance was assured at high loads for medium durations and at low loads for long durations
Fontaine, Julien. „Elaboration, caractérisation et tribologie de couches minces DLC (diamond-like carbon) pour la lubrification des mécanismes spatiaux“. Ecully, Ecole centrale de Lyon, 2000. http://bibli.ec-lyon.fr/exl-doc/TH_T1850_jfontaine.pdf.
Der volle Inhalt der QuelleLubrication of onboard space mechanisms is a key technological issue, considering the functional and operational requirements. This study aims to broaden the performances of solid lubricants already used in spacecraft, like MoS2. Current solid lubricants exhibit a short lifetime and a high sensitivity to environment, and they may pollute surrounding equipment due to wear debris formation. Among the thin coatings which arouse strong interests in various scopes (microelectronics, optics, biomedical. . . ), Diamond-Like Carbon (DLC) coatings present a very large spectra of structures and compositions, that can be tuned by process type and parameters. We focused our research on the optimization of a range of DLC coatings that would be likely to meet the requirements of at least one. Thus, in collaboration with the HEF group, we have deposited and adjusted the composition and structure of a functionally graded layer based on titanium, carbon and hydrogen (Ti/TiC(H)/a-C:H) by an hybrid PVD/PECVD deposition chamber. These coatings were obtained on lab samples as well as on real mechanisms, like bail bearings. We have shown that low and noiseless friction under high vacuum were related to the hydrogen content in the top-layer, which should be more than 45 at. %. The adhesion of the coatings on their substrates depends on the titanium-based graded layer. Experiments performed on laboratory tribometers and test machines at CNES facilities (Toulouse) confirmed that the optimized functionally graded layers could be selected for further qualification, both in terms of low and stable friction and of wear resistance. Concomitantly to this technological study, we concentrated on the phenomena that lead to low friction values under vacuum, that were also obtained on DLC coatings deposited on silicon by IBM Watson Research Center (USA). A better understanding of the hydrogen role on stabilized friction could be achieved, either as an element included in the coating or as a gas surrounding the contact. We have also shown the effect of surface chemistry on the kinetics of transient friction preceding the stabilized regime. The concept of "Chemical Hardness" was applied and discussed from experimental results. This work, supported by "Région Rhônes-Alpes", was achieved under the supervision of the Laboratoire de Tribologie et Dynamique des Systèmes, from Ecole Centrale de Lyon, and the Laboratoire de Mécanique des Contacts, from INSA-Lyon. This both laboratories are members of the Institut Européen de Tribologie
Faure, Jean-Baptiste. „Application des techniques d'homogénéisation à la prise en compte des phénomènes de rugosité en lubrification hydrodynamique“. Lyon 1, 1986. http://www.theses.fr/1986LYO10068.
Der volle Inhalt der QuelleTran, Viet Tuan. „Contribution à l'étude des phénomènes thermiques dans les butées hydrodynamiques“. Poitiers, 1997. http://www.theses.fr/1997POIT2296.
Der volle Inhalt der QuelleNogueira, Isabel. „Transformations des couches superficielles des matériaux induites par la phase de rodage lors de régimes de lubrification mixte et limite“. Paris, ENSAM, 2004. http://www.theses.fr/2004ENAM0001.
Der volle Inhalt der QuelleDuring certain working stages of mechanical components such as guiding parts or gear-wheels, the thickness of the oil film can not be sufficient to separate totally the surfaces. The summits of the asperities can be in contact, increasing wear and friction. This situation with a discontinuous film is classically defined as mixed or limited lubrication. In that case, the forces are supported partially by the solids and by the lubricant film. Such situations can occur during the starting and stopping stages, accidental overloads and especially during the running-in. These situations are critical for the mechanical components in particular for their working life and performance in service. The contact problem between solid surfaces has been studied in this work in order to clarify the complexity of the running-in in contact working in mixed lubrication. Firstly, a study of dry contact without sliding has been carried out analysing the geometrical variation of the rough surface and the physical alterations caused by a normal load. Secondly, the influence of the lubricant and the sliding motion on the friction and wear are introduced to study the mixed and boundary lubrication. The tests have been conducted using a pin-on-disc tribometre. The influence of a friction modifier added in to the base oil has been analysed depending on the friction, the wear and the superficial alterations
Dadouche, Azzedine. „Etude des phénomènes thermiques dans les butées hydrodynamiques“. Poitiers, 1998. http://www.theses.fr/1998POIT2291.
Der volle Inhalt der QuelleAttar, Saad-Eddin. „Palier hybride : contribution des alvéoles au champ de pression et au couple de frottement“. Poitiers, 1995. http://www.theses.fr/1995POIT2329.
Der volle Inhalt der QuelleAlaoui, Talibi Mohamed El. „Sur un problème à frontière libre en mécanique des films minces“. Lyon 1, 1986. http://www.theses.fr/1986LYO10067.
Der volle Inhalt der QuelleJaï, Mohammed. „Analyse numérique d'un schéma aux différences finies "mixtes" L. P. D. E. M. Et d'un algorithme de cavitation“. Lyon 1, 1990. http://www.theses.fr/1990LYO19005.
Der volle Inhalt der QuelleAghzer, Samir. „Contribution à l'optimisation des paliers hydrodynamiques“. Poitiers, 1998. http://www.theses.fr/1998POIT2280.
Der volle Inhalt der QuelleDiew, Mohamadou Bocar. „Contribution à la compréhension des mécanismes d'action des additifs modificateurs de frottement et du couplage additif/surface dans tous les régimes de lubrification“. Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0042/document.
Der volle Inhalt der QuelleThe combustion engine used in automotive industry is constantly changing for economic and ecological reasons. To achieve low fuel consumption and pollutants emissions, one of research axes studied is the reduction of the mechanical friction loss of the motor which constitute 15-20 % of the total energy consumption of the engine. 50% of these come from friction contacts cylinder /piston rings and conrod bearing. Thereby understanding of tribology of the contact, optimizing lubrication and lubricants aging become paramount. The objective of this thesis is to study the mechanisms of lubrication of these contact (piston ring/cylinder and conrod bearing), and in particular to understand the influence of the additive coupling surface and material in the different lubrication regimes. This will answer the question : how to control the friction and wear by controlling the chemistry of the lubricant, the topography and the material ? The experimental approach chosen is based on the analysis of the tribological behavior of two friction modifiers additives ashless at first time, and on the impact of material and finally the influence of topography on the second time. XPS Analysis of the evolution of the coefficient of friction and wear track under boundary regime have enabled to identify mechanisms to reduce friction induced by the two modifiers studied
Corneci, Magdalena Carla. „Fonctionnement tribologique des articulations synoviales pathologiques : Rôle des interfaces phospholipidiques“. Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0083.
Der volle Inhalt der QuelleIn order to improve the effectiveness of joint diseases’ treatments, given their complexity and magnitude, recent studies have highlighted the role of lipid assemblies associated with the discontinuous structure of the synovial fluid (SF) in the tribological performance of joint operation. Thus, an ex vivo tribological model (AM Sfarghiu, PhD thesis, 2006) providing a "basic pattern" for joint biolubrification was developed. It consists of the stack of phospholipidic interfaces and aqueous layers. Using this model, the objective of this work was to study the evolution of phospholipidic interfaces of SF within pathological state. Therefore, a nano-bio-tribological methodology combining biochemical, physicochemical, nano-mechanical and tribological analysis was used. The results of these analyses show: the influence of even small rubbing surfaces’ roughness characteristics of early stage illness and that of phospholipidic interfaces’ properties (related to their composition change) on the mechanical strength, changes in friction and in situ degradation of lipidic assemblies of pathological SF. The tribological operation is highlighted by enzymes’ associated with diseases. Thus, joint operation depends on the mechanical strength of phospholipidic interfaces and to obtain very low friction coefficients, velocity accommodation must be done at the level of hydration layers surrounding ions in the aqueous solution. These results would therefore allow better understanding of the evolution of phospholipidic interfaces in joint diseases and of the proper cause/consequence sequence responsible for a joint disease in order to develop more effective, targeted and non prosthetic treatments
Bonaventure, Julien. „Influence of random surface roughness on friction in elastohydrodynamic, mixed and boundary lubrication“. Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC038/document.
Der volle Inhalt der QuelleMost mechanical systems include lubricated contacts submitted to important strengths. The present work deals with the influence of surface roughness on friction in the elastohydrodynamic (EHD), mixed and boundary lubrication regimes, with operating conditions that are typically those found in an internal combustion engine. Most of the surfaces used in the experiments are machined steel, with or with a Diamond-Like Carbon (DLC) coating. Given the friction in boundary and mixed lubrication being higher than in EHD lubrication, it is crucial to predict the transitions between these regimes. These strongly depend on surface roughness. There are very few experimental works that deal with this issue, and the theoretical attempts to include the influence of random surface roughness are based on roughness parameters that are difficult to measure because of their dependence towards the sampling conditions and their non-stationarity. Based on numerous topographical surveys (using interferometry and AFM), a method is implemented to ensure the representativeness of roughness statistical parameters in order to characterize a range of surface roughnesses within the interval [0.001 ; 1] μm. Then, these surfaces are rubbed against each other using Stribeck procedures in order to correlate their morphology to their friction behaviour. The high-pressure rheology of poly-α olefins is measured in smooth contacts with respect to the pressure and the temperature. This not only allows to quantify the friction force for any contact operating in EHD lubrication, but also to set a criterion to spot the onset of mixed lubrication. At high entrainment speed, the viscous shear stress vanishes, which is often attributed to shear heating. It is shown that thermal effects can not explain such a drop of friction for our own experiments. However, the widening of the pressure profile — which becomes significant when the film thickness becomes comparable to a tenth the contact length — is more likely to explain this behaviour. Our results show that the product of the inlet viscosity with the entrainment speed, spotted at the mixed-EHD transition, follows a super linear power law with the RMS roughness, whatever the materials involved, which allows to predict whether a contact operate in mixed lubrication or not. The transition from mixed to boundary lubrication reveals material and roughness-dependent with a clearly different behaviour between DLC/DLC contacts and contacts involving at least one steel body. Regarding the DLC/DLC contacts, the boundary friction is due to the plastic shearing of the lubricant, which explains why surface roughness has no influence on boundary friction for these contacts. With Steel/DLC and steel/steel contacts, the boundary friction presents two monotonous trends versus the composite RMS roughness. Eventually, a mixed bearing model based on the Greenwood-Willimason assumptions was implemented and allowed to reproduce quite closely the experimentally obtained Stribeck curves. This implementation indicates in particular the sampling conditions that are optimal to capture relevant asperity parameters
Ayadi, Khouloud. „Optimisation de la modélisation des régimes de fonctionnement des garnitures mécaniques d'étanchéité : analyse théorique et expérimentale“. Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2325/document.
Der volle Inhalt der QuelleMechanical face seals are sealing components for rotating shafts. It basically consists of two annular flat surfaces lubricated with a very thin film of sealed fluid.The "Seals lubrication" group of the Pprime institute has developed different modeling tools of mechanical face seals behavior by analytical, semi analytical and numerical methods. The objective of this thesis is to define a preliminary methodology to optimize the modeling of the mechanical seal taking into account the seal design. This analysis provides a suggestion of modeling tools among the existing types. A set of indicators and criteria are developed to determine the dominating physical phenomena during the operation of the seal under given conditions. The selected modeling tools should take into account the identified phenomena. Experimental validations were performed for a mechanical seal working in different operating conditions. Studies of the evolution of the friction faces topography, the friction torque, the leakage rate and the thermal effect were carried out. Experiments have shown that the behavior of the mechanical seal strongly depends on the lubrication regime: mixed, hydrodynamic and thermo-elasto-hydrodynamic.Theoretical models were compared with experimental results. A good correlation is obtained into their range of validity defined with preliminary analysis. Larger differences are observed when the models are used in conditions where unconsidered physical phenomena occur. This comparison showed that the indicators and criteria of the proposed method of choice are relevant and allows a good identification of the physical phenomena that should be taken into account
Grec, Bérénice. „Fluides complexes en films minces“. Phd thesis, Ecole Centrale de Lyon, 2008. http://tel.archives-ouvertes.fr/tel-00351462.
Der volle Inhalt der Quelle* le caractère complexe des fluides eux-mêmes, comme pour des fluides non-newtoniens ;
* l'hétérogénéité de l'écoulement, dans le cas de mélanges de fluides par exemple.
Il est important d'analyser comment ces modèles peuvent être simplifiés dans le cas de domaines minces, et d'étudier rigoureusement les modèles approchés.
Dans une première partie, des écoulements de fluides non newtoniens visco-élastiques représentés par une loi de comportement de type Oldroyd-B couplée aux équations de Navier-Stokes sont étudiés. Dans le cas de géométries minces, un modèle approché a été proposé. On justifie la validité de cette approximation ; la démonstration repose sur des estimations et des résultats de régularité fins.
Dans une deuxième partie, on considère un modèle d'écoulement piezovisqueux utilisé en lubrification hydrodynamique. Ce modèle fait aussi intervenir la déformation élastohydrodynamique du domaine (déformation du type Hertz), et l'aspect diphasique de la cavitation, qui est décrit par le modèle d'Elrod-Adams (en pression-saturation). On montre l'existence d'une solution à ce problème pour des lois pression-viscosité réalistes.
Dans une troisième partie, on introduit un modèle diphasique à interface diffuse, permettant de rendre compte de phénomènes plus fins tels que les gouttes. Pour cela, un paramètre d'ordre est introduit (fraction volumique d'une phase dans le mélange), gouverné par le modèle de Cahn-Hilliard. Un système approché est obtenu de manière heuristique pour un domaine de faible épaisseur. On étudie les propriétés mathématiques de ce système, et on montre un résultat d'existence, avec prise en compte ou non de la tension de surface.
Dans la dernière partie, un schéma numérique est mis en place pour simuler le modèle décrit précédemment d'écoulements diphasiques en domaines minces. Il permet de prendre en compte différents phénomènes physiques, comme de grandes variations de la viscosité ou la présence de recirculations à l'intérieur d'une goutte, ainsi que de simuler des mélanges dans le cadre d'écoulements lubrifiés.
Kilman, Laureline. „Modification des propriétés de surface de couches DLC obtenues par PECVD/PVD dans le but d'optimiser leur comportement tribologique en milieu lubrifié : application aux moteurs thermiques pour véhicules terrestres“. Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0077.
Der volle Inhalt der QuelleDiamond-Like Carbon thin films are commonly used in automotive engines. Thanks to their very low friction coefficient and high hardness, it is indeed possible to optimize the performances and the lifetime of vehicles. However, most of the lubricants that are used in engines are designed to be in contact with metallic surfaces. So it might be possible to improve the global tribological behaviour of DLC films by giving them a metallic character. This can be achieved with the introduction of doping elements in limited and controlled amount (maximum 15 at. %) in the amorphous carbon matrix. An industrial scale reactor has been used with a hybrid coating technology combining PECVD for the deposition of hydrogenated DLC and magnetron sputtering for the introduction of the dopants. Four elements have been tested with various amounts in the DLC: aluminium, copper, molybdenum and niobium. The physico-chemical properties of the films have been characterized by XPS (chemical composition and bonding) and Raman spectroscopy (structure). Hardness, friction and wear in both dry and lubricated conditions, and surface energy have also been determined. Two in situ studies under temperature have been conducted by Raman spectroscopy for deposited thin films. Compared to a pure DLC, doping led to a modification of the structure resulting in a decrease in hardness. However, except for copper doping, a significant reduction of friction and wear in dry conditions is observed. Despite this promising result, the impact of doping on lubricated tribological behaviour is limited and strongly dependent on the composition of the lubricant itself. Finally, the industrial transfer of DLC metallic doping has been studied and validated
Bonetto, Alexis. „Etude de l'indentation et de la fatigue des contacts roulants“. Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI030.
Der volle Inhalt der QuelleSurface fatigue is currently the main cause of rolling element bearings failures. This type of fatigue can appear due to the presence of surface asperities but is exacerbated by the presence of surface defects such as dents. Handling the contamination of the lubricants that causes the denting of the surfaces is expensive and imperfect since the particles are not only already present in brand new oil but also generated during the operation of the system. Consequently, the lubricant carts particles of various nature into the contact. As they pass through the contact, the particles are crushed and dent the bearing surfaces, creating surface defects that will turn into initiation site for fatigue phenomena. As it is impossible to avoid debris denting, a better understanding of the denting and fatigue mechanisms is required to guarantee the reliability of the components and reduce their maintenance costs. During this PhD, a “coupled Euler-Lagrange” finite element model has been developed to reproduce the realistic debris denting process and study its effects. Then, the surface fatigue of dented surfaces was investigated using fatigue criteria in dry contact conditions. Finally, the effect of the lubricant on the dented surface was introduced using a multigrid solver for the transient EHL problem
Koshigan, Komlavi Dzidula. „Understanding the influence of environment on the solid lubrication processes of carbon-based thin films“. Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0023/document.
Der volle Inhalt der QuelleLike Carbon (DLC) coatings that exhibit outstanding mechanical properties, thermal stability and tribological performance. It is well established that the frictional and wear performances of a-C:H:Si:O are less dependent on environment than that of pure hydrogenated amorphous carbon (a-C:H). However the fundamental mechanisms accounting for such excellent tribological behavior of a-C:H:Si:O are still not fully understood. The present work, which is part of a collaboration between the Laboratoire de Tribologie et Dynamique des Systèmes of Ecole Centrale de Lyon and the department of Mechanical Engineering and Applied Mechanics of University of Pennsylvania, consists in using a multi-scale, multidisciplinary and multi-technique experimental approach for understanding the influence of environment on the tribological response of a-C:H:Si:O. A wide rang of complementary techniques, including nanoindentation, Atomic Force Microscopy (AFM), Friction Force Microscopy (FFM), optical and electron microscopy, Raman, X-ray Photoelectron Spectroscopy (XPS) and near edge x-ray absorption fine structure spectroscopy (NEXAFS), have thus been used to fully characterize the structure, composition and mechanics of the studied material, as deposited as well as after tribological testing. Control of the environment has been achieved first thanks to an open air linear reciprocating tribometer that we equipped with a gas blowing system, thus allowing a quick change of the sliding environment, and a environment-controlled analytical tribometer operating from high vacuum to elevated pressures of desired gases. We were able to evidence the strong influence of the amount of water vapor in the environment on the friction behavior of a- C:H:Si:O, with a reversible behavior when abruptly changing the environment. Contrary to water vapor, oxygen promotes the wear of a-C:H:Si:O. SEM observations revealed that while sliding a-C:H:Si:O against 52100 steel, the frictional response is controlled by the build-up and the release of adhesive junctions within the interface. Under high vacuum and below a threshold pressure of water vapor (1 mbar), oxygen (10 mbar) and hydrogen (50 mbar), adhesive junctions are released in the steel, resulting in a transfer of material from steel to a-C:H:Si:O and in a high coefficient of friction (μ≈1.2). However, as the gas pressure is increased above the threshold, the adhesive junctions break on the a-C:H:Si:O side, leading to a material transfer in the opposite direction, from the a-C:H:Si:O to the steel. NEXAFS spectroscopy revealed that a dissociative reaction occurs between the gaseous species and the strained C–C atoms in the near surface region ofa-C:H:Si:O, thus resulting in a drastic decrease of the steady state coefficient of friction by at least an order of magnitude. In light of these observations, an analytical model has been proposed to describe the fundamental interaction mechanisms between the environment and the a-C:H:Si:O/steel tribopairs
Gadari, M’hammed El. „Étude expérimentale et numérique du comportement des joints à lèvre“. Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2304/document.
Der volle Inhalt der QuelleIt's about sixty years that we are interested in understanding and modeling the Elastohydrodynamic behavior (EHD) of rotary lip seals. However, we can consider that, until now, their modeling has not been accurately treated. Even though many studies have been devoted to this model, several questions have been raised and are still the subject of controversy among researchers, namely the parameters influencing on the rotary lip seals performance, such as: the shaft surface textured, the law adopted for the mechanical behavior of lip seals, the approach used to develop the matrix of compliance, the importance of assuming the smooth or rough shaft, and finally the ratio between the width of contact and the wavelength according the circumferential direction of the lip roughness.The main goal of this thesis is to answer rigorously these questions by developing and validating a numerical tool for EHD rotary lip seals modeling, that takes into account: the lip law behavior, the compliance matrix rigorously validated by assuming smooth shaft case, or rough and textured shaft case. In addition, an analytical approach is proposed, models the vibratory behavior of the "squeeze film". This implies a nonlinear comportment that is taken into account
Corneci, Magdalena. „Fonctionnement tribologique des articulations synoviales pathologiques : rôle des interfaces phospholipidiques“. Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00766779.
Der volle Inhalt der QuelleWerda, Ben Slima Sana. „Influence de la conception d'un outil de fraisage dédié à la microlubrification (MQL) sur l'interaction outil-matière-lubrifiant : études expérimentales et numériques“. Thesis, Tours, 2016. http://www.theses.fr/2016TOUR4030/document.
Der volle Inhalt der QuelleIn machining industry, manufacturers tend to limit conventional lubrication and are moving increasingly towards Minimum Quantity Lubrication (MQL) for economic and ecological reasons, and with a view to safeguarding operator health and safety. A very small amount of lubricant at low pressure requires optimized design of the tools internal channels in order to minimize pressure drops and gain benefit from MQL. First, a literature review introduces the study by presenting the benefits induced by switching to MQL. Thereafter, some tool designs with internal lubrication for rake face or flank face lubrication are presented