No description available.

In this study, a model has been developed for the elastohydrodynamic lubrication with binary mixtures of compressible fluids, which can be used to represent emulsions with suspended deformable particles. The coupled modified Reynolds, elasticity, and rheology equations are solved simultaneously by combining the advanced multilevel method and the Newton-Raphson method. The effects of speed, load, dimensionlesss materials parameter, inlet oil volume fraction, droplet radius, surface tension group, elasticity of mixture, and equivalent viscosity models of emulsions on the lubrication characteristics of the emulsions are investigated. The speed, load, and oil volume fraction combinations studied in this study represent a broad range of operating conditions previously not investigated. The results of this study are in good agreement with the tests conducted by Kimura et al. and Zhu et al. indicating the effects of droplet radius of oil phase and the speed on the film thickness. The film thickness increases with increasing droplet size for the droplet size smaller than the film thickness. At the low oil volume fraction and low speed, the oil volume fraction increases rapidly with coordinate x to form the oil pool in the region close to the Hertzian contact area. With the increase of speed, the extent of the oil pool decreases significantly so that the oil volume fraction at the contact area decreases rapidly. Consequently, the film thickness also decreases due to the decrease in the effective viscosity of the mixture. When the speed is getting higher, the oil and water phases enter the contact conjunction so that the oil volume fraction is closer to the inlet one.

No description available.

Abstract This paper proposes a model that integrates the microscale asperity contact and macroscale elastohydrodynamic lubrication (EHL) to simulate the pressure distribution in the chemical mechanical planarization (CMP). This model involves modified Reynolds equation used to describe the status of fluid field, the equation of the average asperity contact pressure by using statistics for solid contact pressure due to asperity contact, and the equation of the elastic pad deformation in bulk. Results show that with increasing relative velocity or load, the magnitude of the sub-ambient pressure decreases, the greater asperity contact pressure is formed to support the load, and the friction force also increases to cause the greater rotation angles. The magnitude of the fluid pressure is of the same order of magnitude as the applied normal load. Therefore, the addition of this fluid pressure may significantly change the distribution of the contact stress. The reason of the sub-ambient pressure existed is the deformation of the pad. In the material removal rate model, the elastic deformation of asperities is assumed, and the contact pressure is determined by Hooke¡¦s law. The indentation depth can be obtained from the force balance imposed on the particles by the wafer and the pad. Results show that the material removal rate decreases with increasing abrasive size, due to the increasing contact area between the abrasive and wafer. Keywords¡GElastohydrodynamic Lubrication, Chemical Mechanical Polishing

The rotary lip seal is the most widely used dynamic seal. It is used extensively in the automotive and appliance industries. Experimentally, it is well known that the microasperities on the shaft surface can significantly affect the performance of a lip seal, even though the shaft roughness, after run-in, is much smaller than the lip roughness. In the present study, several deterministic numerical models are developed to investigate the effect of shaft surface finish on rotary lip seal behavior, through an understanding of the basic physics of lip seal operation. This project is performed in a step by step manner with gradually increasing complexity. Four models are included in this study: hydrodynamic analysis, elastohydrodynamic analysis for full film lubrication, mixed-EHL model for mixed lubrication with asperity contact, and transient dynamic mixed-EHL model for startup and shutdown processes. Those analyses allow the examination of some important seal characteristics, such as the load support sharing between hydrodynamic and contact pressure, contact and cavitation area ratio, reverse pumping rate, liftoff speed for tracing the liftoff process and average film thickness. The development of fluid, contact and cavitation areas as a result of the changing operation condition is also examined. The results of the present deterministic modeling indicate that shaft surface roughness can produce significant desirable effects on lip seal behavior. An appropriate shaft surface profile could improve the sealing ability and prevent seal failure.

Abstract Elastohydrodynamically lubricated conjunctions are often subjected to impact loading. In such case the squeeze effect plays an important role. This research uses a self-development EHL tester to explore the effects of squeeze velocity, load and viscosity of lubricant on the dimple film thickness occurs between two components approach each other. The contact region is studied by means of optical interferometry using white light, a microscope and a CCD camera recording equipment. The results of the test show that increasing squeeze velocity makes the dimple deeper. Furthermore, the maximum central dimple film thickness becomes greater as the viscosity of lubricant increases at the same experiment condition. When the squeeze load is larger, it will keep the dimple film longer.

Cette thèse étudie de nouvelles approches pour contrôler le coefficient de frottement dans les contacts en lubrification elastohydrodynamique (EHL) grâce à l'utilisation de surfaces texturées. Par l'expérimentation et la simulation numérique, les phénomènes gouvernants le frottement en EHL sont tout d'abord identifiés, puis l'effet de différentes surfaces texturées (cavités, rainures, ripples) sur le coefficient de frottement est mis en évidence. Les résultats indiquent que le coefficient de frottement peut être contrôlé par l'ajustement adéquat de la géométrie des textures. / This thesis focuses on finding new ways to control the friction coefficient in elastohydrodynamically lubricated (EHL) contacts through the use of surface textures. Experiments and numerical simulations are employed to first identify the governing phenomena responsible for friction in EHL and then to assess the effect of different surface textures (dimples, grooves and ripples) on the friction coefficient. The findings indicate that the coefficient can be controlled by carefully adjusting the texture geometry.

In this study, the mixed lubrication of line contact is numerically calculated and analyzed. The surface asperities are in contact for mixed lubrication which differs from elastohydrodynamic lubrication. In this study, the Poiseuille term is neglected when the film thickness was smaller than the cut-off value about 0.5 nanometer, so that the surface asperities in contact or not contact can be solved in a system equation using the Newton-Raphson method. The mixed lubrication was studied in three parts, including the steady-state, the transient state and the start-up process. The effect of amplitude and wavelength on the film thickness and the pressure are investigated using the deterministic quantifiable method. The mixed lubrication zone in terms of rolling speed and load is established for the smooth surface under the steady-state conditions. For a single asperity on the surface, results show that the maximum pressure increases with increasing amplitude and decreasing wavelength. At high load situation, the film thickness is flattened around the asperity in the steady-state conditions, but it is increased due to the squeezing effect in transient state. For the start-up process, two surfaces are gradually separated due to the growth of film thickness, so that the contact area of two surfaces decreases linearly with time. However, the interval of contact time decreases with increasing roller speed and Young¡¦s modulus, but decreasing load.

Abstract With the advent of new technology, various machine structures and elements appear delicate and diminutive so that the nanotribological studies are needed in the modern mechanical technological development. Thin film lubrication will be indispensable as the basis of key-technology in high-technological devices and ultra-precision machines. Therefore, the research of thin film lubrication in the nanometer order is very important. In this research uses a self-development optical elastohydrodynamic lubrication (EHL) tester to simulate the oil film characteristics in the contact region between steel ball and sapphire under the pure rolling condition. First, the variation of oil film thickness on the contact region is observed by using the optical interference principle. An inverse approach of EHL is employed to investigate the pressure distribution on the contact region of lubricant. Final, the oil thickness and pressure distribution are substituted into Reynolds equation to predict the pressure-viscosity index of lubricant. Results show that the oil film thickness increases with increasing rolling speed, and curvature radius of steel ball, but decreases with increasing load. Moreover, when the oil thickness of ester lubricant is less than 17nm, the film thickness is obviously deviated that predicted by the classical EHL theory, and the pressure-viscosity index increases from 0.8195 to 0.9093. This result indicates that the ratio of the adsorbent layer to the oil film increases and causes the increase of the lubricant viscosity.

Reciprocating rod seals are widely used in hydraulic systems to prevent the hydraulic fluid from leaking into and polluting the environment. In this research an elastohydrodynamic model of a generalized reciprocating hydraulic rod seal, including mixed lubrication and surface roughness, has been successfully developed. This model consists of coupled fluid mechanics, contact mechanics, thermal analysis and deformation analyses. Such model is capable of predicting the key seal performance characteristics, especially net leakage and friction force. This allows evaluation of potential seal designs and serves as design tools. Also as this model has been developed, the basic physics of seal operation has been clarified, which stimulates the development of innovative seal concepts, such as seals with engineered sealing surfaces. The results of this study indicate that in general, hydraulic rod seals operate in the mixed lubrication regime, although under certain conditions full film lubrication may occur over a portion of the sealing zone. The roughness of the seal surface and the rod speeds play important roles in determining whether or not a seal will leak. Cavitation during the outstroke and partial full film lubrication during the instroke tend to prevent net leakage. The behavior of a reciprocating hydraulic rod seal with a double lip or two seals in tandem arrangement can be very different from that of a similar seal with a single lip. For the double lip seal, the secondary lip can strongly affect the behavior of the primary lip by producing an elevated pressure in the interlip region. The same seal characteristics that promote effective sealing in a single lip seal and, in addition structural decoupling of multiple lips, are found to promote effective sealing in a multiple lip seal. The model is validated through comparisons of model predictions with experimental measurements and observations by industry partners. The results have shown the predicted leakage and friction force for various seal and operation conditions are consistent with the measurements. A seal with micro-pattern on the sealing surface also has been investigated. The results indicate that an elaborately designed pattern can improve the sealing characteristics of the seal, without significantly affecting the friction force. In the end, the selection of the rod seal for a specific application using this analytical model is demonstrated. The best design can be picked up before a prototype being built.