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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.

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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

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.

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.

Elastohydrodynamic lubrication (EHL) allows transfer of power and forces in gears and rolling bearings without surface-to-surface contact and is the basis for a continuously variable transmission studied in this report. Previous research constructed models and derived solution methods, but often lacked full explanations of the approach and was usually applied to limited and specific cases. This report precisely develops the numerical solution of EHL contact and includes the more general cases of elliptical contacts and side-slip. The model and numerical method are validated on known benchmark cases and test results. Side-slip is investigated and the results shown in this report. Finally, the model is used to determine the film thickness and pressure of a contact patch under identical conditions to that in a physical drive developed by Fallbrook Technologies in Austin, TX. A minimum film thickness of 0.8978 [mu]m is found, setting a benchmark for the maximum allowable surface roughness values to prevent surface-to-surface contact. Additionally, under normal drive conditions the film thickness to surface roughness ratio is in the range of ideal values for maximum life. / text

<p>Rolling contact fatigue (RCF) is the primary mode of failure in tribological contacts like rolling-element bearings (REBs), gears, and cam-follower systems. RCF processes have a crack initiation phase followed by a propagation and coalescence phase, resulting in spalls that lead to catastrophic failure. Crack initiation is a highly localized process that is strongly influenced by the inhomogeneity of the material microstructure. Therefore, a microstructure-sensitive model is required to simulate the damage evolution and failure due to RCF loading. This document presents the development of a microstructure-based finite element (FE) framework for RCF, which accounts for the inhomogeneity of bearing steel microstructure by using an explicit definition of polycrystal topology and material anisotropy. The granular topology of the bearing steel microstructure is described using randomly generated Voronoi tessellations. A cubic elastic material definition with a random spatial orientation is specified for each Voronoi grain to simulate the material anisotropy. The Voronoi grains generated using this approach were used to model the critically stressed microstructural volume in RCF loading. A domain size study was conducted to estimate the minimum number of grains that need to be contained by the critically stressed volume such that the macroscopic material response of the polycrystalline aggregate matches the linear elastic material properties of bearing steel. The estimated critically stressed volume was then embedded into a semi-infinite domain for the FE simulation of RCF line contact loading. The RCF domains developed were then subjected to a moving Hertzian pressure over the surface to simulate a bearing load cycle. A boundary averaging scheme was used to estimate the effective stresses along the grain boundaries of the Voronoi cells. Due to the anisotropy of the polycrystalline material, local stress concentrations occur at the grain boundaries as compared to isotropic models. The resolved grain boundary stresses were used to predict critical locations for RCF crack initiation, which closely match observations from RCF bench test data. Since RCF failures typically exhibit subsurface locations for the first crack initiation, the model uses the critical resolved shear stress (RSS) reversal along the grain boundaries and the corresponding subsurface location of the maxima as the driving parameters for RCF fatigue failures. The parameters from the model were fit into a Weibull distribution to estimate the stochasticity in initiation life. The Weibull predictions corroborate well with experimentally measured RCF life scatter. The framework was then extended using a coupled damage mechanics - cohesive element method (DM-CEM) to individually model the crack initiation and propagation phases in RCF. An explicit definition of the grain boundaries was incorporated using cohesive elements. Damage is initiated at the grain boundaries by degradation of the cohesive elements and the rate of damage/degradation is used to characterize the evolution of fatigue life. The rate of damage was calculated at each grain boundary using a fatigue damage law based on the RSS reversal parameter. The model is able to simulate the crack initiation and the propagation/ coalescence phases in RCF, with distinct life estimates for each phase. This model framework is further extended to investigate the effects of lubrication conditions in RCF by integrating an elastohydrodynamic lubrication (EHL) model to simulate the pressure load with the DM-CEM model. Further improvements to the fatigue life predictions using the DM-CEM model are made by coupling it with a crystal plasticity (CP) based submodel approach to predict the crack initiation life in RCF. CP-based metrics are used to correlate the microplasticity developed under RCF loading with the formation of fatigue micro-cracks and the corresponding initiation life estimations. The resulting final spall patterns and RCF life estimates were found to match well with experimental data available in the open literature.</p> <p><br></p>

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