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To further extend knowledge about fluid film friction in elastohydrodynamic contact, it is important to examine how lubricant flows. In this paper, several film thickness results obtained by interferometry technique for different kinds of experiments were analyzed and discussed based on lubricant flow continuity. Results of two steady-state and two transient experiments are presented. Possible speed profiles that can explain observed film thickness distributions were suggested. It is shown that major part of present experiments can be explained by a single speed profile known as a plug flow. This finding is in contradiction to usual linear speed profile predicted by Reynolds equation. [ABSTRACT FROM AUTHOR]

Surface roughness plays an important role in transition from full to mixed elastohydrodynamic regime. One kind of features appearing on a real rough surface are grooves longer than contact diameter. It has already been reported that these grooves cause a local film reduction or a complete collapse. In this study, a ball-on-disc optical tribometer was used to quantitatively study the effect of grooves on film thickness in a point contact. It was observed that the main dependence on speed, the so-called lift-off curve, generally follows the logarithm function. The effects of build-up material, load, slide/roll ratio and groove geometry are presented. These results were fitted to the analytical description, which enables the estimation of groove effects on point contact lubrication. [ABSTRACT FROM AUTHOR]

The transient film thickness and pressure distributions in point elastohydrodynamic lubri-cation (EHL) contacts during start-stop-start motion are discussed based on experimen-tal and numerical analyses. When the machine element starts to move after the stopping, where the oil is entrapped between two surfaces, the pressure at the exit area increases very much. The pressure increase depends markedly on the overall film thickness before the stopping of the motion, but is hardly controlled by the acceleration after the stopping. It can be considered that this phenomenon affects the rolling contact fatigue damage. [ABSTRACT FROM AUTHOR]

ABSTRACT The microgrooves are formed in the surface ridges by local pressure increases caused by impact loading in elliptical elastohydrodynamic contacts. It has been elucidated through isothermal Newtonian numerical analyses that the depth and the distribution of microgrooves are influenced by the height, shape and orientation of the ridges, the initial impact gap, the maximum load and time being exposed to the maximum load. The formation of the microgrooves induced by local high pressures will influence the surface failure of machine elements. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The phenomena that occur when an elliptical steel body impacts a stationary steel plate with surface asperities are discussed through isothermal Newtonian numerical analysis using sinusoidal roughness. The ridges of the surface asperities produce large local pressures, especially at a large ellipticity ratio, when the surfaces are approaching each other under the applied load. The values of the local pressures are larger when the ridges are along the major axis than when the ridges are along the minor axis. Furthermore, as the loading speed increases, the pressure increases. As a result, the microgrooves are produced in the ridges and the horseshoe-shaped constrictions are formed at the ridges located around the contact edge. [ABSTRACT FROM AUTHOR]

The squeeze effect is an important subject in studies ofelas-tohydrodynamic lubrication (EHL). By impact loading, the oil between point contact surfaces is entrapped at the central region or the peripheral region depending on the initial conditions. The effects of the loading process, surface roughness, and ellip-ticity ratio of contacts on the film thickness and pressure distri-butions are not fully understood yet. In the current study, those effects are elucidated through numerical analyses by specified initial impact gaps, which produce the central or the periph-eral oil entrapments. The loading process, which can produce rather low pressure, has been proposed. Moreover, conditions, under which a microdimple is produced in the central circular bump are clarified. [ABSTRACT FROM AUTHOR]

The purpose of this study is to reveal the connection between the film thickness and the friction for a uniform surface texture on transition from full film to mixed lubrication in non-conformal contacts. The current study tries to clarify the processes leading to the friction increase during the transition that is usually seen in the Stribeck curve. The transition to mixed lubrication and the friction increase are usually associated with a direct contact between surface irregularities. However, the experimental results showed that friction increases much earlier before the first contact was detected. It was revealed that a standard mixed friction modeling based on the area in a direct contact has significant limitations. Numerous possible explanations for this phenomenon are discussed. [ABSTRACT FROM AUTHOR]

The purpose of this study is to describe the influence of artificially produced surface grooves longer than a diameter of the contact area on the transition from a full EHL regime to mixed lubrication in the point contact using optical interferometry. This article focuses on the influences of grooves orientation, length in the contact area, elastic modulus of contact surfaces, and different types of lubricants defined by pressure-viscosity coefficient. An empirical prediction model of groove influence on film thickness was established based on experimental data. The groove influence was incorporated into lubrication parameter. This modified definition was compared with the classic one. It showed that avoiding the groove influence leads to a significant underestimation. [ABSTRACT FROM AUTHOR]

Abstract: This paper is focused on the effect of impact loading on micro-deformation of asperities in elliptical elastohydrodynamic contacts. Based upon isothermal Newtonian numerical analyses, it is elucidated that a micro-groove, which appears in the ridge under impact loading in elliptical contacts, is brought about by two different mechanisms. One is the smooth surface local pressure difference across the virtual ridge and the other is the macroscopic pressure difference along the ridge. The formation of the micro-groove due to the former mechanism is influenced by the shape, size and orientation of the ridge, and the smooth surface pressure distribution depending on the initial impact gap and loading speed, and that due to the latter is markedly influenced by the loading speed. [Copyright &y& Elsevier]