Lubrication theory

About: Lubrication theory is a research topic. Over the lifetime, 1713 publications have been published within this topic receiving 50261 citations. The topic is also known as: Fluid bearing.

Mixed lubrication—Experiment and theory

Abstract: In recent years progress in understanding mixed lubrication has been quite rapid. On the experimental side it is now possible to map lubricant film thickness in low lambda ratio, thin film contacts, while computer models of mixed lubrication with load sharing between fluid film and asperity contact have recently been developed. This paper reviews the state of our knowledge of mixed lubrication and related fields and highlights areas where further work is badly needed. Key such areas are (i) fluid rheology under high pressure-high shear rate conditions, (ii) the physical properties of layers of fluid just one to five molecules thick at asperity conjunctions, (iii) new experimental methods for mapping thin films in rough surface contacts in the sub 2 nm range.

Effects of rough boundary and nonzero boundary conditions on the lubrication process with micropolar fluid

Abstract: The lubrication theory is mostly concerned with the behaviour of a lubricant flowing through a narrow gap. Motivated by the experimental findings from the tribology literature, we take the lubricant to be a micropolar fluid and study its behaviour in a thin domain with rough boundary. Instead of considering (commonly used) simple zero boundary conditions, we impose physically relevant (nonzero) boundary conditions for the microrotation and perform the asymptotic analysis of the corresponding 3D boundary value problem. We formally derive a simplified mathematical model acknowledging the roughness-induced effects and the effects of the nonzero boundary conditions on the macroscopic flow. Using the obtained asymptotic model, we study numerically the influence of the roughness on the performance of a linear slider bearing. The numerical results clearly indicate that the use of the rough surfaces may contribute to enhance the mechanical performance of such device.

A unified mixed-lubrication model of rolling-sliding line contacts from elastohydrodynamic lubrication to boundary lubrication

Abstract: This paper presents a unified mathematical model spanning the entire mixed lubrication for rolling-sliding line contacts. A load-sharing parameter is defined to divide the lubrication spectrum into three regions with increasing proportion of solid load sharing: light-mixed lubrication, significant-mixed lubrication and near-boundary lubrication. The main effort of the work is to develop a model for significant-mixed lubrication and integrate it with two previously developed governing-equation based models for light-mixed and near-boundary lubrication. A preliminary model is first developed by means of smooth, monotonically increasing interpolations of key contact variables obtained by the light-mixed and near-boundary lubrication models. The variables include surface temperature in the contact, friction coefficient, friction power intensity and proportion of solid contact area to the area of the line contact. The model is then refined by factoring in a potential transition of surface tribofilm breakdown w...

Boundary lubrication with a liquid crystal monolayer.

Abstract: We study boundary lubrication characteristics of a liquid crystal (LC) monolayer sheared between two crystalline surfaces by nonequilibrium molecular dynamics simulations, using a simplified rigid bead-necklace model of the LC molecules. We consider LC monolayers confined by surfaces with three different atomic structures, subject to different shearing velocities, thus approximating a wide variety of materials and driving conditions. The time dependence of the friction force is studied and correlated with that of the orientational order exhibited by the LC molecules, arising from the competition between the effect of the structure of the confining surfaces and that of the imposed sliding direction. We show that the observed stick-slip events for low shear rates involve order-disorder transitions, and that the LC monolayer no longer has enough time to reorder at high shear rates, resulting in a smooth sliding regime. An irregular stick-slip phase between the regular stick-slip and smooth sliding is observed for intermediate shear rates regardless of the surface structure.

Influence of wear on the performance of hole-entry hybrid misaligned journal bearing in turbulent regime

Abstract: Purpose – The present work aimed to study analytically the influence of wear on the performance of a capillary-compensated hole-entry hybrid misaligned journal bearing system operating in a turbulent regime. The numerically simulated results are presented for the chosen values of restrictor design parameter, Reynolds numbers, wear depth and misalignment parameters. Design/methodology/approach – The wear caused on the bearing surface due to start/stop operations is modeled using the Dufrane’s abrasive wear model. The modified Reynolds equation based on Constantinescu’s lubrication theory is solved using finite element method together with capillary restrictor flow equation. Findings – It is found that the value of minimum fluid-film thickness increases significantly for a constant value of restrictor design parameter when unworn aligned bearing operates in turbulent regime vis-a-vis laminar regime. Further, it has also been observed that when a worn bearing operates in laminar/turbulent regimes, the reduct...