Title

Modeling of Line Contacts With Degrading Lubricant

Document Type

Article

Publication Date

6-19-2003

Publication Title

Journal of Tribology

Abstract

A plane isothermal elastohydrodynamic problem for a lubricated line contact is studied. The lubricant represented by a base stock with some polymer additive undergoes stress-induced degradation due to scission of polymer additive molecules. The polymer molecules have linear structure. The degradation process of a polymer additive dissolved in a lubricant while the lubricant passes through the contact is described by a kinetic equation. The kinetic equation is solved along the lubricant flow streamlines. The solution of the kinetic equation predicts the density of the probabilistic distribution of the polymer molecular weight versus polymer molecule chain length. The changes in the distribution of polymer molecules affect local lubricant properties. In particular, the lubricant viscosity changes as polymer molecules undergo scission. These irreversible changes in the lubricant viscosity alter virtually all parameters of the lubricated contact such as film thickness, frictional stresses and pressure. As a result of the polymer additive degradation the lubricant experiences a significant viscosity loss. The viscosity loss (up to 60 percent), in turn, leads to a noticeable reduction in the lubrication film thickness (up to 12 percent) and frictional stresses applied to contact surfaces in comparison with the case of a nondegrading lubricant. Moreover, the pressure distribution in degrading lubricants exhibits extremely sharp spikes of about 2.15 to 2.82 (depending on the slide-to-roll ratio) times greater than the maximum Hertzian pressure. That may lead to noticeable variations in fatigue life of the contact surfaces.

Volume

125

Issue

3

First Page

513

Last Page

522

DOI

https://doi.org/10.1115/1.1538193

ISSN

0742-4787

Comments

ESSN: 1528-8897

Rights

ASME

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