TY - JOUR

T1 - Soft micro-elastohydrodynamic lubrication and friction at rough conformal contacts

AU - Wennehorst, Bengt

AU - Poll, Gerhard

N1 - Publisher Copyright: © Institution of Mechanical Engineers 2016. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.

PY - 2017/3/1

Y1 - 2017/3/1

N2 - Conformal surfaces in parallel sliding lack a macroscopic hydrodynamic pressure and fluid film formation mechanism. However, such a mechanism still exists on a microscopic level due to roughness. It is common to translate roughness into a variation of fluid film thickness which in turn yields a hydrodynamic pressure distribution resulting in a net hydrodynamic lift. Reynolds equation and a suitable cavitation algorithm suffice to describe this effect mathematically. In case one surface consists of a compliant material with low modulus of elasticity, the deformation of asperities due to pressures and shear stresses in the fluid cannot be neglected - in fact, besides cavitation, it significantly contributes to the net hydrodynamic lift. Therefore, a coupling between fluid dynamics and elastic solid body deformations needs to be introduced. An additional complication arises when the hydrodynamic lift and the subsequent separation of the mean lines of the contacting rough surfaces is not enough to prevent asperity contacts completely. This situation is known as mixed lubrication where part of the normal load is transmitted at asperity contacts. These contacts are commonly treated as solid body contacts with a Coulomb-like friction law or more sophisticated solid friction models. However, when considering asperities as contraformal Hertzian contacts, elastic deformation may allow for the existence of thin micro-elastohydrodynamic lubricant films preventing direct solid body contact even at speeds which otherwise would be regarded as deep within the mixed lubrication regime close to boundary lubrication. These films may not be able to prevent wear completely, but may reduce friction significantly in comparison to dry friction. In this paper, the existence of such effects is demonstrated both by simulation and by experiments with elastomeric radial lip seals.

AB - Conformal surfaces in parallel sliding lack a macroscopic hydrodynamic pressure and fluid film formation mechanism. However, such a mechanism still exists on a microscopic level due to roughness. It is common to translate roughness into a variation of fluid film thickness which in turn yields a hydrodynamic pressure distribution resulting in a net hydrodynamic lift. Reynolds equation and a suitable cavitation algorithm suffice to describe this effect mathematically. In case one surface consists of a compliant material with low modulus of elasticity, the deformation of asperities due to pressures and shear stresses in the fluid cannot be neglected - in fact, besides cavitation, it significantly contributes to the net hydrodynamic lift. Therefore, a coupling between fluid dynamics and elastic solid body deformations needs to be introduced. An additional complication arises when the hydrodynamic lift and the subsequent separation of the mean lines of the contacting rough surfaces is not enough to prevent asperity contacts completely. This situation is known as mixed lubrication where part of the normal load is transmitted at asperity contacts. These contacts are commonly treated as solid body contacts with a Coulomb-like friction law or more sophisticated solid friction models. However, when considering asperities as contraformal Hertzian contacts, elastic deformation may allow for the existence of thin micro-elastohydrodynamic lubricant films preventing direct solid body contact even at speeds which otherwise would be regarded as deep within the mixed lubrication regime close to boundary lubrication. These films may not be able to prevent wear completely, but may reduce friction significantly in comparison to dry friction. In this paper, the existence of such effects is demonstrated both by simulation and by experiments with elastomeric radial lip seals.

KW - elastomeric radial lip seal

KW - fluid structure interaction

KW - friction in lubricated elastomeric contacts

KW - mixed lubrication

KW - Soft micro-elastohydrodynamic lubrication

UR - http://www.scopus.com/inward/record.url?scp=85011854072&partnerID=8YFLogxK

U2 - 10.1177/1350650114558322

DO - 10.1177/1350650114558322

M3 - Article

AN - SCOPUS:85011854072

VL - 231

SP - 302

EP - 315

JO - Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

JF - Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

SN - 1350-6501

IS - 3

ER -