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Lubricants
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Elastohydrodynamic (EHD) Lubrication
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Elastohydrodynamic (EHD) Lubrication

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (30 December 2019) | Viewed by 21497

Special Issue Editor

Dr. Marcus Björling

E-Mail Website
Guest Editor
Division of Machine Elements, Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
Interests: contact mechanics; tribology; elastohydrodynamic lubrication
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Lubrication is vital in society to reduce friction and wear to consequently increase energy efficiency and service life of mechanical components. Elastohydrodynamic (EHD) lubrication is found in many of today’s most common machine components like gears, rolling element bearings and cam followers. EHD lubrication features many distinct challenges where the non-conformal nature of the contacts gives rise to elastic deformation of the surfaces and contact pressures up to several gigapascals. This means high contact stresses and high shear rates in rolling/sliding contacts. Research in EHD covers many areas such as lubricant rheology, lubricant film formation, tribofilms, efficiency of machine components, surface coatings, textures, pitting, micro-pitting, machine component design etc.

This Special Issue deals with current advances within the field of EHD lubrication and papers dealing with the aforementioned topics or related that can increase the knowledge of EHD lubrication and its applications. Contributions from both academic and industrial research are welcome.

We are enthusiastically looking forward to your submission.

Dr. Marcus Björling
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Elastohydrodynamic lubrication
  • EHD
  • EHL
  • Traction
  • Friction
  • Mixed lubrication
  • Thermal effects
  • Coatings
  • Film formation
  • Pitting

Published Papers (4 papers)

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Research

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19 pages, 8726 KiB  
Article
Misalignment-Induced Micro-Elastohydrodynamic Lubrication in Rotary Lip Seals
by F. Xavier Borras, Matthijn B. de Rooij and Dik J. Schipper
Lubricants 2020, 8(2), 19; https://doi.org/10.3390/lubricants8020019 - 10 Feb 2020
Cited by 9 | Viewed by 5523
Abstract
In literature the lubrication of rotary lip seals is explained by hydrodynamic action on a microscopic scale. This theory assumes perfect concentricity between the seal and the shaft which in reality seldomly occurs. Focusing on the stern tube seals application, an analysis is [...] Read more.
In literature the lubrication of rotary lip seals is explained by hydrodynamic action on a microscopic scale. This theory assumes perfect concentricity between the seal and the shaft which in reality seldomly occurs. Focusing on the stern tube seals application, an analysis is performed on the phenomena distorting the axisymmetric operation of rotary lip seals. Radial and angular shaft misalignments together with pressure and temperature gradients have been modelled. The model predictions are validated using a dedicated setup. Additionally, applying the soft-EHL film thickness expressions at the asperity level, an equivalent film thickness along the circumferential direction is estimated. The Reynolds PDE is solved to predict the misalignment-induced hydrodynamic pressure build-up. The film thickness variation derived and accompanying non-uniform contact pressure distribution was shown to be sufficient for hydrodynamic action and, depending on the minimum film thickness, the hydrodynamic pressure build-up can exceed the static contact pressure. Additionally, significant differences were observed between the radial and angular misalignment configurations. Full article
(This article belongs to the Special Issue Elastohydrodynamic (EHD) Lubrication)
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11 pages, 2620 KiB  
Article
On the Relation between Friction Increase and Grease Thickener Entraining on a Border of Mixed EHL Lubrication
by Tomas Zapletal, Petr Sperka, Ivan Krupka and Martin Hartl
Lubricants 2020, 8(2), 12; https://doi.org/10.3390/lubricants8020012 - 29 Jan 2020
Cited by 2 | Viewed by 3419
Abstract
This paper deals with an experimental study of film thickness and friction of commercial-grade grease and its base oil in a highly loaded contact. In-situ measurements were conducted for two surface textures on a ball-on-disc optical tribometer at the border of mixed lubrication. [...] Read more.
This paper deals with an experimental study of film thickness and friction of commercial-grade grease and its base oil in a highly loaded contact. In-situ measurements were conducted for two surface textures on a ball-on-disc optical tribometer at the border of mixed lubrication. At high speeds, the film thickness and the friction of grease correspond with the base oil, while, the thickener enters the contact area and locally affects the film thickness and friction at low speeds. It was found out that the thickener starts to enter the contact area approximately at the same speed when the base oil friction increases on Stribeck curve but without direct solid to solid contact. It indicates that both effects can have the same origin. Change of lubricant flow in contact inlet area was discussed as a possible explanation. Full article
(This article belongs to the Special Issue Elastohydrodynamic (EHD) Lubrication)
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14 pages, 3808 KiB  
Article
Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction
by Aleks Vrček, Tobias Hultqvist, Yannick Baubet, Marcus Björling, Pär Marklund and Roland Larsson
Lubricants 2019, 7(5), 42; https://doi.org/10.3390/lubricants7050042 - 16 May 2019
Cited by 10 | Viewed by 5056
Abstract
Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article [...] Read more.
Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article studies micro-pitting and wear damages of bearing steel surfaces under mixed lubrication conditions in a ball-on-disc setup, lubricated with different engine oils. Based on the results, micro-pitting and wear damage is shown to be highly case-dependent. In general, PAO-based engine oil tends to eliminate micro-pitting damage compared to mineral-based engine oil at less severe lubricating conditions. Moreover, a critical lambda was found for both oils, where the highest micro-pitting damage was observed. Full article
(This article belongs to the Special Issue Elastohydrodynamic (EHD) Lubrication)
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Review

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30 pages, 8837 KiB  
Review
Elastohydrodynamic Lubrication
by James A. Greenwood
Lubricants 2020, 8(5), 51; https://doi.org/10.3390/lubricants8050051 - 6 May 2020
Cited by 32 | Viewed by 6264
Abstract
The development of EHL theory from its tentative beginnings is outlined, with an account of how Ertel explained its relation to Hertz contact theory. The problems caused by the failure of the early numerical analysts to understand that the film thickness depends on [...] Read more.
The development of EHL theory from its tentative beginnings is outlined, with an account of how Ertel explained its relation to Hertz contact theory. The problems caused by the failure of the early numerical analysts to understand that the film thickness depends on only two variables are emphasised, and answers of the form H = F ( P , S ) given. Early methods of measuring the film thickness are described, but these became archaic with the development of optical EHL. The behaviour of surface roughness as it passes through the high pressure region and suffers elastic deformation is described, and the implication for the traditional Λ -ratio noted. In contrast, the understanding of traction is far from satisfactory. The oil in the high pressure region must become non-Newtonian: the early explanation that the viscosity reduction is the effect of temperature proved inadequate. There must be some form of shear thinning (perhaps according to the Eyring theory), but also a limiting shear stress under which the lubricant shears as an elastic solid. It seems that detailed, and difficult, measurements of the high pressure, high shear-rate behaviour of individual oils are needed before traction curves can be predicted. Full article
(This article belongs to the Special Issue Elastohydrodynamic (EHD) Lubrication)
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