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Hua, J. (2020). Controllable Friction of Green Ionic Liquids via Environmental Humidity. Advanced Engineering Materials, Article ID 1901253.
Open this publication in new window or tab >>Controllable Friction of Green Ionic Liquids via Environmental Humidity
2020 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, article id 1901253Article in journal, News item (Refereed) Published
Abstract [en]

Intelligent control of friction is an attractive but challenging topic. In this work, it is investigated if it would be possible to adjust friction in a lubricated contact by controlling environmental humidity. By exploiting the ability to adjust the environmental humidity by various saturated salt solutions, friction behavior of contacts lubricated with Choline l‐Proline ([Cho][Pro]) is modulated in a wide range of relative humidity (RH). The friction increases when the environmental humidity is increased and decreases when water is partially evaporated to a lower RH. It is thus possible to control friction by environmental humidity. The addition of water in ionic liquids (ILs) causes a decrease in viscosity, but as the tests are calculated to be performed in boundary lubrication the viscosity change is not the main factor for the change in friction. The friction sensitivity of RH can be explained by the effect of adhesion on the water uptake from humid air by [Cho][Pro]. Furthermore, the reversible changes of H‐bond types determined by the water content could be another explanation to the altered friction.

Place, publisher, year, edition, pages
Boschstrasse 12 69469 Weinheim Germany: , 2020
Keywords
friction control
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-77681 (URN)10.1002/adem.201901253 (DOI)
Funder
Swedish Research Council Formas, 2016-01098Swedish Research Council, 2017-04914Swedish Energy Agency, 2018-003910
Available from: 2020-02-10 Created: 2020-02-10 Last updated: 2020-02-10
Hansen, J., Björling, M. & Larsson, R. (2020). Lubricant Film Formation in Rough EHL Contacts. In: : . Paper presented at TAE 22nd International Colloquium Tribology, Esslingen, Germany, Jan 28-30, 2020.
Open this publication in new window or tab >>Lubricant Film Formation in Rough EHL Contacts
2020 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

Conference: 22nd International Colloquium Tribology, Technical Academy Esslingen, 28–30 January 2020, Stuttgart / Ostfildern, Germany

Main subject: Fundamentals of Tribology

Title: Lubricant film formation in rough EHL contacts

Author(s): Jonny Hansen1,2, Marcus Björling1, Roland Larsson1

Affiliation: 1) Machine Elements, Luleå University of Technology, Luleå, Sweden

2) Gear Technology, Transmission Development, Scania CV AB, Södertälje, Sweden

 

Abstract:

Downsizing of machine elements and thinner lubricating oils, with simultaneous improved power density, is an on-going pursuit in automotive industry and lubrication science. The outcome is shifting the performance of e.g. gear contacts to operate under more severe lubricating regimes. In extension, this sets the role of surface finish in the view of increased importance since roughness amplitude in combination with thin films generally is considered to activate surface degradation mechanisms such as wear, fatigue, and ultimately machine failure. Thus, in order to meet the present demands, it is of critical importance to better understand the interplay between surface roughness and elastohydrodynamic oil film (EHL) formation.

Recently, our research [1] has shown that the default model [2] for estimation of lubrication quality strongly deviates from the supposed proportional relationship between film thickness and composite surface roughness (). Thus, with the present approach, false assumptions about lubrication quality are possible. An adequately run-inned surface may operate under elasto-hydrodynamic performance even at such conditions when  suggests substantial contact interference. The latter suggest that the more detrimental opposite situation also would be possible under a certain surface roughness configuration. This research was therefore set out as part of a long term goal of improving the present engineering design tool so that better and more safe estimates of the lubrication quality can be made.

This work explores the mechanisms involved in the formation of an elasto-hydrodynamic (EHD) oil film under heavily loaded mixed rolling/sliding operation of circular contacts. A WAM ball-on-disc machine was operated under conditions representative for those found in heavy duty transmission assemblies. Specimens were prepared with isotropic engineering surface finishes to capture the effect of roughness amplitude on the contacts capability to form a protective EHD film. Electrical contact resistance (ECR) and the coefficient of friction was monitored during running-in tests to reveal how surface roughness affects the number of cycles to EHL lift-off, and the associated response to friction. Specific emphasis was set out to investigate what changes surface topographies must undergo in order to reach a steady state in EHL when starting in mixed lubrication. A surface-re-location technique was developed to enable for detailed examination of the most active sites that typically involve the most prominent asperity features. Surface analysis was conducted with the aim of clarifying the importance to lubrication quality of parameters from all families, i.e. spatial, feature and hybrid parameters in addition to the present approach that only accounts for the surfaces height by root-mean-square-average (RMS/). A strong correlation between friction change and the modification of surface topography was found as the contact went through the running-in process for EHL lift-off. Additionally, it was observed that surface roughness still significantly affect the coefficient of friction at EHL steady state operation.

 

[1]      Hansen J, Björling M, Larsson R. Mapping of the lubrication regimes in rough surface EHL contacts. Tribol Int 2018. doi:10.1016/j.triboint.2018.11.015.

[2]      ISO/TR 15144-1:2014. Calculation of micropitting load capacity of cylindrical spur and helical gears. Geneva: n.d.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:ltu:diva-77708 (URN)
Conference
TAE 22nd International Colloquium Tribology, Esslingen, Germany, Jan 28-30, 2020
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-14
Hultqvist, T., Hansen, J., Björling, M., Marklund, P. & Larsson, R. (2020). On the Effects of Two-Sided Roughness in Rolling-Sliding EHL Contacts.. In: : . Paper presented at 22nd International Colloquium Tribology: Industrial and Automotive Lubrication.
Open this publication in new window or tab >>On the Effects of Two-Sided Roughness in Rolling-Sliding EHL Contacts.
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2020 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-77713 (URN)978-3-943563-11-5 (ISBN)
Conference
22nd International Colloquium Tribology: Industrial and Automotive Lubrication
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-14
Hansen, J., Björling, M. & Larsson, R. (2020). Topography transformations due to running-in of rolling-sliding non-conformal contacts. Tribology International, 144, Article ID 106126.
Open this publication in new window or tab >>Topography transformations due to running-in of rolling-sliding non-conformal contacts
2020 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 144, article id 106126Article in journal (Refereed) Published
Abstract [en]

A ball-on-disc machine was operated under conditions relevant to heavily loaded gears. Various levels of isotropic surface finishes were evaluated to reveal the influence on elasto-hydrodynamic lubrication (EHL). Stribeck tests were conducted for insight about roughness effects in all regimes, whereas lift-off tests were conducted to investigate the influence on running-in. A 3D surface re-location approach was developed to enable studies of the topography on exactly the same area before and after test. This helps to find asperity level details about how topographies must transform to allow a shift from the mixed- and boundary lubrication regimes, into the full film micro-EHL regime. The micro-conformity was highlighted to play a key-role for EHL lift-off that precedes the completion of running-in.

Place, publisher, year, edition, pages
Elsevier, 2020
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-77299 (URN)10.1016/j.triboint.2019.106126 (DOI)
Note

Validerad;2020;Nivå 2;2020-01-07 (johcin)

Available from: 2020-01-07 Created: 2020-01-07 Last updated: 2020-01-07Bibliographically approved
Hultqvist, T., Vrček, A., Marklund, P., Prakash, B. & Larsson, R. (2020). Transient analysis of surface roughness features in thermal elastohydrodynamic contacts. Tribology International, 141, Article ID 105915.
Open this publication in new window or tab >>Transient analysis of surface roughness features in thermal elastohydrodynamic contacts
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2020 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 141, article id 105915Article in journal (Refereed) Published
Abstract [en]

Understanding the influence of surface roughness in elastohydrodynamically lubricated (EHL) contacts is essential to improve durability and friction performance of machine elements employing non-conformal contacting surfaces. In this work, the transient event of a surface feature passing through a thermal EHL line contact operating under different sliding conditions is investigated with the purpose of providing a deeper understanding of surface roughness influence. This is achieved by solving the EHL problem in space and time. It was seen that sliding influences the temperature rise in the contact significantly, especially in the vicinity of the asperity. However, due to the characteristic behaviour of EHL contacts, the local temperature rise mainly influence the film thickness during exiting of inlet perturbations and the asperity.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Thermal elastohydrodynamic lubrication, Transient conditions, Surface features, Numerical modelling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75817 (URN)10.1016/j.triboint.2019.105915 (DOI)2-s2.0-85071778495 (Scopus ID)
Funder
Swedish Energy Agency, 41215-1
Note

Validerad;2019;Nivå 2;2019-09-10 (johcin)

Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-20Bibliographically approved
Tosic, M., Larsson, R., Jovanović, J., Lohner, T., Björling, M. & Stahl, K. (2019). A Computational Fluid Dynamics Study on Shearing Mechanisms in Thermal Elastohydrodynamic Line Contacts. Lubricants, 7(8), Article ID 69.
Open this publication in new window or tab >>A Computational Fluid Dynamics Study on Shearing Mechanisms in Thermal Elastohydrodynamic Line Contacts
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2019 (English)In: Lubricants, E-ISSN 2075-4442, Vol. 7, no 8, article id 69Article in journal (Refereed) Published
Abstract [en]

A computational fluid dynamics (CFD) model of the thermal elastohydrodynamically lubricated (EHL) line contact problem has been developed for the purpose of exploring the physical processes that occur inside a thin EHL film subjected to shearing motion. The Navier–Stokes equations are solved by using the finite volume method (FVM) in a commercial CFD software, ANSYS Fluent. A set of user-defined functions (UDF) are used for computing viscosity, density, heat source, temperature of moving surfaces and elastic deformation of the top roller according to well-established equations commonly used in the EHL theory. The cavitation problem is solved by taking into account multiphase mixture flow. The model combinations of Houpert and Ree–Eyring and of Tait and Carreau were used for modeling the non-Newtonian behavior of Squalane and the results were compared. Both rheological models suggest the existence of shear-band and plug-flow at high fluid pressure. Due to the differences in viscosity at GPa-level pressure, the chosen model has substantial influence on the computed shear stress and temperature distributions in the high-pressure region. This shows the importance of using correct rheology information in the whole range of pressure, temperature, and shear strain rate.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
EHL, TEHL, CFD, finite volume, non-Newtonian fluid, cavitation, rheology, fluent
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75819 (URN)10.3390/lubricants7080069 (DOI)000482956800010 ()2-s2.0-85071170341 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-09 (johcin)

Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-13Bibliographically approved
Hua, J., Björling, M., Grahn, M., Larsson, R. & Shi, Y. (2019). A smart friction control strategy enabled by CO2 absorption and desorption. Scientific Reports, 9(1), Article ID 13262.
Open this publication in new window or tab >>A smart friction control strategy enabled by CO2 absorption and desorption
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 13262Article in journal (Refereed) Published
Abstract [en]

Intelligent control of friction is an attractive but challenging topic and it has rarely been investigated for full size engineering applications. In this work, it is instigated if it would be possible to adjust friction by controlling viscosity in a lubricated contact. By exploiting the ability to adjust the viscosity of the switchable ionic liquids, 1,8-Diazabicyclo (5.4.0) undec-7-ene (DBU)/ glycerol mixture via the addition of CO2, the friction could be controlled in the elastohydrodynamic lubrication (EHL) regime. The friction decreased with increasing the amount of CO2 to the lubricant and increased after partial releasing CO2. As CO2 was absorbed by the liquid, the viscosity of the liquid increased which resulted in that the film thickness increased. At the same time the pressure-viscosity coefficient decreased with the addition of CO2. When CO2 was released again the friction increased and it was thus possible to control friction by adding or removing CO2.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Chemical Process Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Chemical Technology; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-76046 (URN)10.1038/s41598-019-49864-w (DOI)000485680900059 ()31519987 (PubMedID)2-s2.0-85072208170 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-18 (johcin)

Available from: 2019-09-18 Created: 2019-09-18 Last updated: 2019-10-25Bibliographically approved
Björling, M., Habchi, W., Bair, S., Larsson, R. & Marklund, P. (2019). Erratum: Towards the true prediction of EHL friction (ed.). Tribology International, 133, 297-297
Open this publication in new window or tab >>Erratum: Towards the true prediction of EHL friction
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 133, p. 297-297Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-73121 (URN)10.1016/j.triboint.2018.10.018 (DOI)
Note

Erratum in: Tribology International, vol. 66, p.19-26, DOI:10.1016/j.triboint.2013.04.008

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-03-06Bibliographically approved
Hultqvist, T., Vrček, A., Prakash, B., Marklund, P. & Larsson, R. (2019). Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts. Journal of tribology, 141(3), Article ID 031502.
Open this publication in new window or tab >>Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts
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2019 (English)In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 141, no 3, article id 031502Article in journal (Refereed) Published
Abstract [en]

In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity-pressure and compressibility-pressure behaviour have been shown to influence the film thickness and pressure distribution in EHL contacts, further influencing the durability. In this work, a finite line EHL contact is analysed with focus on the oil compressibility- and viscositypressure response, comparing two oils with relatively different behaviour and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller

Place, publisher, year, edition, pages
ASME Press, 2019
Keywords
Elastohydrodynamic lubrication, Finite line contacts, Sub-surface stress, Transient loading
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-71551 (URN)10.1115/1.4041733 (DOI)000457029800007 ()2-s2.0-85057759100 (Scopus ID)
Funder
Swedish Energy Agency, 41215-1
Note

Validerad;2018;Nivå 2;2018-12-07 (johcin)

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-09-13Bibliographically approved
Hansen, J., Björling, M. & Larsson, R. (2019). Mapping of the lubrication regimes in rough surface EHL contacts. Tribology International, 131, 637-651
Open this publication in new window or tab >>Mapping of the lubrication regimes in rough surface EHL contacts
2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 131, p. 637-651Article in journal (Refereed) Published
Abstract [en]

Understanding film formation in rough surface elastohydrodynamically lubricated (EHL) contacts have been an ongoing pursuit in lubrication science for more than half a century. This study furthers that quest by establishing a single combined friction and electrical contact resistance map that forms a clear and comprehensive overview of the lubrication performance. A ball-on-disc machine was operated under a wide variety of heavily loaded rolling/sliding contact conditions. Results show that while sweeping the contact over the SRR- and entrainment speed-domain, the primary sweep direction significantly affects running-in and consequently the transition from full-film to the mixed lubrication regime. Such knowledge sheds new light into the mechanisms that governs EHL film formation and the concurrent interplay with the mixed lubricated friction coefficient.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rough surface EHL, Friction, Stribeck curve, Running-in
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-71681 (URN)10.1016/j.triboint.2018.11.015 (DOI)000456766000062 ()2-s2.0-85057507855 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-12-05 (johcin)

Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2019-02-21Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-9110-2819

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