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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.
Show others...
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)000518699700032 ()
Note

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

Available from: 2020-01-07 Created: 2020-01-07 Last updated: 2020-04-02Bibliographically 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
Hansen, J., Björling, M. & Larsson, R. (2019). Small changes in surface roughness can make a dramatic difference!. In: : . Paper presented at Tribology Days, Swerim AB, 12-13th, Stockholm, Sweden, November, 2019.
Open this publication in new window or tab >>Small changes in surface roughness can make a dramatic difference!
2019 (English)Conference paper, Oral presentation only (Refereed)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:ltu:diva-77706 (URN)
Conference
Tribology Days, Swerim AB, 12-13th, Stockholm, Sweden, November, 2019
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-14
Hansen, J., Björling, M. & Larsson, R. (2018). Improved performance by ionic additives in hydrocarbon base fluids for mixed-rolling/sliding contacts. In: : . Paper presented at The 18th Nordic Symposium on Tribology – NORDTRIB, Uppsala, Sverige, June 18-21.
Open this publication in new window or tab >>Improved performance by ionic additives in hydrocarbon base fluids for mixed-rolling/sliding contacts
2018 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:ltu:diva-75805 (URN)
Conference
The 18th Nordic Symposium on Tribology – NORDTRIB, Uppsala, Sverige, June 18-21
Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-09-02
Hansen, J., Björling, M., Minami, I. & Larsson, R. (2018). Performance and mechanisms of silicate tribofilm in heavily loaded rolling/sliding non-conformal contacts. Tribology International, 123, 130-141
Open this publication in new window or tab >>Performance and mechanisms of silicate tribofilm in heavily loaded rolling/sliding non-conformal contacts
2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 123, p. 130-141Article in journal (Refereed) Published
Abstract [en]

Lubricant performance is vital as heavy-duty gear manufacturers increase power density in their efforts towards increased efficiency. In this work, a recently developed ionic liquid is introduced as a multifunction additive for use in hydrocarbon base fluid. A ball-on-disc tribological test machine was used to evaluate friction and wear in heavily loaded mixed rolling/sliding conditions. The novel multifunctional additive is benchmarked against conventional axle-gear oil additives, and results shows excellent tribological performance in terms of friction and wear. Post-test surface analysis of the wear scars revealed a silicate based tribofilm derived from the novel ionic additive, contrary to conventional phosphorous and/or sulfur based. The silicate tribofilm is correlated to a significantly increased wear resistance and vastly improved running-in performance.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-67928 (URN)10.1016/j.triboint.2018.03.006 (DOI)000431161600014 ()2-s2.0-85043594654 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-03-20 (andbra)

Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-06-11Bibliographically approved
Hansen, J., Björling, M., Nyberg, E. & Larsson, R. (2017). Elastohydrodynamic performance of a hydrocarbon mimicking ionic liquid additive. In: : . Paper presented at STLE Annual Meeting & Exhibition, Atlanta, USA, May 22-25.
Open this publication in new window or tab >>Elastohydrodynamic performance of a hydrocarbon mimicking ionic liquid additive
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Machine elements operating under lubricated conditions will eventually fail due to high stresses and fatigue-related causes. In order to find optimum protective measures, it is important to understand how the stresses arise and what factors that influence their magnitude. With the current shift for more sever lubricating regimes, the role of tribo-improvers is becoming vital. At this point, the interplay between the chemisorption mechanism of various lubricant compounds and surface failure is not yet fully understood. To obtain a better understanding of this, a newly developed ionic structured tribo-improving additive, based on silicon, was investigated and benchmarked against conventional heavy-duty gearbox additives. A ball on disc device was operated under heavily loaded rolling/sliding conditions, at elevated temperature to simulate gear like conditions, and lubricating performance was subsequently evaluated in terms of friction and wear. Such results highlight the importance of properly designed lubricants for optimal tribo-performance under rolling-sliding conditions

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-66451 (URN)
Conference
STLE Annual Meeting & Exhibition, Atlanta, USA, May 22-25
Available from: 2017-11-07 Created: 2017-11-07 Last updated: 2018-01-13Bibliographically approved
Hansen, J. & Larsson, R. (2015). Gear contact simulation on asperity level. In: : . Paper presented at Tribology Days, Nynas AB, Nynäshamn, Sweden, 7-8th October, 2015.
Open this publication in new window or tab >>Gear contact simulation on asperity level
2015 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Gears used in gearboxes and those used in rear axles are subject to constantly increasing demands for reliability, performance and efficiency. To meet the requirements of the future market computer aided engineering, CAE, is becoming more and more vital in order to understand the onset and cause to failure and to optimize for best possible performance. The aim of this master thesis was to pave the way for numerical modelling as a complement to testing and to give insight in how the problem of simulating gears with oil and surface roughness incorporated can be addressed. Moreover, as part of this, the work was to be conducted in order to give insight in possibilities as well as shortcomings with present tools. Therefore a numerical tool which is capable of indicating the load carried by the asperities and the separating lubricant film during the event of a gear mesh has been developed. Several contact mechanics codes and different EHL formulas has been studied in order to provide alternative foundations to the gear simulation model. The model accounts for real surface topographies, different oil formulations as well as operational conditions and gear designs. Results show that the model visually correlates to test gears subjected to similar conditions in terms of critical areas on the gear flank. Even though validation is required to reveal model accuracy, at present, the model can be utilized to indicate how different conditions affect the asperity and lubricant load share and thus what combination that is most beneficial in terms of better performance and prolonged service life. In addition, a local scale asperity simulation where single asperities have been subjected to numerous collisions has also been developed. Results show that there is very promising potential in terms of future development as the model comprises the ability to potentially capture the initial state on the formation and development of a micropit.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:ltu:diva-77749 (URN)
Conference
Tribology Days, Nynas AB, Nynäshamn, Sweden, 7-8th October, 2015
Available from: 2020-02-17 Created: 2020-02-17 Last updated: 2020-02-17
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3637-9078

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