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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)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: 2019-01-11Bibliographically 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)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: 2018-12-10Bibliographically approved
Vrček, A., Hultqvist, T., Baubet, Y., Björling, M., Marklund, P. & Larsson, R. (2019). Micro-pitting and wear assessment of engine oils operating under boundary lubrication conditions. Tribology International, 129, 338-346
Open this publication in new window or tab >>Micro-pitting and wear assessment of engine oils operating under boundary lubrication conditions
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 129, p. 338-346Article in journal (Refereed) Published
Abstract [en]

Current state-of-the-art engine oils tend to enhance micro-pitting damage in rolling contacts under certain operating conditions. ZDDP anti-wear additive was shown to promote such behavior. However, in order to optimize an engine oil formulation for rolling contacts, further studies are needed to assess engine oils in terms of micro-pitting and wear damage. This investigation studies the micro-pitting and wear performance of a number of engine oils for rolling contacts in a ball-on-disc configuration under conditions prevalent in crankshaft roller bearing applications. Based on the results it was concluded that an engine oil containing higher blend of PAO base oil compared to the oil mixture of Group III and PAO has a lower tendency towards micro-pitting and wear.

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-70731 (URN)10.1016/j.triboint.2018.08.032 (DOI)000447575600028 ()2-s2.0-85052642062 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-09-24 (inah)

Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-11-01Bibliographically approved
Wu, J., Mu, L., Feng, X., Lu, X., Larsson, R. & Shi, Y. (2019). Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease. Advanced Materials Interfaces
Open this publication in new window or tab >>Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease
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2019 (English)In: Advanced Materials Interfaces, ISSN 2196-7350Article in journal (Refereed) Epub ahead of print
Abstract [en]

Polymers prepared from ionic liquids are widely called polymerized ionic liquids (PILs). Compared to monocationic and dicationic ILs, PILs have higher molecular weights, charge, and greater intermolecular interactions, which make PILs have a higher possibility to generate better lubricity. PILs of poly‐alkylimidazolium bis(trifluoromethylsulfonyl)imide (PImC6NTf2) is studied herein. Dicationic ILs of 1,1′‐(pentane‐1,5‐diyl)‐bis(3‐butylimidazolium) bis(trifluoromethylsulfonyl)imide (BIm5‐(NTf2)2) is used as additive to decrease the crystallization temperature of PImC6NTf2. Lubricity of PImC6NTf2 and PImC6NTf2+BIm5‐(NTf2)2, as well as BIm5‐(NTf2)2 for comparison is evaluated under severe conditions, i.e., 3.0 to 3.5 GPa and 200 °C. The rheological study suggests that PImC6NTf2 can be classified into grease. Tribological test results show that PImC6NTf2 has much better antiwear property than BIm5‐(NTf2)2, especially at 3.5 GPa. Adding 4% BIm5‐(NTf2)2 to PImC6NTf2 is able to reduce friction under high pressure. At 200 °C, PImC6NTf2 exhibits excellent lubricity. The mixture of 96%PImC6NTf2+4%BIm5‐(NTf2)2 shows even better antiwear property than neat PImC6NTf2 and exhibits the highest friction reducing property among the ILs at 200 °C. It is speculated that the robust strength of PILs and strong adhesion between PILs and solids are key factors in achieving the excellent antiwear property.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
grease, high pressure and high temperature, lubricity, polymerized ionic liquids
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72623 (URN)10.1002/admi.201801796 (DOI)
Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-01-18
Björling, M., Habchi, W., Bair, S., Larsson, R. & Marklund, P. (2018). Correction to: Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation (ed.) [Letter to the editor]. Tribology letters, 66(4), 1-1
Open this publication in new window or tab >>Correction to: Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation
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2018 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 4, p. 1-1Article in journal, Letter (Refereed) Published
Abstract [en]

The original version of this article unfortunately contained a mistake. The correct information is given below. [ABSTRACT FROM AUTHOR]  Copyright of Tribology Letters is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-71140 (URN)10.1007/s11249-018-1079-x (DOI)
Available from: 2018-10-08 Created: 2018-10-08 Last updated: 2018-10-08Bibliographically approved
Wu, J., Huang, X., Berglund, K., Lu, X., Feng, X., Larsson, R. & Shi, Y. (2018). CuO nanosheets produced in graphene oxide solution: An excellent anti-wear additive for self-lubricating polymer composites. Composites Science And Technology, 162, 86-92
Open this publication in new window or tab >>CuO nanosheets produced in graphene oxide solution: An excellent anti-wear additive for self-lubricating polymer composites
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2018 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, p. 86-92Article in journal (Refereed) Published
Abstract [en]

In the present work, graphene oxide is used as template to produce CuO nanosheets, which solves aggregation and dispersion problems of CuO nanosheets resulting in improved lubricating performance. SEM and AFM studies show that CuO nanosheets are present in fusiform flake shape with a thickness, width and length of around 13, 400 and 1000 nm, respectively. CuO nanosheets were added to the carbon fibers reinforced Polytetrafluoroethylene (CF/PTFE) to study their lubricating performance. It is interesting, from fractured surfaces of composites, to find that CuO nanosheets enhance the interface properties between carbon fibers and PTFE. The wear resistance property of CF/PTFE is remarkably improved after filling CuO nanosheets. For example, the wear rate is reduced by 51% after filling 1.5 wt % CuO nanosheets. The wear resistance improvement effect of CuO nanosheets is much better than that of commercial CuO nanogranules and CuO nanorods. Worn surfaces and counter-surfaces studying indicates that CuO nanosheets can not only prevent the rubbed-off of PTFE or the detachment of CF, but also improve the properties of transfer films, which greatly reduce the adhesive wear and abrasive wear.

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-68387 (URN)10.1016/j.compscitech.2018.04.020 (DOI)000438180500010 ()2-s2.0-85046114065 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-09 (andbra)

Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2018-08-09Bibliographically approved
Hultqvist, T., Shirzadegan, M., Vrček, A., Baubet, Y., Prakash, B., Marklund, P. & Larsson, R. (2018). Elastohydrodynamic lubrication for the finite line contact under transient loading conditions. Tribology International, 127, 489-499
Open this publication in new window or tab >>Elastohydrodynamic lubrication for the finite line contact under transient loading conditions
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, p. 489-499Article in journal (Refereed) Published
Abstract [en]

Research related to elastohydrodynamic lubrication (EHL) has led to improved performance and durability of machine elements where non-conformal contact geometries interact. Only a relatively small portion of the EHL literature has, however, dealt with the lubricating performance of finite line contacts under non-steady conditions, commonly found in many practical applications. The purpose of this work has thus been to further understand the behaviour of finite line EHL contacts under transient conditions by studying a finite length roller subjected to a time varying load using a full-system finite element approach. The transient load was shown to initiate oscillations in the system, governed by waves of lubricant moving through the contact, affecting both pressure and film thickness throughout the contact.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Elastohydrodynamic lubrication, Finite line contacts, Transient loading, Finite elements
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-70211 (URN)10.1016/j.triboint.2018.06.035 (DOI)000442334100048 ()2-s2.0-85049452630 (Scopus ID)
Funder
Swedish Energy Agency, 41215-1
Note

Validerad;2018;Nivå 2;2018-08-06 (andbra)

Available from: 2018-08-06 Created: 2018-08-06 Last updated: 2018-09-10Bibliographically approved
Linjamaa, A., Lehtovaara, A., Larsson, R., Kallio, M. & Söchting, S. (2018). Modelling and analysis of elastic and thermal deformations of a hybrid journal bearing. Paper presented at 17th Nordic Symposium on Tribology - NORDTRIB 2016, Aulanko, Hämeenlinna, Finland, 14th - 17th June 2016. Tribology International, 118, 451-457
Open this publication in new window or tab >>Modelling and analysis of elastic and thermal deformations of a hybrid journal bearing
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 451-457Article in journal (Refereed) Published
Abstract [en]

The continuous demand for higher power density leads to a very challenging operational environment for sliding bearings regarding pressures and deformations. Understanding of the deformation behavior of heavily loaded bearings becomes even more pronounced when modern hybrid multilayer designs are considered. The aim of this study is to develop a numerical, multi-physical model for the evaluation of journal bearing performance. Hydrodynamics were based on the Reynolds equation and deformations were calculated using the integrated finite element method. Elastic and thermal deformations have a significant effect on bearing performance and those deformations can be adjusted with properties of polymer layer. The design of hybrid bearings is delicate and their properties must be tailored according to the operating conditions.

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-62146 (URN)10.1016/j.triboint.2017.02.029 (DOI)000423004700045 ()2-s2.0-85013776815 (Scopus ID)
Conference
17th Nordic Symposium on Tribology - NORDTRIB 2016, Aulanko, Hämeenlinna, Finland, 14th - 17th June 2016
Note

2018-02-01 (rokbeg);Konferensartikel i tidskrift

Available from: 2017-02-23 Created: 2017-02-23 Last updated: 2018-02-01Bibliographically approved
Pérez-Ràfols, F., Larsson, R., van Riet, E. J. & Almqvist, A. (2018). On the flow through plastically deformed surfaces under unloading: A spectral approach. Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, 232(5), 908-918
Open this publication in new window or tab >>On the flow through plastically deformed surfaces under unloading: A spectral approach
2018 (English)In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, no 5, p. 908-918Article in journal (Refereed) Published
Abstract [en]

This study considers flow through the gap left between two surfaces during unloading, in other words, when an applied load is gradually reduced after loading to a state where plastic deformation occurs. In particular, the permeability of the gap is studied. It was found that a substantial reduction of the applied load is required before the permeability starts to increase significantly. The explanation for this phenomenon is given by the combination of components with different wavelengths present in the surface. Components with long wavelengths deform elastically and those with shorter wavelengths may also deform plastically. We found that plastic deformation acts to keep the permeability nearly constant at the beginning of the unloading and elastic spring-back is responsible for the rapid increase at lower loads. This principle constitutes a basis for the strategy that was developed in order to predict the load at which the rapid increase of permeability starts.

Place, publisher, year, edition, pages
Sage Publications, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-62112 (URN)10.1177/0954406217690180 (DOI)000429913000015 ()
Note

Validerad;2018;Nivå 2;2018-02-26 (svasva)

Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2018-04-27Bibliographically approved
Ràfols, F. P., Larsson, R., Van Riet, E. J. & Almqvist, A. (2018). On the loading and unloading of metal-to-metal seals: A two-scale stochastic approach. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 232(12), 1525-1537
Open this publication in new window or tab >>On the loading and unloading of metal-to-metal seals: A two-scale stochastic approach
2018 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, no 12, p. 1525-1537Article in journal (Refereed) Published
Abstract [en]

During operation, the mating surfaces of a metal-to-metal seal typically undergo significant plastic deformation, which in turn can have beneficial effect on its performance. In previous studies, it has, for instance, been shown that plastic deformation can provide for better sealing during unloading. Those studies did, however, only consider flow through unrealistically small domains. Therefore, it is possible that this might be a size effect, which would not be apparent in a real situation with a much larger domain. In this paper, we develop a model which can handle real-sized seal domains at the same time as fine details of the surface topography. More precisely, we construct a two-scale model, in which the global scale represents the seal domain and where the influence of the fine details at the local scale are represented by a stochastic element. By means of this stochastic two-scale model, we show that the beneficial effect associated with the plastic deformation persists also when real-sized seal domains are considered.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
Contact mechanics, load cycle, Reynolds equation, seals, stochastic, two-scale modelling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-67695 (URN)10.1177/1350650118755620 (DOI)000450295800004 ()2-s2.0-85044080716 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-19 (johcin)

Available from: 2018-02-20 Created: 2018-02-20 Last updated: 2018-12-03Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9110-2819

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