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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
Deng, L., Pelcastre, L., Hardell, J., Prakash, B. & Oldenburg, M. (2018). Experimental Evaluation of Galling Under Press Hardening Conditions. Tribology letters, 66(3), Article ID 93.
Open this publication in new window or tab >>Experimental Evaluation of Galling Under Press Hardening Conditions
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2018 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 3, article id 93Article in journal (Refereed) Published
Abstract [en]

Severe adhesion, also referred to as galling, is a critical problem in press hardening, especially in stamping tools used for hot forming of Al–Si-coated ultra-high strength steel. Galling is known to develop rapidly on the tool surface and it negatively affects the quality of the formed products. Earlier research on this topic has focused on the galling initiation. However, studies on the galling development during extended sliding and the corresponding quantitative measurement still lack depth. In the present study, a tribological test is established to study the galling development under press hardening conditions. The tribological test set-up aims to simulate extended sliding between the Al–Si-coated boron steels and the tool die material. The contact conditions in the interface are studied by a numerical model of the tribological test. The friction coefficients and material transfer are discussed taking into account the variation of the different test conditions. Using the results from the tribological tests, the galling simulation is performed in the numerical model. A geometry-updated sample based on the galling (transferred material build-up) height is simulated and the consequent pressure fluctuation is obtained in the numerical model. This contributes to the explanation of the severe transferred material accumulation during the test.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Applied Mechanics
Research subject
Machine Elements; Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-69943 (URN)10.1007/s11249-018-1023-0 (DOI)000436540000001 ()2-s2.0-85049356784 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-06-27 (andbra)

Available from: 2018-06-27 Created: 2018-06-27 Last updated: 2018-07-23Bibliographically approved
Hernandez, S., Hardell, J. & Prakash, B. (2018). High-Temperature Friction and Wear of Boron Steel and Tool Steel in Open and Closed Tribosystems. Tribology Transactions, 61(3), 448-458
Open this publication in new window or tab >>High-Temperature Friction and Wear of Boron Steel and Tool Steel in Open and Closed Tribosystems
2018 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 3, p. 448-458Article in journal (Refereed) Published
Abstract [en]

More and more components in automotive, material processing and mining industries are operating under harsh conditions involving high temperatures and high contact pressures. Tribotesting for such applications is done using both open (one surface meeting a fresh counter-surface) and closed (one surface follows the same track on the counter-surface) test configurations. In order to enable development of new materials and processes intended for such conditions, there is a need for better understanding pertaining to tribological phenomena occurring under these different test configurations.

In this work, friction and wear characteristics of quenched and tempered tool steel sliding against boron steel (22MnB5) have been studied. The experiments were conducted using a specially designed hot strip tribometer (HST) under dry conditions at R.T. and 400°C in open as well as closed configurations. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were carried out to analyse the worn surfaces. Additionally, the results from the closed test configuration were compared to previous tests carried out with the same materials and parameters using a pin-on-disk (POD) test rig. The results have shown that wear was reduced at higher temperatures as well as with repeated sliding on the same contacting surfaces (i.e. closed configuration) compared to those with open configuration. A good correlation of wear mechanisms and coefficient of friction between closed configuration tests and those carried out with the POD test rig was observed especially at 400°C.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-65170 (URN)10.1080/10402004.2017.1350310 (DOI)000444573200006 ()2-s2.0-85028558287 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-08 (johcin) 

Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2018-10-08Bibliographically approved
Hultqvist, T., Vrček, A., Prakash, B., Marklund, P. & Larsson, R. (2018). Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts. Journal of tribology
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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2018 (English)In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897Article in journal (Refereed) Accepted
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

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)
Funder
Swedish Energy Agency, 41215-1
Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2018-11-13
Burkhart, C., Johansson, J., Uukonsari, J. & Prakash, B. (2018). Performance of lubricating oils for wind turbine gear boxes and bearings. Paper presented at 17th Nordic Symposium on Tribology - NORDTRIB 2016, Hämeenlinna, Finland, 14th - 17th June 2016. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 232(1), 62-72
Open this publication in new window or tab >>Performance of lubricating oils for wind turbine gear boxes and bearings
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 1, p. 62-72Article in journal (Refereed) Published
Abstract [en]

In this study, the friction and wear properties of six different new and used wind turbine gear oils (ISO VG 320), with different base oil formulations and additives packages, were investigated. For that purpose, a four-ball tribometer and an Optimol SRV were used. Moreover, the lubricants extreme pressure properties were also evaluated, using the same four-ball tribometer. The study also includes a characterization of the lubricants. The main objective was to compare the new and used gear oils in order to identify performance differences and predict oil change intervals. The results indicate that a use of 3 to 4 years is within the lifetime of the lubricant.

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-66356 (URN)10.1177/1350650117739764 (DOI)000419852700007 ()2-s2.0-85040449368 (Scopus ID)
Conference
17th Nordic Symposium on Tribology - NORDTRIB 2016, Hämeenlinna, Finland, 14th - 17th June 2016
Note

Konferensartikel i tidskrift

Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-01-25Bibliographically approved
Gebretsadik, D., Hardell, J. & Prakash, B. (2018). Seizure behaviour of Pb-free engine bearing materials under dry condition. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 232(2), 106-116
Open this publication in new window or tab >>Seizure behaviour of Pb-free engine bearing materials under dry condition
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 2, p. 106-116Article in journal (Refereed) Published
Abstract [en]

Due to new environmental regulations, Pb-free engine bearing materials are becoming more common and there is a need for studying their tribological performance. Under severe operating conditions, failure due to seizure can occur in engine bearings. In this work, seizure behaviour of different multi-layered engine bearing materials has been studied by using a block-on-ring test setup under dry condition. These materials included Al–Sn-based lining with no overlay, bronze lining with polyamide-imide-based overlay containing MoS2 and graphite, bronze lining with two overlays of Al–Sn-based and polyamide-imide-based material, bronze-based lining with Sn-based overlay and bismuth (Bi)-containing bronze with Sn-based overlay. The tests were performed by gradually increasing the load at a specific time interval and in a stepwise manner and at a constant speed under unidirectional dry sliding conditions. The test materials, counter surfaces and the wear debris were analysed using SEM with a view to understand the seizure mechanisms. Bronze-based lining with a polyamide-imide-based overlay containing MoS2 and graphite does not exhibit seizure up to a load of 475 N. For Al–Sn-based lining without overlay, seizure occurs at a relatively lower load of 125 N. The Al–Sn-based lining with no overlay shows higher friction and the polyamide-imide-based overlay containing MoS2 and graphite shows lower friction during the seizure test. In most cases, there is material transfer onto the test ring counter surface. Material transfer onto the counter surface either due to severe adhesion or wear debris adhered and smeared on it. Al–Sn-based lining and an exposed Al–Sn-based overlay show severe adhesion that causes seizure. On the other hand, exposed Pb containing lining and Bi containing lining seize due to mechanical interlocking caused by the adhered wear debris on both surfaces.

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-63437 (URN)10.1177/1350650117706641 (DOI)000424781600002 ()2-s2.0-85042873912 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-12 (svasva)

Available from: 2017-05-18 Created: 2017-05-18 Last updated: 2018-03-16Bibliographically approved
Torres, H., Vuchkov, T., Slawik, S., Gachot, C., Prakash, B. & Rodríguez Ripoll, M. (2018). Self-lubricating laser claddings for reducing friction and wear from room temperature to 600 °C. Wear, 408-409, 22-33
Open this publication in new window or tab >>Self-lubricating laser claddings for reducing friction and wear from room temperature to 600 °C
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2018 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 408-409, p. 22-33Article in journal (Refereed) Published
Abstract [en]

In this work, laser cladding has been employed for the preparation of nickel-based self-lubricating coatings featuring the addition of different combinations of soft metal solid lubricants such as Ag and Cu. Transition metal dichalcogenides (WS2, MoS2) were evaluated as precursors for encapsulating and uniformly distributing the soft metals throughout the microstructure. The tribological behaviour of the resulting claddings was evaluated under high temperature reciprocating sliding conditions, including two different counter body geometries that lead to very different ranges of contact pressures during testing. An improved tribological behaviour was observed for the self-lubricating claddings compared to the unmodified nickel-based alloy up to 600 °C, attributed to the presence of silver and the formation of lubricous sulfides during sample preparation due to the thermal degradation of the transition metal dichalcogenides precursors. Additionally, the role of the contact conditions observed when testing the self-lubricating claddings against flat pins instead of spherical counter bodies are discussed in terms of frictional and wear microstructural mechanisms.

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-68661 (URN)10.1016/j.wear.2018.05.001 (DOI)000436482000003 ()2-s2.0-85046630173 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-15 (rokbeg)

Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-08-07Bibliographically approved
Mozgovoy, S., Hardell, J., Deng, L., Oldenburg, M. & Prakash, B. (2018). Tribological Behavior of Tool Steel under Press Hardening Conditions Using Simulative Tests. Journal of tribology, 140(1), Article ID 011606.
Open this publication in new window or tab >>Tribological Behavior of Tool Steel under Press Hardening Conditions Using Simulative Tests
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2018 (English)In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 140, no 1, article id 011606Article in journal (Refereed) Published
Abstract [en]

Press hardening is employed in the automotive industry to produce advanced high-strength steel components for safety and structural applications. This hot forming process depends on friction as it controls the deformation of the sheet. However, friction is also associated with wear of the forming tools. Tool wear is a critical issue when it comes to the dimensional accuracy of the produced components and it reduces the service life of the tool. It is therefore desirable to enhance the durability of the tools by studying the influence of high contact pressures, cyclic thermal loading, and repetitive mechanical loading on tool wear. This is difficult to achieve in conventional tribological testing devices. Therefore, the tribological behavior of tool-workpiece material pairs at elevated temperatures was studied in a newly developed experimental setup simulating the conditions prevalent during interaction of the hot sheet with the tool surface. Uncoated 22MnB5 steel and aluminum-silicon (Al-Si)-coated 22MnB5 steel were tested at 750 °C and 920 °C, respectively. It was found that higher loads led to lower and more stable friction coefficients independent of sliding velocity or surface material. The influence of sliding velocity on the coefficient of friction was only marginal. In the case of Al-Si-coated 22MnB5, the friction coefficient was generally higher and unstable due to transfer of Al-Si coating material to the tool. Adhesion was the main wear mechanism in the case of uncoated 22MnB5

Place, publisher, year, edition, pages
ASME Press, 2018
National Category
Applied Mechanics Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Solid Mechanics; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-65268 (URN)10.1115/1.4036924 (DOI)000415376300018 ()2-s2.0-85027285991 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-08-28 (andbra)

Available from: 2017-08-23 Created: 2017-08-23 Last updated: 2018-01-13Bibliographically approved
Torres, H., Vuchkov, T., Rodríguez Ripoll, M. & Prakash, B. (2018). Tribological behaviour of MoS2-based self-lubricating laser cladding for use in high temperature applications. Tribology International, 126, 153-165
Open this publication in new window or tab >>Tribological behaviour of MoS2-based self-lubricating laser cladding for use in high temperature applications
2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 126, p. 153-165Article in journal (Refereed) Published
Abstract [en]

Many high temperature (HT) forming processes require the use of solid lubricants in order to control friction and reduce wear. In an attempt to eliminate the need for solid lubrication in high temperature sliding applications, nickel-based self-lubricating coatings with the addition of Ag and MoS2 were prepared by means of laser cladding on stainless steel substrates.

The behaviour of the resulting laser claddings was thoroughly evaluated up to 600 °C, including the oxidation behaviour and reciprocating tribotesting using different counter body geometries (ball and flat pin). The self-lubricating coatings showed lower friction than the unmodified reference alloy at all tested temperatures, in addition to a significant microstructural stability after prolonged exposure at high temperatures. The addition of solid lubricants to the claddings was also found to be beneficial in terms of the counter body wear at HT, as no material loss could be measured for the bearing balls after testing at 600 °C against the self-lubricating claddings, despite the significant softening experienced by AISI 52100 bearing steel at HT.

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-68937 (URN)10.1016/j.triboint.2018.05.015 (DOI)000437075900016 ()2-s2.0-85047212660 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-28 (andbra)

Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2018-08-10Bibliographically approved
Torres, H., Rodríguez Ripolla, M. & Prakash, B. (2018). Tribological behaviour of self-lubricating materials at high temperatures. International Materials Reviews, 63(5), 309-340
Open this publication in new window or tab >>Tribological behaviour of self-lubricating materials at high temperatures
2018 (English)In: International Materials Reviews, ISSN 0950-6608, E-ISSN 1743-2804, Vol. 63, no 5, p. 309-340Article in journal (Refereed) Published
Abstract [en]

Self-lubricating materials are becoming more widespread in fields like metal forming or power generation due to the inability to use conventional lubricants in high-temperature (HT) applications. In an effort to summarise the progress done in this field, a detailed literature review has been carried out, ranging from micron-thickness thin films to hardfacings and bulk materials, and classified by the reported solid lubricants. Moreover, the most-cited deposition techniques have been reviewed for each lubricant class in addition to their advantages and limitations. HT friction and wear data for self-lubricating materials have also been examined in order to identify effective lubrication ranges and general trends in their tribological behaviour, which is expected to be useful for researchers interested in this field. Finally, several apparent research gaps have been described, with suggestions for new experimental work that could lead to the development of new high-temperature self-lubricating materials.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-67041 (URN)10.1080/09506608.2017.1410944 (DOI)000427943900002 ()
Note

Validerad;2018;Nivå 2;2018-03-22 (rokbeg)

Available from: 2017-12-18 Created: 2017-12-18 Last updated: 2018-08-07Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1454-1118

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