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Publications (10 of 16) Show all publications
Hultqvist, T., Vrček, A., Johannesson, T., Marklund, P. & Larsson, R. (2021). Transient plasto-elastohydrodynamic lubrication concerning surface features with application to split roller bearings. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 235(2), 453-467
Open this publication in new window or tab >>Transient plasto-elastohydrodynamic lubrication concerning surface features with application to split roller bearings
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2021 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 235, no 2, p. 453-467Article in journal (Refereed) Published
Abstract [en]

The use of roller bearings as crankshaft main bearings has shown potential in reducing the fuel consumption of internal combustion engines. An effective way to mount the roller bearing onto the crankshaft is to split the outer ring. However, this may lead to a severe out-of-roundness in the split region when the bearing is mounted, further implying increased noise, vibrations and contact stresses. In this work, a novel approach to study the plasto-elastohydrodynamic contact using commercial finite element software is developed. The modelling approach is based on the contact moving in space, allowing for the stress history based on the lubricant pressure to be studied in a straight-forward manner. The model is first utilised to study the influence of asperities on the lubricating conditions, indicating that stresses may exceed the yield strength of the material due to the transient effects taking place when the surface feature is over-rolled. Thereafter, the model is used to analyse the step in a mounted crankshaft roller bearing with the purpose of specifying a critical step height, which implies zero plasticity and thereby a reduced risk of accumulated damage in the vicinity of the step.

Place, publisher, year, edition, pages
Sage Publications, 2021
Keywords
Split roller bearings, Plasto-elastohydrodynamic lubrication, Elastohydrodynamic lubrication, Transient conditions, Numerical modelling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-78887 (URN)10.1177/1350650120927566 (DOI)000538261600001 ()2-s2.0-85086005834 (Scopus ID)
Funder
Swedish Energy Agency, P41215-1
Note

Validerad;2021;Nivå 2;2021-01-26 (alebob);

Artikeln har tidigare förekommit som manuskript i avhandling.

Available from: 2020-05-15 Created: 2020-05-15 Last updated: 2023-09-05Bibliographically approved
Vrček, A., Hultqvist, T., Johannesson, T., Marklund, P. & Larsson, R. (2021). Tribological characterization of potential crankshaft bearing steels for roller bearing engines. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 235(7), 1365-1378
Open this publication in new window or tab >>Tribological characterization of potential crankshaft bearing steels for roller bearing engines
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2021 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 235, no 7, p. 1365-1378Article in journal (Refereed) Published
Abstract [en]

A crankshaft roller bearing internal combustion engine (ICE) offers a five percent or more improvement in overall engine efficiency and, thereby, a reduction in a five percent of CO2 emissions, compared to a plain bearing supported crankshaft. Current forged crankshaft steels represent the limiting factor of the rolling component, therefore, a replacement of the crankshaft steel is required. Apart from this, the tribology of the rolling contacts has been shown to be detrimental when lubricated with current engine oils. Therefore, this paper investigates the tribological performance of potential crankshaft bearing steels, i.e. DIN C56E2 (G55); DIN 50CrMo4 (G50); and DIN 100Cr6 (G3), while utilizing a state-of-the-art low viscosity 0W20 engine oil and under conditions prevalent to ICE. For this, damage mode investigation was performed in a disc-on-disc setup. Based on the results, wear damage of DIN 100Cr6 discs was shown to be dependent on the steel grade of which the counterpart disc was made from and surface hardness difference between both discs. In addition, surface fatigue and wear damage can be completely eliminated by selecting a proper surface roughness and hardness combination. Also, while under an elevated roughness level, engine oil was shown to promote both surface fatigue and wear damage through the work of ZDDP additives, which under extreme conditions can act as an extreme pressure (EP) additive. The residual stress measurements using the XRD technique revealed relatively high compressive residual stresses for G55 and G50 in comparison to G3 steel after surface induction hardening. In addition, no significant changes in residual stress for G55 and G50 were observed after the test. In contrast, relatively high tensile stress was observed for G3 near the surface region. This suggests that the most commonly used 100Cr6 bearing steel, in this case, is the most susceptible to surface fatigue.

Place, publisher, year, edition, pages
Sage Publications, 2021
Keywords
ZDDP tribofilm, surface fatigue, wear, medium carbon steels, induction hardening
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-80861 (URN)10.1177/1350650120957780 (DOI)000571120000001 ()2-s2.0-85091041312 (Scopus ID)
Funder
Swedish Energy Agency, P41215-1
Note

Validerad;2021;Nivå 2;2021-06-18 (beamah)

Available from: 2020-09-21 Created: 2020-09-21 Last updated: 2023-09-05Bibliographically approved
Hultqvist, T., Vrček, A., Johannesson, T., Marklund, P. & Larsson, R. (2020). Analysis of Split Crankshaft Roller Bearings with Focus on Lubrication and Contact Stresses. In: : . Paper presented at 22nd International Colloquium Tribology: Industrial and Automotive Lubrication, January 28-30, 2020, Stuttgart/Ostfildern, Germany.
Open this publication in new window or tab >>Analysis of Split Crankshaft Roller Bearings with Focus on Lubrication and Contact Stresses
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2020 (English)Conference paper, Oral presentation only (Refereed)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-78735 (URN)
Conference
22nd International Colloquium Tribology: Industrial and Automotive Lubrication, January 28-30, 2020, Stuttgart/Ostfildern, Germany
Funder
Swedish Energy Agency, 41215-1
Available from: 2020-04-30 Created: 2020-04-30 Last updated: 2023-09-05Bibliographically approved
Vrček, A., Hultqvist, T., Johannesson, T., Marklund, P. & Larsson, R. (2020). Micro-pitting and wear characterization for different rolling bearing steels: Effect of hardness and heat treatments. Wear, 458-459, Article ID 203404.
Open this publication in new window or tab >>Micro-pitting and wear characterization for different rolling bearing steels: Effect of hardness and heat treatments
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2020 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 458-459, article id 203404Article in journal (Refereed) Published
Abstract [en]

The current trend of increased power density and reduction of oil viscosity in machine components is forcing engineers and scientists to engineer surfaces to endure higher contact pressures and stresses induced from rolling/sliding motion. Typically, surface-initiated rolling contact fatigue represents the main failure mode and has been gaining more and more attention lately. In this paper, the extent and morphology of the surface damage of different bearing steels in disc-on-disc contact under reduced lubrication conditions are studied. For this, rough-on-smooth contact was selected to promote surface fatigue damage on the smoother surface. Special attention was given to study both the effect of the hardness difference of the discs and the influence of different heat treatments, i.e. surface induction hardening (SIH) or through hardening (TH), on micro-pitting and wear performance. It was demonstrated through tribo-testing that the faster, rough surface undergoes only mild wear and plastic deformation of asperities. However, three different damage modes were observed and assessed on the slower, smoother surface, where the damage mode showed a strong dependence on a surface hardness difference between the smooth and the rough surface. Furthermore, it was observed that a plain medium carbon steel (DIN 56E2) showed better surface fatigue resistance than a low alloy high carbon steel (DIN 100Cr6) at similar surface hardness levels if SIH is applied on the former.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Surface-initiated rolling contact fatigue, Micro-pitting, Wear, Surface induction hardening, Hardness
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-80201 (URN)10.1016/j.wear.2020.203404 (DOI)000572439700002 ()2-s2.0-85089816181 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-08-31 (alebob)

Available from: 2020-07-09 Created: 2020-07-09 Last updated: 2023-09-05Bibliographically approved
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)
Conference
22nd International Colloquium Tribology: Industrial and Automotive Lubrication
Note

ISBN för värdpublikation: 978-3-943563-11-5

Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2023-09-05Bibliographically approved
Hultqvist, T., Vrček, A., Marklund, P. & Larsson, R. (2020). On Waviness and Two-Sided Surface Features in Thermal Elastohydrodynamically Lubricated Line Contacts. Lubricants, 8(6), Article ID 64.
Open this publication in new window or tab >>On Waviness and Two-Sided Surface Features in Thermal Elastohydrodynamically Lubricated Line Contacts
2020 (English)In: Lubricants, ISSN 2075-4442, Vol. 8, no 6, article id 64Article in journal (Refereed) Published
Abstract [en]

Machine components are designed to endure increasingly severe operating conditions due to the strive for improved energy efficiency of mechanical systems. Consequently, lubricated non-conformal contacts must rely on thin lubricant films where the influence of surface topography on the lubricating conditions becomes significant. Due to the complexity of the multiphysical problem, approximate assumptions are often employed to facilitate numerical studies of elastohydrodynamically lubricated (EHL) contacts. In this work, the rough, time dependent, thermal EHL problem is solved with focus on two main analyses. The first analysis focuses on the influence of sinusoidal roughness and the difference between a thermal non-Newtonian approach and an isothermal Newtonian approach. The second analysis is focused on the lubricating mechanisms taking place when two-sided surface features overtake within the thermal EHL contact. The results indicate that the film thickness in the outlet of the contact may be significantly overestimated by an isothermal Newtonian approach and that differences in the high-pressure region may also occur due to viscosity variations in the inlet of the contact. Moreover, for the studied two-sided surface features, it became evident that not only the surface feature combination but also the overtaking position influence the film thickness and pressure variations significantly.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
thermal elastohydrodynamic lubrication, elastohydrodynamic lubrication, waviness, surface features, transient analysis, numerical modelling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-79397 (URN)10.3390/lubricants8060064 (DOI)000551243100002 ()2-s2.0-85087513880 (Scopus ID)
Funder
Swedish Energy Agency
Note

Validerad;2020;Nivå 2;2020-07-09 (johcin)

Available from: 2020-06-11 Created: 2020-06-11 Last updated: 2023-09-05Bibliographically 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)000505271400031 ()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: 2023-09-05Bibliographically approved
Hultqvist, T. (2020). Transient elastohydrodynamic lubrication: Effects of geometry, surface roughness, temperature, and plastic deformation. (Doctoral dissertation). Luleå University of Technology
Open this publication in new window or tab >>Transient elastohydrodynamic lubrication: Effects of geometry, surface roughness, temperature, and plastic deformation
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The urgent need to reduce greenhouse gas emissions in combination with an increased use of sustainable energy resources have led to immense efforts on improving energy efficiency of mechanical systems. Consequently, modern machine elements are typically lubricated with low viscosity oils and designed to endure an increasingly high power density. This typically implies that the surfaces in contact are separated by thinner lubricant films that must carry higher loads. Thereby, in order to improve the durability and efficiency of future machine elements, an improved fundamental understanding of the predominant lubrication mechanisms must be achieved. This thesis concerns numerical simulation of non-conformal lubricated contacts where significant elastic deformations in combination with hydrodynamic effects govern the lubricating film formation, typically found in e.g., rolling element bearings, gears, and cam-follower systems. Such contacts relate to a lubrication regime known as elastohydrodynamic lubrication (EHL), which is often studied using simplifying assumptions due to its multiphysical nature. Typical simplifications of the EHL problem may include e.g., steady-state conditions, perfectly elastic surfaces, isothermal conditions, and Newtonian lubricant behaviour. However, such simplifications may be progressively relieved because of a continuously improved computer performance and the use of increasingly efficient numerical methods. In this work, time dependent simulations of EHL contacts are conducted with the purpose of improving the fundamental understanding of the predominant lubrication mechanisms. This is achieved by the development and utilisation of novel models and modelling techniques, specifically developed for the conducted investigations focusing on e.g., temperature, plastic deformation, surface roughness, and contact geometry. The developed models are all an extension of a full-system finite element modelling approach that was relatively recently introduced to the EHL community. Important findings from this work relate to the influence of transient fluctuations in EHL contacts, which occur due to both transient loads and moving surface roughness. It is shown that in the case of transient loading of a finite line EHL contact, a steady state assumption may overestimate the minimum film thickness and underestimate the maximum pressure over time due to the formation of lubricant waves travelling through the contact. Furthermore, thermal and non-Newtonian effects on viscosity may be necessary to consider in both qualitative and quantitative studies of roughness within the EHL contact, especially under sliding conditions and short wavelength roughness. Lastly, transient fluctuations related to the over-rolling of surface features are shown to potentially increase the pressure within the EHL contact to such an extent that plastic deformations of the contacting surfaces occur. The models established in this work may provide researchers and engineers with ways to improve their studies of transient EHL contacts. The salient findings from the conducted studies also open up for interesting directions that may be extended to potentially improve the lubrication theories currently in use and thereby improve the design of future machine elements that employ non-conformal contacts.

Place, publisher, year, edition, pages
Luleå University of Technology, 2020
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-78886 (URN)978-91-7790-603-2 (ISBN)978-91-7790-604-9 (ISBN)
Public defence
2020-09-25, E632, Luleå, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, P41215-1
Available from: 2020-05-19 Created: 2020-05-15 Last updated: 2023-09-05Bibliographically 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
American Society for Mechanical Engineers (ASME), 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: 2023-09-05Bibliographically 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: 2023-09-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7285-6639

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