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  • 101.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A New Film Parameter for Rough Surface EHL Contacts with Anisotropic and Isotropic Structures2021In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 69, no 2Article in journal (Refereed)
    Abstract [en]

    Numerous tribological contacts worldwide rely on adequate lubrication quality for proper functionality. Despite this, there is no existing approach to accurately predict the state of lubrication. The default model since introduced in the 1960s—the Λ-ratio, defined as the oil film thickness over the surface roughness height—is unpredictable and may yield erroneous results. Here, we put forward a framework for a new updated film parameter, Λ∗, which accounts for the elasto-hydrodynamic lubrication (EHL) effects induced by surface irregularities on the microscopic scale (micro-EHL). This new film parameter was validated in ball-on-disc tribological tests with engineering surfaces comprising isotropic and anisotropic structures. As expected, the new model was found to accurately predict the experimentally measured true mixed and full-film EHL regimes. The ability to accurately predict the mode of lubrication represents a major advance in designing tribological interfaces for optimal efficiency and durability.

  • 102.
    Hansen, Jonny
    et al.
    Gear Technology & NVH, Scania CV AB, Södertälje, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A new film parameter with micro elasto-hydrodynamics2022In: 7th World Tribology Congress (WTC 2022), 2022, article id MON-T1-S2-R4Conference paper (Other academic)
    Abstract [en]

    A new semi-analytical model for estimating the lubrication quality in rough surface elasto-hydrodynamiclubricated (EHL) contacts is presented. The model was derived upon the basis of an idealized micro-EHLcontact, and was subsequently extended to account for real engineering surfaces comprising isotropic andanisotropic roughness lay. Model validation was made against ball-on-disc experiments in which the true mixedand EHL regimes where identified by means of the electrical-contact-resistance signal (ECR). While, theconventional approach, the Λ-ratio, was found to grossly mispredict the transition to the EHL and mixedlubrication(ML) regime boundary, the new film parameter was found to be surprisingly accurate.

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  • 103.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    How a small change in surface roughness dramatically changes the transition to full-film lubrication in EHL2019Conference paper (Refereed)
    Abstract [en]

    To improve the efficiency in non-conformal type of machine elements, it is of crucial importance to gain knowledge about the underlying mechanism that governs the formation of an elastohydrodynamic (EHD) oil film. This study was set out to explore the dependency of surface roughness and operating conditions on the transition to full film elastohydrodynamic lubrication (EHL). A ball-on-disc device, arranged for monitoring electrical contact resistance (ECR), was operated under a wide variety of heavily loaded rolling/sliding conditions. To reduce complexity in the film formation process, any tribo-chemical effects were minimized by the selection of a neat synthetic lubricant. Two types of tests were set-up to examine, in particularly, the role of load and slide-to-roll ratio (SRR) on the EHD film formation. In the first, the contact was mapped over the speed and SRR parameter space to capture the transition from EHL to mixed lubrication when starting in EHL. The contact was then operated under different loads to reveal the EHL transitions dependency to variations in Hertzian contact pressure. In the second set of tests, the contact was initiated in mixed lubrication, and film formation was monitored until surfaces achieved lift-off for EHL by adequate surface modification due to running-in. Subsequently, special emphasis was set out to investigate what transformations those surfaces had to undergo in order for EHL lift-off to take place.

  • 104.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Gear Technology, Transmission Development, Scania CV AB, Södertälje, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubricant Film Formation in Rough EHL Contacts2020Conference paper (Refereed)
    Abstract [en]

    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.

  • 105.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Transmission Development, Scania CV AB, Södertälje, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubricant film formation in rough surface non‑conformal conjunctions subjected to GPa pressures and high slide‑to‑roll ratios2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1, article id 22250Article in journal (Refereed)
    Abstract [en]

    A ball-on-disc machine was employed in a highly idealised setting to study the interplay between oil film formation and surface irregularities in single-sided rough elasto-hydrodynamic lubricated (EHL) conjunctions. The tests were operated under GPa pressures and high slide-to-roll ratios in a situation where the separating gap was smaller than the combined surface roughness height. Under the initial state of solid contact interference and with the operating conditions held fixed, surfaces were found to gradually conform such that a fully separating oil film of nanometre thickness eventually developed—a thin film lubrication state known as micro-EHL. Additionally, with a previously developed approach for 3D surface re-location analysis, we were able to very precisely specify the pertained nature of surface transformations, even at the asperity scale, by comparing the post-test surfaces to those in the virgin state. The surface roughness Sq was reduced by up to 17% after running-in, while the speed required for full film EHL was reduced by a remarkable 90%. Hence, full film EHL is possible even in cases where the Λ-ratio falsely suggests boundary lubrication. This discrepancy was attributed to the way surfaces are deformed inside the contact, i.e., through the establishment of micro-EHL.

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  • 106.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Gear Technology, Transmission Development, Scania CV AB, Södertälje.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mapping of the lubrication regimes in rough surface EHL contacts2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 131, p. 637-651Article in journal (Refereed)
    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.

  • 107.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the full film to mixed lubrication transition in rolling/sliding Non-conformal Contacts2018Conference paper (Refereed)
  • 108.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the surface lift-off transition in rough surface EHL contacts2019In: 74th STLE Annual Meeting & Exhibition: Program Guide and Schedule, Society of Tribologists and Lubrication Engineers (STLE) , 2019, p. 31-31Conference paper (Refereed)
    Abstract [en]

    The pumping and churning losses in transmission assemblies are minimized when gears are operated in low viscosity lubricants. Therefore, in order to improve gear efficiency, it is of crucial importance to gain knowledge about the underlying mechanism that governs elastohydrodynamic (EHL) contacts ability to form a separating oil film. This study was set out to explore the necessary requirements for EHL contacts to achieve a state of full film separation. A ball on disc device, arranged for electrical contact resistance (ECR) measurement, was operated under a wide variety of heavily loaded rolling/sliding conditions. Friction and ECR-signal were simultaneously monitored to capture the contact performance until surfaces achieved lift-off by adequate surface modification due to running-in. Special emphasis was set on post-test surface analysis to reveal whether any surface roughness parameter could provide insights in the pre-requisite for surface lift to take place.

  • 109.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Scania.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Small changes in surface roughness can make a dramatic difference!2019Conference paper (Refereed)
  • 110.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Scania.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The new lubrication film parameter2021Conference paper (Other academic)
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  • 111.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Transmission Development, Scania CV AB, Södertälje, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Topography transformations due to running-in of rolling-sliding non-conformal contacts2020In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 144, article id 106126Article in journal (Refereed)
    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.

  • 112.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Improved performance by ionic additives in hydrocarbon base fluids for mixed-rolling/sliding contacts2018Conference paper (Refereed)
  • 113.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Gear Technology, Transmission Development, Scania CV AB, Södertälje.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Performance and mechanisms of silicate tribofilm in heavily loaded rolling/sliding non-conformal contacts2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 123, p. 130-141Article in journal (Refereed)
    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.

  • 114.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic performance of a hydrocarbon mimicking ionic liquid additive2017Conference paper (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

  • 115.
    Hasan, Mushfiq
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. CAE Motion, China-Euro Vehicle Technology CEVT, Gothenburg, Sweden.
    Mohammed, Omar D.
    CAE Motion, China-Euro Vehicle Technology CEVT, Gothenburg, Sweden; Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar, KSA.
    Kolar, Christian
    Applied Nano Surfaces Sweden (Tribonex) AB, Uppsala, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Study of wear and micropitting in rolling/sliding contacts operating under boundary lubrication conditions2022In: Procedia Structural Integrity, E-ISSN 2452-3216, Vol. 42, p. 1169-1176Article in journal (Refereed)
    Abstract [en]

    Rolling contact fatigue is a common failure mode in gears and bearings. However, this failure mode is getting greater attention due to the increasing tendency to use lower viscosity lubricants to reduce losses. Though several types of research have been done over the past decades, there are still scopes for further investigations. This study aims to study the effect of the slide to roll ratios (SRR), surface roughness and surface treatment on wear and pitting behaviour under realistic contact conditions. Fatigue and wear damages were quantified by studying the surface topography alteration at different contact cycle intervals.

    It was found that under boundary lubrication, initiation of micropitting took place in almost all test runs. However, once the adhesive wear mechanism activated at a higher contact cycle, the initially formed micropitted area started to wipe off. Moreover, for an extended test period and high sliding, wear volume is almost similar irrespective of SRR. Later, a surface treatment was studied, which was found effective in delaying the micropitting initiation by improving the tribological parameters compared to the untreated samples.

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  • 116.
    Hindér, Gustav
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kalliorinne, Kalle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Education and Technology, Health, Medicine and Rehabilitation. School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On Ski–Snow Contact Mechanics During the Double Poling Cycle in Cross-Country Skiing2024In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 72, no 2, article id 44Article in journal (Refereed)
    Abstract [en]

    Of the medals awarded during the Winter Olympics Games, most are awarded for sports involving cross-country (XC) skiing. The Double Poling (DP) technique, which is one of the sub-techniques used most frequently in XC skiing, has not yet been studied using simulations of the ski–snow contact mechanics. This work introduces a novel method for analysing how changes in the distribution of pressure on the sole of the foot (Plantar Pressure Distribution or PPD) during the DP motion affect the contact between the ski and the snow. The PPD recorded as the athlete performed DP, along with an Artificial Neural Network trained to predict the geometry of the ski (ski-camber profile), were used as input data for a solver based on the boundary element method, which models the interaction between the ski and the snow. This solver provides insights into how the area of contact and the distribution of pressure on the ski-snow interface change over time. The results reveal that variations in PPD, the type of ski, and the stiffness of the snow all have a significant impact on the contact between the ski and the snow. This information can be used to improve the Double Poling technique and make better choices of skis for specific snow conditions, ultimately leading to improved performance.

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  • 117.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A smart friction control strategy enabled by CO2 absorption and desorption2019In: Scientific Reports, E-ISSN 2045-2322, Vol. 9, no 1, article id 13262Article in journal (Refereed)
    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.

  • 118.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controllable Friction of Green Ionic Liquids via Environmental Humidity2020In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 22, no 5, article id 1901253Article in journal (Refereed)
    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.

  • 119.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controllable superlubricity achieved with mixtures of green ionic liquid and glycerol aqueous solution via humidity2022In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 345, article id 117860Article in journal (Refereed)
    Abstract [en]

    In this work, superlubricity between steel surfaces lubricated by mixtures of [Choline][Proline] ([Cho][Pro]) ionic liquid and glycerol aqueous solution has been reached by using a rotating tribometer. Stable superlubricity could be obtained even under the humidity between 7 to 9% RH. The lowest friction is observed when the lubricant contains 3 wt.% ionic liquid. It is found that adding 3 wt.% [Cho][Pro] is helpful to maintain enough water in the steady period to retain a low viscosity. According to the calculation, the superlubricity achieved in thin film lubrication region, which is attributed to the stern layer formed by [Cho][Pro] and hydrogen-bond network that enabled a thin water layer at the interface. Interestingly, it is observed that humidity can be used to control lubrication state between superlubricity and non-superlubricity. This study provides a new method to accomplish switchable superlubricity under low humidity.

  • 120.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Controlling friction in Ionic Liquid/Glycerol Aqueous Solution lubricated contacts by adjusting CO2 and water content2021In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 161, article id 107070Article in journal (Refereed)
    Abstract [en]

    Nowadays, the awareness for the importance of green lubricants and green lubricating additives is increasing. In this work, [Choline][Proline] ([Cho][Pro]) was added into glycerol aqueous solution to receive a high-performance green lubricant. The effect of environment condition, e.g., CO2 and water, on the green lubricant was studied. It is found that the properties of the green lubricant could be modulated by CO2 and water content. As CO2 was absorbed by the liquid, the viscosity of the liquid increased, while the viscosity of liquid diminished after adding more water. The presence of CO2 led to an obvious increase of friction. At the same time, it is also found that the friction could be altered by water content. Thus, it is possible to control friction by changing CO2 and water content.

  • 121.
    Hua, Jing
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction Control of Chitosan-Ag Hydrogel by Silver Ion2022In: ES Materials & Manufacturing, ISSN 2578-0611, Vol. 16, p. 30-36Article in journal (Refereed)
    Abstract [en]

    The tunable friction behavior of Chitosan (CS)-Ag hydrogel enabled by altering metal ions is evaluated. Friction control could be achieved under boundary lubrication. When adding Ag+ into a CS solution, the formed gel provided lower friction. The difference in friction coefficient between the two phases can be reversibly switched by adding Cl- or excessive Ag+ ions. It also can be found that the gel phased lubricant has a better anti-wear ability under boundary lubrication conditions. Both solution and gel typed lubricants could achieve superlubricity under elastohydrodynamic lubrication. The switchable and tunable frictional hydrogels can extend the application in the design of smart control equipment.

  • 122.
    Huang, De
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yan, Xiang
    Saint-Gobain, Bristol, RI 02809, USA.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Boundary element method for the elastic contact problem with hydrostatic load at the contact interface2021In: Applied Surface Science Advances, E-ISSN 2666-5239, Vol. 6, article id 100176Article in journal (Refereed)
    Abstract [en]

    When a seal is applied to prevent leakage of a pressurized fluid it must be designed to sustain the hydrostatic load it is subjected to. One important aspect that the design must take into consideration is the possibility that the hydrostatic fluid load may deform the sealing surfaces to such an extent that leakage occurs. In this paper, we describe the development and implementation of a novel boundary element method (BEM) that can be used to study the effects of the pressurized fluid presents at the interface between the sealing surfaces. The proposed method utilizes a connected region labeling algorithm to identify the fluid-filled regions and it solves the coupled solid-solid and fluid-solid contact problem with an FFT-based boundary element method (DC-FFT). When benchmarked against a FEM implementation of the same problem, it is found that the results are in good agreement. In particular, it is shown that the proposed method can capture the deformation of the sealing surfaces, and how the fluid front advances when the hydrostatic pressure increases.

  • 123.
    Huang, De
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yan, Xiang
    Saint-Gobain, Bristol, RI, 02809, USA.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Leakage Threshold of a Saddle Point2023In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 2, article id 40Article in journal (Refereed)
    Abstract [en]

    The threshold condition for leakage inception is of great interest to many engineering applications, and it is essential for seal design. In the current study, the leakage threshold is studied by means of a numerical method for a mechanical contact problem between an elastic bi-sinusoidal surface and a rigid flat surface. The coalesce process of the contact patches is first investigated, and a generalized form of solution for the relation between the contact area ratio and the average applied pressure is acquired. The current study shows that the critical value of the average applied pressure and the corresponding contact area required to close the percolation path can be represented as a power law of a shape parameter, if the effect of the hydrostatic load from the pressurized fluid is ignored. With contact patches merged under a constant applied load, the contact breakup process is investigated with elevated sealed fluid pressure condition, and it is shown that the leakage threshold is a function of the excess pressure, which is defined as a ratio between the average applied pressure and the critical pressure under dry contact conditions.

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  • 124.
    Huang, De
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Yan, Xiang
    Saint-Gobain, Bristol, RI 02809, USA.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Numerical Simulation of Static Seal Contact Mechanics Including Hydrostatic Load at the Contacting Interface2021In: Lubricants, ISSN 2075-4442, Vol. 9, no 1, article id 1Article in journal (Refereed)
    Abstract [en]

    A finite element model of a static seal assembled in its housing has been built and is utilized to study how the seal deforms under varying loading conditions. The total contact load on the sealing surface is balanced by the sealed fluid pressure and the friction between the seal and the housing sidewall perpendicular to the sealing surface. The effect of the sealed fluid pressure between the sealing surfaces was investigated and the simulation showed that the surface profile is distorted due to the hydrostatic pressure. We study the distorted contact profile with varying sealed fluid pressure and propose five parameters to describe the corresponding contact pressure profile. One of these parameters, overshoot pressure, a measure of the difference between maximum contact pressure and the sealed fluid pressure, is an indicator of sealing performance. The simulations performed show different behaviors of the overshoot pressure with sealed fluid pressure for cosinusoidal and parabolic surfaces with the same peak to valley (PV) value. 

  • 125.
    Huang, De
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yan, Xiang
    Saint-Gobain, Bristol, RI, 02809, USA.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The Critical Pressure for Bulk Leakage of Non-planar Smooth Surfaces2022In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 70, no 3, article id 74Article in journal (Refereed)
    Abstract [en]

    The sealing surfaces subjected to the hydrostatic load from the sealed fluid can deform to such an extent that leakage occurs when the sealed fluid pressure is sufficiently high, and this critical pressure that the seal can sustain without leakage is a fundamental aspect of the seal design. This paper presents a new numerical method based on the bisection algorithm and the boundary element method, which can be utilized to capture the critical pressure with high accuracy. The present method is employed to study the relationship between the critical pressure and the non-planar geometry of the sealing surfaces, under a wide range of loading conditions. The results show that the critical pressure can be acquired from the surface’s dry contact state with a dimensionless correction factor.

  • 126.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hansen, Jonny
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the Effects of Two-Sided Roughness in Rolling-Sliding EHL Contacts2020Conference paper (Refereed)
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  • 127.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shirzadegan, Mohammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Baubet, Yannick
    SKF, Nieuwegein.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic lubrication for the finite line contact under transient loading conditions2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, p. 489-499Article in journal (Refereed)
    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.

  • 128.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Johannesson, Tomas
    Volvo Cars Corporation.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Analysis of Split Crankshaft Roller Bearings with Focus on Lubrication and Contact Stresses2020Conference paper (Refereed)
  • 129.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Johannesson, Tomas
    Volvo Car Corporation, Volvo Cars Torslanda, Sweden.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient plasto-elastohydrodynamic lubrication concerning surface features with application to split roller bearings2021In: 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)
    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.

  • 130.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On Waviness and Two-Sided Surface Features in Thermal Elastohydrodynamically Lubricated Line Contacts2020In: Lubricants, ISSN 2075-4442, Vol. 8, no 6, article id 64Article in journal (Refereed)
    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.

  • 131.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Department of Mechanical Engineering, Tsinghua University, Beijing, China.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient analysis of surface roughness features in thermal elastohydrodynamic contacts2020In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 141, article id 105915Article in journal (Refereed)
    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.

  • 132.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts2019In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 141, no 3, article id 031502Article in journal (Refereed)
    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

  • 133. Höglund, Erik
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modelling non-steady EHL with focus on lubricant density1997In: Elastohydrodynamics -'96: fundamentals and applications in lubrication and traction : proceedings / [ed] D. Dowson, Amsterdam: Elsevier, 1997, p. 511-521Conference paper (Refereed)
  • 134. Isaksson, Patrik
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of simplified energy equation to the solution of temperature in conformal contacts2009Conference paper (Refereed)
  • 135. Isaksson, Patrik
    et al.
    Nilsson, Daniel
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elasto-hydrodynamic simulation of complex geometries in hydraulic motors2009In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 10, p. 1418-1423Article in journal (Refereed)
    Abstract [en]

    As many other machines, the radial piston hydraulic motor contains a lot of tribological interfaces. One important area is the piston assembly and the journal bearing contact between the piston and cam roller. There exists good models to describe the performance of simpler geometries such as journal bearings, but when put into a system or when having a more complex geometry, the models do not apply very well. To be able to predict the tribological performance of such components, it is important to have a model that is able to include the real geometry and the properties of the system.A simulation model of the piston assembly in Hägglunds Compact hydraulic motor was built using FE software which made it easy to include the complex geometries. The model includes the deformation of the piston. The hydrodynamics is solved by using Reynolds equation.Density/pressure and viscosity/pressure dependency for the oil are included.Simulation results such as friction, hydrodynamic pressure and oil leakage was compared with test results. Good agreement between simulation and tests shows that this kind of model can be a useful tool in development and optimization of tribological systems.

  • 136. Isaksson, Patrik
    et al.
    Nilsson, Daniel
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elasto-hydrodynamic simulation of complex geometries in hydraulic motors2008In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    As many other machines, the radial piston hydraulic motor contains a lot of tribological interfaces. One important area is the piston assembly and the journal bearing contact between the piston and cam roller. There exists good models to describe the performance of simpler geometries such as journal bearings, but when put into a system or when having a more complex geometry, the models do not apply very well. To be able to predict the tribological performance of such components, it is important to have a model that is able to include the real geometry and the properties of the system. A simulation model of the piston assembly in Hägglunds Compact hydraulic motor was built using FE software which made it easy to include the complex geometries. The model includes the deformation of the piston. The hydrodynamics is solved by using Reynolds equation. Density/pressure and viscosity/pressure dependency for the oil are included. The whole model was solved with the built in solvers in the software. Simulation results such as friction, hydrodynamic pressure and oil leakage was compared with test results. Good agreement between simulation and tests shows that this kind of model can be a useful tool in development and optimization of tribological systems.

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  • 137.
    Isaksson, Patrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Nilsson, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of surface roughness on friction in a flexible hybrid bearing2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no J10, p. 975-985Article in journal (Refereed)
    Abstract [en]

    The effect of surface roughness on friction in all lubrication regimes is studied for a flexible hybrid bearing of a radial piston hydraulic motor. The effect is studied by performing experiments in a specially designed test rig and numerical simulations of the real measured surface topographies of the bearings. The simulations are performed with a two-scale model where surface roughness is treated on a local asperity level by homogenized flow factors and a global scale where the bearing structure is included. Three bearings with different surface topographies are included in the study and both experimentally measured and simulated friction are analysed for each of them. Comparison of friction predicted by the model and experimentally measured friction is performed and it reveals that the model is a valuable tool for analysing the effect of surface roughness in this type of bearing

  • 138.
    Jolkin, Alexei
    et al.
    Luleå University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Determination of lubricant compressibility in EHL conjunctions using the Hybrid Technique2000In: Thinning films and tribological interfaces: proceedings of the 26th Leeds-Lyon Symposium on Tribology held in the Institute of Tribology, School of Mechanical Engineering, The University of Leeds, UK 14th - 17th September, 1999 / [ed] D. Dowson, Amsterdam: Elsevier, 2000, p. 589-596Conference paper (Refereed)
    Abstract [en]

    Detailed two-dimensional EHL film thickness maps can be obtained experimentally by using a Ball&Disc Apparatus, optical interferometry and image analysis. It is possible to compute the deformation of the surfaces, from the measured film thickness map, since the undeformed contact geometry of the ball and disc is known. By assuming linear elastic deformation it is also possible to numerically determine the contact pressure distribution. This experimental/numerical approach has been called the Hybrid technique. The problem addressed here can be stated as follows: Can the very detailed film thickness map, and its corresponding pressure distribution, be used for the determination of lubricant parameters such as bulk modulus and density? The answer is yes but the quality of the results are very much dependent on the accuracy of the film thickness measurements and the corresponding pressure calculation. The refractive index have to be known everywhere in the EHL contact, i.e. the relationship between pressure and refractive index is required if refractive index cannot be measured directly. The method was applied on a PAO oil and the bulk modulus was determined over a pressure range of 250 MPa to 500 MPa. By using dilatometry results for the pressure range from zero to 100 Mpa it was also possible to determine the density in the pressure range from zero up to 500 MPa. The results are promising and if the accuracy can be improved further the method described can be a useful tool for determining lubricant pressure-deformation relationships

  • 139. Jolkin, Alexei
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Film thickness, pressure distribution and traction in sliding EHL conjunctions1999In: Lubrication at the frontier: the role of the interface and surface layers in the thin film and boundary regime : proceedings of the 25th Leeds-Lyon Symposium on Tribology, held in the Institut national des sciences appliquées de Lyon, France, 8th-11th September, 1998, Amsterdam: Elsevier, 1999, p. 505-516Chapter in book (Other academic)
    Abstract [en]

    The lubricant film thickness in an EHL conjunction has been studied under mixed sliding and rolling conditions using optical interferometry. A hybrid method was developed to combine the experimental study and advanced numerical calculations including a fast algorithm for evaluation of pressure distribution. A multi-channel image analyser was employed to evaluate a 3-D film thickness map. This map was used for calculating pressure distribution by solving the film thickness equation. The influence of sliding on film thickness and its corresponding pressure distribution has been investigated in this paper. The traction force has also measured. The investigations found that at relatively low entrainment velocities the sliding has only a slight influence on the pressure distribution. The characteristic shape of the pressure remains nearly the same for all tested slide/roll ratios. The difference between pressures at various degrees of sliding is seen mostly along the horseshoe shaped constriction. It has also been shown that the lubricant type has influence on the shape of the pressure spike at the outlet.

  • 140. Jolkin, Alexei
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ultrathin film Hybrid technique applied to coated surfaces2001In: Tribology research : from model experiment to industrial problem ; a century of efforts in mechanics, materials science and physico-chemistry: proceedings of the 27th Leeds-Lyon Symposium on Tribology held in the Institut National des Sciences Appliquées de Lyon, Lyon, France, 5th - 8th September 2000 / [ed] Gérard Dalmaz, Amsterdam: Elsevier, 2001, p. 505-513Conference paper (Refereed)
    Abstract [en]

    An established Hybrid technique has been extended to study lubricant film in EHL conjunctions using ultra thin film interferometry i.e. the spacer layer method. The Hybrid technique combines experimental study with advanced numerical calculations including a fast algorithm for evaluation of pressure distribution. Image analysis is employed to evaluate a 3-D film thickness map from a colour interferogram. The map is then used for calculating pressure distribution by solving the film thickness equation. The general theory of stresses and displacements in a two-layer system is applied in the present work to a circular point contact of an elastic layer firmly bonded to an elastic substrate. The numerical formulation was employed for computing pressure distribution in the EHL contact from the measured elastic deformations and correction of measured film thickness. The dynamic and static results are presented and discussed. A simple tool to estimate the compression of elastic layer based on calculations of static dry contact is suggested. The calculations were performed for sapphire discs with silica and diamond-like coatings.

  • 141.
    Jolkin, Alexei
    et al.
    Luleå University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ehret, Pascal
    Leeds University.
    Elastohydrodynamic lubrication during a sudden reversal of the rolling direction2001In: Proceedings of the International tribology conference: ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japanese Society of Tribologsts , 2001Conference paper (Other academic)
  • 142.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Education and Technology, Health, Medicine and Rehabilitation.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the multi-scale nature of ski-snow friction in cold conditionsManuscript (preprint) (Other academic)
  • 143.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Education and Technology, Health, Medicine and Rehabilitation.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Characterisation of the Contact between Cross-Country Skis and Snow: On the Multi-Scale Interaction between Ski Geometry and Ski-Base Texture2023In: Lubricants, E-ISSN 2075-4442, Vol. 11, no 10, article id 427Article in journal (Refereed)
    Abstract [en]

    In elite endurance sports, marginal differences in finishing times drive ongoing equipment improvement to enhance athlete performance. In cross-country skiing, researchers, since the 1930s, have faced the challenge of minimising the resistance caused by friction in the contact between skis and snow. This study was designed to evaluate the multi-scale interaction between the macro-scale ski-camber profile and the micro-scale ski-base texture. Considerations included real contact area, average interfacial separation, and total reciprocal interfacial separation between the ski and snow, which are properties that are intimately coupled to ski–snow friction. We found that both the profile of the ski camber and the texture of the ski base play decisive roles in determining viscous friction. At the same time, the texture of the ski base exerts a greater impact on the average real contact pressure, real contact area, and minimal average interfacial separation between the ski and snow than the ski-camber profile.

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  • 144.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Learning and Technology, Health, Medicine and Rehabilitation.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The impact of cross-country skiers' tucking position on ski-camber profile, apparent contact area and load partitioning2023In: Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology, ISSN 1754-3371Article in journal (Refereed)
    Abstract [en]

    In cross-country skiing races, the difference between the fastest and the second fastest time can be minuscule. As in all endurance sports, cross-country skiing requires the use of energy to overcome resistive forces, in this case primarily aerodynamic drag and friction between the skis and snow. Even a slight reduction in either of these can determine the outcome of a race. The geometry of the ski exerts a profound influence on the friction between the skis and snow. As a result of the flexible modern cross-country skis, the camber profile and gliding properties to be influenced by the skiers' position. Here, based on the location of the normal force corresponding to the plantar pressure, we characterize the ski camber while performing three variations of the downhill tucking position. We found that when gliding on a classic ski, the risk of contact between the kick wax and snow can be reduced by tucking in a leaning backwards position (i.e. by moving the skier's center of mass backwards). With the tucking position, the percentage of the skier's body weight that is distributed onto the friction interface at the rear of the skis varies between 63.5% in Gear 7 (leaning forward) on a skating ski and 93.0% in Gear 7 (leaning backwards) on a classic ski.

  • 145.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Application of topological optimisation methodology to hydrodynamic thrust bearings2021In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 235, no 8, p. 1669-1679Article in journal (Refereed)
    Abstract [en]

    The bearing geometry has a big impact on the performance of a hydrodynamic thrust bearing. For this reason, shape optimisation of the bearing surface has been carried out for some time, with Lord Rayleigh’s early publication dated back to 1918. There are several recent results e.g. optimal bearing geometries that maximise the load carrying capacity for hydrodynamic thrust bearings. Currently, many engineers are making an effort to include sustainability in their work, which increases the need for bearings with lower friction and higher load carrying capacity. Improving these two qualities will result in lower energy consumption and increase the lifetime of applications, which are outcomes that will contribute to a sustainable future. For this reason, there is a need to find geometries that have performance characteristics of as low coefficient of friction torque as possible. In this work, the topological optimisation method of moving asymptotes is employed to optimise bearing geometries with the objective of minimising the coefficient of friction torque. The results are both optimised bearing geometries that minimise the coefficient of friction torque and bearing geometries that maximise the load carrying capacity. The bearing geometries are of comparable aspect ratios to the ones uses in recent publications. The present article also covers minimisation of friction torque on ring bearing geometries, also known as thrust washers. The results are thrust washers with periodical geometries, where the number of periodical segments has a high impact on the geometrical outcome.

  • 146.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pérez-Ràfols, Francesc
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Liwicki, Marcus
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Artificial Neural Network Architecture for Prediction of Contact Mechanical Response2021In: Frontiers in Mechanical Engineering, E-ISSN 2297-3079, Vol. 6, article id 579825Article in journal (Refereed)
    Abstract [en]

    Predicting the contact mechanical response for various types of surfaces is and has long been a subject, where many researchers have made valuable contributions. This is because the surface topography has a tremendous impact on the tribological performance of many applications. The contact mechanics problem can be solved in many ways, with less accurate but fast asperity-based models on one end to highly accurate but not as fast rigorous numerical methods on the other. A mathematical model as fast as an asperity-based, yet as accurate as a rigorous numerical method is, of course, preferred. Artificial neural network (ANN)-based models are fast and can be trained to interpret how in- and output of processes are correlated. Herein, 1,536 surface topographies are generated with different properties, corresponding to three height probability density and two power spectrum functions, for which, the areal roughness parameters are calculated. A numerical contact mechanics approach was employed to obtain the response for each of the 1,536 surface topographies, and this was done using four different values of the hardness per surface and for a range of loads. From the results, 14 in situ areal roughness parameters and six contact mechanical parameters were calculated. The load, the hardness, and the areal roughness parameters for the original surfaces were assembled as input to a training set, and the in situ areal roughness parameters and the contact mechanical parameters were used as output. A suitable architecture for the ANN was developed and the training set was used to optimize its parameters. The prediction accuracy of the ANN was validated on a test set containing specimens not seen during training. The result is a quickly executing ANN, that given a surface topography represented by areal roughness parameters, can predict the contact mechanical response with reasonable accuracy. The most important contact mechanical parameters, that is, the real area of contact, the average interfacial separation, and the contact stiffness can in fact be predicted with high accuracy. As the model is only trained on six different combinations of height probability density and power spectrum functions, one can say that an output should only be trusted if the input surface can be represented with one of these.

  • 147.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Persson, Bo N. J.
    Peter Grünberg Institute (PGI-1), Forschungszentrum Jülich, 52428 Jülich, Germany; Multiscale Consulting, 52428 Jülich, Germany.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Learning and Technology, Health, Medicine and Rehabilitation.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Characterisation of the Contact between Cross-Country Skis and Snow: A Micro-Scale Study Considering the Ski-Base Texture2023In: Lubricants, E-ISSN 2075-4442, Vol. 11, no 5, article id 225Article in journal (Refereed)
    Abstract [en]

    In winter sports, the equipment often comes into contact with snow or ice, and this contact generates a force that resists motion. In some sports, such as cross-country skiing, this resistive force can significantly affect the outcome of a race, as a small reduction in this force can give an athlete an advantage. Researchers have examined the contact between skis and snow in detail, and to fully understand this friction, the entire ski must be studied at various scales. At the macro scale, the entire geometry of the ski is considered and the apparent contact between the ski and the snow is considered and at the micro-scale the contact between the snow and the ski-base textures. In the present work, a method for characterising the contact between the ski-base texture and virtual snow will be presented. Six different ski-base textures will be considered. Five of them are stone-ground ski bases, and three of them have longitudinal linear textures with a varying number of lines and peak-to-valley heights, and the other two are factory-ground “universal” ski bases. The sixth ski base has been fabricated by a steel-scraping procedure. In general, the results show that a ski base texture with a higher 𝑆𝑝𝑘 value has less real contact area, and that the mutual differences can be large for surfaces with similar 𝑆𝑎 values. The average interfacial separation is, in general, correlated with the 𝑆𝑎 value, where a “rougher” surface exhibits a larger average interfacial separation. The results for the reciprocal average interfacial separation, which is related to the Couette type of viscous friction, were in line with the general consensus that a “rougher” texture performs better at high speed than a “smoother” one, and it was found that a texture with high 𝑆𝑎 and 𝑆𝑝𝑘 values resulted in a low reciprocal average interfacial separation and consequently low viscous friction. The reciprocal average interfacial separation was found to increase with increasing real contact area, indicating a correlation between the real area of contact and the Couette part of the viscous friction.

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  • 148.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Education and Technology, Health, Medicine and Rehabilitation.
    Supej, Matej
    University of Ljubljana, Slovenia.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Novel Method for Quantifying Ski-Snow Friction Using an Rtk-Gnss Equipped SledManuscript (preprint) (Other academic)
    Abstract [en]

    In most winter sports, the athletes interact with snow with their equipment. In some of these sport, e.g. in cross-country skiing, a large amount of energy is spent by the athlete to overcome the restive force of friction. Consequently, a reduction in friction can be the difference between winning and coming second in a race. Over the years, researchers have come up with many ways of measuring the friction between snow and sports equipment, such as different types of skis. However, only a few of these experimental setups can be used to test the glide of real-sized skis under natural conditions during both accelerating and deceleration motion. In the present work, a novel experimental setup consisting of a sled and a base station that uses GNSS receivers communicating internally by radio, thus making up an RTK-GNSS system which can measure the position of the sled with centimetre accuracy, was established. The sled is equipped with authentic cross-country skis and accelerated and decelerated on a track with natural height variation prepared with a conventional snow-track setter mounted on a snowcat. The recorded altitude and velocity data are used to quantify the coefficient of friction (COF), both for accelerating and decelerating motion, with a model based on the preservation of energy. The results show that the COF during acceleration was more than 28% higher than during deceleration, while the difference in the COF during deceleration on flat ground at loading conditions resembling the acceleration and deceleration phases was less than 5%. This is an important discovery, as when all types of skiing techniques are executed, the athlete is either accelerating or decelerating while moving forward along the track. The ability of the current experimental set-up to distinguish between them may thus have positive implications for further development.

  • 149.
    Kalliorinne, Kalle
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sandberg, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Learning and Technology, Health, Medicine and Rehabilitation.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Characterisation of the Contact between Cross-Country Skis and Snow: A Macro-Scale Investigation of the Apparent Contact2022In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 11, article id 279Article in journal (Refereed)
    Abstract [en]

    In a cross-country skiing competition, the time difference between the winner and the skier coming in at second place is typically very small. Since the skier spends much of the energy on overcoming resistive forces, a relatively small reduction in these forces can have a significant impact on the results. The resistive forces come partly from the friction, at the tribological interface between the ski and the snow, and as with many tribological processes, the characterisation of its origin plays an important role in determining the frictional properties. Furthermore, in cross-country ski friction, there are several scales impacting the frictional performance, with the major contributors being the ski-camber profile and ski-base structure. Macro-scale measurements of the ski-camber profile under loading are often used to determine how adequate the ski is for use under specific conditions. The characteristic properties usually assessed are the force required to collapse the ski in order to obtain a certain camber height, the topography of the kick-wax zone, and the length (determined by simple means) of the frictional interfaces associated with the rear- and front glide zones, i.e., the apparent contact length. These measurements are, however, commonly performed by loading the ski against a much stiffer counter surface than snow and this affects the quantification of the characteristic properties. To date, some mathematical models have been proposed, but there is no reliable approach for determining the macro-scale properties of the contact between a cross-country ski and a counter surface using simulations. In the present paper, an Artificial Neural Network (ANN) has been trained to predict the ski-camber profile for various loads applied at different positions. A well-established deterministic approach has been employed to simulate the contact between the ANN-predicted ski-camber profile and a linearly elastic body with a flat upper surface, representing the snow. Our findings indicate that this method is feasible for the determination of relevant macro-scale contact characteristics of different skis with snow. Moreover, we show that the apparent contact area does not linearly depend on the load and that the material properties of the counter surface also exert a large impact when quantifying the apparent contact area and the average apparent contact pressure.

  • 150. Kang, Shaojie
    et al.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Two-dimensional finite element analysis of elastic-plastic deformation in asperity-asperity collision2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    The collision of cylindrical asperities is simulated by means of a commercial multiphysics software in this paper. The model combines a computational structure mechanics approach with a contact algorithm. Numerical results are first compared to classical Hertzian theory. Effects of the bulk material under the mating surfaces have been included in the simulation. Materials of top and bottom surfaces have been assigned different properties. Development of plastic deformation and friction are presented along the process of collision. Strain hardening is included in the elastic-plastic deformation. The effect of interference change and friction coefficient variation on deformation and friction has been studied. Deformed shape and subsurface residual stress in asperity are output parameters from this study.

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