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Sandberg, J., Kalliorinne, K., Hindér, G., Holmberg, H.-C., Almqvist, A. & Larsson, R. (2023). A Novel Free-Gliding Ski Tribometer for Quantification of Ski–Snow Friction with High Precision. Tribology letters, 71(4), Article ID 111.
Open this publication in new window or tab >>A Novel Free-Gliding Ski Tribometer for Quantification of Ski–Snow Friction with High Precision
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2023 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 4, article id 111Article in journal (Refereed) Published
Abstract [en]

The nature of snow and the ever-changing environment makes measuring friction on snow and ice challenging. Additionally, due to the low friction involved, the equipment used must exhibit high sensitivity. Previous investigations of ski–snow friction have ranged from small-scale model experiments performed in the laboratory to experiments with full-sized skis outdoors. However, few have been conducted under conditions similar to those encountered during actual skiing. Here, we present a novel sled tribometer which provides highly reproducible coefficient of friction (COF) values for full-sized skis gliding at relevant speeds (approximately 5.9 m/s) in a controlled indoor environment. The relative standard deviation (RSD) of the COF is as low as 0.5%. The continuous recording of velocity allows for innovative investigations into COF variations when skis are permitted to free-glide in a natural setting. Different methods of analysing the results are presented which shows that the precision is not a single number, but a function of the range of velocities over which the average COF is calculated.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
Winter sports, Full-size skis, Narrow skis, Cross-country, Biathlon, Ski–snow friction, Ski tribometers, Sled systems
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Sport and Fitness Sciences
Research subject
Machine Elements; Physiotherapy
Identifiers
urn:nbn:se:ltu:diva-101471 (URN)10.1007/s11249-023-01781-w (DOI)2-s2.0-85171473273 (Scopus ID)
Funder
The Kempe Foundations, JCK-2107
Note

Validerad;2023;Nivå 2;2023-09-28 (hanlid);

Funder: Swedish Olympic Committee (SOK)

Available from: 2023-09-28 Created: 2023-09-28 Last updated: 2023-12-12Bibliographically approved
Choudhry, J., Almqvist, A., Prakash, B. & Larsson, R. (2023). A Stress-State-Dependent Sliding Wear Model for Micro-Scale Contacts. Journal of tribology, 145(11), Article ID 111702.
Open this publication in new window or tab >>A Stress-State-Dependent Sliding Wear Model for Micro-Scale Contacts
2023 (English)In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 145, no 11, article id 111702Article in journal (Refereed) Published
Abstract [en]

Wear is a complex phenomenon taking place as two bodies in relative motion are brought into contact with each other. There are many different types of wear, for example, sliding, fretting, surface fatigue, and combinations thereof. Wear occurs over a wide range of scales, and it largely depends on the mechanical properties of the material. For instance, at the micro-scale, sliding wear is the result of material detachment that occurs due to fracture. An accurate numerical simulation of sliding wear requires a robust and efficient solver, based on a realistic fracture mechanics model that can handle large deformations. In the present work, a fully coupled thermo-mechanical and meshfree approach, based on the momentum-consistent smoothed particle Galerkin (MC-SPG) method, is adapted and employed to predict wear of colliding asperities. The MC-SPG-based approach is used to study how plastic deformation, thermal response, and wear are influenced by the variation of the vertical overlap between colliding spherical asperities. The findings demonstrate a critical overlap value where the wear mechanism transitions from plastic deformation to brittle fracture. In addition, the results reveal a linear relationship between the average temperature and the increasing overlap size, up until the critical overlap value. Beyond this critical point, the average temperature reaches a steady-state value.

Place, publisher, year, edition, pages
American Society of Mechanical Engineers (ASME), 2023
Keywords
dry friction, flash temperature, MC-SPG, particle methods, sliding, wear mechanisms, Wear model
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-102317 (URN)10.1115/1.4063082 (DOI)2-s2.0-85175354354 (Scopus ID)
Funder
Swedish Research Council, 2020-03635
Note

Validerad;2023;Nivå 2;2023-11-13 (joosat);

License fulltext: CC BY

Available from: 2023-11-06 Created: 2023-11-06 Last updated: 2023-11-13Bibliographically approved
Kalliorinne, K., Persson, B. N. J., Sandberg, J., Hindér, G., Larsson, R., Holmberg, H.-C. & Almqvist, A. (2023). Characterisation of the Contact between Cross-Country Skis and Snow: A Micro-Scale Study Considering the Ski-Base Texture. Lubricants, 11(5), Article ID 225.
Open this publication in new window or tab >>Characterisation of the Contact between Cross-Country Skis and Snow: A Micro-Scale Study Considering the Ski-Base Texture
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2023 (English)In: Lubricants, E-ISSN 2075-4442, Vol. 11, no 5, article id 225Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
winter sports, sports equipment, snow, cross-country skiing, ski friction, ski-base texture
National Category
Sport and Fitness Sciences Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements; Physiotherapy; Centre - Swedish Sports Technology and Performance Research Centre (SPORTC)
Identifiers
urn:nbn:se:ltu:diva-97973 (URN)10.3390/lubricants11050225 (DOI)2-s2.0-85160250027 (Scopus ID)
Funder
Swedish Research Council, 2019-04293
Note

Validerad;2023;Nivå 2;2023-06-07 (joosat);

Part of Special Issue: Multiscale and Modern Solutions in the Simulation of Lubricated Contacts

Licens fulltext: CC BY License

Available from: 2023-06-07 Created: 2023-06-07 Last updated: 2023-10-11Bibliographically approved
Kalliorinne, K., Hindér, G., Sandberg, J., Larsson, R., Holmberg, H.-C. & Almqvist, A. (2023). Characterisation of the Contact between Cross-Country Skis and Snow: On the Multi-Scale Interaction between Ski Geometry and Ski-Base Texture. Lubricants, 11(10), Article ID 427.
Open this publication in new window or tab >>Characterisation of the Contact between Cross-Country Skis and Snow: On the Multi-Scale Interaction between Ski Geometry and Ski-Base Texture
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2023 (English)In: Lubricants, E-ISSN 2075-4442, Vol. 11, no 10, article id 427Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Multidisciplinary Digital Publishing Institute (MDPI), 2023
Keywords
contact mechanics, cross-country skiing, multi-scale, ski-base texture, ski-camber profile, sports equipment
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Sport and Fitness Sciences Applied Mechanics
Research subject
Machine Elements; Physiotherapy
Identifiers
urn:nbn:se:ltu:diva-102313 (URN)10.3390/lubricants11100427 (DOI)2-s2.0-85175021351 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-11-13 (joosat);

Funder: Swedish Research Council (DNR 2019-04293);

License fulltext: CC BY

Part of: Special Issue Multiscale and Modern Solutions in the Simulation of Lubricated Contacts

Available from: 2023-11-06 Created: 2023-11-06 Last updated: 2023-11-13Bibliographically approved
Huang, D., Yan, X., Larsson, R. & Almqvist, A. (2023). Leakage Threshold of a Saddle Point. Tribology letters, 71(2), Article ID 40.
Open this publication in new window or tab >>Leakage Threshold of a Saddle Point
2023 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 2, article id 40Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2023
Keywords
Contact mechanics, Critical pressure, Leakage, Seal
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-96189 (URN)10.1007/s11249-023-01693-9 (DOI)2-s2.0-85149535738 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-03-20 (joosat);

Funder: Vetenskapsrådet (2020-03635, 2019-04293)

Licens fulltext: CC BY License

Available from: 2023-03-20 Created: 2023-03-20 Last updated: 2023-09-05Bibliographically approved
Kalliorinne, K., Hindér, G., Sandberg, J., Larsson, R., Holmberg, H.-C. & Almqvist, A. (2023). The impact of cross-country skiers' tucking position on ski-camber profile, apparent contact area and load partitioning. Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology
Open this publication in new window or tab >>The impact of cross-country skiers' tucking position on ski-camber profile, apparent contact area and load partitioning
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2023 (English)In: Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology, ISSN 1754-3371Article in journal (Refereed) Epub ahead of print
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.

Place, publisher, year, edition, pages
SAGE Publications, 2023
Keywords
Cross-country skiing, plantar pressure, load conditions, sports equipment, cross-country ski, ski camber, nordic ski, winter sports, winter olympics
National Category
Sport and Fitness Sciences
Research subject
Machine Elements; Physiotherapy; Centre - Swedish Sports Technology and Performance Research Centre (SPORTC)
Identifiers
urn:nbn:se:ltu:diva-95465 (URN)10.1177/17543371221141748 (DOI)000911752300001 ()2-s2.0-85145502326 (Scopus ID)
Funder
Swedish Research Council, 2019-04293
Note

Funder: Swedish Olympic Committee

Available from: 2023-01-31 Created: 2023-01-31 Last updated: 2023-09-11
Tošić, M., Larsson, R., Stahl, K. & Lohner, T. (2023). Thermal Elastohydrodynamic Analysis of a Worm Gear. Machines, 11(1), Article ID 89.
Open this publication in new window or tab >>Thermal Elastohydrodynamic Analysis of a Worm Gear
2023 (English)In: Machines, E-ISSN 2075-1702, Vol. 11, no 1, article id 89Article in journal (Refereed) Published
Abstract [en]

This study explores the elastohydrodynamic lubrication (EHL) between the contacting tooth flanks of a worm gear with nonconjugate meshing action. The contact is characterized by a slender-like elliptical shape and high sliding. The geometry and contact conditions for the considered worm gear were obtained using tooth contact analysis. Based on that, the complete area of the worm gear contact was analyzed using a validated numerical EHL model considering non-Newtonian, thermal, and transient effects. The geometrical and kinematic design factors that influence EHL film formation in worm gears were identified and discussed. The results show the specific characteristics of worm gear EHL contacts, such as the very slender contact in the tooth root flank area, which diminishes the effect of the entrainment speed on film thickness. EHL film formation could be supported by increasing conformity between the flanks to make the contact less slender. By comparing the film thickness results against analytically obtained ones, relatively large differences were observed except for one formula for minimum film thickness.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
elastohydrodynamic lubrication (EHL), finite element method (FEM), Reynolds equation, slender contact, worm gear
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-95543 (URN)10.3390/machines11010089 (DOI)000914796200001 ()2-s2.0-85146736936 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-02-08 (joosat);

Funder: German Academic Exchange Service (DAAD)

Licens fulltext: CC BY License

Available from: 2023-02-08 Created: 2023-02-08 Last updated: 2023-09-05Bibliographically approved
Fadaei Naeini, V., Björling, M., Larsson, A. & Larsson, R. (2023). Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations. Journal of Molecular Liquids, 390(part A), Article ID 122990.
Open this publication in new window or tab >>Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations
2023 (English)In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 390, no part A, article id 122990Article in journal (Refereed) Published
Abstract [en]

In order to increase the usage and explore new applications of glycerol as a replacement for fossil-based lubricants its properties needs to be known at the fundamental level. In this study, the viscosity of pure glycerol at high pressures and strain rates has been investigated using of molecular dynamics (MD) simulations, utilizing both the Green-Kubo (GK) formalism and the SLLOD algorithm. Although the viscosity acquired by the GK method is in agreement with the corresponding experimental values at low pressure, a significant distinction was identified between the viscosity obtained by the GK method and the experimental values at higher pressures (P > 0.5 GPa). This results in a clear difference between the viscosity-pressure coefficient attained by the GK method and the corresponding experimental value. The SLLOD method using a non-equilibrium MD (NEMD) platform was exploited to take into account the simultaneous effects of strain rate and pressure on viscosity. As a result, the pressure-viscosity coefficient acquired by the SLLOD algorithm approaches the experimental value. By combining the experimental outputs for viscosity at low strain rates ( < 104 s−1) with the SLLOD outputs at higher rates ( > 105 s−1), the evolutions of glycerol viscosity with pressure and strain rate were ultimately achieved. Implementing this computational platform depicts the shear thinning process in pure glycerol in a wide range of pressures and strain rates.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Glycerol, Pressure-viscosity coefficient, Green-Kubo Formalism, SLLOD algorithm, Shear thinning, Molecular dynamics simulation
National Category
Condensed Matter Physics
Research subject
Machine Elements; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-102857 (URN)10.1016/j.molliq.2023.122990 (DOI)2-s2.0-85171625047 (Scopus ID)
Funder
The Kempe Foundations, JCK-1903.2Knut and Alice Wallenberg FoundationSwedish Research Council, 2021-05621
Note

Validerad;2023;Nivå 2;2023-11-23 (joosat);

CC BY 4.0 License

Available from: 2023-11-23 Created: 2023-11-23 Last updated: 2023-11-23Bibliographically approved
Rudnytskyj, A., Larsson, R. & Gachot, C. (2022). A Closer Look at the Contact Conditions of a Block-on-Flat Wear Experiment. Lubricants, 10(7), Article ID 131.
Open this publication in new window or tab >>A Closer Look at the Contact Conditions of a Block-on-Flat Wear Experiment
2022 (English)In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 7, article id 131Article in journal (Refereed) Published
Abstract [en]

Specific wear rates of tribosystems always rely on the data obtained from wear experiments. Nonetheless, the events taking place during an experiment may often lead to wide variations and low repeatability of the results. In this work, the authors attempt to take a closer look into the dynamic contact conditions of a dry linearly reciprocating block-on-flat wear experiment. The finite element method and Archard’s wear model are used through COMSOL Multiphysics® 5.2a and LiveLink™ for MATLAB® software to model the wear and study the influence of different conditions of the block surface and alignment of the sample. Changes of the geometry of the block and the contact pressure are quantified for several back and forth motions, using an extrapolation scheme in the wear modelling methodology. The tracking of such changes allow a dynamic overview of how the block contact area and the contact pressure distribution change throughout time. The results show how the assumption of a constant contact area and use of a nominal contact pressure in calculating the wear rate in such experiments can be inappropriate, especially in the presence of roughness and misalignments of the block.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
wear modelling, block-on-flat, roughness, wear rate, Archard’s equation, contact evolution, finite element method
National Category
Chemical Process Engineering Energy Engineering
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-92133 (URN)10.3390/lubricants10070131 (DOI)000831406300001 ()2-s2.0-85132896185 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-07-12 (joosat);

Funder: Austrian COMET-Program (K2 Project In Tribology, no. 872176); TU Wien

Available from: 2022-07-12 Created: 2022-07-12 Last updated: 2023-09-05Bibliographically approved
Hansen, J., Björling, M. & Larsson, R. (2022). A new film parameter with micro elasto-hydrodynamics. In: 7th World Tribology Congress (WTC 2022): . Paper presented at 7th World Tribology Congress (WTC 2022), Lyon, France, July 10-15, 2022. , Article ID MON-T1-S2-R4.
Open this publication in new window or tab >>A new film parameter with micro elasto-hydrodynamics
2022 (English)In: 7th World Tribology Congress (WTC 2022), 2022, article id MON-T1-S2-R4Conference paper, Oral presentation with published abstract (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.

Keywords
Λ-ratio, micro-EHL, mixed lubrication, running-in
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-92911 (URN)
Conference
7th World Tribology Congress (WTC 2022), Lyon, France, July 10-15, 2022
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council
Note

Funder: Norrbottens forskningsråd; Scania CV AB

Available from: 2022-09-09 Created: 2022-09-09 Last updated: 2023-09-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9110-2819

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