| 1. |
- Bair, Scott, et al.
(författare)
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Comment on “History, Origins and Prediction of Elastohydrodynamic Friction” by Spikes and Jie
- 2015
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- Progress in the classical field of EHL has for decades been paralyzed by the assumption that shear thinning should be indistinguishable from the shear dependence of the viscosity of a liquid heated by viscous dissipation and that the parameters of this simple shear dependence can be obtained from the shape of a friction curve. In the last few years, by abandoning this assumption and employing real viscosity measured with viscometers, there has been revolutionary progress in predicting film thickness and friction. Now, Spikes and Jie conclude that the previous assumption has as much merit as the use of viscosity measured in viscometers. This suggestion may be popular among those who wish to ignore viscometer measurements in favor of extracting properties from friction curves. However, within the subject article, there are numerous misstatements of fact and misrepresentations by omission, and the recent progress using real viscosity is not acknowledged. The debate has degenerated into a friction curve fitting competition which is not helpful. The great progress of the last few years would not have been possible using the concepts and methods espoused in this article
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| 2. |
- Bair, Scott S., et al.
(författare)
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New EHL Modeling Data for the Reference Liquids Squalane and Squalane Plus Polyisoprene
- 2018
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Ingår i: Tribology Transactions. - : Society of Tribologists and Lubrication Engineers. - 1040-2004 .- 1547-397X. ; 61:2, s. 247-255
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Tidskriftsartikel (refereegranskat)abstract
- An important part of the new quantitative approach to elastohydrodynamic lubrication (EHL) is the use of reference liquids with well-characterized thermophysical properties. New measurements are reported for the thermal and rheological properties of squalane to high pressure and of high shear rate and high-frequency viscosity of squalane thickened with polyisoprene (SQL + PIP) at ambient pressure. The glass transition viscosity of squalane at ambient pressure was found from published viscosity measurements and new glass transition measurements by transient hot wire. The glass transition viscosity so determined was incorporated into the improved Yasutomi model and the calculated glass transition temperatures as a function of pressure are comparable to those directly measured, although the hybrid model yields better agreement. The glass transition viscosity of squalane by any definition must be substantially lower than the “universal value” of 1012 Pa·s. The second Newtonian inflection cannot be characterized in steady shear at ambient pressure for SQL + PIP due to cavitation; however, acoustic viscometry with matching layer does characterize the second Newtonian inflection. To form the analogy between steady and oscillatory shear requires that the steady shear rate be compared with the ordinary frequency rather than the angular frequency for SQL + PIP.
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| 3. |
- Björling, Marcus, et al.
(författare)
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Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid
- 2017
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 17:10
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Tidskriftsartikel (refereegranskat)abstract
- To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common lubricant base stocks like mineral oils or vegetable oils. One such example is ionic liquids. Ionic liquids have been defined as molten salts with melting points below 100 °C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a bio-based, non-corrosive, [choline][L-proline] ionic liquid is evaluated in terms of pressure-viscosity response, film forming capability and friction. The results show a pressure-viscosity coefficient of below 8 GPa-1 at 25 °C, among the lowest reported for any ionic liquid. The ionic liquid generated up to 70% lower friction than a reference paraffin oil with a calculated difference in film thickness of 11%. It was also shown that this ionic liquid is very hygroscopic, which is believed to explain part of the low friction results, but also has to be considered in practical applications since the water content will influence the properties and thus the performance of the lubricant.
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| 4. |
- Björling, Marcus, et al.
(författare)
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Elastohydrodynamic Performance of a Non-Corrosive Non-Protic Ionic Liquid
- 2017
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Konferensbidrag (refereegranskat)abstract
- Ionic liquids have been defined as molten salts with melting points below 100 degrees C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, Ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a non-corrosive, non-protonic ionic liquid is studied to assess the feasibility to use this kind of ionic liquid in machine components such as gears, rolling bearings and cam followers. This study includes ball on disc friction experiments in rolling sliding full film elastohydrodynamic lubrication at high slide to roll ratios, as well as film thickness measurements with optical interferometry. A commercially available paraffin oil has been used as a reference.
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| 5. |
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| 6. |
- Björling, Marcus, et al.
(författare)
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Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation
- 2014
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 53:2, s. 477-486
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Tidskriftsartikel (refereegranskat)abstract
- Reducing friction is of utmost importance to improve efficiency and lifetime of many products used in our daily lives. Thin hard coatings like diamond-like carbon (DLC) have been shown to reduce friction in full-film-lubricated contacts. In this work, it is shown that contrarily to common belief, the friction reduction stems mainly from a thermal phenomenon and not only a chemical/surface interaction one. It is shown that a few micrometer-thin DLC coating can significantly influence the thermal behavior in a lubricated mechanical system. The presented simulations, validated by experiments, show that applying a thin DLC coating to metal surfaces creates an insulating effect that due to the increased liquid lubricant film temperature at the center of the contact, locally reduces lubricant viscosity and thus friction. The results of the investigation show that the addition of thin insulating layers could lead to substantial performance increases in many applications. On a component level, the contact friction coefficient in some common machine components like gears, rolling element bearings, and cam followers can potentially be reduced by more than 40 %. This will most likely open up the way to new families of coatings with a focus on thermal properties that may be both cheaper and more suitable in certain applications than DLC coatings
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| 7. |
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| 8. |
- Björling, Marcus, et al.
(författare)
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Warm carbon coat reduces friction
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 505:7483, s. 264-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A coating material made of carbon reduces friction not just by providing a slippery surface, but also by keeping the points of contact warm. Marcus Björling at Luleå University of Technology in Sweden and his team coated steel balls with ``diamond-like-carbon'' - a material in which carbon atoms have a bonding pattern similar to that of diamond. They rolled the balls against a metal disk with an oil lubricant in between, and showed that the carbon coating acts as an insulator, lowering the viscosity of the lubricant and thus reducing the fricion between the ball and the disk. These findings could encourage the development of lubricant coatings made from insulating materials.
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| 9. |
- Habchi, W, et al.
(författare)
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Influence of pressure and temperature dependence of thermal properties of a lubricant on the behaviour of circular TEHD contacts
- 2010
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 43:10, s. 1842-1850
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to study the effects of pressure and temperature dependence of a conventional lubricant's thermal properties on the behaviour of heavily loaded thermal elastohydrodynamic lubrication (TEHL) contacts. For this purpose, a typical mineral oil (Shell T9) is selected and the dependence of its transport properties on pressure and temperature is investigated. Appropriate models are then developed for these dependencies. The latter are included in a TEHL solver in order to investigate their effect on the behaviour of circular EHD contacts. The results reveal the necessity of a thermal analysis including the pressure and temperature dependence of thermal properties for a good estimation of film thicknesses and mostly traction coefficients in circular EHD contacts operating under severe conditions. Numerical results are compared with experiments, showing a very good agreement over the considered ranges. This thorough validation of a thermal EHL framework for the calculation of film thickness and friction offers a previously unavailable opportunity to investigate the effects of variations in material properties.
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| 10. |
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| 11. |
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| 12. |
- Aad, G., et al.
(författare)
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- 2012
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swepub:Mat__t (refereegranskat)
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