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Sökning: LAR1:uu > Konferensbidrag > Jacobson Staffan

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  • Alfredsson, Sara, et al. (författare)
  • Tribological conditions of curling - the ultimate friction sport?
  • 2011
  • Ingår i: 18th International Conference on Wear of Materials, Philadelphia, USA, April 3-7, 2011.
  • Konferensbidrag (refereegranskat)abstract
    • Curling is an Olympic winter sport in which 8 players forming two teams slide stones across a sheet of ice towards a target area. The two teams have eight stones each and take turns to slide the stones over to the target area, some 28 m away from the release line. After being released, the stone is only affected by the sliding friction. However, this friction may be somewhat modified by sweeping the ice just in front of the sliding stone, using special curling brooms. Further, the trajectory of the stone becomes slightly curled. By slowly turning the stone clockwise when it is released, it will turn to the right, and vice versa. The best team in each round of 16 stones score one point for each stone resting closer to the target than the best stone from the opponent team.The game makes up a very interesting tribological system, presenting a number of challenging problems. These problems include understanding exactly:what determines the level of friction, and how it is affected by the sweeping,how the roughness of the stone influences the friction, and how the sliding surface should best be prepared to give a stable and repeatable friction,how the intentionally bumpy "pebbled" ice structure influences the friction,the size and distribution of the contact spots between the rough stone and the pebbled ice,the mechanism causing the curl of the stone - "Why does the stone curl?".This poster is based on an experimental project, and presents this very intriguing tribological system. It offers some ready explanations and challenges the visiting tribologists to contribute their insights.
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  • Andersson, Joakim, et al. (författare)
  • Phase transformations in CVD diamond wear tracks revealed by NEXAFS mapping
  • 2004
  • Ingår i: Nordtrib 2004, Tromsö, Norway.
  • Konferensbidrag (refereegranskat)abstract
    • The origin of the different Li+ intercalation behavior of raw and jet-milled natural graphite has been investigated. Jet-milled graphite is found to cycle reversibly in equal solvent mixture of propylene carbonate (PC) and etylene carbonate (EC), whereas raw graphite does not. Using both Al Ka and synchrotron radiation (SR) Photoelectron Spectroscopy, new insight is obtained inti the formation of the solid electrolyte interphase (SEI) on the two different graphite materials during electrochemical cycling in 1 M LiPF6 in either PC:EC (1:1) or in PC with 5% vinylene carbonate (VC) as additive. Solvent reduction products are found at the surface of both raw and jat-milled graphite cycled in PC:EC (1:1), but differed in composition. The addition of VC reduces primarily the quantities of salt reaction products (LiF and LixPFy compounds) and produces a mainly organic SEI layer. Electron diffraction from the edges for raw and jet-milled graphite particles shows a physical barrier hindering PC co-intercalation and faciltating the formation of a stable SEI layer.
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  • André, Benny, et al. (författare)
  • Performance and Tribofilm Formation of a Low-Friction Coating Incorporating Inorganic Fullerene Like Nano-Particles
  • 2009
  • Konferensbidrag (refereegranskat)abstract
    • A new tribological coating with potential as a coating for components for low-friction applications is tested and compared to three, state of the art, commercial low-friction PVD coatings. The new coating is an electrodeposited coating composed by a Ni-P matrix incorporating fullerene like nanoparticles of WS2. The performance of the new coating is compared with three reference coatings in a ball-on-disc setup. The tribological tests involved ball bearing steel balls slid on coated discs, under different conditions of humidity and also with or without oil lubrication. Both mating surfaces were closely investigated in a scanning electron microscope and the low-friction tribofilms formed were further analysed. The correlations found between coefficient of friction, surface roughness of the wear scar, tribofilm formation and contact conditions are discussed. The new coating exhibits a very low coefficient of friction at low humidity, a behaviour closely resembling that of the MoS2-based commercial reference, whereas the carbon based PVD coatings tested exhibit the reversed dependence of humidity. The low-friction behaviour of the new coating is correlated to the formation of a WS2 tribofilm with a superficial alignment of the basal planes parallel to the sliding direction. When lubricated with a base oil, the beneficial tribofilm is not formed and the coefficient of friction is much higher. The results show that even though the coating is an electrodeposited coating it can compete with state of the art commercial PVD coatings.
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  • Elo, Robin, 1988-, et al. (författare)
  • Formation and degradation of protective tribofilms on diesel engine valve surfaces
  • 2014
  • Konferensbidrag (refereegranskat)abstract
    • In modern heavy duty diesel engines, the valve system plays an important part. The intake valves open to let air flow in to the combustion chamber, the combustion takes place and then the exhaust valves open the let the combustion products flow out of the chamber. This is repeated as the engine drives the vehicle forward and at all other time, the valves must be closed to avoid any leakage of the combustion chamber which would reduce the power output. This process takes place at high temperature, high chamber pressure and high frequency and the wear rate of the valve surfaces must be extremely low to allow them to operate satisfactory during the life-time of the engine.In today’s engines, a tribofilm is formed from elements from the engine oil, which lowers the wear rate and thus gives the valves the wanted long life-time. However, little is known about the mechanisms of how this tribofilm is formed and how it behaves to lower the wear rate. When analyzing field samples, it appears as if additive elements from the oil have been trapped between the valve and valve seat insert surfaces and then as the valve closes, is smeared out into a smooth layer protecting the metal surfaces. The question is how fast this process takes place and if the tribofilm can function without continuous addition of new tribofilm forming elements.In this work, the build-up phase of these tribofilm has been studied by running real valves and valve seat inserts in an in-house rig which allows the addition of oil into a hot air stream which passes the opening and closing valve. The rig allows stopping a test at any point, taking the valve and valve seat insert out to analyze the surfaces and then re-starting the test. To see the build-up phase of the tribofilm, tests have been run for 10; 100; 1000 and 10000 cycles with the addition of engine oil. Also, test have been continued after 1000 and 10000 cycles, without the addition of engine oil, for 1000 cycles to see if the tribofilm can sustain the wear rate without the addition of new tribofilm forming elements.The results will be presented and discussed regarding their effect on future work to develop the valve system as they will see less and less tribofilm forming elements due to harder legislation on exhaust limits—e.g. the euro class which is implemented in Europe—which may reduce the amount of additives that can be put into future engine oils.
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