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  • 51. Åhrström, Bert-Olof
    et al.
    Lindqvist, S.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modified split Hopkinson pressure bar method for determination of the dilatation-pressure relationship of lubricants used in elastohydrodynamic lubrication2002In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 216, no 2, p. 63-74Article in journal (Refereed)
    Abstract [en]

    In theoretical calculations of film thickness, pressure distribution and friction in an elastohydrodynamically lubricated (EHL) conjunction it is necessary to model the physical/mechanical behaviour of the lubricant. It is important to know, for example, the dilatation-pressure or the density-pressure relationship. In this paper a modified split Hopkinson pressure bar system for determination of the compressibility of oil is presented. It makes it possible to test oils under conditions similar to those found in real EHL contacts: loading duration in the range of 100-300 μs and pressures of almost 2 GPa. An empirical model has been suggested for mathematical description of the dilatation-pressure relation of the specific oils. A naphthenic mineral oil and a synthetic oil, 5P4E, have been tested under adiabatic conditions and at pressures up to 1.5 and 1.9 GPa respectively. The adiabatic results have been recalculated to isothermal conditions for comparison

  • 52. Åhrström, Bert-Olof
    et al.
    Penchinat, C.
    Option Matériaux, Ecole Centrale de Nantes.
    Norrby, Thomas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    An experimental study of the influence of heat storage and transportability of different lubricants on friction under transient elastohydrodynamic conditions2003In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 217, no 1, p. 27-37Article in journal (Refereed)
    Abstract [en]

    Lubricated transient elastohydrodynamic (EHD) conjunctions are extremely difficult to simulate numerically since lubricant properties such as temperature and viscosity vary significantly during the loading-unloading event. Nevertheless, industry has invested considerable time and effort in trying to create such models in order to improve performance and to reduce emissions and friction. One of the essential requirements for a successful model is accuracy in the implementation of frictional properties. The experimental method presented in this paper used an impact on the end surface of a beam to generate propagating waves that were subjected to fast Fourier transform analysis. The method yielded detailed information about the build-up and decay of normal and frictional forces as a function of time for various lubricants at three different initial temperatures (20, 40 and 80 °C) and at relevant EHD pressures. A variety of lubricants were studied to a peak Hertzian pressure of 2.5 GPa for loading-unloading times of 200-400 µs (typical for elastohydrodynamically lubricated conjunctions in ball bearings and gears). A qualitative study of the thermal properties of the lubricants and their influence on viscosity and friction coefficient was also undertaken and, finally, a plausible explanation of the observed behaviour is presented and parallels to dynamic simulations of polyatomic gases are drawn.

  • 53.
    Östensen, Jan Ove
    et al.
    Luleå University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Venner, C H
    Twente University.
    Determination of viscosity and pressure in an EHD rolling contact by using optical interferometry1996In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 210, no 4, p. 259-268Article in journal (Refereed)
    Abstract [en]

    Optical interferometry has been used during the last 30 years for film thickness measurements in elastohydrodynamic (EHD) contacts. In the work presented in this paper the possibility of using optical interferometry for determining pressure and apparent viscosity in a fully flooded EHD point contact has been theoretically investigated. The pressure in the contact is computed from elastic deformation theory and force balance. The apparent viscosity can be obtained from the Reynolds equation when the film thickness and the pressure are known. To theoretically examine the sensitivity to measurement errors, different errors have been implemented in a set of 'exact' numerical data. From the theoretical study it can be seen that a film thickness map obtained from optical interferometry can be used for determination of both pressure and apparent viscosity measurement in an EHD point contact. The simulated errors that have been used do not influence the pressure within the Herzian region by more than a few per cent. However, to obtain reliable results from the apparent viscosity calculations, the measurements of film thickness, load and elastic modulus must be very accurate. It is seen, for example, that the resolution of the film thickness measurement has to be less than 1 nm to achieve high accuracy.

  • 54. Östensen, J.O.
    et al.
    Åström, H.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Analysis of a grease-lubricated roller bearing under arctic conditions1995In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 209, no 3, p. 213-220Article in journal (Refereed)
    Abstract [en]

    This paper summarizes measurements of starting torque and motion of the rollers in a roller bearing during start-up at a temperature of -30 °C. The bearing was lubricated with three different greases and the tests were carried out after a running-in procedure at +20 °C. The results were compared with measurements obtained at +20 °C and with results from one base oil at +20 °C. A model for the roller motion was also built and simulations of the roller motion were compared with the measurements. Independent of temperature and lubricant the rollers rolled in the loaded zone and slipped, more or less, in the unloaded zone. The degree of sliding in the unloaded zone was found to be governed mainly by the local lubricant distribution and the position of the roller in the cage pocket. Some differences are also seen in the slide-roll ratio between the lubricants. A roller diameter difference of 1.3 μm gave a significant difference in roller motion, with the slightly thinner roller slides more in the unloaded zone of the bearing.

  • 55.
    Östenson, J.-O.
    Luleå tekniska universitet.
    Prediction of film thickness in an elastohydrodynamic point contact lubricated with a viscosity index improved base oil1995In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 209, p. 235-242Article in journal (Refereed)
12 51 - 55 of 55
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