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  • 151.
    Kang, Shaojie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Furustig, Joel
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A running-in model for the boundary lubricated contact2013Conference paper (Other academic)
    Abstract [en]

    During the running-in period of a boundary lubricated contact, the surface roughness will be dramatically changed, involving large plastic deformation and wear on the asperity summits. This paper presents a running-in model. The model is based on the Boundary Element Method (BEM) and will focus on the investigation of large plastic deformations. The BEM model is based on the minimization of the complementary potential energy and deals with the contact at interfaces. The BEM model used in this paper previously adopted a linearly elastic- perfectly plastic material model and was frictionless, therefore a correction factor is needed for the model to improve its ability to account for high friction and large plastic deformation. The correction factor is made by improving the yield criterion and is derived with the assistance of the Finite Element Method (FEM). Both the friction and the strain hardening mechanism taken from the real material are implemented in the FEM model; the load and the contact area are required to match in both simulations. With the correction factor, results are promising for the current model to simulate the running-in process.

  • 152.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Aktivitet: Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology2001Other (Other (popular science, discussion, etc.))
  • 153.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bouncing ball lubrication2021In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 235, no 12, p. 2582-2587Article in journal (Refereed)
    Abstract [en]

    My interest in the lubrication mechanisms of a ball bouncing and impacting an oily plate brought me into contact with Professor Duncan Dowson. Our very first meeting was at a conference where we presented almost identical results. After that, in 1995, I was invited to Leeds University for a one-semester visit. I was still a PhD student and the visit helped me a lot to develop as a person and as a scientist Duncan helped me in this development through his skilful guidance and by putting me in touch with other knowledgeable people in my field. The bouncing ball problem was about understanding elastohydrodynamic lubrication (EHL) under non-steady conditions. In fact, most EHL contacts operate under non-steady conditions since load, speed and curvature often varies rapidly during the operation of machine elements such as gears, rolling bearings and cam mechanisms. In this paper, I will tell you about the bouncing ball problem and how Duncan Dowson became an important person for me. 

  • 154.
    Larsson, Roland
    Luleå University of Technology.
    Editorial: Special Issue on Experimental Investigations for the Understanding of EHL and Lubricant Rheology2001In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 215, no 3, p. i-Article in journal (Other academic)
  • 155.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    EHL Film Thickness Behavior2013In: Encyclopedia of Tribology, Springer-Verlag New York Inc. , 2013, p. 817-827Chapter in book (Refereed)
  • 156.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    EHL Governing Equations2013In: Encyclopedia of Tribology, Springer-Verlag New York Inc. , 2013, p. 827-832Chapter in book (Refereed)
  • 157.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic lubrication under non-steady conditions1996Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The six papers presented in this thesis consider the effects on elastohydrodynamic lubrication (ehl) of non-steady conditions. The vast majority of ehl investigations, both experiemental and theoretical, utilise steady state conditions, i.e. constant load, velocity, geometry and temperature. The lubricant is, however, in conditions that are far from those of steady state. Many components operate with varying load, velocity and geometry. Some examples are gears, rolling element bearings, cams and follower mechanisms and reciprocating seals. To predict the operation of these components it is necessary to consider the transient effects. The theory of elastohydrodynamic lubrication under non-steady conditions is presented in this thesis and applied to some practical cases. Papers A and B deal with the simulation of the lubrication in the contact between an impacting ball and a lubricated surface. These investigations give understanding of lubrication under impact loading and also fundamental understanding of the dynamics of an ehl contact. Paper C is an experimental investigation of the impacting ball problem. The deformation of the surfaces in the contact region is studied for different combinations of lubricant viscosities and impact velocities. Paper D and E deal with the breakdown mechanisms of a lubricant film. It is shown that lubricant film failure occurs at high sliding velocities if the load is non-stationary. This contradicts elastohydrodynamic theory since increasing sliding velocity implies increasing entrainment of lubricant and thus thicker lubricant film and less risk for failure. It is, however, shown in Paper E that starvation can be the reason why film failure occurs even if the conjunction is lubricated by a thick layer of lubricant. Paper F is a transient simulation of a meshing involute spur gear. Film thickness, pressure, friction and subsurface stresses are computed at different positions along the line of action. Two different sets of lubricant properties are used, the first one

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  • 158.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Keynote lecture: A framework for modelling of boundary lubrication2018Conference paper (Other academic)
  • 159.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubrication at impact loading1994Licentiate thesis, comprehensive summary (Other academic)
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  • 160.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modelling the effect of surface roughness on lubrication in all regimes2009In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 4, p. 512-516Article in journal (Refereed)
    Abstract [en]

    A model of lubrication in all regimes is presented. Two length scales are defined, cell and global length scale levels. Surface roughness effects are modelled on the local cell level, while the actual lubrication problem is solved on the global level. Surface roughness influences contact mechanics, when surfaces are boundary lubricated, as well as hydrodynamic film formation. The all-regimes lubrication model is applied to thrust bearings and wet clutches. The cell level model can be further improved to also include wear and better friction estimation.

  • 161.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modelling the effect of surface roughness on lubrication in all regimes2007In: Proceedings: ECOTRIB 2007, Joint European Conference on Tribology and Final Conference of COST 532 Action: Triboscience and Tribotechnology, 12. - 15. June, Ljubljana, Slovenia / [ed] Joze Vizintin, Ljubljana: Slovenian Society for Tribology , 2007, p. 165-173Conference paper (Refereed)
    Abstract [en]

    A model of lubrication in all regimes is presented. Two length scales are defined, cell and global length scale levels. Surface roughness effects are modelled on the local cell level while the actual lubrication problem is solved on the global level. Surface roughness influences contact mechanics, when surfaces are boundary lubricated, as well as hydrodynamic film formation. The all-regimes lubrication model is applied to thrust bearings and wet clutches. The cell level model can be further improved to also include wear and better friction estimation.

  • 162.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Point Contact EHL2013In: Encyclopedia of Tribology, Springer-Verlag New York Inc. , 2013, p. 2549-2550Chapter in book (Refereed)
  • 163.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Simulations of tribological phenomena – What can we learn from them?2011Conference paper (Other academic)
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  • 164.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient non-Newtonian elastohydrodynamic lubrication analysis of an involute spur gear1997In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 207, no 1, p. 67-73Article in journal (Refereed)
    Abstract [en]

    The meshing of a gear is a typical example where non-stationary conditions exist. Load, velocities and curvature vary along the line of action. In this analysis, pressure and film thickness are computed at several points along the line of action by taking the transient effect into consideration. Isothermal full film lubrication is assumed and the fluid model is a non-Newtonian model which includes the effect of a limiting shear strength.The gear teeth are assumed to be rigid. The load is first assumed to be carried by either two pairs of gear teeth or by only one pair. This transition from two to one pair and vice versa is modelled as a step variation of the load.The results show that the transient effect is most pronounced at the load transitions where the previous pair of teeth goes out of action and where the next pair of teeth comes into action. Due to the squeeze effect, the minimum film thickness increases for a moment when the load is doubled. The opposite happens when the load is halved again, the film thickness decreases for a moment until it stabilises.The friction coefficient is computed at the different contact points and so are also the sub-surface stresses. Results are presented for two different lubricants, a paraffinic mineral oil and an oil of the poly-α-olefin type.

  • 165.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient non-Newtonian elastohydrodynamic lubrication analysis of an involute spur gear1996In: Proceedings of the Seventh International Conference inTribology, Nordtrib'96: June 16th - 19th, 1996, Bergen / [ed] K. Tönder; T. Syverud, 1996Conference paper (Refereed)
    Abstract [en]

    The meshing of a gear is a typical example where non-stationary conditions exist. Load, velocities and curvature vary along the line of action. In this analysis, pressure and film thickness are computed at several points along the line of action by taking the transient effect into consideration. Isothermal full film lubrication is assumed and the fluid model is a non-Newtonian model which includes the effect of a limiting shear strength. The gear teeth are assumed to be rigid. The load is first assumed to be carried by either two pairs of gear teeth or by only one pair. This transition from two to one pair and vice versa is modelled as a step variation of the load. The results show that the transient effect is most pronounced at the load transitions where the previous pair of teeth goes out of action and where the next pair of teeth comes into action. Due to the squeeze effect, the minimum film thickness increases for a moment when the load is doubled. The opposite happens when the load is halved again, the film thickness decreases for a moment until it stabilises. The friction coefficient is computed at the different contact points and so are also the sub-surface stresses. Results are presented for two different lubricants, a paraffinic mineral oil and an oil of the poly-α-olefin type.

  • 166.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribologen föredrar ytliga kontakter2003In: Thule: Kungliga Skytteanska samfundets årsbok 2003, Umeå: Kungl. Skytteanska samfundet , 2003Chapter in book (Other (popular science, discussion, etc.))
  • 167.
    Larsson, Roland
    et al.
    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.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Hägglunds Drives AB, Mellansel, Sweden.
    Simulations of lubricated interfaces – a way to obtain efficient machines2010Conference paper (Other academic)
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  • 168.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andersson, Ove
    Umeå university.
    Lubricant thermal conductivity and heat capacity under high pressure2000In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, no 4, p. 337-342Article in journal (Refereed)
    Abstract [en]

    The thermal conductivity λ and the heat capacity per unit volume, ρcp, have been measured for a number of common lubricating oils. The oils tested were paraffinic and naphthenic mineral oils and a 50/50 blend of these. Polyα-olefin, polyglycol, Santotrac, ester and rapeseed oils have also been tested. The measurements, using the transient hot-wire method, were carried out under isothermal conditions over a pressure range from atmospheric to 1.1 GPa and at two temperatures, 295 and 380 K (22 and 107°C respectively). The temperature had only a marginal effect on thermal conductivity; however, the thermal conductivity was doubled as the pressure was increased to 1 GPa. The heat capacity per unit volume was influenced by both the pressure and the temperature. Some of the lubricants solidified as the pressure increased and the transition from a fluid to a solid state could be detected in the measurements of ρcp,The relationship between the thermodynamic properties and the pressure and temperature are described by two empirical equations. These equations can be used in thermal elastohydrodynamic analyses.

  • 169.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Elastohydrodynamic lubrication2004In: Tribology of mechanical systems: a guide to present and future technologies, New York: American Society of Mechanical Engineers , 2004Chapter in book (Other academic)
  • 170.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Elastohydrodynamic lubrication at impact loading1994In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 116, no 4, p. 770-776Article in journal (Refereed)
    Abstract [en]

    The case of a ball impacting a flat lubricated surface is investigated theoretically. This case implies transient conditions and the lubricating effect is due to pure squeeze action in the contact. Results of the analysis show that increasing the velocity, increases the minimum value of film thickness achieved during the total impact time. The damping capacity of the lubricating film is very high at low impact velocity and small ball mass. Thickness of lubricant layer has little effect on the results if it is thicker than certain critical values. If the pressure-viscosity coefficient is increased, the film becomes thicker

  • 171.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Elastohydrodynamic lubrication at pure squeeze motion1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 179, no 1-2, p. 39-43Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies of elastohydrodynamically lubricated contacts normally assume static or quasi-static conditions. Non-steady conditions are, however, common. In this paper the case of a ball impacting a flat lubricated surface is investigated theoretically. This case implies transient conditions and the lubricating effect is due to pure squeeze action. Pressure and film thickness distributions are computed during impact and rebound. The results of the analysis show the effects of ball mass, initial impact velocity, lubricant properties and the thickness of the applied lubricant layer on the minimum film thickness. Increased impact velocity increases the minimum value of film thickness achieved during the bounce. The damping capacity of the lubricating film is very high at low impact velocity and small ball mass. In fact, the damping is so high that no rebound occurs if the velocity or the ball mass are smaller than certain critical values. The thickness of the lubricant layer has no influence on the results if it is greater than a certain value. If the pressure-viscosity coefficient is increased, the film becomes thicker

  • 172.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Elastohydrodynamic lubrication at pure squeeze motion1994In: Nordtrib '94: proceedings of the 6th Nordic Symposium on Tribology ; 12 - 15 June 1994, Uppsala, Sweden / [ed] P. Hedenquist, Uppsala, 1994, p. 103-110Conference paper (Refereed)
  • 173.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Numerical simulation of a ball impacting and rebounding a lubricated surface1995In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 117, no 1, p. 94-102Article in journal (Refereed)
    Abstract [en]

    The case of a ball bouncing on a flat surface covered by a thin lubricant layer is analyzed theoretically. Both impact and rebound are studied. A Newtonian lubricant and perfect elastic solids are assumed. As long as the ball approaches the flat surface the pressure in the contact increases and a lubricant entrapment is formed at the center of the contact. When the ball begins to leave the surface, cavitation occurs. At the periphery of the contact a pressure spike is formed. Just before the ball leaves the lubricated surface, very high pressure values arise at and near the contact center. These results are compared with the case of nonlubricated impact. It is found that the pressure in the contact at lubricated impact is higher than in the case of dry impact. Due to the elastic and damping properties of the lubricant film and the impacting surfaces, a time delay is observed between the time of maximum impact force and minimum film thickness. Comparing the theoretical results with experimental results, presented by other authors, shows good correlations.

  • 174.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kassfeldt, Elisabet
    Byheden, Åke
    Norrby, Thomas
    Base fluid parameters for EHL and friction calculations and their influence on lubrication capability2000In: Tribology 2000 - plus / [ed] W.J. Bartz, Techn. Akad. Esslingen , 2000, p. 1525-1536Conference paper (Refereed)
  • 175.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kassfeldt, Elisabet
    Byheden, Åke
    Norrby, Thomas
    Base fluid parameters for elastohydrodynamic lubrication and friction calculations and their influence on lubrication capability2001In: Journal of Synthetic Lubrication, ISSN 0265-6582, Vol. 18, no 3, p. 183-198Article in journal (Refereed)
    Abstract [en]

    In this study, base fluid parameters for elastohydrodynamic lubrication (EHL) and friction analyses have been determined experimentally. The viscosity at atmospheric pressure, η0, the pressure-viscosity index, α and the EHL friction coefficient, γ, are important parameters in EHL theory and they are crucial in the selection of efficient lubricants for different applications. This investigation focuses on three important lubrication mechanisms: The capability of forming a separating lubricants film, the friction generated in a lubricated contact, and the height of pressure peaks, such as the outlet pressure spike and pressure ripple caused by surface roughness. The influence of different lubricant parameters on these three mechanism is discussed. The value of α is measured in a Couette high-pressure viscometer, and the value of γ is obtained from a jumping-ball device. Other parameters discussed are temperature-viscosity coefficient, β, bulk modulus, BO, thermal conductivity at atmospheric pressure, λO, and heat capacity unit volume, ρCpO. A comparison between traditional mineral base oils and environmentally adapted oil based on rapeseed oil and synthetic esters contributes to the further understanding of the performance of these new materials in lubrication applications. It is shown that rapeseed oil and synthetic esters have good lubricating properties and are, in most cases, better than mineral oils.

  • 176.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson-Kråik, Per-Olof
    Swedish National Rail Administration, Region North.
    Internet based tribological analyses2002In: 10th Nordic Symposium on Tribology: NORDTRIB 2000 : Hotel Foresta and KTH, Stockholm, Sweden, June 9-12, 2002, Stockholm: Kungl. Tekniska Högskolan , 2002, p. 147-Conference paper (Other academic)
  • 177.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson-Kråik, Per-Olof
    Luleå University of Technology.
    Eriksson, Erland
    Luleå University of Technology.
    Sjöberg, Martin
    Luleå University of Technology.
    Höglund, Erik
    Luleå University of Technology.
    Lubricant properties for input to hydrodynamic and elastohydrodynamic lubrication analyses2000In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 214, no 1, p. 17-27Article in journal (Refereed)
    Abstract [en]

    The properties of a number of common lubricants have been measured, namely the viscosity, elastohydrodynamic lubrication (EHL) friction coefficient, density, thermal conductivity and heat capacity per unit volume. These properties have been measured within relatively broad pressure and temperature ranges. The lubricants tested were naphthenic and paraffinic mineral oils, blends of these, polyalphaolefins and a polyglycol. Physical--empirical expressions have been developed upon the basis of the measurement results and a number of lubricant constants, or lubricant parameters, have been determined for each lubricant. These expressions can be used in engineering computational tools for lubrication analysis. The use of such analyses is expected to increase into the new millennium and it is thus important to provide reliable and relevant input data

  • 178.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lord, John
    Film-forming capability in rough surface EHL investigated using contact resistance2006In: Nordtrib 2006, 12th Nordic Tribology Symposium, Denmark: [LO-skolen, Helsingør, Denmark, June 7 - 9 2006], Kongens Lyngby: Technical University of Denmark , 2006Conference paper (Refereed)
  • 179.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Observations in transiently loaded EHL contacts under pure sliding conditions1998In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 41, no 4, p. 489-496Article in journal (Refereed)
    Abstract [en]

    An elastohydrodynamically lubricated contact is experimentally investigated during loading and pure sliding motion. This is a combination of motions where lubricant film failures sometimes occur. The experimental setup consists of a 70-mm diam. ball segment mounted on a pendulum. The ball segment can be rotated while it impacts a lubricated glass disc. The deformation of the surfaces in the contact region is studied by means of optical interferometry and high-speed video recording equipment. Two poly-α-olefin-type lubricants with viscosities of 94 and 2600 mm2/s are used in the experiments. The squeeze velocity, i.e., the normal approach velocity, is approximately 0.06 m/s, giving an impact time of about 20 ms. The sliding velocity is varied from 0 to 34 m/s. Some of the observed phenomena are that lubricant film breakdown occurs at high sliding velocities while full film is maintained at no or low sliding velocity and that the traditional horseshoe-shaped fringes are found even for this load situation. At very high sliding velocities, the interferograms are distorted from their normal circular shape to a pear-like shape. (

  • 180.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Simplified solution to the combined squeeze-sliding lubrication problem1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 173, no 1-2, p. 85-94Article in journal (Refereed)
    Abstract [en]

    The unfavourable elastohydrodynamic lubrication situation in combined squeeze and sliding motion has been analysed both theoretically and experimentally. In experiments a rotating roller impacted and rebounded on a lubricated surface. It was found that oil film breakdown always occurs at the end of the impact time, when the contact force is low. It has also been found that there exists an upper limit for the sliding velocity. Below this limiting velocity no oil film breakdown occurs. This paper is an initial attempt to explain theoretically why oil film breakdown takes place towards the end of the impact, and why an increasing sliding velocity reduces the capability of the oil film to separate the lubricated surfaces. If the oil film's elastic and damping behaviour are taken into consideration it can be shown that a considerable phase shift between maximum contact force and oil film breakdown will arise. It has been found that the squeeze action dominates the pressure formation in the contact and thus the hydrodynamic effect of sliding motion is moderate. Furthermore, several effects, such as non-Newtonian behaviour, surface roughness, temperature rise, starvation and deformations, which are not included in the theoretical model, may decrease the oil film thickness if the sliding velocity increases

  • 181.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Study of lubricated impact using optical interferometry1995In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 190, no 2, p. 184-189Article in journal (Refereed)
    Abstract [en]

    An experimental study of lubricated impacts between a steel ball and a flat glass surface has been performed. The experimental set-up consists of a Ø70 mm ball mounted on a pendulum which impacts onto a lubricated glass disc. The contact region is studied by means of optical interferometry using a monochromatic light source, a microscope and a high-speed video recording equipment. The lubricants are of PAO type and the viscosity ranges from 27 to 2600 mm2 s-1 at the test temperature. The impact velocity is varied between 0.08 and 0.29 m s-1. A dimple occurs at the centre of the contact where the lubricant is trapped. The influence of viscosity and impact velocity on the dimple's depth and diameter is studied.

  • 182.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Study of lubricated impact using optical interferometry1994In: Frontiers in tribology: proceedings of the 4th International Tribology Conference - AUSTRIB '94, Perth, Western Australia, 5 - 8 Decemnber 1994 / [ed] G.W. Stachowiak, Perth, 1994Conference paper (Refereed)
  • 183.
    Larsson, Roland
    et al.
    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.
    Special issue on tribology research in Scandinavia: Guest editorial2011In: 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. 973-974Article in journal (Other academic)
  • 184. Larsson-Kråik, Per-Olof
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Combined experimental/numerical approach: Influence of different lubricant properties1998In: 10th ELGI annual general meeting: Eurogrease, European Lubrications Grease Institute , 1998, p. 15-27Conference paper (Other academic)
  • 185.
    Larsson-Kråik, Per-Olof
    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.
    Jolkin, Alexei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Olov
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Pressure fluctuations as grease soaps pass through an EHL contact2000In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 33, no 3-4, p. 211-216Article in journal (Refereed)
    Abstract [en]

    Soap lumps entering a grease-lubricated elastohydrodynamic lubrication (EHL) contact were traced as they passed through the contact by using optical interferometry in a standard Ball & Disc apparatus and a high-speed video camera with light enhancer. One specific soap lump could be traced when it was passing through the contact and sharp images of the passing lump could be captured. This paper presents a combined experimental and numerical approach to determine what is happening when such lumps pass through the contact. From the fringe pattern, obtained by optical interferometry, a film thickness map is created by using image processing. This is done for every time step (1 ms) as the lump is passing through the contact. These maps serve as input to a numerical computation of the pressure by assuming elastic deformation theory. Consequently, no assumptions about the rheological behaviour of the grease have to be made. Two greases were studied, based on the same synthetic poly-α-olefin but thickened with Li-12-OH and Li-complex respectively. It is seen that the soap thickened lumps can cause deep elastic indentations accompanied by large pressure fluctuations. The pressure level will in some cases be more than doubled due to lumps entering the contact region. The effects on noise level and operational life are also discussed.

  • 186. Lindholm, P.
    et al.
    Larsson, Roland
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological test of iron powder lubricants and iron powder mixtures1996In: Modelling in materials science and processing., European Commission Joint Research Centre, 1996Conference paper (Refereed)
  • 187.
    Linjamaa, Aki
    et al.
    Department of Materials Science, Tampere University of Technology.
    Lehtovaara, Arto
    Department of Materials Science, Tampere University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kallio, Marke
    Research & Development, Metso Minerals Oy.
    Söchting, Sven
    Materials & Tribology, Component Expertise, Engines R&D, Wärtsilä Finland Oy.
    Modelling and analysis of elastic and thermal deformations of a hybrid journal bearing2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 451-457Article in journal (Refereed)
    Abstract [en]

    The continuous demand for higher power density leads to a very challenging operational environment for sliding bearings regarding pressures and deformations. Understanding of the deformation behavior of heavily loaded bearings becomes even more pronounced when modern hybrid multilayer designs are considered. The aim of this study is to develop a numerical, multi-physical model for the evaluation of journal bearing performance. Hydrodynamics were based on the Reynolds equation and deformations were calculated using the integrated finite element method. Elastic and thermal deformations have a significant effect on bearing performance and those deformations can be adjusted with properties of polymer layer. The design of hybrid bearings is delicate and their properties must be tailored according to the operating conditions.

  • 188.
    Lord, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Jolkin, Alexei
    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.
    Marklund, Olov
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    A hybrid film thickness evaluation scheme based on multi-channel interferometry and contact mechanics2000In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 122, no 1, p. 16-22Article in journal (Refereed)
    Abstract [en]

    A hybrid evaluation scheme for EHL film thickness determination is proposed and discussed. The film thickness profile in the contact region is measured using interferograms produced with a novel multi channel interferometry method. Since the refractive index distribution in the contact is pressure-dependent, and the initial film thickness profile will be evaluated assuming atmospheric pressure, a refractive index correction scheme is employed. The correction scheme is based on the Lorenz-Lorentz equation and a pressure-density relation together with a numerical pressure solver taking the initial film thickness measurement as input. The film thickness determination scheme is applied to an interesting phenomenon that can be observed at sliding conditions when the discrepancy occurred in the form of a deep and large dimple in the conjunction. Such a dimple appeared instead of the conventional plateau. The phenomenon was studied under different degrees of sliding. The detailed film thickness maps and pressure distributions for highly loaded EHL conjunctions at high degrees of sliding are produced using a hybrid evaluation scheme. The results are analyzed and discussed.

  • 189.
    Lord, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Jonsson, Ulf
    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.
    Marklund, Olov
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Eriksson, Erland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Uusitalo, Östen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The Luleå ball and disc apparatus2001In: Bench testing of industrial fluid lubrication and wear properties used in machinery applications: papers presented at the Symposium on Bench Testing of the Lubrication and Wear Properties of Industrial Fluids Used in Machinery Application held in Seattle, Washington in 26 - 27 June 2000 / [ed] George E. Totten, West Conshohocken, Pa: ASTM International, 2001, p. 53-67Conference paper (Refereed)
    Abstract [en]

    The ability to measure lubricant film thickness in elastohydrodynamic point contacts was greatly improved when the method of interferometry was introduced in the late 1960s. Constant refinements of the technique have made it possible to measure the thickness of thin films with an accuracy of a few nanometers. In order to further develop the technique and provide a tool for advanced lubricant experiments, a Ball and Disc Apparatus was developed. The aim was to accomplish an apparatus with an open architecture for easy expansion and the ability to use several sub-methods for film thickness determination.

  • 190. Lord, John
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of slide-roll ratio and lubricant properties on elastohydrodynamic lubrication film thickness and traction2001In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 215, no 3, p. 301-308Article in journal (Refereed)
    Abstract [en]

    With tribology research aimed at decreasing energy consumption, two factors are inherently in focus: lubricant film thickness and traction. These factors are effectively decoupled and depend on lubricant properties which are sometimes contradictory - favourable for one factor and disadvantageous for the other. The film thickness ought to be maximized to reduce the number of asperities in contact and thus wear, whilst the traction should be minimized in order to reduce energy losses. In this experimental investigation the tested lubricants were investigated to see whether they possess beneficial properties for forming thick lubricant films under severe operating conditions while maintaining low traction forces. This is done by experimentally studying the film thickness reduction due to thermal and rheological effects for a fully flooded electrohydrodynamic lubrication (EHL) contact. The base oils tested were a naphthenic mineral VG150, a synthetic poly-α-olefin VG68 and a synthetic ester VG46. It was found that the synthetic ester maintained a relatively thicker lubricant film during sliding than the poly-α-olefin and mineral oil. The film thickness reduction for the mineral oil was greater than for the poly-α-olefin.

  • 191. Lord, John
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Film-forming capability in rough surface EHL investigated using contact resistance2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 831-838Article in journal (Refereed)
    Abstract [en]

    Highly loaded machine elements such as gears and cams have a non-smooth surface topography that is created during manufacturing. It is well known that the film-building properties of such surfaces may be different from those that are perfectly smooth. The capability to form a separating film may also be altered in time due to run-in phenomena. In this study, a smooth steel ball was loaded against rough steel discs and run under pure rolling as well as sliding conditions. Several different steel surfaces were tested under nominal EHL conditions, where the contact was monitored by means of its electrical resistance and capacitance. Each surface was first run in for 15 min, followed by a sweep-in speed determining the lift-off curve. Electrical contact measurements were continuously conducted during run in as well as lift-off. Fully formulated gear oil and its base fluid were used as test lubricants. Results show that run in of a surface seems to be a competition between conformation of surface topography and tribofilm formation. At the tested conditions, the formation of a tribofilm is dependent on the initial surface topography and is created rapidly causing less metal-metal contact. This film also seems to effectively prohibit changes in surface topography causing less structural run in than expected.

  • 192.
    Lord, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Olov
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Multi channel interferometry for measurement of the thickness of very thin EHL lubricant films2000In: 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. 711-718Conference paper (Refereed)
    Abstract [en]

    The possibilities for studying thin film EHL using optical interferometry has improved considerably with the introduction of spacer layer techniques. Film thicknesses down to zero can now be measured using different interferometric evaluation techniques. One technique is based on image analysis and a two-dimensional film thickness map can be obtained for the whole contact between a ball and a transparent disc. The image analysis techniques that have been employed normally requires a calibration table which couples separation with the measured colour parameters. There are a number of disadvantages with such a calibration procedure and the proposed Multi channel method makes it possible to avoid calibration in the same time as the evaluation time is much reduced. This paper presents a first attempt to apply the Multi channel method on the measurement of very thin film and a comparison with a calibration method (the HSI colour calibration method). A spacer layer is used in order to obtain high resolution even for very thin films. It is seen from the results that both methods correspond well at thicker films (>30 nm) while there are large differences for very thin films. The Multi channel results are promising and the method has a potential to be even further improved.

  • 193. Marklund, Pär
    et al.
    Berglund, Kim
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence on boundary friction of the permeability of sintered bronze2008In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 31, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Components made of sintered bronze are often used in tribological systems. Examples of applications are self lubricated bearings, wet clutches and brakes and synchromesh components for manual gearboxes. The bronze material in these applications is often porous and permeable. However, the required level of permeability i.e., the ability for a fluid to flow inside the material varies widely for different applications. This implies the need to investigate if the permeability can influence the properties of a tribological system. Various studies have been performed in order to investigate the permeability of different materials but a possible relationship between permeability and boundary lubrication performance has not yet been thoroughly investigated. In this article this relationship has been investigated in a pin-on-disk apparatus for test specimens with a permeability that is well-defined. Materials with three different permeabilities were investigated together with non-permeable test specimens. The results indicate that permeability has a small influence on the friction coefficient when the tribological system is operating with good lubrication of the contact. The function of the tribological system when working under starved conditions is also investigated and a very clear relationship between permeability and the ability to cope up with starved running conditions is shown. This is explained in terms of the varying ability of the materials' to store lubricant in pores. Non-porous test specimens were also tested as a comparison with the permeable test specimens in the investigation with starved running conditions . The results show that a material with high permeability works much better under starved running conditions than that with low permeability.

  • 194. Marklund, Pär
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modeling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 76-Conference paper (Other academic)
  • 195. Marklund, Pär
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modeling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions2008In: Tribology for tomorrow: iCAT 2008, 2nd International Conference on Advanced Tribology 2008 ; 3 - 5 December 2008, Singapore ; extended abstracts, Singapore, 2008, p. 518-520Conference paper (Other academic)
  • 196. Marklund, Pär
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet clutch friction characteristics obtained from simplified pin on disc test2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 824-830Article in journal (Refereed)
    Abstract [en]

    The frictional behavior of wet clutches in vehicle drivetrains is critical for their overall behavior. During the development of new wet clutch systems there is a need to know this friction behavior. The transferred torque is normally investigated in test rigs where the friction in a sliding interface between a friction disc and separator disc is investigated. These test rigs can be designed differently, depending on the working conditions of the investigated clutch. However, it is possible today to simulate the clutch behavior and not limit ourselves to only using measurements from test rigs for the design of the wet clutch. The torque transferred by the clutch during engagement can be roughly divided into full film torque and boundary lubrication torque. The full film regime is possible to simulate quite well, whereas the friction in the boundary regime is much more difficult to simulate due to its strong additive dependency. To obtain a good prediction of the total engagement, friction measurements in the boundary lubrication regime are still needed. These measurements should be easy to perform and fast tests are preferable. Friction coefficients for the whole range of sliding speed, interface temperature and nominal surface pressure should be measured. To use these measurements in simulations and get a better understanding of the friction behavior, it is also preferable to conduct these measurements on a small test sample, for which the temperature and sliding speed can be regarded as constant.Here, the friction of a small sample of a wet clutch friction disc is investigated in a pin on disc test and the temperature is measured in the sample during the tests. Measurements are compared with measurements from a test rig for whole friction discs. A good correspondence between the frictional behaviors of the different measurement methods is achieved.

  • 197. Marklund, Pär
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet clutch friction characteristics obtained from simplified pin on disc test2006In: Nordtrib 2006, 12th Nordic Tribology Symposium, Denmark: [LO-skolen, Helsingør, Denmark, June 7 - 9 2006], Kongens Lyngby: Technical University of Denmark , 2006Conference paper (Refereed)
  • 198.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Wet clutch under limited slip conditions: simplified testing and simulation2007In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 221, no 5, p. 545-551Article in journal (Refereed)
    Abstract [en]

    When designing new wet clutch systems, simulations and laboratory tests are important to obtain a functional system. An engineering tool is here developed to simulate wet clutches working under boundary lubrication conditions. Boundary lubrication friction is measured by a pin-on-disc test, and cooling oil flow is simulated by solving the Reynolds equation. Depending on the generated heat, the temperature in the clutch pack changes during engagement, affecting the transferred torque. With the developed method it is possible to easily and quickly investigate the behaviour of wet clutches with a variety of friction materials and groove patterns. The model is validated in a wet clutch test rig and the predicted torque agrees well with experimental data.

  • 199.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2008In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 51, no 3, p. 303-309Article in journal (Refereed)
    Abstract [en]

    The characteristics of wet clutches are of great importance for the overall behavior of the drive trains of many modern vehicles. It is considered that the clutch characteristic is affected by the permeability of the friction material. The permeability is considered to influence both the time of engagement and the temperature in the clutch due to the lubricant flow in the permeable material. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of a friction material made of sintered bronze. This friction material is suitable for application such as limited slip differentials or other wet clutches that have to withstand high temperature and high torque transfer. The permeability is also investigated for friction materials with pressed groove patterns. Wet clutch friction material permeability is often accounted for in simulations but the method used to measure the permeability is seldom described. The permeability of the investigated friction material is shown to be so small that it will hardly will affect the temperature in the material due to cooling oil flow inside the material. However, the engagement time can be influenced by the permeability. It is also shown that pressed groove patterns can seal the friction material so that it becomes almost impermeable.

  • 200.
    Marklund, Pär
    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.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2007In: 62nd annual meeting of the Society of Tribologists and Lubrication Engineers 2007 : May 6 - 10, 2007, Philadelphia, Pennsylvania, USA, STLE , 2007Conference paper (Refereed)
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