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  • 51.
    Choudhry, Jamal
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Validation of a Multi-Scale Contact Temperature Model for Dry Sliding Rough Surfaces2022In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 3Article in journal (Refereed)
    Abstract [en]

    A multi-scale flash temperature model is validated against existing experimental work. The model shows promising results and proves itself to be a reliable tool for the accurate prediction of the flash temperature development between rough surfaces in sliding systems. Model predictions for the maximum flash temperatures as well as the bulk temperature fields were in very good agreement with the experimentally measured values. The model was also able to accurately predict the formation of hotspots as well as the temperature variations around the hotspots. From the model predictions, it is concluded that it is sufficient to only assess the flash temperatures on a small portion of the contact area and thus save both computational time and memory.

  • 52.
    Choudhry, Jamal
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Department of Mechanical Engineering, Tsinghua University, Shenzhen 518000, China.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Stress-State-Dependent Sliding Wear Model for Micro-Scale Contacts2023In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 145, no 11, article id 111702Article in journal (Refereed)
    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.

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  • 53.
    Choudhry, Jamal
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Stress-State-Dependent Thermo-Mechanical Wear Model for Micro-Scale Contacts2022In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 9, article id 223Article in journal (Refereed)
    Abstract [en]

    Wear is a complex phenomenon that depends on the properties of materials and their surfaces, as well as the operating conditions and the surrounding atmosphere. At the micro-scale, abrasive wear occurs as material removal due to plastic deformation and fracture. In the present work, it is shown that fracture is stress-state-dependent and thus should be accounted for when modelling wear. For this reason, a three-dimensional finite element model has been adopted to simulate and study the main mechanisms that lead to wear of colliding asperities for a pair of metals. The model is also fully coupled with a non-linear thermal solver to account for thermal effects such as conversion of plastic work to heat as well as thermal expansion. It is shown that both the wear and flash temperature development are dependent on the stress triaxiality and the Lode parameter.

  • 54.
    Cousseau, T.
    et al.
    INEGI, Universidade do Porto.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graça, B.
    INEGI, Universidade do Porto.
    Campos, A.
    ISEP, Instituto Superior de Engenharia do Porto.
    Seabra, J.
    FEUP, Universidade do Porto.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Film thickness in a ball-on-disc contact lubricated with greases, bleed oils and base oils2012In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 53, p. 53-60Article in journal (Refereed)
    Abstract [en]

    Three different lubricating greases and their bleed and base oils were compared in terms of film thickness in a ball-on-disc test rig through optical interferometry. The theoretical values calculated according to Hamrock's equation are in close agreement with the base oil film thickness measurements, which validates the selected experimental methodology.The grease and bleed oil film thickness under fully flooded lubrication conditions presented quite similar behaviour and levels. Therefore, the grease film thickness under full film conditions might be predicted using their bleed oil properties, namely the viscosity and pressure-viscosity coefficient. The base and bleed oil lubricant parameter LP are proportional to the measured film thickness.A relationship between grease and the corresponding bleed oil film thickness was evidenced

  • 55.
    Cousseau, Tiago
    et al.
    FEUP, Universidade do Porto, INEGI, Universidade do Porto.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graça, Beatriz
    INEGI, Universidade do Porto.
    Campos, Armando
    ISEP, Instituto Superior de Engenharia do Porto.
    Seabra, Jorge
    FEUP, Universidade do Porto.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Film thickness and friction torque prediction of lubricant greases using bleed oil properties2012In: Film thickness and friction torque prediction of lubricant greases using bleed oil properties, 2012Conference paper (Refereed)
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  • 56.
    Cousseau, Tiago
    et al.
    FEUP, Universidade do Porto.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graça, Beatriz
    INEGI, Universidade do Porto.
    Campos, Armando
    ISEP, Instituto Superior de Engenharia do Porto.
    Seabra, Jorge
    FEUP, Universidade do Porto.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of grease bleed oil on ball-on-disc lubrication2013Conference paper (Refereed)
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  • 57.
    Croné, Philip
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Thermal Turbulent Flow in Leading Edge Grooved and Conventional Tilting Pad Journal Bearing Segments—A Comparative Study2018In: Lubricants, ISSN 2075-4442, Vol. 6, no 4, article id 97Article in journal (Refereed)
    Abstract [en]

    A comparative study between a conventional- and leading edge grooved (LEG) tilting pad journal bearing (TPJB) segment is performed. The developed model uses the Shear Stress Transport (SST) turbulence model, coupled with the energy equation and a partial differential equation for the fluid domain mesh displacement to predict the thermal flow characteristics. Instead of using an effective boundary condition to determine the inlet temperature of the LEG pad and excluding the additional LEG portion, as is common practice, the whole geometry of the LEG is modeled. Several sizes of the LEG portion is investigated and it is shown to have quite a small influence on pressure, temperature, film thickness and turbulence intensity. Moreover, the results also show that the conventional pad gives rise to higher levels of turbulence in the mid plane compared to its LEG counterpart, while the latter has a marginally higher value of turbulence when the volume average value is computed. The maximum value of turbulence is however present in the conventional model. 

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  • 58.
    Dowson, D.
    et al.
    University of Leeds.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Discussion on the paper "Evaluation of the minimum film thickness in ball-plane impact experiments" by Dr I Musca et al1996In: The third body concept: interpretation of tribological phenomena ; proceedings of the 22nd Leeds-Lyon Symposium on Tribology, held in the Laboratoire de Mécanique des Contacts, Institut National des Sciences Appliquées de Lyon, France, 5th-8th September 1995 / [ed] Duncan Dowson, Amsterdam: Elsevier, 1996, p. 738-740Conference paper (Refereed)
  • 59. Ehret, P.
    et al.
    Felix-Quinonez, A.
    Lord, John
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Experimental analysis of microhydrodynamic lubricatoin conditions2000In: Proceedings of the International Tribology Conference: ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japan Society of Tribologists , 2000Conference paper (Refereed)
  • 60.
    Ehret, Pascal
    et al.
    Leeds University.
    Felix-Quinonezi, A.
    Leeds University.
    Lord, John
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Olov
    Experimental analysis of micro-elastohydrodynamic lubrication conditions2001In: Proceedings of the International tribology conference: ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japanese Society of Tribologsts , 2001Conference paper (Other academic)
  • 61.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Enqvist, Evelina
    Larsson, Roland
    Gracio, José
    University of Aveiro.
    Kumar, Sunil
    University of South Australia.
    Friction, wear and surface characterization of metal-on-metal implant in protein rich lubrications2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently - in metal on metal (MOM) hip implant- the local and systematic effects of interaction between metal surfaces and protein rich lubrication in body are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCrMo) alloys have been used in MOM implants extensively. In the present study the samples were immersed in four different biological lubricants (Human serum, synovial fluid, MEM and distill water) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whit in the top few nanometers of materials. Friction and wear behavior of CoCrMo substrate in different biological lubricatin were also studied. Results and discussion: Spectra from P2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant for different time intervals. The four lubricants reacted differently with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCrMo alloys depending on the lubricant and the immersion period. Specimens immersed in synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. Synovial fluid gave lowest coefficient of friction when distill water gave the highest value. Generally wear was higher for disc in comparison to the pin (in the pin on plate test).

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  • 62.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Höglund, Erik
    Biotribology: surface chemistry characterization of metal-on-metal implants in rich environment2008In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    Introduction: Osteolysis induced by wear particles in metal-on-polyethylene hip implants has been the key motivation to look for alternative bearings and in fact emergence and development of new metal-on-metal (MOM) implant materials for joint replacement. However, while the volume of wear particles produced in metal-on-metal articulations is lower the number of particles produced is higher per volume of wear, due to the reduced size of wear particles. Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently the local and systematic effects of metal debris are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCr) alloys have been used in MOM implants extensively. Metallic samples were cut and mirror polished. In the present study The samples were immersed in four different biological lubricants (Human serum, synovial fluid, MEM and Milli-Q water) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whitin the top few nanometers of materials. Significant differences in the absorbed layers and differences in the corrosive nature of Ti and CoCr implant substrates and wear particles were found. Results and discussion: Spectra from P 2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant. The four lubricants reacted different with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCr alloys depending on the lubricant and the immersion period. Specimens immersed into synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. For many reactive metals, dissolution of ions from the metal surface takes place along with thickening of the metal oxide during passivation, or surface corrosion.Conclusion: Glycoaminoglycans (GAG) and related proteins may hinder calcium phosphate deposition on samples immersed in synovial fluid. ToF-SIMS measurements showed that the resulting corrosion products depend upon the nature of the environment. The thickness of the calcium phosphate deposits was different for different metal substrate.

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  • 63.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Direct low lateral slip roadgrip measurement compared with surface reflection of three laser beams2011Conference paper (Other academic)
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  • 64.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Discrepancies between longitudinal high slip and lateral low slip friction measurements on prepared ice surfaces2009In: Compendium of papers DVD, TRB 88th annual meeting: January 11 - 15, 2009, Washington, D.C, Washington, DC: TRB , 2009Conference paper (Refereed)
    Abstract [en]

    The Swedish road administration requested that an independent organization facilitate friction tests with several types of friction measuring devices. These tests were done on the following three surfaces: macro rough and micro smooth ice, macro- and micro smooth ice and macroand micro rough ice. The objective was to evaluate lateral low slip measuring devices against traditional longitudinal high slip devices. This was done by evaluating how they measure road grip, i.e. friction differences between road surfaces and the measuring tire. Tests were performed on Lake Kakel near Arjeplog, northern Sweden on March 18th, 2008. Weather conditions were stable with ice temperatures between -4°C (24.8°F) and -3°C (26.6°F). Tests showed that changes on the ice surfaces were readily detected with all four of the lateral low slip friction measurement devices and the two longitudinal high slip devices. Friction resolutions were higher with low lateral slip devices compared to high longitudinal slip devices. The tires on the devices were of different types and are the main reason for the difference in friction resolution. One major difference was detected; the lateral low slip method measured higher friction between its regular winter tire and the macro rough, micro smooth surfacecompared to the friction on the macro- and micro rough ice. Longitudinal high slip devices measured higher friction between its industrial friction tire and macro- and micro rough ice. Capacity to measure friction in curves was only displayed by the high longitudinal slip devices.

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  • 65.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Stop distances for ten studless winter tires2009Report (Other academic)
    Abstract [sv]

    Denna rapport innehåller stoppsträckor för tio omgångar dubbfria vinterdäck. Arbetets huvudmål är att kunna skapa en grund för vinterdäcksklassificering. Så småning om skall traffikanter kunna få relevant information om olika däckens förmåga att skapa tillräckligt väggrepp på farliga vinterväglag. Vägverket ser ett ökat behov av kunskap då dubbdäcksanvändandet kommer att minskas i framtiden.

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  • 66.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nybacka, Mikael
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Road grip test in Arjeplog2008Report (Other academic)
    Abstract [en]

    The Swedish road administration sees a need to improve the road grip estimation capacity for the Swedish road system. The challenge is to find methods to measure road grip fast and reliable. There where six different system types at the tests in Arjeplog, three continuous, two system measuring road grip through deceleration and one system based on GPS and accelerometers. Two system types used air craft runway tires. The other systems used either studded winter tires or friction winter tires. Test runs where performed and road grip where recorded for three different surface types, old system 2000 ice, polished ice and new system 2000 ice. Weather data was collected during the three days. It is clear that all systems can detect changes in road grip. It is clear that continuous systems hold an information advantage over the sequence oriented systems. For measurements of road grip on winter roads, we recommend that rubber compounds adapted for cold conditions are used, as the resolution of the road grip measurement where better. In extreme condition like on polished ice, studded winter tires increase the road grip significantly.

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  • 67.
    Engström, Niclas
    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.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Direct low lateral slip roadgrip measurement compared with surface reflection of three laser beams2010Conference paper (Refereed)
    Abstract [en]

    Road grip on roads depend on many factors and different techniques are available to estimate available road grip. To ensure that entrepreneurs have successfully restored the road grip to an acceptable level both entrepreneurs and road keepers need tools to evaluate present road grip. Information about road grip can also be utilized directly in a vehicle if available, for systems such as ABS, traction control, etc. To evaluate a non-contact method based on three laser beams with different frequency this equipment was mounted on a car equipped with a fifth wheel behind the car. The wheel is angled about 1.5 degrees compared with the centreline of travel. A force sensor in the hub measures forces acting on a standard winter tire also mounted to the hub, this is considered to be one measurement of road grip. The main reason is to see how well one can estimate road grip with a low cost non contact device made with Laser beams in combination with a photodiode.

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  • 68.
    Eriksson, Patrik
    et al.
    Luleå University of Technology.
    Wikström, Victoria
    SKF Coated Bearings, Gothenburg, Sweden.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grease passing through an elastohydrodynamic contact under pure rolling conditions2000In: 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. 309-316Article in journal (Refereed)
    Abstract [en]

    Using optical interferometry in a standard ball-and-disc apparatus and a high-speed video camera with light enhancer, thickener particles entering a grease-lubricated elastohydrodynamic (EHD) contact were traced as they passed through the contact in pure rolling. In previous studies, it has not been possible to track specific particles but, due to the short exposure time and high recording rates used here, sharp images of a passing particle could be captured. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex respectively were studied and for a freshly lubricated track it could be documented that the lithium complex thickener causes fewer, but larger, particles to pass the contact. The influence of the base oil bleeding on film formation is also discussed in the paper

  • 69. Eriksson, Patrik
    et al.
    Wikström, Victoria
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grease soap particles passing through an elastohydrodynamic contact under side slip conditions2000In: 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. 317-325Article in journal (Refereed)
    Abstract [en]

    In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used. Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.

  • 70.
    Fadaei Naeini, Vahid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations2023In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 390, no part A, article id 122990Article in journal (Refereed)
    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.

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  • 71.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Degradation mechanism of water contaminated automatic transmission fluid (ATF) in wet clutch system2013Conference paper (Refereed)
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  • 72.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    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.
    Degradation Mechanism of Automatic Transmission Fluid by Water as a Contaminant2015In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 229, no 1, p. 74-85Article in journal (Refereed)
    Abstract [en]

    The degradation mechanism of water contaminated Automatic Transmission Fluids (ATF) was experimentally investigated. Water contaminated ATF was tribotested in a full-scale wet clutch test rig to monitor the friction durability during clutch ageing, and was also statically aged in oven to evaluate the interaction of ATF with water. The bulk properties and chemical nature of the ATF were analysed using viscosity measurements, Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). It was shown that water presence in the ATF can increase the mean friction coefficient over a short time period, though in the long term perspective there is a higher loss of mean friction. Phase separation of the water-in-oil emulsion by centrifugation at 20000 rpm made it possible to examine the water phase using infrared 2spectroscopy. The spectroscopic analysis revealed the hydrophilic nature of certain ATF constituents, although the impact of water on the bulk properties like lubricant viscosity and thermal stability was insignificant. The analysis of the tribotests showed that the friction increase for water contamination was a short-term effect and likely due to the interaction between polar surface active additives and water. Even though no significant change has been found for thermal degradation or in bulk properties of the lubricant, the initially changed action of the water soluble additives and generation of high friction resulted in a total deterioration of the clutch performance during long term use.

  • 73.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    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.
    Influence of clutch output shaft inertia and stiffness on the performance of the wet clutch2013In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, no 2, p. 310-319Article in journal (Refereed)
    Abstract [en]

    Being a part of the complex mass, spring and damper system in a driveline, the choice of design factors like, output shaft stiffness and inertia of a wet clutch system can influence its performance. The effects of these parameters are experimentally evaluated in this paper. Widely used commercial paper based friction plates with standard steel reaction plates are tested with four different stiffness and inertia combinations in a recently developed wet clutch test rig. A low inertia system in general showed a faster degradation and shorter clutch life for high torsional oscillation. Besides the system becomes more shudder sensitive for lower natural frequency in case of less stiff system. The less stiff output shaft with low inertia showed the highest shudder tendency among the four conditions. The differences in performance for different output shaft conditions become noticeable for numerous clutch engagements or a degraded system. The effect of different shaft design conditions is also illuminated in the topographical analysis of the separators’ surfaces and morphological study of frictional surfaces. This study reveals the influence of both inertia and stiffness not only on shudder sensitivity of the system but also on the clutch frictional performance as well as the overall clutch life.

  • 74.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    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.
    Study on the wet clutch friction interfaces for humid lubrication condition2013Conference paper (Refereed)
    Abstract [en]

    The friction influencing parameters also influence the wet clutch sliding surface conditions. The tribofilm formations as well as the chemical and mechanical degradation for frictional interfaces can be different for the choice of the lubricant conditions. The present investigations revealed the effects of water contamination in automatic transmission fluid (ATF) not only on the frictional performance, but also on the friction interfaces. The surface profiles of the tested separator plates, the EDS-SEM (Scanning Electron Microscopy-Energy-dispersive X-ray spectroscopy) analysis of the friction interfaces and optical microscopy for the used friction liners showed the difference in surface morphology, adsorption of additive elements, permeability and porosity for a humid clutch environment.

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  • 75.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    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.
    Water contamination effect in wet clutch system2013In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 227, no 3, p. 376-389Article in journal (Refereed)
    Abstract [en]

    Water contamination in wet clutch systems can be a problem since both torque characteristics and wear resistance can be influenced by water presence. The present paper reveals the effect of externally added water on the wet clutch frictional performance. Commercially available standard paper based friction plates and steel separator plates lubricated in commercially available automatic transmission fluid were investigated in a recently developed automated test rig implementing a well confined experimental approach. Frictional response was observed for three different situations with different water amount and water exposure time. There is observed undesirable friction increase with increasing water amount in the system. The rate of increase in friction coefficient does not linearly depend on the amount of added water and this is a noticeable outcome from the common possible water contamination effects like change in lubricant viscosity, inadequate additive performance and weakening of friction material. The more reduced separator plates’ surface roughness (Ra) in a water contaminated clutch system compared to an uncontaminated one can be a reason for the change in friction. It is also shown that different water exposure time has no large impact on the change in friction level and separator plate’s roughness.

  • 76.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions2016In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 59, no 3, p. 441-450Article in journal (Refereed)
    Abstract [en]

    The performance of wet clutches used for automatic transmissions or other applications usually includes the desired positive friction characteristics and a shudder-free torque generation. Changes in the operating variables such as the lubricant conditions influence the formation of tribofilm, friction characteristics and can alter the degradation of the friction interfaces. In this work, the friction characteristics and degradation of the paper-steel friction interfaces were monitored when a commercial fully-formulated automatic transmission fluid (ATF) was contaminated with water. It was found that water in ATF influenced the clutch stability by increasing the mean coefficient of friction (µ) and the negative friction-velocity slope. Surface studies of the post-test friction interfaces clearly indicated reduced surface porosity and permeability, increased wettability and changed elemental composition on the contacting surfaces after tested with water- contaminated ATF. Moreover, water-contaminated paper-liners’ thermal decomposition shifted to a lower temperature compared to an uncontaminated liner during thermal analyses. These results displayed faster degradation and reduced service life of the clutch friction interfaces for water contamination. The resultant surface condition can be associated with the observed unstable friction and negative friction-velocity slopes.

  • 77.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    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.
    Influence of water on the tribological properties of zinc dialkyl-dithiophosphate and over-based calcium sulfonate additives in wet clutch contacts2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 87, p. 113-120Article in journal (Refereed)
    Abstract [en]

    Usually the wet clutch lubricant properties vary with different formulations of base oil types and additives. The aim of this paper was to evaluate the effect of water on the performance of additives in ATF. Simplified lubricants, ZDDP and over-based Ca-sulfonates detergent additives in an API Group I mineral base oil, were employed to compare with the commercial fully-formulated automatic transmission fluid (DEXRON®VI) during water-contamination. A full-scale wet clutch test rig was used to evaluate the frictional response due to water contamination of the lubricants. Fourier Transform Infrared Spectroscopy was utilized to evaluate the variation in the solubility of these polar organic additives in the water phase and Karl-Fischer titration was utilized to evaluate the post-test water content for different formulations.

  • 78.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    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.
    Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions2014Conference paper (Refereed)
    Abstract [en]

    Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.

  • 79.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    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.
    Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions2014Conference paper (Refereed)
    Abstract [en]

    Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.

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  • 80.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    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.
    Surface chemistry of wet clutch influenced by water contamination in automatic transmission fluids2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, p. 395-401Article in journal (Refereed)
    Abstract [en]

    Lubricated friction interfaces used for wet clutches produces different friction behaviour depending on the lubricant conditions. Usually the lubricant conditions vary for water contamination in automatic transmission fluid (ATF). The presence of water retards the ATF performance by increasing the friction and can influence the deterioration of the clutch plates. Water as a polar contaminant can change the absorbability of the surface active additives, which might cause the characteristic friction behaviour. The aim of this paper is to verify the surface chemistry of tribotested standard friction interfaces lubricated with water contaminated commercial ATF (DEXRON® VI). The evidences of the influence of water on ATF performances were shown by surface analyses

  • 81.
    Francesc, Pérez Ràfols
    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.
    Numerical study of the effect of coatings in static metal-to-metal seals2016In: STLE 2016 Annual Meeting and Exhibition, 2016, 2016Conference paper (Refereed)
  • 82.
    Fransson, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Manufacture of well-described ice surfaces for ice/rubber friction tests2007In: ISCORD 2007, 2007Conference paper (Other academic)
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  • 83.
    Furustig, Joel
    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.
    Bates, C.A.
    Danfoss Power Solutions ApS, Nordborgvej 81, DK-6430 Nordborg, Denmark.
    Ennermark, P.
    Danfoss Power Solutions ApS, Nordborgvej 81, DK-6430 Nordborg, Denmark.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A two scale mixed lubrication wearing-in model, applied to hydraulic motors2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 90, p. 248-256Article in journal (Refereed)
    Abstract [en]

    Wearing-in of a machine component can increase the conformity between contacting pairs and smoothen the surface topography. A two scale model, combining the wearing-in effects, resulting in changes in the surface topography, with the wear that occurs on the component, is presented. The geometry of the components are represented with measured coordinates. Wear leads to changes of the geometry, which has an effect on several tribological conditions, such as contact forces, relative velocities and conformity. Due to the wear on the topography scale, the load sharing is also affected. The model is applied to orbital hydraulic motors. The wear depth predicted with the model, is qualitatively in good agreement with the wear depth recorded in experiments.

  • 84.
    Furustig, Joel
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On a strategy of wear analysis using numerical and experimental tools2014Conference paper (Refereed)
  • 85.
    Furustig, Joel
    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.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bates, Charles Anthony
    Danfoss Power Solutions ApS, Nordborg.
    Ennemark, Poul
    Danfoss Power Solutions ApS, Nordborg.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A strategy for wear analysis using numerical and experimental tools, applied to orbital type hydraulic motors2016In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 230, no 12, p. 2086-2097Article in journal (Refereed)
    Abstract [en]

    An accurate and reliable wear analysis requires detailed knowledge of the tribological conditions of the studied system. In this work, a numerical model which can quantify wear and is applicable to hydraulic motors is developed. Detailed tribological knowledge can be acquired through strategic experimental testing and numerical simulations. The model is constructed to include the effect on wear from varying lubricant film thickness. The development of the wear model includes consideration of wear observed in the Scanning Electron Microscopy (SEM) analysis of tested motors. The model is of the Archard type, in which the k-value is estimated from experiments, after considering the effect of lubrication. The contact pressure is the solution to a lubrication model that governs both the hydrodynamics of the lubricant film and the direct contact between the rough surfaces. To validate the model, a hydraulic motor is run at different operating conditions and the apparent wear depth is analysed after the tests. Numerical simulations mimicking the same configuration are performed and the predicted wear depths are compared to the experimental results. Similarities and differences are discussed and it is evident that a clear correlation exists between the wear predicted with the model and the measurement data of the apparent wear in the hydraulic motor. There are also discrepancies because of the model simplicity and the uncertainty in the specifications of the tested system. The results imply that wear analysis using numerical simulations aid the understanding of wear in machinery. The combined knowledge of physical conditions on different important scales enables in-depth analysis with numerical tools which cannot be achieved through experimental investigations alone. Furthermore, the numerical model can be refined leading to better wear predictions.

  • 86.
    Furustig, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The measurement of wear using AFM and wear interpretation using a contact mechanics coupled wear model2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 350-351, p. 74-81Article in journal (Refereed)
    Abstract [en]

    Detailed understanding of wear processes is required to improve the wear resistance and lifetime of machine components. Atomic force microscopy (AFM) is used to measure surface height profiles with high precision, before and after a wear experiment. The distribution and depth of wear on steel surfaces is then calculated using a relocation method. A numerical investigation of wear based on Archard's equation is conducted on the same measured surfaces. A good correlation was found between the model and experiment for wear larger than a hundred nm. The wear mechanisms considered in the numerical simulation was thus found to be the cause of the majority of the wear. On the scale of tens of nm the correlation was limited, but the measured wear was still analysed in detail.

  • 87.
    Furustig, Joel
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bates, C.A.
    Danfoss Power Solutions ApS, Nordborg.
    Ennermark, P.
    Danfoss Power Solutions ApS, Nordborg.
    A wear model for EHL contacts in gerotor type hydraulic motors2015In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 229, no 2, p. 254-264Article in journal (Refereed)
    Abstract [en]

    The heart of gerotor motors is a gear-set. The gear-set consists of an inner gear which is rotating and orbiting in contact with an outer gear. Wear in these contacts is investigated experimentally and with a numerical implementation of an Archard based wear model in combination with a load sharing concept. The model utilizes the symmetry of the motor and is based on a three-scale approach to estimate the wear on the gears. The global model calculates contact forces, relative surface velocities and contact radii in the contacts between inner and outer gear. The calculations performed on the local scale are used to collect information about the influence of the surface roughness on lubricant film thickness. The wear depth is calculated on a semi-local scale, involving only one tooth on the outer gear. In partial elastohydrodynamic lubrication, load is carried by the part of the conjunction where there is direct contact between the mating surfaces and by the lubricant pressure. In the wear model, wear only occurs as a direct consequence of contact between the mating surfaces. Experimental results are compared with the model predictions for equivalent running conditions. The wear predicted by the model agrees with the experimental results. For this reason, it is concluded that wear in the gerotor motor is dominated by the wear mechanisms which are considered in the tribological model.

  • 88.
    Glavatskih, Sergei B.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fillon, Michel
    Laboratory of Solid Mechanics, University of Poitiers, SP2MI, 86962 Futuroscope Cedex, France.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The significance of oil thermal properties on the performance of a tilting-pad thrust bearing2002In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 124, no 2, p. 377-385Article in journal (Refereed)
    Abstract [en]

    This paper is a report into an experimental and theoretical investigation of the effect of oil thermal properties on the performance of a tilting-pad thrust bearing. Three oils, namely poly-α-olefin, ester and mineral base, were chosen for this study. These oils all have same viscosity grade (ISO VG46) but differ in their rates of viscosity variation with temperature and in their heat capacity and thermal conductivity values. Mineral base oil of a higher viscosity grade (ISO VG68) was also analyzed for comparison. Experimental data were obtained from an equalizing tilting-pad thrust bearing with an outer diameter of 228.6 mm operating in a flooded lubrication mode. Simultaneous measurements of pad and collar temperatures, friction torque, pressures and oil film thickness were taken. In the tests, oil supply temperature and flow rate were held constant for all load-speed combinations. The theoretical analysis of oil performance was based on a three-dimensional TEHD model. In the analysis, thermal effects were locally taken into account and heat transfer into the pads was considered. The displacements of the active surface of the pads, due to pressure and temperature fields, were determined. The effect of initial pad crowning on the oil film thickness is discussed. Experimental and theoretical results are compared and analyzed in terms of the inlet and outlet oil film thickness, bearing operating temperature and power loss.

  • 89. Glavatskih, Sergei
    et al.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Hydrodynamic thrust bearing experimental apparatus for testing environmentally adapted oils1998In: Tribologia : Finnish Journal of Tribology, ISSN 0780-2285, Vol. 17, no 2, p. 27-30Article in journal (Refereed)
    Abstract [en]

    There are indications that some environmentally friendly oils provide performance advantages in hydrodynamic bearings compared to mineral oils. To verify and to quantify the advantages of the synthetic oils in hydrodynamic lubrication in terms of operating film thickness, bearing power loss and operating temperature, a test rig for laboratory experiments has been designed and manufactured. At the first stage of the project temperature and pressure distributions, power loss and oil film thickness for ISO VG46 and VG68 mineral and synthetic oils will be measured at different loads and rotational speeds. At the next stage several other lubricants will be tested. Among them rape seed oil and pine tree oil can be mentioned.

  • 90. Glavatskih, Sergei
    et al.
    Höglund, Erik
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hydrodynamic thrust bearing experimental apparatus for testing environmentally adapted oils1998In: COST 516 Tribology Symposium, Espoo, Finland, 14 - 15 May 1998: Organised by Technical Research Centre of Finland, Manufacturing Technology / [ed] Helena Ronkainen, Espoo: Technical Research Centre of Finland (VTT) , 1998Conference paper (Refereed)
  • 91.
    Glavatskih, Sergei
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Larsson, Roland
    Influence of oil type on hydrodynamic thrust bearings performance2000In: Tribology at work, Elsevier, 2000Conference paper (Refereed)
  • 92. Glavatskih, Sergei
    et al.
    Höglund, Erik
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On power measurement in hydrodynamic thrust bearings1999In: COST 516 Tribology Symposium: Antwerpen, Belgium, 20 - 21 May 1999 / [ed] Karen Vercammen; Jan Meneve, Mol: Flemish Institute for Technological Research , 1999Conference paper (Refereed)
  • 93.
    Glavatskih, Sergei
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Larsson, Roland
    Testing environmentally adapted oils for hydrodynamic lubrication2000In: Proceedings of the 3rd COST 516 Tribology symposium: Eibar, Spain, 18 and 19 May 2000 / [ed] Amaya Igartua; Alberto Alberdi, Elbar: Tekniker , 2000Conference paper (Refereed)
  • 94.
    Glavatskih, Sergei
    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.
    Improved efficiency with the use of environmentally adapted lubricants2000Report (Other academic)
  • 95. Glavatskih, Sergei
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oil film thickness measurement by means of an optic lever technique1998In: Proceedings of the 8th International Conference on Tribology: Hotel Ebeltoft Strand, Ebeltoft, Denmark, June 7 - 10, 1998 / [ed] Svend S. Eskildsen, Aarhus: DTI Tribology Centre , 1998Conference paper (Refereed)
  • 96.
    Glavatskih, Sergei
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Performance of synthetic oils in the hydrodynamic regime: I. Experimental2003In: Journal of Synthetic Lubrication, ISSN 0265-6582, Vol. 20, no 1, p. 15-24Article in journal (Refereed)
    Abstract [en]

    An investigation of the performance of environmentally adapted synthetic oils in the hydrodynamic lubrication regime has been carried out. Four oils have been tested: polyalphaolefin and ester based ISO VG46 oils as well as mineral ISO VG68 and VG46 oils. Tests were conducted in a facility containing two identical tilting-pad thrust bearings typical of the design in general use. The differences between the mineral and synthetic oils in terms of maximum operating temperature, minimum oil film thickness, and bearing power loss have been examined. Substitution of the mineral ISO VG68 oil with an ISO VG46 oil slightly reduces the bearing operating temperature. This is due to a decrease in the basic viscosity. It is concluded that the ester base ISO VG46 oil can be used as an environmentally adapted replacement for the mineral ISO VG68 oil without sacrificing bearing safety. Such a change also offers noticeable energy savings. If the ester based oil is used instead of a mineral oil of the same viscosity grade, bearing reliability is improved by the increased oil film thickness.

  • 97.
    Glavatskih, Sergei
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Performance of synthetic oils in the hydrodynamic regime: II. Generalisation2003In: Journal of Synthetic Lubrication, ISSN 0265-6582, Vol. 20, no 2, p. 139-150Article in journal (Refereed)
    Abstract [en]

    In Part I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting-pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity-temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity-temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.

  • 98.
    Glavatskih, Sergei
    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.
    Special issue: 14th Nordic Symposium on Tribology, NORDTRIB 2010: Editorial2012In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 48, no AprilArticle in journal (Other academic)
    Abstract [en]

    The Nordic Symposium on Tribology, NORDTRIB, is arranged every second year in one of the Nordic countries: Denmark, Finland, Norway or Sweden. In June 2010 the 14th NORDTRIB, organized by Luleå University of Technology, was held in a picturesque location at Storforsen, Sweden.One hundred and seventy eight tribologists from thirty countries participated in the symposium. It is the highest number of participants recorded during NORDTRIB history.The fact that interest in tribology continues to grow internationally was also reflected during a workshop held before the symposium. The theme of the workshop was “Why tribology is more important than ever”. The discussions focused on what tribology can do for sustainable growth and to limit climate change. Prominent scientists from Australia, Austria, China, Finland, Japan, Slovenia, and UK described current and future trends in tribology research as well as how such research is motivated in their home countries.One hundred and thirty four papers were presented at the symposium. The keynote lectures covered tribological challenges in wind turbine gearboxes, advancements of tribology in nano-manufacturing, atomic level studies, smart tribological coatings, and numerical methods for solving tribological problems.There was also a special poster session for young tribologists. This time the session was organized by the Swedish Research School in Tribology (www.ltu.se/tribology-school), which is a collaborative project between four Swedish Universities; Halmstad University, Luleå University of Technology, KTH Royal Institute of Technology and Uppsala University. Doctoral students presented their research projects and latest findings. The session was an inspiring and rewarding forum for the next generation of tribologists.Many excellent papers were presented at the symposium covering a wide range of research activities and recent developments in tribology. A selection of 7 papers, representing both experimental and theoretical studies, is included in this Special issue.We hope that those of you who were unable to attend the symposium will catch up on the latest research findings you missed and enjoy reading this issue.The next Nordic Symposium on Tribology will be held in Norway in June 2012.We are grateful to Tribology International for excellent cooperation and possibility to publish the selected contributions in this Special issue.

  • 99.
    Glavatskih, Sergei
    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.
    Special issue on NORDTRIB: The Nordic Symposium on Tribology 2010: 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 7, p. 563-564Article in journal (Other academic)
  • 100.
    Glavatskikh, Sergei B.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Oil film thickness measurement by means of an optic lever technique2000In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 13, no 1, p. 23-35Article in journal (Refereed)
    Abstract [en]

    Oil film thickness in hydrodynamic bearings is a fundamental parameter influencing overall hydrodynamic bearing performance. Knowledge of this thickness allows bearing performance to be optimized. For the small hydrodynamic bearings that are usually used in laboratory test facilities, a very small sensor (e.g., <2 mm) is required because of space limitations. Commercially available eddy-current and capacitance sensors are too large to be mounted in the pad of such a bearing. An alternative approach is to use sensors based on optical methods, such as the optic lever technique. The main idea in this technique is to detect the intensity of a light beam reflected from a target surface. This intensity is a function of the distance between the sensor and the target. This paper reports the specific features of the optic lever technique as used for measurements of oil film thickness. The design, calibration procedure, and main characteristics of an optical sensor are discussed. A test rig for the calibration of oil film thickness sensors is also presented. The sensor response curve has two parts, linear and non-linear; using the linear part results in high sensitivity in the micrometre range. The influence of different types of oil on the output signal of the sensor has also been investigated. Experiments with different target velocities have shown that this sensor can be used for accurate and reliable measurement of oil film thickness in hydrodynamic bearings

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