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  • 1.
    Almqvist, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    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.
    Selected papers from those presented at the 3rd International Tribology Symposium of IFToMM2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 5, p. 273-275Article in journal (Refereed)
  • 2.
    Berglund, Kim
    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.
    Olsson, Richard
    Borgwarner TTS.
    Evaluating lifetime performance of limited slip differentials2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 3, p. 189-201Article in journal (Refereed)
    Abstract [en]

    Extensive research has been performed regarding wet clutch function and performance. Although wet clutches are used in both automatic transmissions and limited slip differentials in cars, most research has been performed for wet clutches incorporated in automatic transmissions. The operating conditions of wet clutches in automatic transmissions differ from the operating conditions of the wet clutches used in limited slip differentials. Therefore, a method and a test bench to use in the investigation of the degradation of limited slip differentials were developed in this work. The typical operating conditions of the limited slip differential and the differences compared with wet clutches incorporated in automatic transmissions were also addressed. Tests performed showed that the developed test bench and method can be used to address differences in frictional response over time for different types of operating condition

  • 3. Eriksson, Erland
    et al.
    Nygård, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Electrical resistivity and conductivity of greases: an initial study2002In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 15, no 1, p. 33-50Article in journal (Refereed)
    Abstract [en]

    Investigations of railway wagons fitted with rolling-element bearings have shown damage to the bearings from the passage of electric current. This also occurs in railway wagons without an electric energy consumption of their own, because of residual currents from electric locomotives. This phenomenon gives rise to technical, financial, and even safety problems. This paper reviews research in the field of rolling-element bearings exposed to electric currents. The paper also reports on an ongoing study undertaken to understand the mechanism of current flow and the role of lubricants in the associated damage, and to identify the possibilities of minimising bearing damage. The obvious solution to this problem is to use optimised greases, i.e., with high electrical conductivity and good lubricating ability. In the preliminary work reported here a number of greases for railway use were tested to determine their electrical conductivity in static and dynamic situations. These tests were performed using specially designed apparatus, and significant initial information about the electrical properties of greases has been obtained in this research, for example, that there is a correlation between the electrical conductance under static and dynamic conditions. All the greases tested showed comparatively high resistivity values, which could be one explanation for the bearing damage observed.

  • 4.
    Glavatskikh, Sergei
    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

  • 5.
    Gondal, A. K.
    et al.
    Indian Institute of Petroleum, Dehradun.
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Studies on tribological behaviour of two oil soluble molybdenum compounds under reciprocating sliding conditions1993In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 5, no 4, p. 337-359Article in journal (Refereed)
    Abstract [en]

    The use of oil-soluble organo-molybdenum compounds in engine oils can help in fuel conservation by reducing engine friction and increase durability by improving wear characteristics. The tribological behaviour of molybdenum dialkyldithiophosphate (MoDDP) was studied with a SRV Optimol tester under reciprocating sliding conditions. The studies were conducted under nonconformal contact conditions on En-31 steel and conformal contact conditions on piston ring and liner materials. The results indicated that the frictional behaviour of these additives is shear sensitive. Shear sensitivity is influenced by materials, operating conditions and the interaction of MoDDP with additives present in the oil. MoDDP when used in base oil was found to increase the scuff resistance of ring and liner materials. The use of the additive reduced friction and wear (running in as well as normal) under nonconformal contact conditions, while under conformal contact conditions its effect was selective and limited.

  • 6.
    Gren, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Feasibility of using digital speckle correlation in the study of seal contacts2009In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 21, no 4, p. 123-134Article in journal (Refereed)
    Abstract [en]

    This paper presents studies of the contact between a soft rubber specimen and glass counterface using the Digital Speckle Correlation method, which provides information of displacements and structural similarities between recorded images. The setup is designed with a real contact and changes in the contact can be varied. Microscopic images using laser light illumination for different displacements are recorded and correlated. The results show that the contact area can be identified both for dry and lubricated contacts. The method can be applied on different geometries, surface roughness and lubricants. Influences of scars and contaminations, e.g. wear particles, may also be analysed.

  • 7.
    Isaksson, Ove
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Measurement of the influence of sliding velocity on oil film thickness in an elastohydrodynamic point contact1991In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 4, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    Experiments have been carried out to measure the film thickness between a sapphire disc and a polished steel ball when slippage is permitted between the two surfaces. The velocity sum of the two surfaces was kept constant during the measurements. The method used to determine the oil film thickness in the contact zone is optical interferometry. It was observed that the change in minimum film thickness was slight. When the sliding velocity was increased, the decrease in central film thickness was considerably larger than that of the minimum film thickness. In addition, the two side lobes, in which the minimum film thickness area occurs, were observed to become flatter as the sliding velocity was increased

  • 8.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, M.T.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the occurrence of pitting in lubricated rolling four-ball tests2015In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 27, no 2, p. 103-126Article in journal (Refereed)
    Abstract [en]

    Pitting, a form of rolling contact fatigue, is a complex phenomenon and several factors influence its occurrence, particularly under lubricated conditions. In this work, studies have been conducted to observe the events that occur during lubricated rolling four-ball tests that may affect or eventually lead to the formation of pits. This is performed to form an understanding of the pit formation process. Included is tribofilm formation, surface degradation, wear mode, material changes and crack initiation sites. These investigations have been performed on the ball samples from rolling four-ball tests, conducted using two API GL-5 gear oils. The analyses revealed the formation of a low hardness region beneath the surface of the running track due to martensite decay. The formation rate and expansion of this region was found to differ for the two lubricating oils. The pitted balls also indicated that the initial fatigue cracks were initiated at or close to the surface

  • 9.
    Lundberg, Jan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    McFadden, Terry
    Creep transport of grease subjected to low frequency vibrations1996In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 9, no 1, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Creep transport is defined as the velocity of a mass of grease when it is subjected to vibrational and gravitational forces. The method developed to assess this, measured the time taken for the grease submitted to low frequency vibrations to creep, under the influence of gravity, a specified distance down a cylindrical tube. The vibrations were characteristic in frequency and amplitude to those commonly experienced by commercial rotating machinery. Vibrational excitation was found to have a widely varying effect on creep transport of grease, suggesting that this parameter may be important in the selection of greases for specific applications where vibration is present; in contrast, the NLGI number gave almost no indication as to the effect of vibration on a particular grease. A vibration number related to the creep rate is suggested for grease selection. The vibration number correlates to the yield stress of the grease, with higher yield stress correlating to higher creep rate. However, no correlations between creep rate and base oil viscosity or bleed rate were found.

  • 10. McCarthy, Donald
    et al.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Assessment of polymer composites for hydrodynamic journal-bearing applications2009In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 21, no 8, p. 331-341Article in journal (Refereed)
    Abstract [en]

    Polymer composites are used as facing materials in hydrodynamic bearings for their low friction and compliant properties, which play an important role during machinery operation. In journal bearings, this low friction property can be of significant importance during start and stop cycles when insufficient oil is available to fully separate the surfaces in relative motion. Current work is aimed at determining a suitable material for use in hydrodynamic journal bearings for applications in hydroelectric power plants. This study investigates friction and wear encountered during the transition from the stationary state to operational speed (acceleration) during initial start-up. This is examined for virgin poly-tetra-fluoro-ethylene (PTFE) together with a series of commercially available PTFE-based composites and a babbitt material in boundary/mixed lubrication conditions. Tests are performed using standard laboratory block-on-ring test apparatus with a VG32 mineral oil.

  • 11. McCarthy, Donald
    et al.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Byheden, Åke
    Statoil.
    Influence of oil type on the performance characteristics of a two-axial groove journal bearing2009In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 21, no 9, p. 366-377Article in journal (Refereed)
    Abstract [en]

    The use of environmentally adapted lubricants (EALs) is a subject of growing interest to industry as legislation increasingly demands the replacement of mineral oil lubricants. Vegetable-based fluids are widely seen as providing lubricants from a renewable source, as well as meeting demands for improved biodegradability. However, at present, utilization of such fluids is limited due to their rapid oxidation. EALs produced from other base stocks (i.e. synthetic esters) have been shown to provide performance benefi ts in hydrodynamic thrust bearings. In the present study, a hydrodynamic journal bearing test rig has been employed to compare the performance of three EALs (a VG32 saturated ester, rapeseed base fluid and a propylene glycoldioleate) relative to three mineral turbine oils (ISOVG32, ISOVG46 and ISOVG68) in the hydrodynamic regime. Results are given in terms of temperature, power loss and minimum fi lm thickness. The impact of oil viscosity index is also discussed.

  • 12.
    Minami, Ichiro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    He, Xin
    Luleå University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Coating-lubricant combination for improving tribo-system performance2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 5, p. 375-386Article in journal (Refereed)
    Abstract [en]

    New tribo-systems composed of green chemicals have been investigated. Compatibility of friction modifiers with DLC was evaluated by using SRV test machine. A Zn-free lubricant formulation showed a steady-state friction coefficient of 0.15 for steel/steel contact. Hydrogenated DLC coating showed similar tribological properties when slid against steel. Interestingly, this lubricant showed low friction coefficient of 0.02 for hydrogen-free amorphous DLC when slid against steel. A model friction modifier improved the running-in performance and reduced wear for hydrogen-free DLC, while it marginally increased steady-state friction coefficient up to 0.04. The importance of material–lubricant combination and lubrication model has been highlighted

  • 13. Mäki, Rikard
    et al.
    Ganemi, Bager
    Svenska Statoil AB.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Olsson, Richard
    Haldex Traction Systems AB.
    Wet clutch transmission fluid for AWD differentials: influence of lubricant additives on friction characteristics2007In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 19, no 2, p. 87-99Article in journal (Refereed)
    Abstract [en]

    In recent years, several electronically controllable automotive transmission systems using wet clutches as intelligent differentials have emerged on the market. These applications place great demands on the anti-shudder properties of the transmission fluids used. The aims of this study were (i) to investigate the influence of different additives on the friction characteristics of a transmission fluid for all-wheel drive systems featuring wet multi-plate clutch with a sintered brass-based friction material and, based on this knowledge, (ii) to formulate a new transmission fluid with the desired frictional properties. In addition to excellent anti-shudder properties, the new fluid was required to lubricate hypoid gears under high load. To meet this requirement, it is necessary to add significant amounts of extreme pressure additives to the base oil, which are known to have an unfavourable influence on anti-shudder properties, necessitating the adoption of novel additive technologies. The additives studied include anti-wear additives, friction modifiers, corrosion inhibitors, detergents, antioxidants and extreme pressure additives. This paper shows how different additives affect friction in different ways, and that the interactions between the different additives are important to consider. It was concluded that it is feasible to combine good anti-shudder properties for wet clutches with good lubrication of hypoid gears.

  • 14.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Viscoelastic behaviour effect of hyaluronic acid on reciprocating flow inside mini-channel2016In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 28, no 8, p. 521-544Article in journal (Refereed)
    Abstract [en]

    One of the most successful surgeries during the 21st century is total joint replacement (TJR) with material combination of polymer-on-metal (PoM). Despite its success, wear particle generation at the interface of the polymer and metal causes eventually implant loosening. Investigating and understanding the wear particles distribution should help in designing implants with better performances. First step towards characterising wear particle distribution is deriving the lubricant behaviour and velocity distribution inside implant gap. Different hyaluronic acid (HA) solutions were subjected to a sinusoidal movement in straight rectangular channels. The velocity profiles along the channel width were measured with Micro Particle Image Velocimetry. HA solution behaviour was found to be dependent on the concentration. Results showed significant differences between the water (Newtonian) and HA behaviour in unsteady flow. The unsteady behaviour of the lubricant depended strongly on its non-Newtonian viscoelastic behaviour which was due to the time dependent nature of HA solution.

  • 15.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Bio-lubricant flow behaviour in mini-channels2016In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 28, no 4, p. 221-242Article in journal (Refereed)
    Abstract [en]

    One of the most common causes of failures in total joint replacements is the generation of wear particles within the joint. This contributes to bone lost and aseptic loosening of the implant, eventually requiring its replacement. Many studies have been carried out to improve the wear characteristics of bearing surfaces in total joint replacement. From the lubrication point of view, the friction behaviour of surfaces and rheology of the joint lubricant (synovial fluid) have been extensively studied. However, little attention has been paid to the interaction between the lubricant and the bearing surfaces. The aim of this study is to develop a methodology for studying the behaviour of bio-based lubricant in mini-channels. For this purpose, micro-particle image velocimetry was used in order to characterise the lubricant behaviour. Channels made of relevant materials such as ultra-high molecular weight polyethylene, cobalt–chromium–molybdenum alloy and titanium–aluminium–vanadium alloy with 1 and 1.5 mm width, 45 mm length and 2 mm depth were experimentally investigated. Results suggested that the used polymeric solution interaction with solid surfaces is very sensitive to the polymer concentration in the lubricant. Moreover, it was observed that there exist differences between water (Newtonian reference fluid) and the polymeric solution behaviour even at very simple movements; although usually, the properties of this lubricant at high shear rates are estimated by water properties.

  • 16.
    Sethuramiah, A.
    et al.
    Indian Institute of Technology, New Delhi.
    Awasthy, K. L.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Mahapatra, P. K.
    Indian Institute of Technology, New Delhi.
    Lubricated wear of PTFE and graphited PTFE1991In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 3, no 3, p. 181-188Article in journal (Refereed)
    Abstract [en]

    Tribological behaviour of PTFE and graphited PTFE have been evaluated under lubricated conditions and compared with dry wear. The stress selected is in the range of 0.44 to 1.64 MPa, and the data generated are relevant to conformal contacts. Mineral oil lubrication can reduce wear of PTFE by one to two orders of magnitude. With graphited PTFE the lubricant effect is lower in comparison to that observed with PTFE. Specific wear rates are plotted on a histogram.

  • 17. Simmons, Gregory F
    et al.
    Mofidi, Mohammadreza
    Department of Mechanical Engineering, Shahid Bahonar University, Kerman.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction evaluation of elastomers in lubricated contact2009In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 21, no 10, p. 427-440Article in journal (Refereed)
    Abstract [en]

    Friction testing of elastomers in lubricated contact is discussed with a focus on developing experimental arrangements that can produce worthwhile results. Practical issues unique to elastomers are covered as well as their solutions, including contact mechanics, material response to loading, contact edges, oil absorption, cleaning and specimen geometry. A critique of reciprocating laboratory testing machines, including high-frequency short stroke and low-frequency long stroke friction and wear machines, is conducted for their usefulness, as is critical analysis of a wide variety of specimen configurations with the aim of helping the laboratory experimenter to overcome many of the pitfalls associated with testing of elastomers in lubricated conditions. Results from experiments using various testing arrangements are analysed, and it is found that the synthetic ester and mineral oil used produced similar results.

1 - 17 of 17
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