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Many Tribology Group publications are Open Access thanks to funding from the EPSRC.

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  • Journal article
    Paynter RJH, Hills DA, Dini D, 2010,

    Separation and slip at the edge of a complete contact: An asymptotic solution

    , INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 47, Pages: 2613-2619, ISSN: 0020-7683
  • Journal article
    Myant C, Fowell M, Spikes HA, Stokes JRet al., 2010,

    An Investigation of Lubricant Film Thickness in Sliding Compliant Contacts

    , Tribology Transactions, Vol: 53, Pages: 684-694, ISSN: 1547-397X
  • Conference paper
    Holtzinger J, Green JH, Lamb GD, Atkinson D, Spikes HAet al., 2010,

    Influence of viscosity modifiers on hydrodynamic friction

    , Pages: 171-177

    In order to understand (and ultimately to predict) the friction reduction resulting from the use of polymer solutions, the rheological properties of model polymer solutions have been measured over a wide range of shear rates. As well as temporary shear thinning, some permanent shear thinning of the higher molecular weight polystyrene solutions has been noted in the USV. Temporary viscosity loss has been observed for polyisoprene blend with a molecular weight of 82 000 g/mol and a polydispersity index of 1.07. The impacts of pure polymer concentration and molecular weight on permanent shear thinning are significant in the case of polystyrene solutions.
  • Conference paper
    Spikes H, 2010,

    Nanotribology and nanoadditives

    , Pages: 34-44

    Nanotechnology concerns the preparation and properties of organised ensembles of atoms and molecules of nanometer dimensions. The growth of nanotechnology is having a profound impact on the development of tribology, to the extent that a new branch of the field, termed "nanotribology" has emerged. This paper outlines some of the main contributions of nanotechnology to tribology to date, including the application of nanoscale experimental techniques, the modelling of tribological systems at the nanoscale and the study and properties of nanoscale structures and processes in rubbing contacts. One of the most interesting recent advances in nanotribology is the development and use of dispersed nanoscale colloidal particles as lubricant additives. The properties and behaviour of these nanoadditives is discussed.
  • Conference paper
    Hoshino K, Yagishita K, Tagawa K, Spikes Het al., 2010,

    Sulphur-free antiwear additives zinc dialkylphosphates (ZPs) - Film forming and friction properties

    , Pages: 178-184

    ZPs (zinc dialkylphosphates) are sulphur-free analogues of ZDDPs (zinc dialkyldithiophosphates) and have been attracting considerable attention from the environmental viewpoint. In this study, to clarify their mechanism of action as antiwear additives, the film-forming and friction properties of ZPs were investigated using a spacer layer interferometry imaging system (SLIM) attached to a rolling-sliding mini-traction machine (MTM). The results show that ZPs form thick tribo-films, although the film-forming rates are slower and the films are thinner than those of ZDDPs. It is also shown that there is no noticeable difference in friction behaviour between ZPs and ZDDPs. In addition, these properties are strongly affected by the structure of the alkyl chains of ZPs and ZDDPs. The antiwear performance of the additives was also studied. Generally, under the condition employed in this study, the antiwear performance of ZPs is better than that of ZDDPs at low sliding speeds, while the performance of ZDDPs is better than that of ZPs at high speeds. The antiwear performance is also influenced by the structure of the alkyl chains.
  • Journal article
    Reina S, Paynter RJH, Hills DA, Dini Det al., 2010,

    Determining the coefficient of friction between solids without sliding

    , WEAR, Vol: 269, Pages: 339-343, ISSN: 0043-1648
  • Journal article
    Andablo-Reyes E, de Vicente J, Hidalgo-Alvarez R, Myant C, Reddyhoff T, Spikes HAet al., 2010,

    Soft Elasto-Hydrodynamic Lubrication

    , Tribology Letters, Vol: 39, Pages: 109-14, ISSN: 1023-8883

    This article examines the use of ferrofluids to control starvation in lubricated contacts. Starvation in a ball-plate contact is experimentally studied under sliding-rolling conditions using a Mini Traction Machine (MTM). Friction is measured and the experimental results are presented in the form of Stribeck curves. The volume of lubricant is controlled in such a way that no free bulk oil is present in the vicinity of the contact. An abrupt change in the slope of the Stribeck curve in the Hydrodynamic Lubrication zone is interpreted as the onset of starvation. It is then shown that the use of ferrofluids in the presence of a magnetic field distribution can change the conditions at which this onset of starvation occurs. Different magnetic field distributions are tested for different values of load and ferrofluid viscosity. It is proposed that ferrofluid lubricants in conjunction with a suitably positioned magnetic field can be used to promote replenishment, and thus control and reduce lubricant starvation.
  • Journal article
    Reddyhoff T, Choo JH, Spikes HA, Glovnea RPet al., 2010,

    Lubricant Flow in an Elastohydrodynamic Contact Using Fluorescence

    , Tribology Letters, Vol: 38, Pages: 207-15, ISSN: 1023-8883

    It is well-documented that parameters, such as film thickness and temperature in EHL contacts, can be measured experimentally using a range of techniques include optical interferometry, ultrasonics, capacitance and infrared emission. Considerably less is known, however, about the flow of lubricant through such contacts. Information about lubricant flow would greatly benefit the prediction of friction in machine components. This article describes initial steps to develop fluorescence as a means of observing lubricant flow. An EHL contact was produced between a steel ball and a glass disc and viewed using a fluorescence microscope. The entrained lubricant was dyed using a fluorescent species, so that when illuminated with laser light, a fluorescence intensity map could be viewed. When the contact was fully flooded with dyed lubricant, the fluorescence intensity within the contact correlated well with optical interferometric film thickness measurements under the same conditions. This suggests useful possibilities for mapping film thickness in contacts where conventional optical methods are impractical, such as between rough surfaces and within soft contacts. In order to observe how lubricant flows in an EHL contact, fluorescer-containing lubricant was placed on the out-of-contact track. The boundary between fluorescent and non-fluorescent lubricant was then entrained into the contact and the passage of the boundary through the contact was monitored.
  • Journal article
    Ingram M, Spikes H, Noles J, Watts Ret al., 2010,

    Contact properties of a wet clutch friction material

    , TRIBOLOGY INTERNATIONAL, Vol: 43, Pages: 815-821, ISSN: 0301-679X
  • Patent
    Ioannides E, Spikes H, Brajdic-Mitidieri P, Gosman ADet al., 2010,

    Sliding bearing with improved surface topography

    , US7682081B2
  • Journal article
    Browne M, Jeffers JRT, Saffari N, 2010,

    Nondestructive Evaluation of Bone Cement and Bone Cement/Metal Interface Failure

    , JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS, Vol: 92B, Pages: 420-429, ISSN: 1552-4973
  • Journal article
    Myant C, Spikes HA, Stokes JR, 2010,

    Influence of load and elastic properties on the rolling and sliding friction of lubricated compliant contacts

    , TRIBOLOGY INTERNATIONAL, Vol: 43, Pages: 55-63, ISSN: 0301-679X
  • Journal article
    Olomolehin Y, Kapadia R, Spikes H, 2010,

    Antagonistic Interaction of Antiwear Additives and Carbon Black

    , TRIBOLOGY LETTERS, Vol: 37, Pages: 49-58, ISSN: 1023-8883
  • Journal article
    Reddyhoff T, Choo JH, Spikes HA, Glovnea RPet al., 2010,

    Lubricant flow in an elastohydrodynamic contact using fluorescence

    , Tribology Letters, Vol: 38, Pages: 207-215, ISSN: 1023-8883

    It is well-documented that parameters, such as film thickness and temperature in EHL contacts, can be measured experimentally using a range of techniques include optical interferometry, ultrasonics, capacitance and infrared emission. Considerably less is known, however, about the flow of lubricant through such contacts. Information about lubricant flow would greatly benefit the prediction of friction in machine components. This article describes initial steps to develop fluorescence as a means of observing lubricant flow. An EHL contact was produced between a steel ball and a glass disc and viewed using a fluorescence microscope. The entrained lubricant was dyed using a fluorescent species, so that when illuminated with laser light, a fluorescence intensity map could be viewed. When the contact was fully flooded with dyed lubricant, the fluorescence intensity within the contact correlated well with optical interferometric film thickness measurements under the same conditions. This suggests useful possibilities for mapping film thickness in contacts where conventional optical methods are impractical, such as between rough surfaces and within soft contacts. In order to observe how lubricant flows in an EHL contact, fluorescer-containing lubricant was placed on the out-of-contact track. The boundary between fluorescent and non-fluorescent lubricant was then entrained into the contact and the passage of the boundary through the contact was monitored. 2010 Springer Science+Business Media, LLC.
  • Conference paper
    Hergert R, Ku ISY, Reddyhoff T, Holmes ASet al., 2010,

    Micro rotary ball bearing with integrated ball cage: Fabrication and characterization

    , Piscataway, NJ, USA, 23rd IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2010), 24-28 Jan. 2010, Publisher: IEEE, Pages: 687-90

    This paper presents a rotary MEMS ball bearing with an integrated silicon ball cage. The device is a deep groove radial ball bearing consisting of steel balls encapsulated between two micromachined silicon wafers. The silicon ball cage is released from the bulk silicon substrate during fabrication. The objective was to show that a simple caged bearing design provides reliable motion at both high and low speeds. The running torque of two identical devices was measured for speeds ranging from 10 to 20,000 rpm. One of the devices was disassembled before failure to provide images of the wear experienced during testing.
  • Conference paper
    Dwyer-Joyce RS, Zhu J, Reddyhoff T, 2010,

    Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication

    , San Francisco, CA, United states, STLE/ASME 2010 International Joint Tribology Conference, IJTC2010, October 17, 2010 - October 20, 2010, Publisher: American Society of Mechanical Engineers, Pages: 111-113

    The reflection of ultrasound can be used to determine oil film thickness from the stiffness of the separating film. However, boundary or mixed film lubrication is a common occurrence in elastohydrodynamic lubricated (EHL) contacts, as the nominal thickness of the separating film approaches the surface asperity height. In this paper an ultrasonic investigation was carried out on the interface between a steel ball sliding on a flat disc as the speed was reduced into the boundary regime. The ultrasonic reflection then depends on the stiffness of the interface that now consists of an oil layer and asperity contacts. To distinguish the stiffness contribution from asperity contact and oil layer, a mixed lubrication model for circular contacts was established. This predicted the lubricant film thickness and proportions of solid and liquid mediated contact. The total stiffness predicted by theoretical models showed a good agreement with experimental measurement for kinematic cases. The model can then be used to extract the proportion of real area of contact, and the oil film thickness, from ultrasonic results. Copyright 2010 by ASME.
  • Conference paper
    Oldfield M, Dini D, Rodriguez y Baena F, 2010,

    Detailed Finite Element Simulations of Probe Insertion into Solid Elastic Material using a Cohesive Zone Approach

    , 32nd Annual International Conference of the IEEE Engineering-in-Medicine-and-Biology-Society (EMBC 10), Publisher: IEEE, Pages: 3198-3201, ISSN: 1557-170X
  • Journal article
    Reina S, Hills DA, Dini D, 2010,

    Incipient slip conditions in the rolling contact of tyred wheels

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE, Vol: 224, Pages: 2049-2054, ISSN: 0954-4062
  • Journal article
    Myant C, Reddyhoff T, Spikes HA, 2010,

    Laser-induced fluorescence for film thickness mapping in pure sliding lubricated, compliant, contacts

    , Tribology International, Vol: 43, Pages: 1960-1969, ISSN: 0301-679X

    A laser-induced fluorescence (LIF) technique has been used to measure fluid film thickness in a compliant, sliding contact under low-load/low-pressure conditions. The soft contact between an elastomer hemisphere and a glass disc is lubricated by a liquid containing fluorescent dye. The contact is then illuminated with 532 nm laser light through the glass disc, and viewed with a fluorescence microscope. From the intensity of emitted radiation, film thickness maps of the contact are determined. Previous calibration procedures have used a separate calibration piece and test specimen with possible errors due to differences in reflectivity between the calibration and test specimens. In the work reported in this paper a new calibration process is employed using the actual test sample, thereby avoiding such errors. Results are reported for a sliding contact between PDMS and glass, lubricated with glycerol and water solutions under fully flooded and starved conditions. It was found that, for glycerol, the measured film thickness is somewhat lower than numerical predictions for both lubrication conditions. It is suggested that a combination of thermal effects and the hygroscopic nature of glycerol may cause the lubricant viscosity to drop resulting in thinner films than those predicted for fully flooded contacts. Starvation occurs above a critical entrainment speed and results in considerably thinner films than predicted by fully flooded I-EHL theory. A numerical study has been carried out to determine the effect of the observed starvation on film thickness. Predicted, starved film thickness values agree well with those obtained experimentally. 2010 Elsevier Ltd.
  • Conference paper
    Medina S, Dini D, Olver AV, 2010,

    ADHESIVE CONTACT BETWEEN ATOMISTIC SURFACES USING A CONTINUUM ANALYSIS

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 35-37
  • Conference paper
    Hili J, Reddyhoff T, Olver AV, Pelletier C, Jacobs Let al., 2010,

    FILM FORMING CHARACTERISTICS OF OIL-IN-WATER EMULSIONS IN ELASTOHYDRODYNAMIC CONTACTS

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 143-145
  • Conference paper
    Balcombe R, Fowell MT, Olver AV, Dini Det al., 2010,

    A COUPLED APPROACH FOR MODELLING ROLLING CONTACT FATIGUE CRACKS UNDER ELASTOHYDRODYANMIC LUBRICATION

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 269-271
  • Conference paper
    Reina S, Dini D, 2010,

    FRICTIONAL SHAKEDOWN IN CONTACT PROBLEMS OF LAYERED SYSTEMS

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 387-389
  • Conference paper
    Myant C, Spikes HA, 2010,

    FILM THICKNESS STUDY OF LUBRICATED, COMPLIANT CONTACTS

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 59-61
  • Conference paper
    Tomala A, Karpinska A, Werner WSM, Olver AV, Stoeri Het al., 2010,

    Tribological Performance of Additives for Water-Based Lubricants

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 447-449
  • Conference paper
    Zografos A, Dini D, 2010,

    AN INDIRECT BOUNDARY ELEMENT FORMULATION FOR THE SOLUTION OF COUPLED 2D CONTACT PROBLEMS

    , ASME/STLE International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 367-369
  • Journal article
    Dickinson AS, Taylor AC, Jeffers JRT, Browne Met al., 2010,

    Performance of the resurfaced hip. Part 2: the influence of prosthesis stem design on remodelling and fracture of the femoral neck

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 224, Pages: 841-851, ISSN: 0954-4119
  • Journal article
    Hili J, Olver AV, Edwards S, Jacobs Let al., 2010,

    Experimental Investigation of Elastohydrodynamic (EHD) Film Thickness Behavior at High Speeds

    , TRIBOLOGY TRANSACTIONS, Vol: 53, Pages: 658-666, ISSN: 1040-2004
  • Conference paper
    Hergert R, Ku ISY, Reddyhoff T, Holmes ASet al., 2010,

    Micro rotary ball bearing with integrated ball cage: Fabrication and characterization

    , Hong Kong, China, 23rd IEEE International Conference on Micro Electro Mechanical Systems, MEMS 2010, January 24, 2010 - January 28, 2010, Publisher: Institute of Electrical and Electronics Engineers Inc., Pages: 687-690, ISSN: 1084-6999

    This paper presents a rotary MEMS ball bearing with an integrated silicon ball cage. The device is a deep groove radial ball bearing consisting of steel balls encapsulated between two micromachined silicon wafers. The silicon ball cage is released from the bulk silicon substrate during fabrication. The objective was to show that a simple caged bearing design provides reliable motion at both high and low speeds. The running torque of two identical devices was measured for speeds ranging from 10 to 20,000 rpm. One of the devices was disassembled before failure to provide images of the wear experienced during testing. 2010 IEEE.
  • Conference paper
    Andablo-Reyes E, De Vicente J, Hidalgo-Alvarez R, Myant C, Reddyhoff T, Spikes HAet al., 2010,

    Soft elasto-hydrodynamic lubrication

    , 233 Springer Street, New York, NY 10013-1578, United States, Publisher: Springer New York, Pages: 109-114, ISSN: 1023-8883

    This article examines the use of ferrofluids to control starvation in lubricated contacts. Starvation in a ball-plate contact is experimentally studied under sliding-rolling conditions using a Mini Traction Machine (MTM). Friction is measured and the experimental results are presented in the form of Stribeck curves. The volume of lubricant is controlled in such a way that no free bulk oil is present in the vicinity of the contact. An abrupt change in the slope of the Stribeck curve in the Hydrodynamic Lubrication zone is interpreted as the onset of starvation. It is then shown that the use of ferrofluids in the presence of a magnetic field distribution can change the conditions at which this onset of starvation occurs. Different magnetic field distributions are tested for different values of load and ferrofluid viscosity. It is proposed that ferrofluid lubricants in conjunction with a suitably positioned magnetic field can be used to promote replenishment, and thus control and reduce lubricant starvation. 2010 Springer Science+Business Media, LLC.
  • Journal article
    Viesca JL, Battez AH, Gonzalez R, Reddyhoff T, Perez AT, Spikes HAet al., 2010,

    Assessing boundary film formation of lubricant additivised with 1-hexyl-3-methylimidazolium tetrafluoroborate using ECR as qualitative indicator

    , Wear, Vol: 269, Pages: 112-117, ISSN: 0043-1648

    Boundary film formation of ionic liquid (IL) 1-hexyl-3-methylimidazolium tetrafluoroborate, [HMIM][BF4], as an additive of hydrocracked mineral oil is evaluated for a steel-steel contact. Accelerated wear testing was carried out using a high frequency reciprocating rig (HFRR) under these test conditions: maximum contact pressure of 1.04 GPa, two different temperatures (40 and 100 C) and three different times (300, 1800 and 3600 s). Wear volumes were measured using a non-contact 3D profilometer while worn surfaces were characterized using XPS. Furthermore, electrical contact resistance (ECR) was used as qualitative indicator of the formation of electrically insulating films in the sliding contact. Experiments show that the rate of boundary film formation of base oil-ionic liquid blend is faster than neat base oil. Moreover, ECR was in good agreement with film formation and friction behaviour. Ionic liquid as additive not only decreases the time of running-in but also the time of wear-in. Results of neat base oil show that wear-in was not reached during any duration of tests. The improved friction and wear results for the blend are closely related to the boundary film formation on the worn surfaces due to the reactivity of the anion with the steel surfaces. 2010 Elsevier B.V. All rights reserved.
  • Journal article
    Ku ISY, Reddyhoff T, Choo JH, Holmes AS, Spikes HAet al., 2010,

    A novel tribometer for the measurement of friction in MEMS

    , Tribology International, Vol: 43, Pages: 1087-1090, ISSN: 0301-679X

    A new tribometer has been developed to determine friction under conditions that are representative of MEMS (micro-electro-mechanical-systems). The tribometer consists of a rotating silicon disc, loaded against a stationary silicon disc. Friction and film thickness values are measured using laser displacement techniques. In this study, two different test set-ups were used: a flat on flat specimen geometry, and a moving flat against a structured surface, similar to that of a miniature thrust pad bearing. Using this tribometer, hydrodynamic tests have been carried out with the specimens fully submerged in hydrocarbon lubricants. Results suggest that friction increases with sliding speed and decreases with increasing applied normal load, which is in accordance with the hydrodynamic theory. 2009 Elsevier Ltd. All rights reserved.
  • Journal article
    Masen MA, van't Spijker A, Kreulen CM, 2010,

    An experimental investigation into dental wear: tooth-tooth contact

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 224, Pages: 589-594, ISSN: 1350-6501
  • Conference paper
    Reddyhoff T, Ku ISY, Choo JH, Holmes AS, Spikes HAet al., 2009,

    Lubrication of high sliding MEMS

    Effective lubrication for micro-electromechanical systems (MEMS) was studied. A new micro-tribometer was developed to measure friction and film thickness under conditions representative of MEMS. For hydrocarbon lubricants, friction increased with sliding speed and decreased with increasing applied normal load, which is in accord with hydrodynamic theory. Using low viscosity fluids, satisfactory friction coefficient values were obtained with negligible wear. Good agreement was obtained between experimental results and a finite difference model. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/209).
  • Conference paper
    Holtzinger J, Green J, Lamb G, Spikes HAet al., 2009,

    Influence of viscosity modifiers on hydrodynamic friction

    , Pages: 405-408

    In order to understand (and ultimately to predict) the friction reduction, resulting from the use of polymer solutions, the rheological properties of model polymer solutions have been measured over a wide shear rate. As well as temporary shear thinning, some permanent shear thinning of the higher molecular weight polymer solutions has been noted in the USV.
  • Conference paper
    Myant C, Fowell M, Stokes J, Spikes Het al., 2009,

    Film thickness study for soft contacts using an optical interferometric technique

    A technique for measuring lubricant film thickness between soft deformable surfaces under low-load/low-pressure conditions using optical interferometry is presented. Results are presented for pure sliding conditions between a rotating PDMS sphere and plain glass flat lubricated with glycerol, sunflower oil, and pure water solutions. Hydrophobic-hydrophilic and hydrophilic-hydrophilic tribopairs of contacting surfaces were studied. Contact profile shapes and film thickness maps were compared to theoretical models and discussed. This is an abstract of a paper presented at the Proceedings of World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Conference paper
    Benedet J, Green J, Lamb G, Spikes HAet al., 2009,

    Tribological characteristics of ashless P- And P-S based antiwear additives

    The tribological properties of phosphorus based and phosphorus-sulfur based antiwear additive in hydrocracked oil were studied under boundary lubrication conditions. Different types of P-based and P-S based antiwear additives were compared to a primary ZDDP. The ashless P- and P-S compounds can form thick, solid-like films similar to ZDDP, with P-compounds producing thicker films than P-S compounds. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Conference paper
    Nakano K, Reddyhoff T, Cann P, Spikes Het al., 2009,

    Film formation of liquid crystals in EHD contacts

    The film formation of two types of liquid crystals, i.e., 4-pentyl-4′-cyanobiphenyl (5CB) and 4-octyl-4′-cyanobiphenyl (8CB), was studied in EHD contacts. The enhancement of film formation by the addition of palmitic acid affected the traction characteristics of 5CB. The traction coefficient of pure 5CB increased significantly with a decrease in the entrainment speed at entrainment speeds below 0.1 m/sec. The change in the EHD film of pure 8CB was similar to that of 5CB with 0.1 wt % palmitic acid. The traction coefficient of 8CB was lower than that of 5CB, ≈ 0.02, which was maintained at low entrainment speeds. These special properties were attributed to the layer structure of the smectic phase. This is an abstract of a paper presented at the Proceedings of World Tribology Conference (Kyoto, Japan 9/6-11/2009).
  • Conference paper
    Vengudusamy B, Spikes HA, Mufti RA, Lamb GD, Green JHet al., 2009,

    Comparison of friction properties of DLC coatings in DLC/DLC contacts

    , Pages: 347-349
  • Conference paper
    Ingram M, Spikes H, Noles J, Watts R, Harris Set al., 2009,

    The mechanisms of wet clutch friction

    The impact of additives on wet clutch friction was studied in a pure sliding regime with speeds of 0.01 to 2 m/sec, and contact pressures of ∼ 3 MPa, using a modified MTM. Simple linear carboxylic acids and mixtures were used as model friction modifiers (FM), including: hexanoic, dodecanoic, and stearic acid, to study the effect of chain length and oleic, elaidic, and 12-hydroxy stearic acids to study the effect of some structural changes on the friction. The model friction modifiers ha lower friction and gave a positive gradient μ-V curve. Friction decreased with model FM chain length, as greater lateral side chain interactions existed, which produced more effective friction reducing layer. The friction was also dependent on the structure of the model FM used. Elaidic acid and 12-hydroxy stearic acid had a higher friction coefficient than the saturated stearic acid. This is an abstract of a paper presented at the Proceedings of World Tribology Conference (Kyoto, Japan 9/6-11/2009).
  • Conference paper
    Reddyhoff T, Underwood RJ, Nikas GK, Sayles RS, Spikes HAet al., 2009,

    Thermal aspects of debris in EHL contacts

    A technique is developed for the measurement of the temperature rise resulting from debris entrainment in an EHL lubricated contact. Under pure rolling, temperature rises are small, because minimal shearing occurs. Under sliding conditions, the temperature rise generally increases from when the particle is entrapped in the inlet zone, to peak near the contact centre where shearing is a maximum. The measured values and the theoretical simulation show a similar trend in temperature rise as the particle passes through the contact. The magnitude of predicted temperatures is significantly higher than those measured. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Conference paper
    Ingram M, Spikes H, Noles J, Watts RF, Harries Set al., 2009,

    Contact properties of wet clutch friction material

    , Pages: 338-340

    Contact units formed by wet clutch friction materials have been studied over a range of pressures and during rubbing. The real contact area increases approximately linearly with applied load, and at nominal pressures of above 2 MPa, the contact units may be deforming elastically and plastically to give larger units. During sliding the real area of contact increases dramatically due to a truncating wear mechanism on the contact units. These findings are supported by AFM images of individual fibres before and after the rubbing test.
  • Journal article
    Balcombe R, Fowell M, Olver AV, Dini Det al., 2009,

    Rolling contact fatigue cracks in the presence of a lubricant

    , Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2009, Pages: 341-343
  • Journal article
    Balcombe R, Fowell M, Olver AV, Ioannides S, Dini Det al., 2009,

    A coupled elastohydrodynamic solution for rolling contact fatigue cracks

    , World Tribology Congress 2009 - Proceedings

    Rolling contact fatigue (RCF) affects the performance of gears, rolling-element bearings, rollers in the steel-making process, rail wheels and lines, and a number of other important machine elements. A coupled fluid-solid algorithm combining an elastohydrodynamic solution with a surface breaking RCF crack is put forward. A cracked semi-infinite body is loaded by a rolling element in the presence of a lubricant, generating an EHD pressure. The transient flow between an RCF crack and the surface film by contact loading has a significant effect on the lubricant pressure inside the crack and the crack face deflection. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Journal article
    Underwood RJ, Sayles RS, Kadiric A, Ioannides Eet al., 2009,

    An investigation of the load support of fluid trapped in dents

    , World Tribology Congress 2009 - Proceedings

    The load support by lubricants trapped in a dent was investigated using combined experimental and modeling study. The plastic deformation of the pre-indent shoulders for the dry case was greater than for the lubricated case, indicating that the entrapped lubricant was supporting a significant proportion of the applied load. By varying the pre-indent geometry, the load support depended on the conformity of the contacting surfaces, the relative change in volume, and thus the pressure increase of the trapped lubricant. For a conforming geometry, and assuming no leakage of oil from the pre-indent, the entrapped lubricant can support 60% of the applied load, assuming 50% leakage, the entrapped lubricant supported 34% of the applied load. By ignoring the effect of lubricants trapped in dents, the fatigue life of rolling element bearings could be underestimated. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/209).
  • Journal article
    Cann P, 2009,

    Grease degradation in rolling element bearings - Development of a simulation tests

    , World Tribology Congress 2009 - Proceedings

    Improvements in rolling element bearing design, manufacturing standards and materials have resulted in significant increase in bearing life and performance. Thus, bearing life is often limited by lubrication failure of the grease. A study was carried out to examine grease degradation under controlled operating conditions simulating those experienced in rolling element bearings. The critical bearing factors determining grease lubrication failure wee considered to be the short replenishment time between over-rolling, thin lubricant films in the raceway, and the presence of metal wear debris. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Journal article
    Arora H, Cann P, 2009,

    Lubrication properties of alkyl imidazolium tetrafluoroborate and hexafluorophosphate ionic liquids under mixed sliding-rolling conditions

    , World Tribology Congress 2009 - Proceedings

    The ionic liquids (IL) lubrication properties in mixed rolling-sliding and rolling EHL conditions were studied. The tribological performance of four neat IL was compared with an additized mineral oil (MO). RITL friction coefficients were less than the MO for all speed and slide-roll conditions studied. The film thickness results showed that three of the fluids demonstrated classical EHL behavior with log film vs. log speed gradients in the range 0.56-0.66. However, the 1-butyl-3-methyl imidazolium tetrafluoroborate fluid gave anomalously thick, time-dependent film results at low speeds. This behavior was associated with the shorter, alkyl chain cations (l-butyl-3-methyl) rather than the anion. Film formation was not due to RTIL decomposition and subsequent anion reaction with the wear surface. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/2009).
  • Journal article
    Reddyhoff T, Spikes HA, Olver AV, 2009,

    Improved infrared temperature mapping of elastohydrodynamic contacts

    , Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Vol: 223, Pages: 1165-1177, ISSN: 1350-6501

    An effective means of studying lubricant rheology within elastohydrodynamic contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. In the current work, the experimental approach initially developed by Sanborn and Winer and then by Spikes et al., has been advanced to include a high specification infrared (IR) camera and microscope. Besides the instantaneous capture of full field measurements, this has the advantage of increased sensitivity and higher spatial resolution than previous systems used. The increased sensitivity enables a much larger range of testable operating conditions: namely lower loads, speeds, and reduced sliding. In addition, the range of test lubricants can be extended beyond high shearing traction fluids. These new possibilities have been used to investigate and compare the rheological properties of a range of lubricants: namely a group I and group II mineral oil, a polyalphaolephin (group IV), the traction fluid Santotrac 50, and 5P4E, a five-ring polyphenyl-ether. As expected, contact temperatures increased with lubricant refinement, for the mineral base oils tested. Using moving heat source theory, the measured temperature distributions were converted into maps showing rate of heat input into each surface, from which shear stresses were calculated. The technique could therefore be validated by integrating these shear stress maps, and comparing them with traction values obtained by direct measurement. Generally there was good agreement between the two approaches, with the only significant differences occurring for 5P4E, where the traction that was deduced from the temperature over-predicted the traction by roughly 15 per cent. Of the lubricants tested, Santotrac 50 showed the highest average traction over the contact; however, 5P4E showed the highest maximum traction. This observation is only possible using the IR mapping technique, and is obscured when measuring the traction
  • Conference paper
    Zografos A, Dini D, Olver AV, 2009,

    Fretting fatigue and wear in bolted connections: A multi-level formulation for the computation of local contact stresses

    , 35th Leeds-Lyon Symposium on Tribology, Publisher: ELSEVIER SCI LTD, Pages: 1663-1675, ISSN: 0301-679X
  • Journal article
    Banerjee N, Hills DA, Dini D, 2009,

    The derivation and application of a semi-infinite flat and rounded asymptotic frictionless contact

    , INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 51, Pages: 662-666, ISSN: 0020-7403

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