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  • Journal article
    Wong JSS, Hong L, Bae SC, Granick Set al., 2010,

    Fluorescence Recovery after Photobleaching Measurements of Polymers in a Surface Forces Apparatus

    , Journal of Polymer Science. Part B, Polymer Physics, Vol: 48
  • Journal article
    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.

    , Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference, Pages: 3198-3201, ISSN: 1557-170X

    In this paper a method is presented for detailed finite element modelling of probe insertion into an elastic material. This is part of an ongoing investigation into the mechanics of a novel, biomimetic, soft-tissue probe currently under development at Imperial College, London. Analysis is performed using a 'cohesive zone' approach by integrating multiple cohesive elements into a finite element mesh using Abaqus software. Cohesive zones with variable crack paths, generated by both remote tensile and contact loading, and substantial probe penetration along an arbitrarily curved crack path are demonstrated. These advances are critical to understanding probe interactions for the development of an existing prototype and control strategy.
  • Conference paper
    Vengudusamy B, Green JH, Lamb GD, Spikes HAet al., 2010,

    Behaviour of lubricant additives in DLC/DLC and DLC/steel contacts

    , Pages: 376-378

    The friction properties of diamond-like coating (DLC), including W-DLC, WC-DLC, Si-DLC, taC, a-C:H and a-C, were studied in DLC/DLC and DLC/Steel sliding-rolling contacts lubricated by additivated mineral oils. DLC showed a reduction in friction when additivated, indicating the presence of tribofilm on the DLC surface. Only W-DLC formed a pad-like structure similar to that of steel. Other DLC either formed very thin film or debris-like species on the surface. ta-C coatings give the lowest boundary friction, followed by a-C:H and a-C coatings. DLC that can form ZDDP pads showed good anti-wear properties. This is an abstract of a paper presented at the STLE Annual Meeting and Exhibition 2010 (Las Vegas, NV 5/16-20/2010).
  • Conference paper
    Benedet J, Green JH, Lamb GD, Spikes HAet al., 2010,

    Tribological characteristics of low and zero SAPS antiwear additives

    , Pages: 323-325

    The tribological properties of a range of low and zero sulphated ash, phosphorus and sulphur antiwear additives that have been suggested as possible alternatives to, or partial replacements for ZDDP, were studied. Zinc dialkyldithiophosphate (ZDDP)1 rapidly developed a thick film, while the low and zero SAPS antiwear additives formed thinner or even negligible tribofilms compared to ZDDP. This is an abstract of a paper presented at the STLE Annual Meeting and Exhibition 2010 (Las Vegas, NV 5/16-20/2010).
  • Journal article
    Spikes HA, 2010,

    Fourth World Tribology Conference

    , LUBRICATION SCIENCE, Vol: 22, Pages: 415-416, ISSN: 0954-0075
  • Journal article
    Giacopini M, Fowell MT, Dini D, Strozzi Aet al., 2010,

    A Mass-Conserving Complementarity Formulation to Study Lubricant Films in the Presence of Cavitation

    , JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 132, ISSN: 0742-4787
  • Journal article
    Myant C, Fowell M, Spikes HA, Stokes JRet al., 2010,

    An Investigation of Lubricant Film Thickness in Sliding Compliant Contacts

    , TRIBOLOGY & LUBRICATION TECHNOLOGY, Vol: 66, Pages: 46-+, ISSN: 1545-858X
  • Journal article
    Arora H, Cann PM, 2010,

    Lubricant film formation properties of alkyl imidazolium tetrafluoroborate and hexafluorophosphate ionic liquids

    , TRIBOLOGY INTERNATIONAL, Vol: 43, Pages: 1908-1916, ISSN: 0301-679X
  • Journal article
    Reina S, Hills DA, Dini D, 2010,

    Contact of a rigid cylinder indenting an elastic layer sliding over a rigid substrate

    , EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, Vol: 29, Pages: 772-783, ISSN: 0997-7538
  • Journal article
    Reina S, Dini D, Hills DA, 2010,

    Interfacial slip and creep in rolling contact incorporating a cylinder with an elastic layer

    , EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, Vol: 29, Pages: 761-771, ISSN: 0997-7538
  • Journal article
    Smeeth M, Spikes H, Gunsel S, 2010,

    Boundary Film Formation by Viscosity Index Improvers

    , TRIBOLOGY & LUBRICATION TECHNOLOGY, Vol: 66, Pages: 54-+, ISSN: 1545-858X
  • 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
    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.
  • 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.
  • 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
    • Cite
    • Citations: 76
  • Journal article
    Ahmad M, Alexandrou I, Al-Nuaimy W, Amavasai BP, An YY, Ariwa E, Arteche J, Audrino F, Ayesh A, Baber C, Bailey C, Balkan N, Barria J, Bartosova J, Benkrid K, Bleijs H, Bluck M, Bose I, Bouzas PR, Braiden PM, Brdys M, Burriesci G, Cannataro M, Carvalho A, Chang CC, Chen D, Chen GG, Chen YS, Chiclana F, Cooke A, Das DB, Davis DN, Dayoub I, Deb S, Demetriou IC, Devai F, Dilmaghani RS, Dini D, Drikakis D, Durkan C, Durodola J, Etebar K, Fenn P, Figueiredo A, Florou G, Freear S, Gabrys B, Galbraith GH, Gaskell PH, Gaura E, Ge ZQ, Ghafouri-Shiraz H, Ghavami M, Giannopoulos K, Gonzalez REP, Gracia AM, Grecos C, Guan L, Gulpinar N, Guo R, Guo Y, Hardalupas Y, He L, Herrero JR, Hicks BJ, Hines EL, Hodgson S, Horsfall A, Hosein P, Hu F, Hu H, Ijomah W, Ming J, James A, Jancovic P, Jhumka A, Kamareddine F, Kannan R, Karsligil ME, Katircioglu ST, Khalid A, Kokossis A, Kontis K, Kulekci MO, Laukaitis A, Leeson M, Limbachiya MC, Li L, Li L, Lin P, Ling WK, Macias Lopez EM, Lovas T, Luglio M, Mainardi S, Mahanti PK, Marinos I, Maropoulos P, Mativenga P, Mavrommatis Get al., 2010,

    WCE 2010 - World Congress on Engineering 2010: Preface

    , Wce 2010 World Congress on Engineering 2010, Vol: 2
  • 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
    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
  • 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.
  • 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
    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
    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
    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
    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.

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