Publications
472 results found
Spikes HA, 2010, Fourth World Tribology Conference, LUBRICATION SCIENCE, Vol: 22, Pages: 415-416, ISSN: 0954-0075
Myant C, Fowell M, Spikes HA, et al., 2010, An Investigation of Lubricant Film Thickness in Sliding Compliant Contacts, TRIBOLOGY & LUBRICATION TECHNOLOGY, Vol: 66, Pages: 46-+, ISSN: 1545-858X
- Author Web Link
- Cite
- Citations: 1
Smeeth M, Spikes H, Gunsel S, 2010, Boundary Film Formation by Viscosity Index Improvers, TRIBOLOGY & LUBRICATION TECHNOLOGY, Vol: 66, Pages: 54-+, ISSN: 1545-858X
- Author Web Link
- Cite
- Citations: 2
Myant C, Fowell M, Spikes HA, et al., 2010, An Investigation of Lubricant Film Thickness in Sliding Compliant Contacts, Tribology Transactions, Vol: 53, Pages: 684-694, ISSN: 1547-397X
Holtzinger J, Green JH, Lamb GD, et 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.
Hoshino K, Yagishita K, Tagawa K, et 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.
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.
Reddyhoff T, Choo JH, Spikes HA, et 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.
Ingram M, Spikes H, Noles J, et al., 2010, Contact properties of a wet clutch friction material, TRIBOLOGY INTERNATIONAL, Vol: 43, Pages: 815-821, ISSN: 0301-679X
- Author Web Link
- Cite
- Citations: 37
Ioannides E, Spikes H, Brajdic-Mitidieri P, et al., 2010, Sliding bearing with improved surface topography, US7682081B2
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
- Author Web Link
- Cite
- Citations: 60
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
- Author Web Link
- Open Access Link
- Cite
- Citations: 44
Viesca JL, Battez AH, Gonzalez R, et 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.
Ku ISY, Reddyhoff T, Choo JH, et 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.
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.
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
Andablo-Reyes E, De Vicente J, Hidalgo-Alvarez R, et 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.
Vengudusamy B, Spikes HA, Mufti RA, et al., 2009, Comparison of friction properties of DLC coatings in DLC/DLC contacts, Pages: 347-349
- Cite
- Citations: 1
Reddyhoff T, Underwood RJ, Nikas GK, et 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).
Ingram M, Spikes H, Noles J, et 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).
Ingram M, Spikes H, Noles J, et 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.
Holtzinger J, Green J, Lamb G, et 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.
Myant C, Fowell M, Stokes J, et 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).
Benedet J, Green J, Lamb G, et 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).
Reddyhoff T, Ku ISY, Choo JH, et 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).
Nakano K, Reddyhoff T, Cann P, et 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).
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
Miklozic KT, Forbus TR, Spikes HA, 2009, Performance of Friction Modifiers on ZDDP-Generated Surfaces, TRIBOLOGY & LUBRICATION TECHNOLOGY, Vol: 65, Pages: 40-+, ISSN: 1545-858X
- Author Web Link
- Cite
- Citations: 2
Ku ISY, Reddyhoff T, Choo JH, et al., 2009, Lubrication performance of liquids of different viscosities in MEMS devices, Lake Buena Vista, FL, United states, Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2009, May 17, 2009 - May 21, 2009, Publisher: Society of Tribologists and Lubrication Engineers, Pages: 178-180
Reddyhoff T, Spikes HA, Olver AV, 2009, Compression heating and cooling in elastohydrodynamic contacts, Tribology Letters, Vol: 36, Pages: 69-80, ISSN: 1023-8883
In this study, the infrared temperature mapping technique, originally developed by Sanborn and Winer (Trans ASME J Tribol 93:262-271, 1971) and extended by Spikes et al. (Tribol Lett 17(3):593-605, 2004), has been made more sensitive and used to study the temperature rise of elastohydrodynamic contacts in pure rolling. Under such conditions lubricant shear heating within the contact is considered negligible and this allows temperature changes due to lubricant compression to be investigated. Pure rolling surface temperature distributions have been obtained for contacts lubricated with a range of lubricants, included a group I, and group II mineral oil, a polyalphaolefin (group IV), the traction fluid Santotrac 50 and 5P4E, a five-ring polyphenyl-ether. Resulting maps show the temperature rise in the contact increases in the inlet due to compression heating and then decreases and in most cases becomes negative in the exit region due to the effect of decompression. Temperature changes increase with entrainment speed but in the current tests are always very small, and less than 1 C. Contact temperature rises from compression were compared to those from sliding contacts (where a slide-roll ratio of 0.5 was applied). Here the contribution to the contact temperature from compression is shown to decrease dramatically with entrainment speed. The lubricant 5P4E is found to behave differently from other lubricants tested in that it showed a peak in temperature at the outlet. This effect becomes more pronounced with increasing speed, and has tentatively been attributed to a phase change in the exit region. Using moving heat source theory, the measured temperature distributions have been converted to maps showing rate of heat input into each surface and the latter compared with theory. Qualitative agreement between theory and experiment is found, and a more accurate theoretical comparison is the subject of ongoing study. 2009 Springer Science+Business Media, LLC.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.