107 results found
Medina S, Dini D, Olver AV, et al., 2009, FAST COMPUTATION OF FRICTIONAL ENERGY DISSIPATION IN ROUGH CONTACTS UNDER PARTIAL SLIP, STLE/ASME 2008 International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 573-575
Hili J, Olver AV, Edwards S, et al., 2009, EXPERIMENTAL INVESTIGATION OF FILM THICKNESS BEHAVIOUR AT VERY HIGH SPEEDS, STLE/ASME 2008 International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 291-+
Fowell MT, Olver A, Spikes HA, et al., 2009, MODELLING OF MICRO TEXTURED BEARINGS WITH MASS-CONSERVING CAVITATION: A TWO DIMENSIONAL PROBLEM, STLE/ASME 2008 International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 343-+
Laine E, Olver AV, Lekstrom MF, et al., 2009, The Effect of a Friction Modifier Additive on Micropitting, TRIBOLOGY TRANSACTIONS, Vol: 52, Pages: 526-533, ISSN: 1040-2004
Reddyhoff T, Spikes HA, Olver AV, 2009, Improved temperature mapping of ehl contacts, Miami, FL, United states, 2008 STLE/ASME International Joint Tribology Conference, IJTC 2008, October 20, 2008 - October 22, 2008, Publisher: ASME, Pages: 265-267
An effective means of studying lubricant film rheology within EHL contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. This provides a way of directly measuring the rheology of lubricant films under true EHL conditions. Furthermore, temperature measurement itself provides a very effective means of testing and validating computer simulations. In the current work, the experimental approach initially developed by Sanborn and Winer [11 and then by Spikes and co-workers , has been advanced to include a high specification infrared (IR) camera and microscope. This is a similar approach to that taken by Yagi and Kyogoku . As well as 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. One additional advantage of instantaneous full field measurements is that the weak infrared optical interference caused by the film can be observed and can used to exactly locate the centre of the contact in the resulting temperature maps. These new possibilities have been used to investigate and compare the rheological properties and compression cooling effects exhibited by a PAO, a group II mineral oil, and a traction fluid. Copyright 2008 by ASME.
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.
Laine E, Olver AV, Beveridge TA, 2008, Effect of lubricants on micropitting and wear, 34th Leeds-Lyon Symposium on Tribology, Publisher: ELSEVIER SCI LTD, Pages: 1049-1055, ISSN: 0301-679X
Choo JW, Olver AV, Spikes HA, et al., 2008, Interaction of asperities on opposing surfaces in thin film, mixed elastohydrodynamic lubrication, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 130, ISSN: 0742-4787
Olver AV, Dini D, Lainé E, et al., 2007, Roughness and lubricant chemistry effects in micropitting, American Gear Manufacturers Association - Fall Technical Meeting of the American Gear Manufacturers Association 2007, AGMA, Pages: 151-160
Micropitting has been studied using a disc machine in which a central carburised steel test roller contacts three, harder, counter-rollers ("rings") with closely controlled roughness. We varied the roughness using different finishing techniques and investigated the effects of different oil base-stocks and additives, whilst keeping the viscosity approximately constant. We also developed a predictive model for the approximate analysis of rough-surface elastohydrodynamic lubrication based on the FFT approach of Hooke. Damage on the test rollers included dense micropitting and "micropitting erosion" in which tens of microns of the test surface were completely removed. This phenomenon is particularly damaging in gear teeth where it has the potential to destroy profile accuracy. It was found that anti-wear additives led to a high rate of micropitting erosion and that the effect correlated more or less inversely with simple sliding wear results. There were also appreciable effects from base-stock chemistry. The key parameter affecting the severity of damage seemed to be the near-surface shear stress amplitude arising from the evolved roughness; different chemistries led to the evolution of different roughness during initial running and thence to different contact stresses and different levels of damage. © AGMA 2007 - All rights reserved.
Olver AV, Dini D, 2007, Roughness in lubricated rolling contact: the dry contact limit, P I MECH ENG J-J ENG, Vol: 221, Pages: 787-791, ISSN: 1350-6501
A difficulty with the standard fast Fourier transform (FFT) perturbation model of roughness in lubricated rolling contacts is that it does not necessarily converge towards the elastic case as the film thickness is reduced; rather it leads to a situation in which all the roughness is completely flattened. This is rarely the case for real engineering surfaces.Here, it is shown that this difficulty can be avoided by carrying out a Fourier transform of the elastostatically flattened roughness and using the resulting (complex) amplitude as the low-film thickness limit of each Fourier component in the elastohydrodynamic lubrication (EHL) analysis.Results give a plausible convergence to the elastostatic solution, which is nevertheless consistent with the expected near-full-film EHL behaviour and which becomes identical to the earlier model for roughness that, statically, can be fully flattened. As expected, hydrodynamic action persists at the finest scale, even for very thin films.
Olver AV, Wilson D, Crofton PSJ, 2007, Investigation of service failures of steel music wire, Engineering Failure Analysis, Vol: 14, Pages: 1224-1232, ISSN: 1350-6307
Fowell M, Olver AV, Gosman AD, et al., 2007, Entrainment and inlet suction: Two mechanisms of hydrodynamic lubrication in textured bearings, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 129, Pages: 336-347, ISSN: 0742-4787
Choo JW, Olver AV, Spikes HA, 2007, The influence of transverse roughness in thin film, mixed elastohydrodynamic lubrication, TRIBOLOGY INTERNATIONAL, Vol: 40, Pages: 220-232, ISSN: 0301-679X
Medina S, Olver AV, Shollock BA, 2006, Rolling contact damage accumulation in two contrasting copper alloys, WEAR, Vol: 260, Pages: 794-802, ISSN: 0043-1648
Choo JW, Olver AV, Spikes HA, et al., 2006, The influence of longitudinal roughness in thin-film, mixed elastohydrodynamic lubrication, TRIBOLOGY TRANSACTIONS, Vol: 49, Pages: 248-259, ISSN: 1040-2004
Fowell MT, Olver AV, Pegg IG, et al., 2006, Two mechanisms of hydrodynamic lubrication in textured bearings
There is currently great interest in the use of textured bearings, where many tiny micropockets are incorporated in one of the bearing surfaces. Such texturing has been found to enhance load support and to reduce hydrodynamic friction in low load conditions, when the two surfaces have very low or zero convergence ratio, i.e. are essentially parallel. It is not immediately clear from hydrodynamic lubrication theory how a bearing with parallel surfaces and internal pockets can entrain any lubricant to form a hydrodynamic film and thus support load. However in a recent technical note the authors have shown that the occurrence of cavitation within micropockets results in suction of lubricant into the bearing, because the pressure inside the pockets is less than the surrounding, atmospheric pressure . For parallel or very low convergence ratio bearings, this supply process replaces fluid entrainment as the main mechanism by which lubricant is drawn into the contact. In previous work this suction mechanism was demonstrated using a simple analytical approach for a 1D parallel bearing having a single pocket. The current paper extends this analytical method to convergent bearings having a single pocket and then applies a numerical solution of the first order Reynolds equation to solve for flow in multi-pocketed bearings. This enables the contribution of fluid suction on the load support of low convergence ratio bearings to be investigated. Copyright © 2006 by ASME.
Olver AV, Fowell MT, Spikes HA, et al., 2006, 'Inlet suction', a load support mechanism in non-convergent, pocketed, hydrodynamic bearings, Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Vol: 220, Pages: 105-108, ISSN: 1350-6501
Olver AV, Glovnea R, Choo JW, et al., 2005, Elastohydrodynamic lubrication of multiple periodic ridges, Pages: 519-520
The lubrication of rolling contacts in which one surface has a roughness consisting of periodic transverse or longitudinal ridges has been widely investigated, both theoretically and experimentally. Results of these investigations now permit a substantially complete picture to emerge in which it is possible to characterize the state of lubrication by evaluating and comparing the (minimum) film thickness near the crests of the roughness to the corresponding thickness in the valleys. Crest and valley film thickness were studied over a wide range of non-dimensional speed. Two lubricants were used, both Group I mineral oils with viscosities of 22 and 453 cp and alpha values of 19.8 and 20.4/GPa. The elastostatic and asperity values agreed well with the corresponding measurements but both crest and valley measured film thicknesses exceeded the predictions of equation 4 for higher speeds. This is an abstract of a paper presented at the World Tribology Congress III (Washington, DC 9/12-16/2005).
Glovnea RP, Olver AV, Spikes HA, 2005, Experimental investigation of the effect of speed and load on film thickness in elastohydrodynamic contact, TRIBOLOGY TRANSACTIONS, Vol: 48, Pages: 328-333, ISSN: 1040-2004
Morales-Espejel GE, Dumont ML, Lugt PM, et al., 2005, A limiting solution for the dependence of film thickness on velocity in EHL contacts with very thin films, TRIBOLOGY TRANSACTIONS, Vol: 48, Pages: 317-324, ISSN: 1040-2004
Glovnea RP, Olver AV, Spikes HA, 2005, Lubrication of rough surfaces by a boundary film-forming viscosity modifier additive, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 127, Pages: 223-229, ISSN: 0742-4787
Glovnea RP, Olver AV, Spikes A V, 2005, Effectiveness of boundary lubricant additives on some coated surfaces, London, Life Cycle Tribology, Proceedings of 31st Leeds-Lyon Symposium, Leeds 2004, Publisher: Elsevier, Pages: 135-143
Olver AV, 2005, The mechanism of rolling contact fatigue: an update, Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, Vol: 219, Pages: 313-330, ISSN: 1350-6501
Olver AV, Tiew LK, Medina S, et al., 2004, Direct observations of a micropit in an elastohydrodynamic contact, WEAR, Vol: 256, Pages: 168-175, ISSN: 0043-1648
Benyajati C, Olver AV, Hamer CJ, 2004, An experimental study of micropitting, using a new miniature test-rig, Amsterdam, 30th leeds-lyon symposium on tribology, Lyon, France, 2 - 5 September 2003, Publisher: Elsevier Science Bv, Pages: 601-610
Benyajati C, Olver AV, 2004, The effect of a ZnDTP anti-wear additive on micropitting resistance of carburised steel rollers, AGMA Technical Paper, Alexandria, VA, Publisher: American Gear Manufacturers Association, 04FTM06
Spikes HA, Olver AV, 2004, Basics of mixed lubrication, Lubrication Science, Vol: 16, Pages: 3-28, ISSN: 0954-0075
Medina S, Olver AV, Shollock B, 2004, Development of rolling contact damage in two bronze alloys, Amsterdam, 30th leeds-lyon symposium on tribology, Lyon, France, 2 - 5 September 2003, Publisher: Elsevier Science Bv, Pages: 619-627
Contaldi GF, Olver AV, 2003, Rotary pump, 6666671
Glovnea RP, Forrest AK, Olver AV, et al., 2003, Measurement of sub-nanometer lubricant films using ultra-thin film interferometry, TRIBOLOGY LETTERS, Vol: 15, Pages: 217-230, ISSN: 1023-8883
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