Imperial College London

Dr Tom Reddyhoff

Faculty of EngineeringDepartment of Mechanical Engineering

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 3840t.reddyhoff Website

 
 
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Location

 

670City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

88 results found

Ku ISY, Chong WWF, Reddyhoff T, Rahnejat Het al., 2015, Frictional characteristics of molecular length ultra-thin boundary adsorbed films, Meccanica, Vol: 50, Pages: 1915-1922, ISSN: 1572-9648

The paper presents measurements of friction of any ultra-thin film entrained into the contact of a pair of very smooth specimen subjected to entrainment in a converging micro-wedge of a special-purpose micro-tribometer. An ultra-thin film is expected to form at the boundary solids through adsorption of boundary active molecules. Fluids with linear and branched molecules are used in the investigation. It is found that the frictional characteristics of these films can be adequately described through use of Eyring thermal activation energy and a potential energy barrier to sustain conjunctional sliding motion. The combined experimental measurement and the simple activation energy approach shows that the thin molecular adsorbed films act like hydro Langmuir–Blodgett layers, the formation and frictional characteristics of which are affected by the competing mechanisms of adsorption, forced molecular re-ordering and discrete-fashion drainage through the contact by the solvation effect. This process is a complex function of the contact sliding velocity as well as a defined Eyring activation density (packing density of the molecules within the conjunction). It is shown that the contribution of solvation to friction is in the form of energy expended to eject layers of lubricant out of the contact, which unlike the case of micro-scale hydrodynamic films, is not a function of the sliding velocity.

Journal article

Reddyhoff T, Dobre O, Le Rouzic J, Gotzen N-A, Parton H, Dini Det al., 2015, Friction Induced Vibration in Windscreen Wiper Contacts, Journal of Vibration and Acoustics-Transactions of the ASME, Vol: 137, ISSN: 1048-9002

This research is aimed at understanding the mechanisms that give rise to friction induced noise in automotive windscreen wipers, with a focus on frequencies between 500 and 3500 Hz. To study this phenomenon, experimental friction, sound, and high-speed video measurements are combined with finite element modeling of a rubber wiper/glass contact. In agreement with previous research, simultaneous sound and friction measurements showed that wiper noise in this frequency range results from the negative damping effect caused by the dependence of friction on speed in the mixed lubrication regime. Furthermore, during sliding, the friction induced noise recorded by the microphone occurred in one of two frequency ranges (close to 1000 Hz and between 2000 and 2500 Hz). These coincided closely with the eigen-frequencies of first two bending modes, predicted by finite element modeling. Experimental observations also showed the wiper to be oscillating backward and forward without any torsional motion and that the thickness of the glass had no effect on the emitted noise. These observations highlight how friction induced noise—although caused by conditions within contact—has characteristics that are determined by the structure of the excited component. A number of additional findings are made. Most importantly, both experiment and finite element modeling showed that the presence of water in contact with the wiper modulates the frequency and amplitude of the emitted noise by effectively adding mass to the vibrating system. While this is occurring, Faraday-like standing waves are observed in the water. In addition to this, friction induced vibration is shown only to occur for glass surfaces with intermediate surface energies, which is possibly due to high contact angles preventing water reaching the contact. Based on the understanding gained, a number of suggestions are made regarding means of reducing windscreen wiper noise.

Journal article

Medina S, Fowell MT, Vladescu S-C, Reddyhoff T, Pegg I, Olver AV, Dini Det al., 2015, Transient effects in lubricated textured bearings, Proceedings of the Institution of Mechanical Engineers Part J - Journal of Engineering Tribology, Vol: 229, Pages: 523-537, ISSN: 1350-6501

Journal article

Ma G, Wang L, Gao H, Zhang J, Reddyhoff Tet al., 2015, The friction coefficient evolution of a TiN coated contact during sliding wear, Applied Surface Science, Vol: 345, Pages: 109-115, ISSN: 0169-4332

Journal article

Liang H, Guo D, Reddyhoff T, Spikes H, Luo Jet al., 2015, Influence of thermal effects on elastohydrodynamic (EHD) lubrication behavior at high speeds, SCIENCE CHINA-TECHNOLOGICAL SCIENCES, Vol: 58, Pages: 551-558, ISSN: 1674-7321

Journal article

Vladescu S-C, Olver AV, Pegg IG, Reddyhoff Tet al., 2015, The effects of surface texture in reciprocating contacts - An experimental study, TRIBOLOGY INTERNATIONAL, Vol: 82, Pages: 28-42, ISSN: 0301-679X

Journal article

Putignano C, Le Rouzic J, Reddyhoff T, Carbone G, Dini Det al., 2014, A theoretical and experimental study of viscoelastic rolling contacts incorporating thermal effects, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 228, Pages: 1112-1121, ISSN: 1350-6501

Journal article

Le Rouzic J, Reddyhoff T, 2014, Spatially Resolved Triboemission Measurements, Tribology Letters, Vol: 55, Pages: 245-252, ISSN: 1573-2711

Journal article

Hernandez Battez A, Viesca JL, Gonzalez R, Garcia A, Reddyhoff T, Higuera-Garrido Aet al., 2014, Effect of Shear Rate, Temperature, and Particle Concentration on the Rheological Properties of ZnO and ZrO2 Nanofluids, TRIBOLOGY TRANSACTIONS, Vol: 57, Pages: 489-495, ISSN: 1040-2004

Journal article

Quinchia LA, Delgado MA, Reddyhoff T, Gallegos C, Spikes HAet al., 2014, Tribological studies of potential vegetable oil-based lubricants containing environmentally friendly viscosity modifiers, TRIBOLOGY INTERNATIONAL, Vol: 69, Pages: 110-117, ISSN: 0301-679X

Journal article

Yang S, Reddyhoff T, Spikes H, 2013, Influence of Lubricant Properties on ARKL Temperature Rise and Transmission Efficiency, TRIBOLOGY TRANSACTIONS, Vol: 56, Pages: 1119-1136, ISSN: 1040-2004

Journal article

Moorhouse BS, Reddyhoff T, Ward-Close M, Ryan MP, Shollock BAet al., 2013, Formation of wear resistant coatings on Ti-6Al-4V by calciothermic reduction, SURFACE & COATINGS TECHNOLOGY, Vol: 221, Pages: 214-221, ISSN: 0257-8972

Journal article

Le Rouzic J, Reddyhoff, Tom, 2013, Development of Infrared Microscopy for Measuring Asperity Contact Temperatures, Journal of Tribology, Vol: 135, Pages: 021504-021504, ISSN: 0742-4787

Journal article

Putignano C, Reddyhoff T, Dini D, Carbone Get al., 2013, Viscoelastic contact mechanics: Numerical simulations with experimental validation, Pages: 1511-1514

Conference paper

Guégan J, Kadiric A, Reddyhoff T, Morales-Espejel G, Spikes Het al., 2013, Friction and lubrication of textured surfaces in elasto-hydrodynamic contacts, Pages: 1659-1661

Conference paper

Hartinger M, Reddyhoff T, 2013, CFD modeling and infrared measurement of an EHL line contact, Pages: 999-1002

Conference paper

Leong JY, Reddyhoff T, Sinha SK, Holmes AS, Spikes HAet al., 2013, Hydrodynamic Friction Reduction in a MAC-Hexadecane Lubricated MEMS Contact, TRIBOLOGY LETTERS, Vol: 49, Pages: 217-225, ISSN: 1023-8883

Journal article

Leong JY, Reddyhoff T, Sinha SK, Holmes AS, Spikes HAet al., 2013, Hydrodynamic friction reduction in a MAC-hexadecane lubricated MEMS contact, Tribology Letters, Vol: 49, Pages: 217-225, ISSN: 1023-8883

Recent research has shown that hydrodynamic lubrication is an effective means of reducing friction in high sliding micro-electromechanical systems (MEMS). At high speeds, however, such lubrication can lead to increased friction due to viscous drag. This article describes a series of hydrodynamic tests on a silicon MEMS contact lubricated with a blend of hexadecane and a multiplyalkylated cyclopentane (MAC). Results show that the presence of the MAC reduces hydrodynamic friction compared with neat hexadecane. Such behaviour is contrary to conventional hydrodynamic theory, since the viscosity of the MAC - a mixture of di and tri(2 octyldodecyl)cyclopentane - is significantly higher than that of neat hexadecane. This effect increases with MAC concentration up to an optimum value of 3 wt%, where the hydrodynamic friction coefficient at 15,000 rpm is reduced from 0.5 to 0.3. Above this concentration, friction begins to rise due to the overriding effect of increasing viscosity. The viscosity of the blended lubricant increased monotonically with MAC concentration, when measured using both a Stabinger and an ultrahigh shear viscometer. In addition to this, no reduction in friction was observed when a squalane-hexadecane blend of equal viscosity was tested. This suggests that some property of the MAC-hexadecane lubricant, other than its viscosity, is influencing hydrodynamic lubrication. A tentative explanation for this behaviour is that the MAC induces the liquid to slip, rather than shear, close to the silicon surfaces. This hypothesis is supported by the fact that the friction reducing ability of the MAC blend was inhibited by the inclusion of octade-cylamine - a substance known to form films on silicon surfaces. Furthermore, the MAC reduces friction in the mixed regime, in a manner suggesting that the formation of a viscous boundary layer. This unusual behaviour may have useful implications for reducing hydrodynamic friction in liquidlubricated MEMS devices. © Sprin

Journal article

Putignano D, 2013, Experimental investigation of viscoelastic rolling contacts: A comparison with theory, Tribology Letters, Vol: 51, Pages: 105-113

Journal article

Ku ISY, Reddyhoff T, Wayte R, Choo JH, Holmes AS, Spikes HAet al., 2012, Lubrication of microelectromechanical devices using liquids of different viscosities, Journal of Tribology, Vol: 134, ISSN: 0742-4787

Lubrication of contacting and sliding surfaces in MEMS (microelectromechanical systems) is particularly challenging because of the predominance of surface forces at the microscale. The current paper explores the possibility of using liquid lubrication in this application. Measurements of friction and lubricant film thickness have been made for liquid lubricants of different viscosities, including low viscosity silicone oil, hexadecane, squalane, and water. Testing was carried out using a newly developed MEMS tribometer in which a rotating silicon disk is loaded against a stationary silicon disk. Two different test setups were used: one where both disks are flat, and the other where the stationary disk is structured as in a thrust pad bearing. In all tests the disks were fully submerged in the lubricant. With the flat-on-patterned disk combination, the variation of friction with rotation speed was found to follow classical Stribeck curves for all the lubricants tested. The friction at high speeds also decreased with increasing normal load, in accordance with hydrodynamic lubrication theory. For the least viscous lubricants, it was found that the hydrodynamic friction coefficients remained relatively low even at higher speeds. In particular, for water the friction coefficient for water was around 0.1 at 10,000 rpm. However, boundary friction was found to be unacceptably high at low speeds where there was insufficient lubricant entrainment. The experimental results have been compared with a finite difference solution of Reynolds equation and reasonable agreement is seen between theory and experiment. The results indicate that liquid lubrication is potentially an effective means of lubricating MEMS components with high levels of sliding.

Journal article

Ku ISY, Reddyhoff T, Wayte R, Choo JH, Holmes AS, Spikes HAet al., 2012, Lubrication of microelectromechanical devices using liquids of different viscosities, Journal of Tribology, Vol: 134, ISSN: 0742-4787

Lubrication of contacting and sliding surfaces in MEMS (microelectromechanical systems) is particularly challenging because of the predominance of surface forces at the microscale. The current paper explores the possibility of using liquid lubrication in this application. Measurements of friction and lubricant film thickness have been made for liquid lubricants of different viscosities, including low viscosity silicone oil, hexadecane, squalane, and water. Testing was carried out using a newly developed MEMS tribometer in which a rotating silicon disk is loaded against a stationary silicon disk. Two different test setups were used: one where both disks are flat, and the other where the stationary disk is structured as in a thrust pad bearing. In all tests the disks were fully submerged in the lubricant. With the flat-on-patterned disk combination, the variation of friction with rotation speed was found to follow classical Stribeck curves for all the lubricants tested. The friction at high speeds also decreased with increasing normal load, in accordance with hydrodynamic lubrication theory. For the least viscous lubricants, it was found that the hydrodynamic friction coefficients remained relatively low even at higher speeds. In particular, for water the friction coefficient for water was around 0.1 at 10,000 rpm. However, boundary friction was found to be unacceptably high at low speeds where there was insufficient lubricant entrainment. The experimental results have been compared with a finite difference solution of Reynolds equation and reasonable agreement is seen between theory and experiment. The results indicate that liquid lubrication is potentially an effective means of lubricating MEMS components with high levels of sliding. 2012 American Society of Mechanical Engineers.

Journal article

Ku ISY, Reddyhoff T, Holmes AS, Spikes HAet al., 2011, Wear of silicon surfaces in MEMS, Wear, Vol: 271, Pages: 1050-8, ISSN: 0043-1648

High levels of friction and wear are problems which currently limit the development of sliding micro-electro-mechanical systems (MEMS) - devices which would otherwise offer significant technological advancement. The current paper focuses on the wear of MEMS silicon surfaces, and specifically looks at the effect of environment and surface preparation on wear behaviour. Included in the study is the assessment of two self-replenishing lubrication mechanisms; namely liquid and vapour phase lubrication. All tests were carried out using a tribometer which operated and measured friction and wear under conditions representative of MEMS.It is shown that friction and wear behaviour depend strongly on subtle changes of the silicon surfaces prior to testing. Greatest wear was measured when the surfaces were tested immediately after plasma-cleaning, while subsequent exposure to ambient air for 15h reduced wear to negligible levels. Exposure of plasma-cleaned surfaces to water-saturated argon prior to testing prevented wear to a limited extent. Based on this, and TOF-SIMS analysis, it is suggested that the observed wear reduction after exposure to air is caused by tiny amounts of lubricious long chain hydrocarbon contaminants present in ambient air.Tests carried out with the specimens submerged in a liquid bath show that the presence of liquid water reduces friction and wear, but only if specimens have been plasma-cleaned beforehand. This behaviour is tentatively attributed to the hydrophilic nature of plasma treated silicon, reducing the corrosive action of water. When hexadecane or 1-pentanol was used as a liquid lubricant, friction was minimal, and wear was undetectable under all sliding conditions. This was the case even though the contact operated in the mixed lubrication regime, suggesting a boundary film is formed on the silicon surfaces by both of these organic liquids.Results of tests carried out with the lubricant being supplied in the form of pentanol vapour also showe

Journal article

Dwyer-Joyce RS, Reddyhoff T, Zhu J, 2011, Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication, Journal of Tribology, Vol: 133, ISSN: 0742-4787

The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiff ness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 m, and the proportion of the load supported by asperity contact varied from 50% to 0%.

Journal article

Reddyhoff T, Ku ISY, Holmes AS, Spikes HAet al., 2011, Friction Modifier Behaviour in Lubricated MEMS Devices, Tribology Letters, Vol: 41, Pages: 239-46, ISSN: 1023-8883

Low viscosity fluids could provide reliable lubrication for certain microelectromechanical system's (MEMS) applications where high-sliding speeds and/or high sliding distances occur. However, while the use of low viscosity fluids leads to reduced hydrodynamic friction, high boundary friction can be a significant issue at low entrainment speeds. This article describes a series of tests of low viscosity fluids, blended with a friction modifier additive so as to provide a combination of both low hydrodynamic and low boundary friction at MEMS scales. The low viscosity fluids tested were hexadecane, low viscosity silicone oil, toluene and water. With the exception of water, the addition of the organic friction modifier octadecylamine to all these lubricating fluids produced a significant reduction in boundary friction. For a MEMS contact lubricated with silicone oil for instance, boundary friction was reduced from 0.5 to close to 0.05. The presence of the amine dissolved in the toluene had the effect of reducing boundary friction from 0.75 to 0.55; this was further reduced to 0.25 after the specimens had been immersed in the toluene-additive blend for 48 h. A water-soluble additive, diethylamine, was added to de-ionized water, at 0.1% by weight concentration. Although an initial reduction in boundary friction was observed (0.45-0.25), under these conditions the rapid onset of severe wear negated these effects. It is suggested that corrosion of silicon by water, followed by abrasion, is the cause of this accelerated wear.

Journal article

Ingram M, Reddyhoff T, Spikes HA, 2011, Thermal behaviour of a slipping wet clutch contact, Tribology Letters, Vol: 41, Pages: 23-32, ISSN: 1023-8883

Wet clutches are used in automatic transmissions to enable gear changes and also to reduce energy loss in the torque converter. These friction devices are susceptible to stick-slip effects, which result in the vehicle giving an unsteady ride. Stick-slip effects can be avoided by ensuring the wet clutch and lubricant combination produces a friction coefficient that increases with sliding speed. Although wet clutches have been studied throughout the industry for many decades, the mechanism of the generated friction is still not fully understood. It is known that, because of the fibrous nature and thus very large roughness of friction material, the overall contact between clutch plates actually consists of many small, independent, contact units, which are the sites of the generated friction. Some authors have suggested that a temperature rise due to friction either at these contact units or of the overall clutch plate may be important in controlling friction behaviour. In this study, the flash temperatures at the contact units formed in the wet clutch contact have been measured using an infrared camera. Three friction materials have been tested. It was found that measured flash temperature in a pure sliding system similar to that present in a slipping clutch remain well below 5 C, and are therefore unlikely to play a major role in the observed friction-speed dependency of slipping wet clutches at speeds below 2 m/s.

Journal article

Dwyer-Joyce RS, Reddyhoff T, Zhu J, 2011, Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication, Journal of Tribology, Vol: 133, ISSN: 0742-4787

The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 ms, the film thickness was found to vary from 0.01 to 0.8 m, and the proportion of the load supported by asperity contact varied from 50% to 0%. 2011 American Society of Mechanical Engineers.

Journal article

Ku ISY, Reddyhoff T, Holmes AS, Spikes HAet al., 2011, Wear of silicon surfaces in MEMS, Wear, Vol: 271, Pages: 1050-1058, ISSN: 0043-1648

High levels of friction and wear are problems which currently limit the development of sliding micro-electro-mechanical systems (MEMS) - devices which would otherwise offer significant technological advancement. The current paper focuses on the wear of MEMS silicon surfaces, and specifically looks at the effect of environment and surface preparation on wear behaviour. Included in the study is the assessment of two self-replenishing lubrication mechanisms; namely liquid and vapour phase lubrication. All tests were carried out using a tribometer which operated and measured friction and wear under conditions representative of MEMS.It is shown that friction and wear behaviour depend strongly on subtle changes of the silicon surfaces prior to testing. Greatest wear was measured when the surfaces were tested immediately after plasma-cleaning, while subsequent exposure to ambient air for 15. h reduced wear to negligible levels. Exposure of plasma-cleaned surfaces to water-saturated argon prior to testing prevented wear to a limited extent. Based on this, and TOF-SIMS analysis, it is suggested that the observed wear reduction after exposure to air is caused by tiny amounts of lubricious long chain hydrocarbon contaminants present in ambient air.Tests carried out with the specimens submerged in a liquid bath show that the presence of liquid water reduces friction and wear, but only if specimens have been plasma-cleaned beforehand. This behaviour is tentatively attributed to the hydrophilic nature of plasma treated silicon, reducing the corrosive action of water. When hexadecane or 1-pentanol was used as a liquid lubricant, friction was minimal, and wear was undetectable under all sliding conditions. This was the case even though the contact operated in the mixed lubrication regime, suggesting a boundary film is formed on the silicon surfaces by both of these organic liquids.Results of tests carried out with the lubricant being supplied in the form of pentanol vapour also sho

Journal article

Reddyhoff T, Ku ISY, Holmes AS, Spikes HAet al., 2011, Friction modifier behaviour in lubricated MEMS devices, Tribology Letters, Vol: 41, Pages: 239-246, ISSN: 1023-8883

Low viscosity fluids could provide reliable lubrication for certain microelectromechanical system's (MEMS) applications where high-sliding speeds and/or high sliding distances occur. However, while the use of low viscosity fluids leads to reduced hydrodynamic friction, high boundary friction can be a significant issue at low entrainment speeds. This article describes a series of tests of low viscosity fluids, blended with a friction modifier additive so as to provide a combination of both low hydrodynamic and low boundary friction at MEMS scales. The low viscosity fluids tested were hexadecane, low viscosity silicone oil, toluene and water. With the exception of water, the addition of the organic friction modifier octadecylamine to all these lubricating fluids produced a significant reduction in boundary friction. For a MEMS contact lubricated with silicone oil for instance, boundary friction was reduced from 0.5 to close to 0.05. The presence of the amine dissolved in the toluene had the effect of reducing boundary friction from 0.75 to 0.55; this was further reduced to 0.25 after the specimens had been immersed in the toluene-additive blend for 48 h. A water-soluble additive, diethylamine, was added to de-ionized water, at 0.1% by weight concentration. Although an initial reduction in boundary friction was observed (0.45-0.25), under these conditions the rapid onset of severe wear negated these effects. It is suggested that corrosion of silicon by water, followed by abrasion, is the cause of this accelerated wear. 2010 Springer Science+Business Media, LLC.

Journal article

Ingram M, Reddyhoff T, Spikes HA, 2011, Thermal behaviour of a slipping wet clutch contact, Tribology Letters, Vol: 41, Pages: 23-32, ISSN: 1023-8883

Wet clutches are used in automatic transmissions to enable gear changes and also to reduce energy loss in the torque converter. These friction devices are susceptible to stick-slip effects, which result in the vehicle giving an unsteady ride. Stick-slip effects can be avoided by ensuring the wet clutch and lubricant combination produces a friction coefficient that increases with sliding speed. Although wet clutches have been studied throughout the industry for many decades, the mechanism of the generated friction is still not fully understood. It is known that, because of the fibrous nature and thus very large roughness of friction material, the overall contact between clutch plates actually consists of many small, independent, contact units, which are the sites of the generated friction. Some authors have suggested that a temperature rise due to friction either at these contact units or of the overall clutch plate may be important in controlling friction behaviour. In this study, the flash temperatures at the contact units formed in the wet clutch contact have been measured using an infrared camera. Three friction materials have been tested. It was found that measured flash temperature in a pure sliding system similar to that present in a slipping clutch remain well below 5 C, and are therefore unlikely to play a major role in the observed friction-speed dependency of slipping wet clutches at speeds below 2 m/s. 2010 Springer Science+Business Media, LLC.

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

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