Measurements of lubricant film thickness in the iso-viscous elastohydrodynamic regime

Gasni, Dedison; Ibrahim, M. K. Wan; Dwyer-Joyce, R. S.

doi:10.1016/j.triboint.2011.03.010

Cited by 22 publications

(17 citation statements)

References 14 publications

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“…This means that the central plateau region, associated with EHL, is completely absent and the resulting film shape is similar to a hydrodynamic wedge. This converging wedge has been observed by other authors [24,41] while in Gasni et al [36] experiments using ultrasonic reflections, the wedge was only prominent at relatively low speeds and the central film became flat at higher entrainment speeds.…”

Section: 1supporting

confidence: 82%

“…Optical interferometry [13,18,3], magnetic resistance [28], laser induced fluorescence (LIF) [29][30][31][32][33][34], Raman spectroscopy [35] and ultrasonic reflection [36] techniques have all been applied to measurement of thin films present in compliant lubricated tribological contacts with varying degree of success. However, each of these techniques has limitations and difficulties due to characteristics of lubricated elastomer contacts including:…”

Section: Introductionmentioning

confidence: 99%

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A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

Fowell

Myant

Spikes

et al. 2014

Tribology International

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A laser induced fluorescence technique was used to investigate the build-up of lubricant films in compliant contacts operating in the isoviscous elasto-hydrodynamic regime (I-EHL). The described technique utilises an optimised optical set-up with a relatively high signal-to-noise ratio and was shown to be able to produce film thickness maps of the complete contact area and measure a very wide span of thicknesses, from 50 nm to 100 m. Maps of film thickness were obtained over a range of entrainment speeds and loads for three different contact configurations and two elastomer materials, polydimethylsiloxane (PDMS) and a fluorocarbon rubber (FKM) which is typically used in rotary seal applications. In a model contact of a nominally smooth PDMS ball sliding on a glass flat, a crescent shaped area of reduced film thickness was observed towards the contact exit. In contrast to typical elasto-hydrodynamic contacts, no side-lobes of reduced film thickness were recorded, while the central film region exhibited a converging wedge shape. The elliptical contact of an FKM O-ring rolling on a glass flat showed a central region of flat film while areas of minimum film thickness were located near the contact edges either side of the centre. The highly conformal contact of relatively rough FKM O-ring sliding against a concave glass lens, a geometry more representative of that found in elastomeric seals, showed discrete regions of reduced film, corresponding to surface roughness asperities. With rising entrainment speed, some lift-off was observed, with surface roughness asperities appearing to be increasingly compressed. Measured films thicknesses were compared to existing theoretical predictions for I-EHL contacts and the level of agreement was found to be highly dependent on contact geometry and applied conditions.

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Section: 1supporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

Fowell

Myant

Spikes

et al. 2014

Tribology International

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“…This expression has already appeared in some references. [25][26][27] Comparisons between the exact values (equation 21) and the approximate values (equation 22) of the contact stiffness K l of two types of lubricant (oil and water) versus the thickness h are shown in Figure 10. It can be seen that there is a very good agreement between the approximate values and the exact values.…”

Section: Contact Stiffness Of the Lubricant Partmentioning

confidence: 99%

“…Gonzalez-Valadez et al 25 studied the elastic contact stiffness of the lubricated surface and separated the total stiffness into two components experimentally based on the reflection coefficient of ultrasound. Gasni et al 26 measured the contact stiffness between a sphere and a disk by using the reflection coefficient of ultrasound. Dwyer-Joyce et al 27 established a model between a sliding ball and a flat disc to separate the solid and lubricant contact stiffness from the ultrasonic experimental data, in which the solid part was predicted using a statistical model.…”

Section: Introductionmentioning

confidence: 99%

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Study on the normal contact stiffness of the fractal rough surface in mixed lubrication

Sun

Xiao

et al. 2018

Proceedings of the Institution of Mechanical Engineers, Part J:

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In this paper, an elastic interface model is developed to theoretically analyze the contact stiffness of a mixed lubrication surface where the solid and the lubricant contacts have to-be-determined contributions to the whole contact stiffness. The interfacial contact stiffness is composed of the solid contact stiffness and the lubricant contact stiffness, in which the two components are associated with each other via the equivalent thickness of lubricant. Based on the combination of two widely acknowledged ultrasonic measurement models and the Taylor approximating equation, the derivation of the lubricant contact stiffness is mostly affected by the material properties and the equivalent thickness of lubricant, and the equivalent thickness is determined by the solid contact properties under the mixed lubrication condition. Results of the mathematical analysis show that the contact stiffness of the mixed lubrication surface is larger than that of the dry rough surface due to the presence of lubricant. The interfacial contact stiffness of the mixed lubrication is obviously affected by the surface topography and the lubricant property. The proportions of contact stiffness contributed from the solid part and the lubricant part are varying with the contact area and the surface topography. Model predictions are compared with experiment results to verify the accuracy of proposed model. The analysis of the interfacial contact stiffness involved in mixed lubrication provides a theoretical basis for the performance prediction of machine tools, and might be useful to elucidate the contact properties by ultrasonic pulse probing in real engineering applications.

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The transition from Elasto‐Hydrodynamic to Mixed Regimes in Lubricated Friction of Soft Solid Surfaces

Dong

Moyle

et al. 2023

Advanced Materials

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Lubricated contacts in soft materials are common in various engineering and natural settings, such as tires, haptic applications, contact lenses, and the fabrication of soft electronic devices. Two major regimes are elasto‐hydrodynamic lubrication (EHL), in which solid surfaces are fully separated by a fluid film, and mixed lubrication (ML), in which there is partial solid‐to‐solid contact. The transition between these regimes governs the minimum sliding friction achievable and is thus very important. Generally, the transition from EHL to ML regimes is believed to occur when the thickness of the lubricant layer is comparable with the amplitude of surface roughness. Here, it is reported that in lubricated sliding experiments on smooth, soft, poly(dimethylsiloxane) substrates, the transition can occur when the thickness of the liquid layer is much larger than the height of the asperities. Direct visualization of the “contact” region shows that the transition corresponds to the formation of wave‐like surface wrinkles at the leading contact edge and associated instabilities at the trailing contact edge, which are believed to trigger the transition to the mixed regime. These results change the understanding of what governs the important EHL–ML transition in the lubricated sliding of soft solids.

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Measurements of lubricant film thickness in the iso-viscous elastohydrodynamic regime

Cited by 22 publications

References 14 publications

A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

Study on the normal contact stiffness of the fractal rough surface in mixed lubrication

The transition from Elasto‐Hydrodynamic to Mixed Regimes in Lubricated Friction of Soft Solid Surfaces

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