Pressure-Viscosity Coefficients of Liquid Lubricants

Lubricant viscosity is a key driver in both the tribological performance and energy efficiency of a lubricated contact. Elastohydrodynamic (EHD) lubrication produces very high pressures and shear rates, conditions hard to replicate using conventional rheometry. In situ rheological measurements within a typical contact are therefore important to investigate how a fluid behaves under such conditions. Molecular rotors provide such an opportunity to extract the local viscosity of a fluid under EHD lubrication. The validity of such an application is shown by comparing local viscosity measurements obtained using molecular rotors and fluorescence lifetime measurements, in a model EHD lubricant, with reference measurements using conventional rheometry techniques. The appropriateness of standard methods used in tribology for high-pressure rheometry (combining friction and film thickness measurements) has been verified when the flow of EHD lubricant is homogeneous and linear. A simple procedure for calibrating the fluorescence lifetime of molecular rotors at elevated pressure for viscosity measurements is proposed.

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“…7). The Barus equation deviates from measurements at high pressure [24]. However, the peak pressures used in this work are less than 0.5 GPa.…”

Section: Optically Accessible High-pressure Rheometrymentioning

confidence: 62%

Quantitative Viscosity Mapping Using Fluorescence Lifetime Measurements

2016

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“…The lubricant fluid used in these calculations is assumed to be compressible and its viscosity‐pressure behaviour is described by the Barus law Equation . However, according with Sargent et al, the application of this equation to pressures above 0.5 GPa can lead to serious errors.

η_{p} = η_{0} e^{αp},

where η p is the lubricant viscosity at pressure p and temperature θ .…”

Section: Methodsmentioning

confidence: 99%

Grooved surface texturing by electrical discharge machining (EDM) under different lubrication regimes

Vilhena

Ramalho

Cavaleiro

2017

Lubrication Science

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The aim of the present research work was to investigate the effectiveness of grooved surface texturing with a rhombic geometry under different lubrication regimes. Tribological investigation under unidirectional sliding was focused on the effect of texturing parameters including pattern area density on the coefficient of friction under different lubrication regimes, achieved by varying sliding speed and lubricant viscosity. Grooved patterns with different textured area densities were produced on steel samples by electrical discharge machining. Results of this investigation showed that under boundary lubrication, textures resist sliding thus resulting in increased friction. The largest improvement of friction reduction was observed under hydrodynamic lubrication, for low‐viscosity oil when using the textured disc with 21% pattern area density. The reduction of the coefficient of friction if compared with the untextured surface was of approximately 24%. Examination of the sliding surfaces has not shown any quantifiable wear for the contact conditions studied.

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“…Coefficients in Eqs. 1:8] and [9] were obtained using a similar procedure after adopting values for Op,OT recommended by Cameron (14). Constants in Eq.…”

Section: Comparison With Other Correlationsmentioning

confidence: 99%

“…These expressions accurately describe data for a variety of liquids up to about 69 MPa (10 ksi). Roelands, et al (8) and Sargent (9) have used more complicated functions to improve agreement with data at higher pressure.…”

mentioning

confidence: 97%