An Experimental Verification of the Significance of the Reciprocal Asymptotic Isoviscous Pressure for EHD Lubricants

Abstract

The classical elastohydrodynamic film thickness solution which assumes a purely exponential variation of viscosity with pressure requires a pressure-viscosity coefficient. In general, liquid lubricant viscosity varies with pressure such that the local pressure-viscosity coefficient is a function of pressure, making the determination of the pertinent parameter for film thickness dqficult. Blok proposed a reciprocal asymptotic isoviscous pressure a* as a replacement for the initial pressure viscosity coefficient ao, based on the Weibull pressure transformation. The pressure-viscosity characteristics of seven liquid lubricants were measured with a falling body viscometer to pressure of 0.76 GPa and a0 and a* were calculated. Viscosity and glass transition results were applied to a model in current usage. The EHD film thickness was measured using interferometry supported by the measurement of the refractive index at elevated pressure. The reciprocal asymptotic isoviscous pressure was found to be more correct as a film thickness parameter than was the initial pressure viscosity coefficient.

On the relevance of analytical film thickness EHD equations for isothermal point contacts: Qualitative or quantitative predictions?

“…In their expressions they preferred to consider α*, the reciprocal asymptotic isoviscous pressure as proposed by Blok [21], instead of the classical secant pressure-viscosity coefficient based on an exponential dependence, i.e., on the so-called Barus law. Interestingly, the use of α* some decades later has confirmed [22,3], by comparison with experiments, that this parameter was really relevant to predict film thickness. Following this agreement, the reciprocal asymptotic isoviscous pressure was used to calculate film thickness from the analytical expressions.…”

Deformation Behavior of Thin Lubricant Films at Elevated Pressure.

“…15 W/m°C and pC=1.85 MJ/m 3 °C, of Richmond, et al [54] and the rheological properties of Yasutomi, et al [ 18] were used. Refractive index was measured in a high pressure refractometer described by Bair [13]. In addition, the properties of this material have a great sensitivity to…”

“…Laboratory high-pressure viscometers can operate to 1 GPa and above and are most often of the falling body type which is described in [13]. Falling body viscometers apply a shear stress typically less than 100 Pa so that the liquid response should be Newtonian; although the rate of shear may exceed 10 4 s-1 for low viscosity.…”

“…In the following discussion, then, only the first type of mechanical shear band is considered. 75 An optical EHD simulator was employed in this work and is described in Ref [13]. The contact consisted of a 25.4 mm radius sapphire disc running over a 7.6 mm radius steel roller.…”

An Analytical Approach for Prediction of Elastohydrodynamic Friction with Inlet Shear Heating and Starvation

“…In the present analysis, it is assumed that the reciprocal asymptotic iso-viscous PV coefficient is responsible for the EHD film formation in the conjunction according to [43].…”