scholarly journals Effect of an Improved Yasutomi Pressure-Viscosity Relationship on the Elastohydrodynamic Line Contact Problem

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Vincenzo Petrone ◽  
Adolfo Senatore ◽  
Vincenzo D'Agostino
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Free Volume ◽  
Experimental Studies ◽  
Line Contact ◽  
Volume Model ◽  
Free Volume Model ◽  
Pressure Area ◽  
New Formulation ◽  
Lubricant Viscosity

This paper presents the application of an improved Yasutomi correlation for lubricant viscosity at high pressure in a Newtonian elastohydrodynamic line contact simulation. According to recent experimental studies using high pressure viscometers, the Yasutomi pressure-viscosity relationship derived from the free-volume model closely represents the real lubricant piezoviscous behavior for the high pressure typically encountered in elastohydrodynamic applications. However, the original Yasutomi correlation suffers from the appearance of a zero in the function describing the pressure dependence of the relative free volume thermal expansivity. In order to overcome this drawback, a new formulation of the Yasutomi relation was recently developed by Bair et al. This new function removes these concerns and provides improved precision without the need for an equation of state. Numerical simulations have been performed using the improved Yasutomi model to predict the lubricant pressure-viscosity, the pressure distribution, and the film thickness behavior in a Newtonian EHL simulation of a squalane-lubricated line contact. This work also shows that this model yields a higher viscosity at the low-pressure area, which results in a larger central film thickness compared with the previous piezoviscous relations.

An Application of a Free Volume Model to Lubricant Rheology 2—Variation in Viscosity of Binary Blended Lubricants

1984 ◽  
Vol 106 (2) ◽  
pp. 304-311 ◽  
Author(s):  
S. Yasutomi ◽  
S. Bair ◽  
W. O. Winer
Keyword(s):  
High Pressure ◽  
Binary Mixture ◽  
Free Volume ◽  
Mineral Oil ◽  
Practical Applications ◽  
Polyphenyl Ether ◽  
Volume Model ◽  
Wlf Equation ◽  
Free Volume Model ◽  
Lubricant Rheology

The modified WLF equation developed in Part 1 was applied to the variation in viscosity, μ(T,P), for two series of binary blended lubricants containing a common synthetic diester (di(2ethylhexyl)sebacate) in a polyphenyl ether (5P4E) and in a naphthenic mineral oil (N1). Dilatometric observations and the viscosity analysis indicate that the relations needed to predict the pressure functions in the modified WLF equation for the binary mixture can be obtained from those of respective components. These relations allow us to estimate μ(T,P) of a binary blended lubricant without measurements of the high pressure viscosity of the blend. For practical applications, the modified WLF equation may also be useful for predicting μ(T,P) of blended lubricant products.

An Application of a Free Volume Model to Lubricant Rheology I—Dependence of Viscosity on Temperature and Pressure

1984 ◽  
Vol 106 (2) ◽  
pp. 291-302 ◽  
Author(s):  
S. Yasutomi ◽  
S. Bair ◽  
W. O. Winer
Keyword(s):  
Free Volume ◽  
Pressure Dependence ◽  
Pressure Effects ◽  
Mineral Oils ◽  
Volume Model ◽  
Free Volume Model ◽  
Synthetic Lubricants ◽  
Temperature And Pressure ◽  
Lubricant Viscosity ◽  
Dielectric Transition

Analyses of the dependence of lubricant viscosity on temperature and pressure, μ(T,P), have been carried out by using a modified WLF equation in which pressure effects on viscosity are given in terms of the pressure dependence of the glass transition temperature, Tg, and of thermal expansivity of free volume, αf. logμ(T,P)=logμg−C1•(T−Tg(P))•F(P)C2+(T−Tg(P))•F(P) where C1 and C2 are well known WLF constants, and μg is a viscosity at Tg. Tg(P) and F(P) are functions for describing the pressure dependence of Tg and αf, respectively. On the basis of the iso-viscous concept for Tg(P), μg has been assumed to have a constant value, 1 TPa•s, at any pressure (SCHEME I). SCHEME I yields a reasonable variation in Tg and αf with pressure for synthetic lubricants, while this analysis suggests a lower μg for mineral oils. In order to improve the applicability of the free volume model, a reference temperature Ts(P), at which the viscosity is 10 MPa•s, has been introduced instead of Tg(P) (SCHEME II). Analyses of dielectric transition for some lubricants and of μ(T,P) in the ASME Pressure-Viscosity Report have confirmed the excellent applicability of the present free volume model over wide ranges of temperature and pressure.

The Influence of Piezo-Viscous Lubricants on EHL Line and Point Contact Problems

2012 ◽  
Author(s):  
V. D’Agostino ◽  
V. Petrone ◽  
A. Senatore
Keyword(s):  
Film Thickness ◽  
Free Volume ◽  
Isothermal Condition ◽  
Point Contact ◽  
Contact Problems ◽  
Shear Thinning ◽  
Volume Model ◽  
Shear Thinning Fluids ◽  
Free Volume Model ◽  
Ehl Contact

A good and accurate prediction of the elastohydrodynamic lubrication behaviour requires consideration of the constitutive equation for the lubricant. In particular, for applications involving synthetic oils or mineral oil with polymeric additives that exhibit shear-thinning behaviour, the use of an appropriate pressure-viscosity relationship for the lubricant is required to predict the EHL behaviour more accurately [1–3]. For this reason, this paper aims to emphasize the importance of implementing piezo-viscous models with accurate treatment methods in EHL applications. Due to the high pressure in an EHL contact, in fact, the elastic deformation of the surfaces and pressure dependence of viscosity play the pivotal role and in many applications, the lubricant exhibits a shear-thinning behaviour which significantly affects the film thickness [4–6]. The effects of different pressure–viscosity relationships, including the exponential model, the Roelands’ model and specifically, the Doolittle model are investigated and a generalized formulation that can efficiently treat shear-thinning fluids with provision for compressibility in the EHL contact is presented. In the light of above facts, models for 1D and 2D EHL contacts for simulating the behaviour of the pressure distribution and the shape of the film thickness using a generalized Reynolds equation and shear-thinning fluids is developed. In particular for EHL 2D problem a more accurate full multigrid approach has been used and both the analysis is based upon the assumptions of isothermal condition. In this work, in fact, we show that the piezo-viscous rheology of the lubricant plays an important role in determining the value of pressure peaks. Pressure profiles and film shapes are showed and variations of the minimum and central film thickness with dimensionless parameters are also presented. It is found that the real pressure–viscosity behaviour predicted by the free-volume model yields a higher viscosity at the low-pressure area which results in a larger central film thickness. Therefore, due to use of the free-volume model, the presented results are more consistent with literature experimental observations and the Doolittle model effectively predicts the film thickness that closely matches experiments and properly characterizes the behaviour of shear-thinning lubricants.

Free volume model for positronium decay in molecular materials

1969 ◽  
Vol 28 (11) ◽  
pp. 760-761 ◽  
Author(s):  
B.V. Thosar ◽  
V.G. Kulkarni ◽  
R.G. Lagu ◽  
Girish Chandra
Keyword(s):  
Free Volume ◽  
Molecular Materials ◽  
Volume Model ◽  
Free Volume Model ◽  
Positronium Decay

scholarly journals Fast Approach for Calculating Film Thicknesses and Pressures in Elastohydrodynamically Lubricated Contacts at High Loads

1986 ◽  
Vol 108 (3) ◽  
pp. 411-419 ◽  
Author(s):  
L. G. Houpert ◽  
B. J. Hamrock
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Line Contact ◽  
Elastic Deformations ◽  
New Approach ◽  
Lubricated Contacts ◽  
Fast Approach ◽  
Pressure Spike

The film thicknesses and pressures in elastohydrodynamically lubricated contacts have been calculated for a line contact by using an improved version of Okamura’s approach. The new approach allows for lubricant compressibility, the use of Roelands viscosity, a general mesh (nonconstant step), and accurate calculations of the elastic deformations. The new approach is described, and the effects on film thickness, pressure, and pressure spike of each of the improvements are discussed. Successful runs have been obtained at high pressure (to 4.8 GPa) with low CPU times.

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