A plane isothermal elastohydrodynamic problem for a line contact lubricated by a degrading fluid with non-Newtonian rheology is studied. The lubricant is represented by a base stock with a polymer additive which undergoes stress-induced degradation caused by scission of polymer molecules. The polymer molecules are considered to be of linear structure. The effective lubricant viscosity experiences reversible and irreversible losses. The reversible loss of the effective lubricant viscosity (shear thinning) is due to the non-Newtonian rheology of the fluid and variations in the fluid shear rate. The irreversible loss of the effective lubricant viscosity is caused by the degradation process of the polymer additive dissolved in the lubricant. The degradation process of the polymer additive while it passes through the contact is described by a kinetic equation. The kinetic equation is solved along the lubricant flow streamlines. The solution of the kinetic equation predicts the density of the probabilistic distribution of the polymer molecular weight versus polymer molecule chain length. The changes in the distribution of polymer molecular weight affect local lubricant properties. In particular, the lubricant viscosity experiences reversible and irreversible losses and, in general, is a discontinuous function. The changes in the lubricant viscosity alter virtually all parameters of the lubricated contact such as film thickness, friction stresses, pressure, and gap. The considered non-Newtonian rheology of the lubricant causes a small reversible loss of its viscosity. As a result of the polymer additive degradation the lubricant may experience a significant irreversible loss of its viscosity which, in turn, leads to a noticeable reduction in the lubrication film thickness in comparison with the case of a non-degrading lubricant with similar rheology. Some comparisons between the cases of lubricants with Newtonian and non-Newtonian rheologies with and without lubricant degradation are considered.

Issue Section:
Technical Papers
Keywords:
non-Newtonian flow, viscosity, molecular weight, lubrication, bifurcation, mechanical contact, rheology, polymer structure, friction
Topics:
Lubricants, Viscosity, Rheology, Flow (Dynamics), Stress, Polymers, Molecular weight
1.
Bair
,
S.
, and
Winer
,
W. O.
,
1979
, “
Shear Strength Measurements of Lubricants at High Pressure
,”
J. Lubr. Technol.
,
101
(
3
), pp.
251
–
257
.
2.
Hoglund
,
E.
, and
Jacobson
,
B.
,
1986
, “
Experimental Investigations of the Shear Strength of Lubricants Subjected to High Pressure and Temperature
,”
ASME J. Tribol.
,
108
(
4
), pp.
571
–
578
.
3.
Eyring
,
H.
,
1936
, “
Viscosity, Plasticity, and Diffusion as Examples of Absolute Reaction Rates
,”
J. Chem. Phys.
,
4
(
4
), pp.
283
–
291
.
4.
Houpert, L. G., and Hamrock, B. J., 1985, “Elastohydrodynamic Lubrication Calculations Used as a Tool to Study Scuffing,” in Mechanisms and Surface Distress: Global Studies of Mechanisms and Local Analyses of Surface Distress Phenomena, D. Dowson et al., eds., Butterworths, England, pp. 146–162.
5.
Kudish, I. I., 1982, “Asymptotic Methods for Studying Plane Problems of the Elastohydrodynamic Lubrication Theory in Heavily Loaded Regimes. Part 1. Isothermal Problem,” Izvestija Akademii Nauk Arm.SSR, Mekhanika, 35(5), pp. 46–64.
6.
Crail
,
I. R. H.
, and
Neville
,
A. L.
,
1969
, “
The Mechanical Shear Stability of Polymeric VI Improvers
,”
J. Inst. Pet.
,
55
(
542
), pp.
100
–
108
.
7.
Casale
,
A.
, and
Porter
,
R. S.
,
1971
, “
The Mechanochemistry of High Polymers
,”
Rubber Chem. Technol.
,
44
(
2
), pp.
534
–
577
.
8.
Walker
,
D. L.
,
Sanborn
,
D. M.
, and
Winer
,
W. O.
,
1975
, “
Molecular Degradation of Lubricants in Sliding Elastohydrodynamic Contacts
,”
ASME J. Lubr. Technol.
,
97
(
3
), pp.
390
–
397
.
9.
Yu
,
J. F. S.
,
Zakin
,
J. L.
, and
Patterson
,
G. K.
,
1979
, “
Mechanical Degradation of High Molecular Weight Polymers in Dilute Solution
,”
J. Appl. Polym. Sci.
,
23
, pp.
2493
–
2512
.
10.
Odell
,
J. A.
,
Keller
,
A.
, and
Rabin
,
Y.
,
1988
, “
Flow-Induced Scission of Isolated Macromolecules
,”
J. Chem. Phys.
,
88
(
6
), pp.
4022
–
4028
.
11.
Covitch, M. J., 1998, “How Polymer Architecture Affects Permanent Viscosity Loss of Multigrade Lubricants,” SAE Technical Paper Series, Paper No. 982638.
12.
Ziff
,
R. M.
, and
McGrady
,
E. D.
,
1985
, “
The Kinetics of Cluster Fragmentation and Depolymerization
,”
J. Phys. A
,
18
, pp.
3027
–
3037
.
13.
Ziff
,
R. M.
, and
McGrady
,
E. D.
,
1986
, “
Kinetics of Polymer Degradation
,”
Macromolecules
,
19
, pp.
2513
–
2519
.
14.
McGrady
,
E. D.
, and
Ziff
,
R. M.
,
1988
, “
Analytical Solutions to Fragmentation Equations With Flow
,”
AIChE J.
,
34
(
12
), pp.
2073
–
2076
.
15.
Montroll
,
E. W.
, and
Simha
,
R.
,
1940
, “
Theory of Depolymerization of Long Chain Molecules
,”
J. Chem. Phys.
,
8
, pp.
721
–
727
.
16.
Saito
,
O.
,
1958
, “
On the Effect of High Energy Radiation to Polymers. I, Cross-Linking and Degradation
,”
J. Phys. S. of Japan
,
13
, pp.
198
–
206
.
17.
Kudish, I. I., and Ben-Amotz, D., 1999, “Modeling Polymer Molecule Scission in EHL Contacts,” in The Advancing Frontier of Engineering Tribology, Proc. of the 1999 STLE/ASME H. S. Cheng Tribology Surveillance, Q. Wang, J. Netzel, and F. Sadeghi, eds., pp. 176–182.
18.
Kudish
,
I. I.
,
Airapetyan
,
R. G.
, and
Covitch
,
M. J.
,
2002
, “
Modeling of Kinetics of Strain-Induced Degradation of Polymer Additives in Lubricants
,”
J. of Mathematical Models and Methods in Applied Sciences
,
12
(
6
), pp.
1
–
22
.
19.
Kudish
,
I. I.
,
Airapetyan
,
R. G.
, and
Covitch
,
M. J.
,
2003
, “
Modeling of Kinetics of Stress-Induced Degradation of Polymer Additives in Lubricants and Viscosity Loss
,”
STLE Tribol. Trans.
,
46
(
1
), pp.
1
–
11
.
20.
Kudish
,
I. I.
, and
Airapetyan
,
R. G.
,
2003
, “
Modeling of Line Contacts With Degrading Lubricant
,”
ASME J. Tribol.
,
125
(
3
), pp.
513
–
522
.
21.
Hamrock, B. J., 1991, “Fundamentals of Fluid Film Lubrication,” NASA Reference Publication 1255.
22.
Billmeyer, F. W., Jr., 1966, Textbook of Polymer Science, John Wiley & Sons.
23.
Crespi, G., Valvassori, A., and Flisi, U., 1977, “Olefin Copolymers,” The Stereo Rubbers, W. M. Saltman, ed., pp. 365–431.
24.
Kudish, I. I., 1996, “Asymptotic Analysis of a Problem for a Heavily Loaded Lubricated Contact of Elastic Bodies. Pre- and Over-Critical Lubrication Regimes for Newtonian Fluids,” Dynamic Systems and Applications, 5(3), Dynamic Publishers, Atlanta, pp. 451–476.
25.
Kudish
,
I. I.
,
1981
, “
Some Problems of Elastohydrodynamic Theory of Lubrication for a Lightly Loaded Contact
,”
Mech. Solids
,
16
(
3
), pp.
81
–
95
.
26.
Kudish
,
I. I.
,
2000
, “
A New Statistical Model of Contact Fatigue
,”
STLE Tribol. Trans.
,
43
(
4
), pp.
711
–
721
.
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