The paper describes an experimental technique combining optical interferometry and ultrasonic attenuation to measure the bulk modulus (compressibility) and film thickness profiles of oil and grease films entrapped between a stationary steel ball and a sapphire plate. Results are presented for lithium- and urea-based greases, and their base oils alone, at contact pressures up to and around 3 GPa, and are compared with some models and results from other studies, extrapolated to the higher pressures achieved here. Results show that the bulk modulus of a particular grease and its base oil are found to be similar, at a given pressure, and largely dependent on the base-oil properties, which is demonstrated to be what is expected with the concentration levels of fillers and solid lubricants present. However, the film shapes measured for the grease and its base oil can be quite different. This is seemingly due to the manner in which the lubricant samples “solidify”, due to the high pressures, and also to the way in which the edges of the squeeze-film entrapped fluid are sealed. This latter sealing effect seems to be assisted by secondary phases, particularly with greases where fillers and solid lubricants are present, creating a very effective sealed contact where the entrapped lubricant samples could be observed to remain stable for several hours.

1.
Dowson
,
D.
, and
Higginson
,
G. R.
, 1977,
Elastohydrodynamic Lubrication
,
Pergamon Press
, Oxford, UK.
2.
Hamrock
,
B. J.
,
Jacobson
,
B. O.
, and
Bergstrom
,
S.
, 1987, “
Measurements of Density of Base Fluids at Pressures to 2.2 Gpa
,”
ASLE Trans.
0569-8197,
30
, pp.
196
202
.
3.
Ramesh
,
K. T.
, 1991, “
The Short-Time Compressibility of Elastohydrodynamic Lubricants
,”
ASME J. Tribol.
0742-4787,
113
, pp.
361
371
.
4.
Paul
,
G. R.
, and
Cameron
,
A.
, 1974, “
Time Dependent Viscosity Effects Measured on an Impact Microviscometer
,”
Nature (London)
0028-0836,
248
, pp.
219
220
.
5.
Hirano
,
F.
,
Kuwano
,
N.
, and
Ohno
,
N.
, 1985, “
Observations of solidification of oils under high pressure
,”
Proc. JSLE Int. Tribology Conf., Tokyo 85
, Vol.
190
, pp.
184
189
.
6.
Safa
,
M. M. A.
, and
Gohar
,
R.
, 1986, “
Pressure Distribution Under a Ball Impacting a Thin Lubricant Layer
,”
ASME J. Tribol.
0742-4787,
108
, pp.
372
378
.
7.
Wong
,
P. L.
,
Lingard
,
S.
, and
Cameron
,
A.
, 1992, “
The High Pressure Impact Microviscometer
,”
STLE Tribol. Trans.
1040-2004,
35
, pp.
500
508
.
8.
Dowson
,
D.
, and
Wang
,
D.
, 1994, “
An Analysis of the Nominal Bouncing of a Solid Elastic Ball on an Oily Plate
,”
Wear
0043-1648,
179
, pp.
29
37
.
9.
Webster
,
M. N.
, and
Sayles
,
R. S.
, 1986, “
A Numerical Model for the Elastic Frictionless Contact of Real Rough Surfaces
,”
ASME J. Tribol.
0742-4787,
108
, pp.
314
420
.
10.
Johnson
,
K. L.
, 1985,
Contact Mechanics
,
Cambridge University Press
, Cambridge, UK.
11.
Marginson
,
H.
,
Sayles
,
R. S.
, and
Olver
,
A. V.
, 1995, “
Limitations of Thin Film Microtransducers in Highly Loaded Contacts
,”
Tribol. Int.
0301-679X,
28
(
8
), pp.
517
521
.
12.
Lowe
,
M. J. S.
, 1995, “
Matrix Techniques for Modelling Ultrasonic Waves in Multilayered Media
,”
IEEE Trans. Ultrason. Ferroelectr. Freq. Control
0885-3010
42
, pp.
525
542
.
13.
Pialucha
,
T. P.
, 1992, “
The reflection from interface layers in NDT of adhesive joints
,” Ph.D. thesis, Imperial College, University of London, UK.
14.
Pialucha
,
T. P.
, and
Cawley
,
P.
, 1994, “
The Detection of Thin Embedded Layers Using Normal Incidence Ultrasound
,”
Ultrasonics
0041-624X,
32
, pp.
431
440
.
15.
Dwyer-Joyce
,
R. S.
,
Drinkwater
,
B. W.
, and
Donohoe
,
C. J.
, 2003, ”
The Measurement of Film Thickness Using Ultrasound
,”
Proc. R. Soc. London, Ser. A
1364-5021,
459
, pp.
957
976
.
16.
Hosten
,
B.
, 1991, “
Bulk Heterogeneous Plane-Wave Propagation through Viscoelastic Plates and Stratified Media With Large Values of Frequency Domain
,”
Ultrasonics
0041-624X,
29
, pp.
445
450
.
17.
Tattersall
,
H. G.
, 1973, “
The Ultrasonic Pulse-Echo Technique as Applied to Adhesion Testing
,”
J. Phys. D
0022-3727,
6
, pp.
819
832
.
18.
Cameron
,
A.
, and
Gohar
,
R.
, 1966, “
Theoretical and Experimental Studies of the Oil Film in Lubricated Point Contact
,”
Proc. R. Soc. London, Ser. A
1364-5021,
291
, pp.
520
536
.
19.
Spikes
,
H. A.
, 1994, “
The Behaviour of Lubricants in Contacts; Current Understanding and Future Possibilities
,”
Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol.
1350-6501,
208
, pp.
3
15
.
20.
Wedeven
,
L. D.
,
Evans
,
D.
, and
Cameron
,
A.
, 1971, “
Optical Analysis of Ball Bearing Starvation
,”
ASME J. Lubr. Technol.
0022-2305,
93
, pp.
349
363
.
21.
Moriuchi
,
T.
,
Machidori
,
W.
, and
Kageyama
,
H.
, 1985, “
Grease Lubrication in Elastohydrodynamic Contacts
,” Part II,
NLGI Spokesman
0027-6782,
49
, pp.
348
356
.
22.
Cann
,
P. M.
, and
Spikes
,
H. A.
, 1992, “
Film Thickness Measurements of Lubricating Greases Under Nominally Starved
,“
NLGI Spokesman
0027-6782,
56
, pp.
61
67
.
23.
Astrom
,
H.
,
Isaksson
,
O.
, and
Hoglund
,
E.
, 1991, “
Video Recordings of a Lubricated Point Contact Lubricated With Grease
,”
Tribol. Int.
0301-679X,
91
, pp.
179
184
.
24.
Cann
,
P. M.
,
Williamson
,
P. B.
,
Coy
,
R. C.
, and
Spikes
,
H. A.
1992, “
The Behaviour of Greases in Elastohydrodynamic Point Contacts
,”
J. Phys. D
0022-3727,
25
, pp.
A124
A132
.
25.
Kondo
,
S.
, 2003, “
Constant Velocity Joint Fatigue Failure
,” Ph.D. thesis, Imperial College; University of London, UK.
26.
Gohar
,
R.
, 2001,
Elastohydrodynamics
,
2nd ed.
,
Imperial College Press
, London, UK.
You do not currently have access to this content.