F. Laplant et al., RAMAN MEASUREMENTS OF LOCALIZED PRESSURE VARIATIONS IN LUBRICANTS ABOVE THE GLASS-TRANSITION PRESSURE, Journal of tribology, 119(4), 1997, pp. 817-822
Spatial pressure variations in synthetic lubricants contained in a sta
tic high-pressure diamond anvil cell (DAC), as well as in a loaded mod
el bearing contact device, have been measured using the frequency shif
t of the lubricant's Raman vibrational modes. Long-lived pressure fluc
tuations of +/-0.5 GPa, with a relaxation time of several days, are ob
served in the static high pressure systems at an average pressure of 2
.5 GPa. Evidence for rapidly varying pressure fluctuations in a concen
trated contact is inferred from the increase in lubricant Raman linewi
dths. These results mise questions about key assumptions made in model
ing EHD contacts. It is suggested that the present results are closely
linked to recent observations of shear localization made by Winer and
Bair.