Optical measurements in elastohydrodynamic rolling-contact bearings
Elastohydrodynamic oil film measurements for rolling
point contact under starvation conditions are obtained using
optical interferometry. Consideration of the measurement
requirements and the requirements for good fringe visibility
has led to the design of a duochromatic interferometric system.
A calibration procedure provides the absolute thickness corresponding
to each fringe and elucidates the effects of phase
change on reflection.
The experimental measurements present a reasonably
clear picture of the starvation phenomenon. Film thickness is
determined by the pressure generated in the inlet region. A
starved inlet region inhibits the generation of this pressure
and, therefore, reduces the film thickness. 1t also causes the
overall pressure, stress and elastic deformation to become
more Hertzian. The experimental film thickness measurements
under starved as well as flooded conditions are shown to agree
with theoretical predictions based on Grubin assumptions. The
results correlate with characteristic dimensions which describe
the degree of starvation in the inlet region. These are used
to predict the onset of starvation and are incorporated in
a theoretical film thickness formula which enables film thickness
under starvation conditions to be predicted.
Additional experiments with interferometry illustrates:
the effect of ball spin, edge effects in line contact,
oil entrapment under 'rolling-normal approach' conditions,
the behaviour of greases under elastohydrodynamic conditions,
and cavitation and its influence on the inlet region.