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DISSERTATIONS
Author: |
Gatsios Stilianos |
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Title: |
Investigation of the physical adsorption of lubricants in mixed film
lubrication conditions leading to scuffing |
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Abstract: |
Contemporary machine elements are often called to operate in mixed
film lubrication regime. Under these conditions one possible mode of
failure is scuffing. The adsorption of lubricant molecules on the
friction surfaces can significantly reduce the risk of scuffing. The
purpose of this work is to study, in a quantitative manner, the role
of the lubricant’s physical adsorption on scuffing under conditions
close to those found during the operation of gears and bearings. The
two-disk test rig of the Laboratory of Machine Elements and Machine
Design was used for the experimental investigation, after making
some necessary improvements. Additionally, a custom device was
created from scratch that allowed for the measurement of roughness
onthe circumference of the disks. After conducting friction
coefficient measurements in very low sliding speedand considering
the effect of lubricant adsorption under these specific conditions,
the heat of adsorption for FVA2 lubricant was determined. Next,
scuffing experiments were conducted in appropriate conditions using
carefully prepared disk specimens and FVA2 lubricant. For each
experiment, in every stage, bulk temperature of each disk, friction
force and other experimental data were collected and recorded. These
data, together with disk surface roughness,were fed into anexisting
numerical model capable of solving the contact of two rough surfaces
operating in mixed film lubrication regime, resulting in the
determination of the pressure distribution. Also, a methodology was
developed that allowed for the calculation of the temperature
distribution at the interface of the rough sliding bodies. Based on
the results of pressure, temperature and activation energy it was
made possible to calculate foreach surface in the contact the
fractional coverage due to lubricant molecules adsorption. The
calculations were conducted both for time-dependent and
time-independent adsorption. The results from the theoretical
investigation and theprocessing of all exper-imental datalead to the
conclusion that the theory of adsorption can be used to describe a
hydrodynamic pressure versus temperature curve that serves as a
limit between scuffing-safe and scuffing-unsafe regions of operating
conditions. It was found that the exact position of the limit-curve
can be correlated with the surface roughness. |
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