The effect of the lubrication regime on gear performance has been recognized, qualitatively, for decades.
Often the lubrication regime is characterized by the specific film thickness defined as the ratio of lubricant
film thickness to the composite surface roughness. It can be difficult to combine results of studies to
create a cohesive and comprehensive dataset. In this work gear surface fatigue lives for a wide range of
specific film values were studied using tests done with common rigs, speeds, lubricant temperatures, and
test procedures. This study includes previously reported data, results of an additional 50 tests, and
detailed information from lab notes and tested gears. The dataset comprised 258 tests covering specific
film values [0.47 to 5.2]. The experimentally determined surface fatigue lives, quantified as 1 0-percent
life estimates, ranged from 8.7 to 86.8 million cycles. The trend is one of increasing life for increasing
specific film. The trend is nonlinear. The observed trends were found to be in good agreement with data
and recommended practice for gears and bearings. The results obtained will perhaps allow for the
specific film parameter to be used with more confidence and precision to assess gear surface fatigue for
purpose of design, rating, and technology development.

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