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The Lambda ratio (λ) has been widely used as an indicator of the lubricant regime in an operating contact within either bearings or gear sets. λ is determined when the lubricant film thickness (h) within the contact is divided by the composite roughness (σ) of the two surfaces forming the contact. Recommendations of an appropriate film thickness equation and surface roughness values are provided to calculate modified lambda ratio (λm) that better represents the lubricant regime within bearings or gears. Bearing performance, especially as related to fatigue life, has increased significantly in recent years. This is primarily due to cleaner steels but includes the influence of better surface finishes and bearing internal geometries. With λm, and an understanding of how contact fatigue damage mode relates to a wide range of λm values, it may be possible to transfer the advances in bearing performance to other system components such as gears.

This paper is a survey introduction to elastohydrodynamic (EHD) lubrication for the practicing engineer. A brief description of the theoretical background and experimental evidence of the EHD lubricant film existing in concentrated contracts as found in bearings and gears is provided. The influence of the range of EHD and partial EHD lubricant conditions on bearing performance and mode of fatigue is next explored. The evidence discussed is drawn primarily from carburized and hardened tapered roller bearings tested under a wide range of environmental conditions.