On the effect of surface roughness in point-contact EHL: Formulas for film thickness and asperity load

• Predictive formulas are presented for film thickness and asperity load in rough EHL.
• Input is dimensionless load, speed, material, roughness, hardness, and ellipticity.
• Statistical elasto-plastic asperity micro-contact is utilized in modeling roughness.
• The results from formulas are in agreement with data available in the literature.

Formulas are derived for predicting the central film thickness, minimum film thickness, and the asperity load ratio in point-contact EHL of rough surfaces. The rough EHL model includes simultaneous solution to the modified Reynolds and surface deformation equations with the consideration of both bulk and asperity deformations. To include the effect of surface roughness, a statistically-based elasto-plastic asperity micro-contact model is utilized. Regression analyses based on the results from an extensive set of simulations are performed to obtain predictive expressions for the film thickness and the asperity load ratio. These formulas are of the form f(κ, W, U, G  , σ¯, V), where the parameters represented are ellipticity, dimensionless load, speed, material, surface roughness and hardness, respectively. The results predicted using these formulas are in good agreement with wide range of data available in the literature.