Surface asperity-enhanced micro electrical discharge in lubricated contact interfaces

Electrically induced bearing damage (EIBD) is a significant challenge to lubricated interfaces in machine elements subjected to electric fields, particularly for applications like battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and wind turbines. When the electric field across a non-conducting lubricant film exceeds its dielectric strength, electrical discharges occur, causing surface damage to machine elements. Surface asperities amplify the local electric field, leading to microscale discharges and micro-pitting in the areas corresponding to the minimum film thickness within the elastohydrodynamic lubrication (EHL) regime. This study investigates the effect of asperities on local electric fields and introduces a field enhancement parameter to quantify the influence of various asperity geometries, including hemispheres, semicylinders, hyperboloid tips, hyperbolic blades, and two-dimensional sinusoidal wavy surfaces. The analysis results indicate that for a given film thickness, the enhancement effect is strongly dependent on the radius of curvature of the asperity tip, and that as the radius increases, the enhancement effect reduces and diminishes. The proposed method helps effectively predict the electrical-breakdown voltage for known asperity characteristics, offering valuable insights into the nature of EIBD, useful for the design of reliable lubricated systems working under high electric fields.