A micro-pitting model for spur gear contacts

This paper proposes a physics-based model to predict the micro-pitting behavior on contact surfaces of spur gears operating under the mixed lubrication condition. The transient mixed elastohydrodynamic lubrication model of Li and Kahraman developed for spur gears is employed to predict surface normal and tangential tractions, capturing the transient effects associated with the time-varying contact radii, surface velocities and normal tooth force. A new boundary element formulation for line contacts of rough surfaces is formulated to compute the multi-axial stress fields, taking into account the influences of surface roughness topography on localized stress concentrations. A multi-axial fatigue criterion is implemented to evaluate micro-pitting fatigue lives according to the stress histories and material fatigue strength. A micro-pitting severity index (MSI), defined as the ratio of micro-pitted area to the entire contact area, is used to quantify micro-pitting activity. Applying the proposed model to an example spur gear pair, the progression of micro-pits on tooth surface is demonstrated.