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 [1] 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.