Prediction of micropitting life in spur gears operating under mixed-lubrication regime using load-sharing concept

Micropitting is a surface fatigue failure of the gear tooth that occurs due to repeated loading and unloading of the tooth surface in a manner that the contact stresses exceed the surface fatigue strength of the material. The micropitting process in essence is a fatigue problem and thus it occurs during millions of cycles of operation. Micropitting can lead to problems such as wearing of the gear tooth, vibrations, noise, and misalignment. Therefore, micropitting life prediction is necessary for design, performance, and reliability improvements. The present study predicts the coefficient of friction for each point along the line of action of the pinion and gear using the load-sharing concept. The subsurface stresses are then calculated and the Von Mises stresses at each point are obtained. Then, the pitting life is predicted by employing a model which was developed by Zaretsky. The predicted pitting lives are compared with the experimental data from the literature. A parametric study on the effect of applied load, speed, and surface roughness on the micropitting life of a pair of spur gears is conducted. It is shown that increasing the applied load results in the decrease in the micropitting life of the gear. Increase in the speed, on the other hand, results in formation of a better lubricant film and therefore the micropitting life increases. An increase in the surface roughness leads to a decrease in the micropitting life.