A deterministic tribofilm growth model considering flash temperature and surface roughness in mixed lubrication

Abstract Although there have been a lot of researches about the drivers of tribofilm growth in recent years, people still argue about the real mechanism of tribofilm formation. In engineering field, plenty of mechanical components are operating under mixed lubricating condition. Therefore, it makes sense to study how tribofilm will form under mixed lubrication, which can provide further analysis on how ZDDP (Zinc dialkyl- and diaryldithiophosphates) would act as an antiwear additive to influence lubricating behavior. This paper presents a numerical model to simulate tribofilm formation process under mixed lubrication condition, considering influences of temperature and stress. In view of real surface roughness at each simulation step, the tribofilm morphology is obtained, as well as a series of lubricating parameters to study the mutual impacts between tribofilm formation and lubrication performance. It can be concluded that with the growth of tribofilm, lubricating performance will decrease to some extent, especially for low entrainment speed conditions, correlating with a noticeable shift in the Stribeck friction curve towards higher entrainment speed. Using the model developed in this paper, the assumption that tribofilm as a solid film can increase surface roughness to block the flow of lubricating fluid is evidently supported.