A Boundary Lubrication Model and Experimental Study Considering ZDDP Tribofilms on Reciprocating Friction Pairs

Boundary lubrication state may dominate the friction pairs operating under severe conditions, yet its mechanism is not clearly understood and related numerical models are still lacking. A boundary lubrication model considering zinc dialkyldithiophosphate (ZDDP) tribofilms, which impact friction and wear performances, was developed in this study. A series of reciprocating experiments were conducted to verify this model and also to investigate the effects of the tribofilm on friction and wear under various temperatures and loads. Moreover, the experimental data were employed to modify the tribofilm removal equation, which enabled the present boundary lubrication model to be applied under a wide range of loads. The results showed that the friction force and wear depth both decline with the increasing lubricant temperature due to thicker tribofilms formed. As the load becomes heavier, the wear depth keeps increasing, while the tribofilm thickness first increases then decreases.