With the advancement of surface technology, boundary slip in lubrication has become increasingly common. However, theoretical analysis in this area remains limited, necessitating further research to explore the impact of boundary slip, particularly thermal slip induced by velocity slip in cases with obvious thermal rise. Additionally, investigating the influence of surface limiting shearing stress on boundary slip is a valuable area of study. This research extends the simple sliding finite line contact thermal elastohydrodynamic lubrication (EHL) model by incorporating velocity slip and thermal slip at boundaries. Firstly, linear slip is examined in three different conditions, and the impact of boundary slip on the lubrication state is analyzed. Building upon this, the study considers the effect of limiting shearing stress on boundary slip and develops a nonlinear slip model. The study conducts a thorough analysis of the influence of limiting shearing stress on the lubrication state in the contact area and reveals that friction reduction can be attained by introducing slip between the static surface and the lubricant. By investigating the impact of boundary slip and limiting shearing stress on thermal EHL under simple sliding conditions, this research puts forward a novel friction reduction approach based on the theory of boundary slip.

Using an optical interferometric technique, the grease film distribution under a pure rolling reciprocating motion is observed on a ball-disk test rig, to explore the transient response of grease, which is expected to fill the contact with thickener fiber and run for a long time under steady-state conditions. It is found that the reciprocating motion reduces the accumulation of the thickener fiber gradually with time. The maximum film thickness forms around the stroke ends. After 1,000 working cycles, very severe starvation occurs so that either the central or minimum film thickness becomes nearly constant over one working period. Thus, the life of grease lubrication under a transient condition is far below that under steady-state conditions. However, it is also found that by selecting a smaller stroke length, the thickener fiber spreads out in the contact instead of being removed from the contact at the 1,000th working period. When increasing the maximum entraining speed of the reciprocating motion to a certain value, during which the thickener fiber is not expected to accumulate under a steady-state condition, severe starvation occurs very quickly, causing surface damage.