Further analysis of the lubrication regime in the Ti6Al4V–
UHMWPE pair was developed as follows. First, the friction coef-
ficient is demonstrated to be higher with the viscosity increasing
under hydrodynamic lubrication regime according to the Stribeck
curve. But the friction coefficient in our study was found to
decrease with the increase of the solution viscosity (shown in
Fig. 6). It indicates that hydrodynamic lubrication is not formed in
the Ti6Al4V–UHMWPE pair. For determining the lubrication
regime, the ratio result (λ) representing relative film thickness was