Hydrodynamic Fluid Film and Tribofilm Formation—Combining the Friction Signals with Contact Resistance

Under unidirectional sliding, the Stribeck-type curve traverses different lubrication regimes. Under mixed/boundary conditions, tribofilms formed by additives in lubricants represent a key mechanism for preventing wear but are difficult to investigate because of the complex composition of lubricants, their small thickness, and their amorphous nature. The formation of a hydrodynamic fluid film depends on the topography and the viscometric fluid properties. Low coefficients of friction do not consequently indicate that hydrodynamic fluid films were formed. The electric contact resistance serves here as a complementary indicator to identify the hydrodynamic fluid film and tribofilm formation under transient or static sliding conditions. The frictional work (WR) is a useful quantity to assess the contribution to the frictional losses of all lubrication regimes in a Stribeck-type curve.