An Experimental Setup for Investigations on the Boundary Layer Dynamics

The frictional behavior of a tribological contact is influenced by the dynamics in the forming boundary layer. Recurring structures, built up through self-organizing effects, were found in various frictional systems. To investigate those phenomena on a macroscopic scale and to better understand dynamical processes such as the formation and decay of contact patches, the first revision of the Wear Debris Investigator (WDI) was introduced in 2017. A friction gap is formed between two coaxial horizontally arranged discs. To mimic the presence of particles, artificial wear dust is fed into the gap. With a camera the formation of the boundary layer is recorded in situ. An implemented normal force and torque sensor enables to recognize correlations between the formed boundary layer and the occurring frictional forces. Numerous measurements revealed an insufficient precision of the previous WDI. Consequently, an innovative measurement and load unit was developed and implemented on the WDI allowing much more accurate statements to be made on the interactions between the contact surfaces and the particles in the friction gap. With the new load unit, much more accurate measurements can be carried out. In combination with an intelligent image data evaluation, it is now possible to show quantitative relationships between the external variables and the patch formation for the first time. We want to show first metrological results on patch dynamics and reservoir dynamics.