Measurement of oil film thickness and wear of nanometer scale under pure sliding conditions with ultrathin film interferometry

This paper describes an experimental study on pure sliding elastohydrodynamic point contact between surfaces having nanometer-scale roughness. Equations for film thickness of lubricating oil, gap in static contact, and loss of spacer thickness in ultrathin film interferometry are introduced. Sliding experiments are conducted in which double-spacer layers for minimizing wear are used; both glass disc and convex lens specimens are coated with silica by sputter deposition. Preliminary tests confirm the applicability of the technique under pure sliding conditions where progressive wear occurs, and it is possible to measure oil film thickness and spacer thickness loss simultaneously. The results also show that, in the mixed lubrication regime, oil film thickness and amount of wear vary under the same sliding velocity, viscosity, and temperature. The variation is due to differences in the initial gap, and in turn in the initial surface geometry.