Thin film colorimetric interferometry

Measurement technique for the study of very thin lubrication films down to one nanometer in a point contact between a steel hall and a transparent dis c is used to explore the relationship between central and minimum film thic kness and rolling speed at the interface between elastohydrodynamic and bou ndary lubrication for a series of lubricating fluids. This technique based on the colorimetric interferometry combines powerful film thickness mapping capabilities with high accuracy. It was confirmed that both hexadecane and mineral base oil obey the linear relationship between log central and minimum film thickness and log rolling speed predicted by elastohydrodynamic theory down to approximately one nan ometer. Conversely, squalane and additive-treated mineral base oil showed f ilm thickness enhancement at slow speeds caused by boundary layers formatio n within the lubricant film. Obtained experimental data was used for the de termination of pressure-viscosity coefficients of test fluids. The measurem ent technique also enabled us to produce information about the influence of boundary layers on film thickness shape.