Elucidation of contact state on various rough surfaces via highly robust colorimetric optical interferometry

Abstract

In this study, we developed and practiced colorimetric optical interferometry for the direct observation of contact states to clarify contact phenomena. We theoretically demonstrated that the effect of roughness diffuse reflection could be neglected using interferometric light intensity according to the relationship between the optical film thickness and hue. Then, we measured the static contact surfaces of spherical test pieces of different root mean square roughnesses. Results indicate that the nominal contact area is significantly larger than that obtained from the Hertzian theory of smooth contact as the surface roughness increases. The contact film thickness on the nominal contact area increases almost in proportion to the root mean square roughness. Our experiment supports the validity of the contact theory and contact simulation with very small roughnesses, which have been difficult to verify experimentally. The advantage of this measurement is that it can simultaneously capture the macroscopic contact area and microscopic film thickness distribution, which is expected to further expand the range of application.

Visualization of oil-lubrication ball bearings at high rotational speeds

“…The optical film thickness was determined by comparing the central interference color at the contact surface of the ball with the optical film thickness color chart shown in Figure 3. In cases with significant variations in the interference color within the contact area, a two-dimensional quantitative analysis using the hue method developed by Tomota et al (2022) was used to calculate the thickness. The calculated optical film thickness includes the thickness of the reflective and spacer films.…”

Measurement of Oil-Film Thickness and Observation of Oil Distribution in High-Speed Deep-Groove Ball Bearings

“…4. When the film thickness at the contact surface varied greatly, a twodimensional quantitative analysis was also performed using the color-phase method proposed by Tomota et al [21]. The optical thickness determined by these methods includes that for both the reflective and spacer layers.…”