The real contact area between transparent non-flat surfaces and a rubber plate under steady contact was analyzed on the basis of visualization images generated by using light-induced fluorescence. We examined the fundamental characteristics of a plano-convex lens, and we developed a technique for extracting the real contact area for a rough surface model by Gaussian distribution fitting. An aqueous rhodamine-B solution was used for fluorescence measurements, where the results confirmed the linearity of the relation between intensity and film thickness for thicknesses up to 0.1 mm. In the case of a plano-convex lens specimen, we determined the starting point of contact, that is, the loading where a peak appeared on the lowest intensity side of the intensity histogram. A Gaussian distribution was fit to the histogram upon obtaining the difference from the histogram at zero loading, in which the extracted distribution domain equivalent to the real contact area agreed with the theoretical Hertzian contact area. In the rough surface model specimen, a peak emerged in the part of the histogram with lowest intensity, and the real contact area was measured by using a fitting method based on a Gaussian distribution.
View full abstract