Measurement of real contact area and analysis of stick/slip region

The real contact area obtained between a rough rubber hemisphere and a glass plate, under unlubricated conditions, was visualized by white light interferometry. The contacting friction condition of the real contact area in the starting friction process was analyzed using interference intensity. The real contact area was extracted by fitting the intensity histogram of interference images to Gaussian distribution. This was seen to decrease with the increase of the applied tangential force, and it became approximately constant after initiation of macroscopic sliding. Real shear stress increased linearly in the micro-sliding regime and then became constant in the macro-sliding regime with the increase of the glass plateʹs displacement. The statistical ratio of stick region to contact area was estimated with the use of a differential histogram of the interference image intensity based on a tangential force coefficient of zero. This ratio showed a tendency to be more than a theoretical solution offered by Mindlin. In addition, we performed particle image velocimetry analysis, which assumed real contact spots as chase markers, and succeeded in the mapping of the stick/slip region within the real contact area.