Measurements of real contact areas using PET films (thickness, 0.9 μm)

Abstract A new method of measuring the distribution of real contact areas between two solid surfaces has been developed. A polyethyleneterephthalate (PET) film was inserted at the contact interface and pressed at a given pressure for 1 min. It was indented by surface asperities at real contact points. The indented areas where plastic deformation occurred were measured automatically by image processing through an optical microscope which was modified so that its stage could be controlled by a microcomputer. A contact microscope which could observe the entire nominal contact area was used to examine the real contact areas measured by the PET film method. One of the two solids in contact must be transparent so that the contact microscope can be used. Thus the real contact areas between the ground surfaces and a right-angled prism were measured by the PET film method and the contact microscope. The distributions of the real contact areas measured by the two different methods were in relatively good agreement with each other. However, the PET film method depended on the surface roughness of the specimens. Surfaces smoother than the thickness of the PET film did not give a sufficient indentation on the PET film.