Experimental determination of the effective contact radius of ruby microspheres

摘要

The real contact area and the effective contact radius of rough bodies are important variables for the tribological characterisation of bearings, the verification of tactile probes in metrology and the analysis of heat transfer and electrical contact. While the macroscopic and nanoscopic contact is a topic of widespread research, radii of curvature in the order of 100 μm and normal forces in the order of 10 mN up to 1 N are investigated only infrequently. In this study ruby spheres with a mean diameter of 200 μm are pressed against a sapphire plate. Prior to the experiment, the roughness parameters were determined by means of scanning force microscopy and the spheres were coated by means of physical vapour deposition. The effective contact radii were determined by means of scanning electron microscopy. It is shown that the measured effective contact-radii are in good agreement with statistical contact models [ 1,2] and, for normal forces exceeding approximately 300 mN, with the Hertzian values.