2015 Volume 60 Issue 2 Pages 144-152
To measure friction characteristics of lubricant films in nanometer thickness, we constituted novel ball suspension assemblies (BSAs) in which ultra-smooth glass balls 2 mm in diameter were employed and a portion of the ball was protruded through a hole fabricated at the end of the suspension. Using BSAs with different protrusion heights of 1.48, 0.81 and 0.41 mm, the sliding tests were performed under the same sliding condition, and the out-of-plane vibration of the suspension and the lateral vibration of the friction-displacement transducer comprised of parallel springs were compared in a wide speed range. From these comparisons, we derived a guideline for BSA design, i.e., reducing protrusion height to around 0.8 mm allows for significant vibration suppression and stable sliding at a high speed up to 209 mm/s. In addition, using this novel type of BSA, we measured friction forces of PFPE Zdol4000 lubricant films in nanometer thickness at loading forces of 0.2-1.6 mN, and speeds of 2.09-209 mm/s. The applicability of the Johnson-Kedall-Roberts (JKR) theory and the Derjaguin-Muller-Toporov (DMT) theory to the experimental results was discussed.
