Micromechanics of friction: effects of nanometre-scale roughness

Nanometre-scale roughness on a solid surface has significant effects on friction, since intersurface forces operate predominantly within a nanometre-scale gap distance in frictional contact. To study the effects of nanometre-scale roughness, two novel atomic force microscope friction experiments wer...

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Bibliographic Details
Published in:Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences Mathematical, physical, and engineering sciences, 2008-05, Vol.464 (2093), p.1319-1343
Main Authors: Li, Qunyang, Kim, Kyung-Suk
Format: Article
Language:English
Subjects:
Adhesion
Adhesives
Capillary Effects
Contact loads
Friction
Friction factor
Mica
Micromechanics Of Friction
Modeling
Nanometre-Scale Plasticity
Nanometre-Scale Roughness
Oblateness
Scale Effects
Sliding
Water pressure
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Summary:Nanometre-scale roughness on a solid surface has significant effects on friction, since intersurface forces operate predominantly within a nanometre-scale gap distance in frictional contact. To study the effects of nanometre-scale roughness, two novel atomic force microscope friction experiments were conducted, each using a gold surface sliding against a flat mica surface as the representative friction system. In one of the experiments, a pillar-shaped single nano-asperity of gold was used to measure the molecular-level frictional behaviour. The adhesive friction stress was measured to be 264 MPa and the molecular friction factor 0.0108 for a direct gold-mica contact. The nano-asperity was flattened in contact, although its hardness at this length scale is estimated to be 3.68 GPa. It was found that such a high pressure could be reached with the help of condensed water capillary forces. In the second experiment, a micrometre-scale asperity with nanometre-scale roughness exhibited a single-asperity-like response of friction. However, the apparent frictional stress, 40.5 MPa, fell well below the Hurtado-Kim model prediction of 208-245 MPa. In addition, the multiple nano-asperities were flattened during the frictional process, exhibiting load- and slip-history-dependent frictional behaviour.
ISSN:1364-5021
1471-2946
DOI:10.1098/rspa.2007.0364