-- MicheleLanzetta? - 16 Jul 2004

All cited articles are included in the Stanford Library licensed e-databases.

(New items added at the top)

  • A Scale-Dependent Model for Multi-Asperity Contact and Friction
George G. Adams, Sinan Muftu, and Nazif Mohd Azhar, J. Tribol. 125, 700 (2003)

Friction models and history, from Coulomb to a multi-asperity one. A Gaussian distribution of asperity peaks is considered. Lot of maths. Simulations on combinations of parameters are considered: surface roughness parameter, friction regime parameter, the surface energy of adhesion parameter, and normal load. Recent and interesting. I need to go back again in it.

  • Analysis of Asperity-Asperity Adhesion Forces Utilizing Statistical Analysis Techniques and the Force Selectivity of the Scanning Probe Microscope
Gerold A. Willing and Ronald D. Neuman Langmuir; 2002; 18(22) pp 8370 - 8374; (Research Article) DOI: 10.1021/la0114474

Application of statistical analysis of bonds at atomic level. Adhesion is due to asperities contact. Examined the case of cellulose molecules, and demonstrated that bridging for capillary condensation dominates the interforces between asperities. Adhesion is then F=4 Pi R Gamma where R is the average radius of asperities in contact and Gamma is the surface free energy. Did measurement and provided literature data and calculations.

  • M. Mata and J. Alcalá, The role of friction on sharp indentation, Journal of the Mechanics and Physics of Solids, Volume 52, Issue 1, January 2004, Pages 145-165.
http://www.sciencedirect.com/science/article/B6TXB-49S7W5W-1/2/ca3cb22fc95169b2e01f00fac5313e7c http://dx.doi.org/10.1016/S0022-5096(03)00075-9

Abstract: Frictional effects on sharp indentation of strain hardening solids are examined in this paper. The results of finite element simulations in a wide range of solids allow us to derive two simplified equations, accounting for the influence of the friction coefficient on hardness. Comparisons between the simulations and instrumented micro-indentation experiments are undertaken to ensure the validity of the former to metallic materials. Quantitative estimates of the role of friction on the development of pileup and sinking-in around the contact boundary are also given in the paper. These results provide a physical insight into the plastic flow features of distinctly different solids brought into contact with sharp indenters. Overall, the investigation shows that the amount of pileup can be used to set the range of validity of the two hardness equations indicated above. Friction has the largest influence on the contact response of solids exhibiting considerable piling-up effects (whose parameter , see text for details), whereas materials developing moderate pileup or sinking-in are less sensitive to friction. Finally, a methodology is devised to assess the influence of the friction coefficient on mechanical properties extracted through indentation experiments.

Hardness (usually measured by indentation) depends on friction (20%) ==> for penetration, CLAWS should be lubricated! Unfortunately, for unpenetrable surfaces friction should be increased.

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