Self-Similar Fluctuations and 1/ f Noise in Dry Friction Dynamics
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UCTION
IN spite of its paramount technological importance, friction, and to a larger extent wear, remains as one of the most elusive material properties. The lack of sound basic theories that may explain, even at a qualitative level, the most important features of wear performance, has long prompted the development of empirical or semiempirical analyses aiming to correlate volume or mass loss with relevant variables such as load, speed, environmental conditions, material properties, etc.[1–6] Two are the most important features, inferred from many experimental observations, of the already classic approach to wear discussed in Reference 1: (1) experimental conditions—wear rate is proportional to the applied load and to the sliding distance (or speed); and (2) material properties—wear rate is inversely proportional to material hardness. While the former remains to a wide extent valid, the applicability of the latter to composites has been recently questioned.[4,7] Altogether, friction and wear, in recent years, have been attracting the interest not only of materials scientists but also of researchers from the field of surface science[8] and physics.[9,10,11] For instance, the use of modern powerful techniques for surface analysis and M. DUARTE, Postdoctoral Student and J.M. MOLINA, Researcher, are with the Departamento de Fı´ sica Aplicada and the Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain. Contact e-mail: [email protected] R. PRIETO, Postdoctoral Student, is with the Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, Alicante, Spain. E. LOUIS, Full Professor, is with the Departamento de Fı´ sica Aplicada, the Instituto Universitario de Materiales de Alicante (IUMA) and the Unidad Associada del Consejo Superior de Investigaciones Cientificas, Universidad de Alicante, Alicante, Spain. J. NARCISO, Associate Professor, is with the Departamento de Quı´ mica Inorga´nica and the Instituto Universitario de Materiales de Alicante (IUMA), Universidad de Alicante, Alicante, Spain. Manuscript submitted May 16, 2006 298—VOLUME 38A, FEBRUARY 2007
topography studies, such as scanning tunneling and atomic force microscopes, provides useful information at the atomic scale.[8,12] Thorough and careful dry-friction experiments on a paper-on-paper system[9] have identified a crossover from creep to the inertial regime as the sliding speed was increased. The results reported in Reference 9 indicate that creep dynamics is characterized by a logarithmically decreasing dynamic friction coefficient, while in the inertial regime, the friction coefficient increases linearly with sliding speed. Although the inertial regime is commonly associated to steady sliding,[5] the experiments of Reference 9 showed a more complex scenario in which stick slip was compatible with the inertial regime provided that the stiffness of the slider was sufficiently low. It is pertinent to remark that although in paper-on-paper experiments wear effects are weak,[9] it
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