Suppression of Friction by Mechanical Vibrations
R. Capozza, A. Vanossi, A. Vezzani, and S. Zapperi
Thorough molecular dynamics simulations, researchers from AFRI and ACOF CRPs have proposed a theoretical explanation of the suppression of friction in a confined system under shear subjected to small mechanical vibrations. The important result could help in improving frictional properties of nano-devices and, as well, in explaining earthquake triggering by small dynamic perturbations.
Figure 1: (a) Friction coefficient µ vs time obtained for three values of the bottom oscillating frequency. (b) Time-averaged value of µ as a function of oscillating frequency for four values of the oscillation amplitude A (ranging from 3% to 9% of the 3-layer lubricant thickness). (c) Time-averaged value of µ vs oscillating frequency for 4-layer bricant and four values of the damping coefficient.
Mechanical vibrations are known to affect frictional sliding and the associated stick-slip patterns causing sometimes a drastic reduction of the friction force. This issue is relevant for applications in nanotribology and to understand earthquake triggering by small dynamic perturbations. We study the dynamics of repulsive particles confined between a horizontally driven top plate and a vertically oscillating bottom plate. Our numerical results show a suppression of the high dissipative stick-slip regime (Figure 1, panel (a)) in a well-defined range of frequencies (panels (b) and (c)) that depends on the vibrating amplitude, the normal applied load, the system inertia and the damping constant. We propose a theoretical explanation of the numerical results and derive a phase diagram indicating the region of parameter space where friction is suppressed. Our results allow to define better strategies for the mechanical control of friction. This research has been also supported by the European Commissions NEST Pathfinder programme TRIGS (http://www.trigs.eu/).
These results have recently appeared in Physical Review Letters 103, 085502 (2009) and selected also by the Virtual Journal of Nanoscale Science & Technology (Volume 20 Issue 9).
