Ferdinando Giacco, Seconda Università di Napoli #
Mechanical vibrations in a spring-block model #
Mechanical vibrations may influence the frictional force between sliding 
surfaces, affecting their
relative motion and the associated stick-slip dynamics. This effe€ect is 
relevant for phenomena
occurring at very different length scales, from atomic to mesoscopic 
systems, as the physics
responsible for friction is expected to be largely the same [1, 2, 3]. The 
study of mechanical
perturbated systems is frequently connected to the geophysical scale, 
where it is possible that
earthquakes, a stick-slip frictional instability [4], may be actually 
triggered by incoming seismic
waves, a phenomenon regularly observed in numerical simulations of seismic 
fault models [5].
The role of external perturbations has also been investigated via 
simulations of vibrated and
sheared Lennard-Jones particles at zero temperature [6]. This work 
revealed the possibility to
suppress the friction coefficientnt by applying perturbations in a well 
defined range  of frequencies.
However, it is not clear whereas the presence of the particles in between 
the sliding surfaces is
essential to reproduce friction suppression.
Via the analytical and numerical study of three variants of the usual 
spring-block model in the
presence of an history dependent frictional force, we identify the 
conditions under which friction is
suppressed and/or recovered [7]. In all the cases the block moves along a 
surface which is vibrated
along the vertical direction, and the role of both the amplitude and the 
frequency of vibration is
explored. An order parameter is introduced to differentiate the 
stick-slip and the flowing phases,
and a phase diagram is proposed for each model.
Results show that by incresing the intensity of the perturbation we 
observe a transition from the
stick-slip to the sliding phase. Only in the presence of a modulated 
surface, and of a block confined
by a force which is always normal to this surface, a further increase of 
the oscillation frequency
leads to a second friction recovery transition, in which the system 
transients from the sliding to the
stickslip phase. This result clarify that the friction recovery transition 
is not a peculiarity of many
particle systems but rather a phenomenon linked to the modulation of the 
surface over which the
block slides.
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[1] M. Urbakh, J. Klafter, D. Gourdon, and J. Israelachvili, Nature 430, 
29 (2004)
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[2] A. Socoliuc, E. Gnecco, S. Maier, O. Pfeiffer, A. Batoff,ff, 
Bennewitz and E. Meyer, Science
313, 207 (2006).
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[3] P.A. Johnson and X. Jia, Nature 437, 871 (2005).
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[4] C. Marone, Nature 391, 69 (1998).
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[5] M. P. Ciamarra, E. Lippiello, C. Godano and L. de Arcangelis, Phys. 
Rev. Lett. 104, 238001
(2010).
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[6] R. Capozza, A. Vanossi, A. Vezzani, and S. Zapperi, Phys. Rev. Lett 
103, 085502 (2009).
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[7] F. Giacco , E. Lippiello, M. Pica Ciamarra. Submitted to Phys. Rev. E.