15,206 research outputs found
Stick-Slip Motion and Phase Transition in a Block-Spring System
We study numerically stick slip motions in a model of blocks and springs
being pulled slowly. The sliding friction is assumed to change dynamically with
a state variable. The transition from steady sliding to stick-slip is
subcritical in a single block and spring system. However, we find that the
transition is continuous in a long chain of blocks and springs. The size
distribution of stick-slip motions exhibits a power law at the critical point.Comment: 8 figure
Intermittent stick-slip dynamics during the peeling of an adhesive tape from a roller
We study experimentally the fracture dynamics during the peeling at a
constant velocity of a roller adhesive tape mounted on a freely rotating
pulley. Thanks to a high speed camera, we measure, in an intermediate range of
peeling velocities, high frequency oscillations between phases of slow and
rapid propagation of the peeling fracture. This so-called stick-slip regime is
well known as the consequence of a decreasing fracture energy of the adhesive
in a certain range of peeling velocity coupled to the elasticity of the peeled
tape. Simultaneously with stick-slip, we observe low frequency oscillations of
the adhesive roller angular velocity which are the consequence of a pendular
instability of the roller submitted to the peeling force. The stick-slip
dynamics is shown to become intermittent due to these slow pendular
oscillations which produce a quasi-static oscillation of the peeling angle
while keeping constant the peeling fracture velocity (averaged over each
stick-slip cycle). The observed correlation between the mean peeling angle and
the stick-slip amplitude questions the validity of the usually admitted
independence with the peeling angle of the fracture energy of adhesives.Comment: Forthcoming in Physical Review
Stick-slip instabilities in sheared granular flow: the role of friction and acoustic vibrations
We propose a theory of shear flow in dense granular materials. A key
ingredient of the theory is an effective temperature that determines how the
material responds to external driving forces such as shear stresses and
vibrations. We show that, within our model, friction between grains produces
stick-slip behavior at intermediate shear rates, even if the material is
rate-strengthening at larger rates. In addition, externally generated acoustic
vibrations alter the stick-slip amplitude, or suppress stick-slip altogether,
depending on the pressure and shear rate. We construct a phase diagram that
indicates the parameter regimes for which stick-slip occurs in the presence and
absence of acoustic vibrations of a fixed amplitude and frequency. These
results connect the microscopic physics to macroscopic dynamics, and thus
produce useful information about a variety of granular phenomena including
rupture and slip along earthquake faults, the remote triggering of
instabilities, and the control of friction in material processing.Comment: 12 pages, 8 figure
Distinct stick-slip modes in adhesive polymer interfaces
Stick-slip, manifest as intermittent tangential motion between two solids, is
a well-known friction instability that occurs in a number of natural and
engineering systems. In the context of adhesive polymer interfaces, this
phenomenon has often been solely associated with Schallamach waves, which are
termed slow waves due to their low propagation speeds. We study the dynamics of
a model polymer interface using coupled force measurements and high speed
\emph{in situ} imaging, to explore the occurrence of stick-slip linked to other
slow wave phenomena. Two new waves---slip pulse and separation pulse---both
distinct from Schallamach waves, are described. The slip pulse is a sharp
stress front that propagates in the same direction as the Schallamach wave,
while the separation pulse involves local interface detachment and travels in
the opposite direction. Transitions between these stick-slip modes are easily
effected by changing the sliding velocity or normal load. The properties of
these three waves, and their relation to stick-slip is elucidated. We also
demonstrate the important role of adhesion in effecting wave propagation.Comment: 22 pages, 9 figure
Surface Roughness and Effective Stick-Slip Motion
The effect of random surface roughness on hydrodynamics of viscous
incompressible liquid is discussed. Roughness-driven contributions to
hydrodynamic flows, energy dissipation, and friction force are calculated in a
wide range of parameters. When the hydrodynamic decay length (the viscous wave
penetration depth) is larger than the size of random surface inhomogeneities,
it is possible to replace a random rough surface by effective stick-slip
boundary conditions on a flat surface with two constants: the stick-slip length
and the renormalization of viscosity near the boundary. The stick-slip length
and the renormalization coefficient are expressed explicitly via the
correlation function of random surface inhomogeneities. The effective
stick-slip length is always negative signifying the effective slow-down of the
hydrodynamic flows by the rough surface (stick rather than slip motion). A
simple hydrodynamic model is presented as an illustration of these general
hydrodynamic results. The effective boundary parameters are analyzed
numerically for Gaussian, power-law and exponentially decaying correlators with
various indices. The maximum on the frequency dependence of the dissipation
allows one to extract the correlation radius (characteristic size) of the
surface inhomogeneities directly from, for example, experiments with torsional
quartz oscillators.Comment: RevTeX4, 14 pages, 3 figure
Multiscale Stick-Slip Dynamics of Adhesive Tape Peeling
Using a high-speed camera, we follow the propagation of the detachment front
during the peeling of an adhesive tape from a flat surface. In a given range of
peeling velocity, this front displays a multiscale unstable dynamics,
entangling two well-separated spatiotemporal scales, which correspond to
microscopic and macroscopic dynamical stick-slip instabilities. While the
periodic release of the stretch energy of the whole peeled ribbon drives the
classical macro-stick-slip, we show that the micro-stick-slip, due to the
regular propagation of transverse dynamic fractures discovered by Thoroddsen et
al. [Phys. Rev. E 82, 046107 (2010)], is related to a high-frequency periodic
release of the elastic bending energy of the adhesive ribbon concentrated in
the vicinity of the peeling front.Comment: to appear in Physical Review Letters (2015
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