1,106 research outputs found
Crumpling of a stiff tethered membrane
first-principles numerical simulation model for crumpling of a stiff tethered
membrane is introduced. In our model membranes, wrinkles, ridge formation,
ridge collapse, as well as the initiation of stiffness divergence, are
observed. The ratio of the amplitude and wave length of the wrinkles, and the
scaling exponent of the stiffness divergence, are consistent with both theory
and experiment. We observe that close to the stiffness divergence there appears
a crossover beyond which the elastic behavior of a tethered membrane becomes
similar to that of dry granular media. This suggests that ridge formation in
membranes and force-chain network formation in granular packings are different
manifestations of a single phenomenon.Comment: For full resolution figures, please send us an emai
Brittle fracture down to femto-Joules - and below
We analyze large sets of energy-release data created by stress-induced
brittle fracture in a pure sapphire crystal at close to zero temperature where
stochastic fluctuations are minimal. The waiting-time distribution follows that
observed for fracture in rock and for earthquakes. Despite strong time
correlations of the events and the presence of large-event precursors, simple
prediction algorithms only succeed in a very weak probabilistic sense. We also
discuss prospects for further cryogenic experiments reaching close to
single-bond sensitivity and able to investigate the existence of a
transition-stress regime.Comment: REVTeX, new figure added, minor modifications to tex
Kinetic Roughening in Slow Combustion of Paper
Results of experiments on the dynamics and kinetic roughening of
one-dimensional slow-combustion fronts in three grades of paper are reported.
Extensive averaging of the data allows a detailed analysis of the spatial and
temporal development of the interface fluctuations. The asymptotic scaling
properties, on long length and time scales, are well described by the
Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To
obtain a more detailed picture of the strong-coupling fixed point,
characteristic of the KPZ universality class, universal amplitude ratios, and
the universal coupling constant are computed from the data and found to be in
good agreement with theory. Below the spatial and temporal scales at which a
cross-over takes place to the standard KPZ behavior, the fronts display higher
apparent exponents and apparent multiscaling. In this regime the interface
velocities are spatially and temporally correlated, and the distribution of the
magnitudes of the effective noise has a power-law tail. The relation of the
observed short-range behavior and the noise as determined from the local
velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3
tables; submitted to Phys. Rev.
Roughening of a propagating planar crack front
A numerical model of the front of a planar crack propagating between two connected elastic plates is investigated. The plates are modeled as square lattices of elastic beams. The plates are connected by similar but breakable beams with a randomly varying stiffness. The crack is driven by pulling both plates at one end in Mode I at a constant rate. We find ζ=1/3, z=4/3, and β=1/4 for the roughness, dynamical, and growth exponents, respectively, that describe the front behavior. This is similar to continuum limit analyses based on a perturbative stress-intensity treatment of the front [H. Gao and J. R. Rice, J. Appl. Mech. 56, 828 (1989)]. We discuss the differences to recent experiments.Peer reviewe
Film dynamics and lubricant depletion by droplets moving on lubricated surfaces
Lubricated surfaces have shown promise in numerous applications where
impinging foreign droplets must be removed easily; however, before they can be
widely adopted, the problem of lubricant depletion, which eventually leads to
decreased performance, must be solved. Despite recent progress, a quantitative
mechanistic explanation for lubricant depletion is still lacking. Here, we
first explained the shape of a droplet on a lubricated surface by balancing the
Laplace pressures across interfaces. We then showed that the lubricant film
thicknesses beneath, behind, and wrapping around a moving droplet change
dynamically with droplet's speed---analogous to the classical
Landau-Levich-Derjaguin problem. The interconnected lubricant dynamics results
in the growth of the wetting ridge around the droplet, which is the dominant
source of lubricant depletion. We then developed an analytic expression for the
maximum amount of lubricant that can be depleted by a single droplet.
Counter-intuitively, faster moving droplets subjected to higher driving forces
deplete less lubricant than their slower moving counterparts. The insights
developed in this work will inform future work and the design of longer-lasting
lubricated surfaces
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