5,685 research outputs found

### Rubber friction on (apparently) smooth lubricated surfaces

We study rubber sliding friction on hard lubricated surfaces. We show that
even if the hard surface appears smooth to the naked eye, it may exhibit short
wavelength roughness, which may give the dominant contribution to rubber
friction. That is, the observed sliding friction is mainly due to the
viscoelastic deformations of the rubber by the substrate surface asperities.
The presented results are of great importance for rubber sealing and other
rubber applications involving (apparently) smooth surfaces.Comment: 7 pages, 15 figure

### Contact mechanics with adhesion: Interfacial separation and contact area

We study the adhesive contact between elastic solids with randomly rough,
self affine fractal surfaces. We present molecular dynamics (MD) simulation
results for the interfacial stress distribution and the wall-wall separation.
We compare the MD results for the relative contact area and the average
interfacial separation, with the prediction of the contact mechanics theory of
Persson. We find good agreement between theory and the simulation results. We
apply the theory to the system studied by Benz et al. involving polymer in
contact with polymer, but in this case the adhesion gives only a small
modification of the interfacial separation as a function of the squeezing
pressure.Comment: 5 pages, 4 figure

### On the dependence of the leak-rate of seals on the skewness of the surface height probability distribution

Seals are extremely useful devices to prevent fluid leakage. We present
experimental result which show that the leak-rate of seals depend sensitively
on the skewness in the height probability distribution. The experimental data
are analyzed using the critical-junction theory. We show that using the
top-power spectrum result in good agreement between theory and experiment.Comment: 5 pages, 9 figure

### Leak-rate of seals: comparison of theory with experiment

Seals are extremely useful devices to prevent fluid leakage. We present
experimental results for the leak-rate of rubber seals, and compare the results
to a novel theory, which is based on percolation theory and a recently
developed contact mechanics theory. We find good agreement between theory and
experiment.Comment: 6 pages, 10 figure

### Influence of frozen capillary waves on contact mechanics

Free surfaces of liquids exhibit thermally excited (capillary) surface waves.
We show that the surface roughness which results from capillary waves when a
glassy material is cooled below the glass transition temperature can have a
large influence on the contact mechanics between the solids. The theory suggest
a new explanation for puzzling experimental results [L. Bureau, T. Baumberger
and C. Caroli, arXiv:cond-mat/0510232] about the dependence of the frictional
shear stress on the load for contact between a glassy polymer lens and flat
substrates. It also lend support for a recently developed contact mechanics
theory.Comment: 4 pages, 2 figure

### Contact mechanics: relation between interfacial separation and load

I study the contact between a rigid solid with a randomly rough surface and
an elastic block with a flat surface. I derive a relation between the (average)
interfacial separation $u$ and the applied normal squeezing pressure $p$. I
show that for non-adhesive inte raction and small applied pressure, p is
proportional to exp (-u/u_0), in good agreement with recent experimental
observation.Comment: 4 pages, 3 figure

### Rolling friction for hard cylinder and sphere on viscoelastic solid

We calculate the friction force acting on a hard cylinder or spherical ball
rolling on a flat surface of a viscoelastic solid. The rolling friction
coefficient depends non-linearly on the normal load and the rolling velocity.
For a cylinder rolling on a viscoelastic solid characterized by a single
relaxation time Hunter has obtained an exact result for the rolling friction,
and our result is in very good agreement with his result for this limiting
case. The theoretical results are also in good agreement with experiments of
Greenwood and Tabor. We suggest that measurements of rolling friction over a
wide range of rolling velocities and temperatures may constitute an useful way
to determine the viscoelastic modulus of rubber-like materials.Comment: 7 pages, 6 figure

### Fluid flow at the interface between elastic solids with randomly rough surfaces

I study fluid flow at the interface between elastic solids with randomly
rough surfaces. I use the contact mechanics model of Persson to take into
account the elastic interaction between the solid walls and the Bruggeman
effective medium theory to account for the influence of the disorder on the
fluid flow. I calculate the flow tensor which determines the pressure flow
factor and, e.g., the leak-rate of static seals. I show how the perturbation
treatment of Tripp can be extended to arbitrary order in the ratio between the
root-mean-square roughness amplitude and the average interfacial surface
separation. I introduce a matrix D(Zeta), determined by the surface roughness
power spectrum, which can be used to describe the anisotropy of the surface at
any magnification Zeta. I present results for the asymmetry factor Gamma(Zeta)
(generalized Peklenik number) for grinded steel and sandblasted PMMA surfaces.Comment: 16 pages, 14 figure

### Molecular dynamics study of contact mechanics: contact area and interfacial separation from small to full contact

We report a molecular dynamics study of the contact between a rigid solid
with a randomly rough surface and an elastic block with a flat surface. We
study the contact area and the interfacial separation from small contact (low
load) to full contact (high load). For small load the contact area varies
linearly with the load and the interfacial separation depends logarithmically
on the load. For high load the contact area approaches to the nominal contact
area (i.e., complete contact), and the interfacial separation approaches to
zero. The present results may be very important for soft solids, e.g., rubber,
or for very smooth surfaces, where complete contact can be reached at moderate
high loads without plastic deformation of the solids.Comment: 4 pages,5 figure

### Interfacial separation between elastic solids with randomly rough surfaces: comparison of experiment with theory

We study the average separation between an elastic solid and a hard solid
with a nominal flat but randomly rough surface, as a function of the squeezing
pressure. We present experimental results for a silicon rubber (PDMS) block
with a flat surface squeezed against an asphalt road surface. The theory shows
that an effective repulse pressure act between the surfaces of the form p
proportional to exp(-u/u0), where u is the average separation between the
surfaces and u0 a constant of order the root-mean-square roughness, in good
agreement with the experimental results.Comment: 6 pages, 10 figure

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