146 research outputs found
CHST11 (carbohydrate (chondroitin 4) sulfotransferase 11)
Review on CHST11, with data on DNA/RNA, on the protein encoded and where the gene is implicated
Modeling the Full Time-Dependent Phenomenology of Filled Rubber for Use in Anti-Vibration Design
Component design of rubber-based anti-vibration devices remains a challenge, since there is a lack of predictive models in the typical regimes encountered by anti-vibration devices that are deformed to medium dynamic strains (0.5 to 3.5) at medium strain rates (0.5/s to 10/s). An approach is proposed that demonstrates all non-linear viscoelastic effects such as hysteresis and cyclic stress softening. As it is based on a free-energy, it is fast and easily implementable. The fitting parameters behave meaningfully when changing the filler volume fraction. The model was implemented for use in the commercial finite element software ABAQUS. Examples of how to fit experimental data and simulations for a variety of carbon black filled natural rubber compounds are presented
Rubber friction on wet and dry road surfaces: the sealing effect
Rubber friction on wet rough substrates at low velocities is typically 20-30%
smaller than for the corresponding dry surfaces. We show that this cannot be
due to hydrodynamics and propose a novel explanation based on a sealing effect
exerted by rubber on substrate "pools" filled with water. Water effectively
smoothens the substrate, reducing the major friction contribution due to
induced viscoelastic deformations of the rubber by surface asperities. The
theory is illustrated with applications related to tire-road friction.Comment: Format Revtex 4; 8 pages, 11 figures (no color); Published on Phys.
Rev. B (http://link.aps.org/abstract/PRB/v71/e035428); previous work on the
same topic: cond-mat/041204
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
Rubber friction: role of the flash temperature
When a rubber block is sliding on a hard rough substrate, the substrate
asperities will exert time-dependent deformations of the rubber surface
resulting in viscoelastic energy dissipation in the rubber, which gives a
contribution to the sliding friction. Most surfaces of solids have roughness on
many different length scales, and when calculating the friction force it is
necessary to include the viscoelastic deformations on all length scales. The
energy dissipation will result in local heating of the rubber. Since the
viscoelastic properties of rubber-like materials are extremely strongly
temperature dependent, it is necessary to include the local temperature
increase in the analysis. At very low sliding velocity the temperature increase
is negligible because of heat diffusion, but already for velocities of order
0.01 m/s the local heating may be very important. Here I study the influence of
the local heating on the rubber friction, and I show that in a typical case the
temperature increase results in a decrease in rubber friction with increasing
sliding velocity for v > 0.01 m/s. This may result in stick-slip instabilities,
and is of crucial importance in many practical applications, e.g., for the
tire-road friction, and in particular for ABS-breaking systems.Comment: 22 pages, 27 figure
Well dispersed fractal aggregates as filler in polymer-silica nanocomposites: long range effects in rheology
We are presenting a new method of processing polystyrene-silica
nanocomposites, which results in a very well-defined dispersion of small
primary aggregates (assembly of 15 nanoparticles of 10 nm diameter) in the
matrix. The process is based on a high boiling point solvent, in which the
nanoparticles are well dispersed, and controlled evaporation. The filler's fine
network structure is determined over a wide range of sizes, using a combination
of Small Angle Neutron Scattering (SANS) and Transmission Electronic Microscopy
(TEM). The mechanical response of the nanocomposite material is investigated
both for small (ARES oscillatory shear and Dynamical Mechanical Analysis) and
large deformations (uniaxial traction), as a function of the concentration of
the particles. We can investigate the structure-property correlations for the
two main reinforcement effects: the filler network contribution, and a
filler-polymer matrix effect. Above a silica volume fraction threshold, we see
a divergence of the modulus correlated to the build up of a connected network.
Below the threshold, we obtain a new additional elastic contribution of much
longer terminal time than the matrix. Since aggregates are separated by at
least 60 nm, this new filler-matrix contribution cannot be described solely
with the concept of glassy layer (2nm)
Determination of the Loading Mode Dependence of the Proportionality Parameter for the Tearing Energy of Embedded Flaws in Elastomers Under Multiaxial Deformations
In this paper, the relationship between the tearing energy and the far-field cracking energy density (CED) is evaluated for an embedded penny-shaped flaw in a 3D elastomer body under a range of loading modes. A 3D finite element model of the system is used to develop a computational-based fracture mechanics approach which is used to evaluate the tearing energy at the crack in different multiaxial loading states. By analysing the tearing energy’s relationship to the far-field CED, the proportionality parameter in the CED formulation is found to be a function of stretch and biaxiality. Using a definition of biaxiality that gives a unique value for each loading mode, the proportionality parameter becomes a linear function of stretch and biaxiality. Tearing energies predicted through the resulting equation show excellent agreement to those calculated computationally
On the nature of surface roughness with application to contact mechanics, sealing, rubber friction and adhesion
Surface roughness has a huge impact on many important phenomena. The most
important property of rough surfaces is the surface roughness power spectrum
C(q). We present surface roughness power spectra of many surfaces of practical
importance, obtained from the surface height profile measured using optical
methods and the Atomic Force Microscope. We show how the power spectrum
determines the contact area between two solids. We also present applications to
sealing, rubber friction and adhesion for rough surfaces, where the power
spectrum enters as an important input.Comment: Topical review; 82 pages, 61 figures; Format: Latex (iopart). Some
figures are in Postscript Level
Modeling of Intermediate Structures and Chain Conformation in Silica-Latex Nanocomposites Observed by SANS During Annealing
The evolution of the polymer structure during nanocomposite formation and
annealing of silica-latex nanocomposites is studied using contrast-variation
small angle neutron scattering. The experimental system is made of silica
nanoparticles (Rsi \approx 8 nm) and a mixture of purpose-synthesized
hydrogenated and deuterated nanolatex (Rlatex \approx 12.5 nm). The progressive
disappearance of the latex beads by chain interdiffusion and release in the
nanocomposites is analyzed quantitatively with a model for the scattered
intensity of hairy latex beads and an RPA description of the free chains. In
silica-free matrices and nanocomposites of low silica content (7%v), the
annealing procedure over weeks at up to Tg + 85 K results in a molecular
dispersion of chains, the radius of gyration of which is reported. At higher
silica content (20%v), chain interdiffusion seems to be slowed down on
time-scales of weeks, reaching a molecular dispersion only at the strongest
annealing. Chain radii of gyration are found to be unaffected by the presence
of the silica filler
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