120 research outputs found
Shear thickening of suspensions of dimeric particles
In this article, I study the shear thickening of suspensions of frictional
dimers by the mean of numerical simulations. I report the evolution of the main
parameters of shear thickening, such as the jamming volume fractions in the
unthickened and thickened branches of the flow curves, as a function of the
aspect ratio of the dimers. The explored aspect ratios range from (spheres)
to (dimers made of two kissing spheres). I find a rheology qualitatively
similar than the one for suspensions of spheres, except for the first normal
stress difference , which I systematically find negative for small
asphericities. I also investigate the orientational order of the particles
under flow. Overall, I find that dense suspensions of dimeric particles share
many features with dry granular systems of elongated particles under shear,
especially for the frictional state at large applied stresses. For the
frictionless state at small stresses, I find that suspensions jam at lower
volume fraction than dry systems, and that this difference increases with
increasing aspect ratio. Moreover, in this state I find a thus far unobserved
alignment of the dimers along the vorticity direction, as opposed to the
commonly observed alignment with a direction close to the flow direction.Comment: 27 pages, 13 fig
Dynamical transition of glasses: from exact to approximate
We introduce a family of glassy models having a parameter, playing the role
of an interaction range, that may be varied continuously to go from a system of
particles in d dimensions to a mean-field version of it. The mean-field limit
is exactly described by equations conceptually close, but different from, the
Mode-Coupling equations. We obtain these by a dynamic virial construction.
Quite surprisingly we observe that in three dimensions, the mean-field behavior
is closely followed for ranges as small as one interparticle distance, and
still qualitatively for smaller distances. For the original particle model, we
expect the present mean-field theory to become, unlike the Mode-Coupling
equations, an increasingly good approximation at higher dimensions.Comment: 44 pages, 19 figure
Cavity method for force transmission in jammed disordered packings of hard particles
The force distribution of jammed disordered packings has always been
considered a central object in the physics of granular materials. However, many
of its features are poorly understood. In particular, analytic relations to
other key macroscopic properties of jammed matter, such as the contact network
and its coordination number, are still lacking. Here we develop a mean-field
theory for this problem, based on the consideration of the contact network as a
random graph where the force transmission becomes a constraint optimization
problem. We can thus use the cavity method developed in the last decades within
the statistical physics of spin glasses and hard computer science problems.
This method allows us to compute the force distribution for random
packings of hard particles of any shape, with or without friction. We find a
new signature of jamming in the small force behavior , whose exponent has attracted recent active interest: we find a
finite value for , along with . Furthermore, we relate
the force distribution to a lower bound of the average coordination number of jammed packings of frictional spheres with
coefficient . This bridges the gap between the two known isostatic limits
(in dimension ) and by extending the naive Maxwell's counting argument to
frictional spheres. The theoretical framework describes different types of
systems, such as non-spherical objects in arbitrary dimensions, providing a
common mean-field scenario to investigate force transmission, contact networks
and coordination numbers of jammed disordered packings
A constitutive model for simple shear of dense frictional suspensions
Discrete particle simulations are used to study the shear rheology of dense,
stabilized, frictional particulate suspensions in a viscous liquid, toward
development of a constitutive model for steady shear flows at arbitrary stress.
These suspensions undergo increasingly strong continuous shear thickening (CST)
as solid volume fraction increases above a critical volume fraction, and
discontinuous shear thickening (DST) is observed for a range of . When
studied at controlled stress, the DST behavior is associated with non-monotonic
flow curves of the steady-state stress as a function of shear rate. Recent
studies have related shear thickening to a transition between mostly lubricated
to predominantly frictional contacts with the increase in stress. In this
study, the behavior is simulated over a wide range of the dimensionless
parameters , and , with the dimensionless shear stress and the coefficient of
interparticle friction: the dimensional stress is , and , where is the magnitude of repulsive force at contact
and is the particle radius. The data have been used to populate the model
of the lubricated-to-frictional rheology of Wyart and Cates [Phys. Rev.
Lett.{\bf 112}, 098302 (2014)], which is based on the concept of two viscosity
divergences or \textquotedblleft jamming\textquotedblright\ points at volume
fraction (random close packing) for the
low-stress lubricated state, and at for
any nonzero in the frictional state; a generalization provides the normal
stress response as well as the shear stress. A flow state map of this material
is developed based on the simulation results.Comment: 12 pages, 10 figure
Shear-induced organization of forces in dense suspensions: signatures of discontinuous shear thickening
Dense suspensions can exhibit an abrupt change in their viscosity in response
to increasing shear rate. The origin of this discontinuous shear thickening
(DST) has been ascribed to the transformation of lubricated contacts to
frictional, particle-on-particle contacts. Recent research on the flowing and
jamming behavior of dense suspensions has explored the intersection of ideas
from granular physics and Stokesian fluid dynamics to better understand this
transition from lubricated to frictional rheology. DST is reminiscent of
classical phase transitions, and a key question is how interactions between the
microscopic constituents give rise to a macroscopic transition. In this paper,
we extend a formalism that has proven to be successful in understanding shear
jamming of dry grains to dense suspensions. Quantitative analysis of the
collective evolution of the contact-force network accompanying the DST
transition demonstrates clear changes in the distribution of microscopic
variables, and leads to the identification of an "order parameter"
characterizing DST.Comment: 4 pages. We welcome comments and criticism
Microscopic theory for the rheology of jammed soft suspensions
We develop a constitutive model allowing for the description of the rheology
of two-dimensional soft dense suspensions above jamming. Starting from a
statistical description of the particle dynamics, we derive, using a set of
approximations, a non-linear tensorial evolution equation linking the
deviatoric part of the stress tensor to the strain-rate and vorticity tensors.
The coefficients appearing in this equation can be expressed in terms of the
packing fraction and of particle-level parameters. This constitutive equation
rooted in the microscopic dynamic qualitatively reproduces a number of salient
features of the rheology of jammed soft suspensions, including the presence of
yield stresses for the shear component of the stress and for the normal stress
difference. More complex protocols like the relaxation after a preshear are
also considered, showing a smaller stress after relaxation for a stronger
preshear.Comment: 5 pages, 1 figur
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