160 research outputs found
Coefficient of tangential restitution for the linear dashpot model
The linear dashpot model for the inelastic normal force between colliding
spheres leads to a constant coefficient of normal restitution,
const., which makes this model very popular for the investigation
of dilute and moderately dense granular systems. For two frequently used models
for the tangential interaction force we determine the coefficient of tangential
restitution , both analytically and by numerical integration of
Newton's equation. Although const. for the linear-dashpot model,
we obtain pronounced and characteristic dependencies of the tangential
coefficient on the impact velocity . The
results may be used for event-driven simulations of granular systems of
frictional particles.Comment: 12 pages, 12 figure
Collision of Viscoelastic Spheres: Compact Expressions for the Coefficient of Normal Restitution
The coefficient of restitution of colliding viscoelastic spheres is
analytically known as a complete series expansion in terms of the impact
velocity where all (infinitely many) coefficients are known. While beeing
analytically exact, this result is not suitable for applications in efficient
event-driven Molecular Dynamics (eMD) or Monte Carlo (MC) simulations. Based on
the analytic result, here we derive expressions for the coefficient of
restitution which allow for an application in efficient eMD and MC simulations
of granular Systems.Comment: 4 pages, 4 figure
Coefficient of Restitution for Viscoelastic Spheres: The Effect of Delayed Recovery
The coefficient of normal restitution of colliding viscoelastic spheres is
computed as a function of the material properties and the impact velocity. From
simple arguments it becomes clear that in a collision of purely repulsively
interacting particles, the particles loose contact slightly before the distance
of the centers of the spheres reaches the sum of the radii, that is, the
particles recover their shape only after they lose contact with their collision
partner. This effect was neglected in earlier calculations which leads
erroneously to attractive forces and, thus, to an underestimation of the
coefficient of restitution. As a result we find a novel dependence of the
coefficient of restitution on the impact rate.Comment: 11 pages, 2 figure
Structural features of jammed-granulate metamaterials
Granular media near jamming exhibit fascinating properties, which can be
harnessed to create jammed-granulate metamaterials: materials whose
characteristics arise not only from the shape and material properties of the
particles at the microscale, but also from the geometric features of the
packing. For the case of a bending beam made from jammed-granulate
metamaterial, we study the impact of the particles' properties on the
metamaterial's macroscopic mechanical characteristics. We find that the
metamaterial's stiffness emerges from its volume fraction, in turn originating
from its creation protocol; its ultimate strength corresponds to yielding of
the force network. In contrast to many traditional materials, we find that
macroscopic deformation occurs mostly through affine motion within the packing,
aided by stress relieve through local plastic events, surprisingly
homogeneously spread and persistent throughout bending
Fractal Substructure of a Nanopowder
The structural evolution of a nano-powder by repeated dispersion and settling
can lead to characteristic fractal substructures. This is shown by numerical
simulations of a two-dimensional model agglomerate of adhesive rigid particles.
The agglomerate is cut into fragments of a characteristic size l, which then
are settling under gravity. Repeating this procedure converges to a loosely
packed structure, the properties of which are investigated: a) The final
packing density is independent of the initialization, b) the short-range
correlation function is independent of the fragment size, c) the structure is
fractal up to the fragmentation scale l with a fractal dimension close to 1.7,
and d) the relaxation time increases linearly with l.Comment: 4 pages, 8 figure
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