7 research outputs found
Universal behavior in fragmenting brittle, isotropic solids across material properties
A bonded particle model is used to explore how variations in the material
properties of brittle, isotropic solids affect critical behavior in
fragmentation. To control material properties, a new model is proposed which
includes breakable two- and three-body particle interactions to calibrate
elastic moduli and mode I and II fracture toughnesses. In the quasistatic
limit, fragmentation leads to a power-law distribution of grain sizes which is
truncated at a maximum grain mass that grows as a non-trivial power of system
size. In the high-rate limit, truncation occurs at a mass that decreases as a
power of increasing rate. A scaling description is used to characterize this
behavior by collapsing the mean squared grain mass across rates and system
sizes. Consistent scaling persists across all material properties studied
although there are differences in the evolution of grain size distributions
with strain as the initial number of grains at fracture and their subsequent
rate of production depend on Poisson's ratio. This evolving granular structure
is found to induce a unique rheology where the ratio of the shear stress to
pressure, an internal friction coefficient, decays approximately as the
logarithm of increasing strain rate. The stress ratio also decreases at all
rates with increasing strain as fragmentation progresses.Comment: 19 pages, 22 figure
A soft departure from jamming: the compaction of deformable granular matter under high pressures
The high-pressure compaction of three dimensional granular packings is
simulated using a bonded particle model (BPM) to capture linear elastic
deformation. In the model, grains are represented by a collection of point
particles connected by bonds. A simple multibody interaction is introduced to
control Poisson's ratio and the arrangement of particles on the surface of a
grain is varied to model both high- and low-frictional grains. At low
pressures, the growth in packing fraction and coordination number follow the
expected behavior near jamming and exhibit friction dependence. As the pressure
increases, deviations from the low-pressure power-law scaling emerge after the
packing fraction grows by approximately 0.1 and results from simulations with
different friction coefficients converge. These results are compared to
predictions from traditional discrete element method simulations which,
depending on the definition of packing fraction and coordination number, may
only differ by a factor of two. As grains deform under compaction, the average
volumetric strain and asphericity, a measure of the change in the shape of
grains, are found to grow as power laws and depend heavily on the Poisson's
ratio of the constituent solid. Larger Poisson's ratios are associated with
less volumetric strain and more asphericity and the apparent power-law exponent
of the asphericity may vary. The elastic properties of the packed grains are
also calculated as a function of packing fraction. In particular, we find the
Poisson's ratio near jamming is 1/2 but decreases to 1/4 before rising again as
systems densify
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Shear Is Not Always Simple: Rate-Dependent Effects of Flow Type on Granular Rheology.
Despite there being an infinite variety of types of flow, most rheological studies focus on a single type such as simple shear. Using discrete element simulations, we explore bulk granular systems in a wide range of flow types at large strains and characterize invariants of the stress tensor for different inertial numbers and interparticle friction coefficients. We identify a strong dependence on the type of flow, which grows with increasing inertial number or friction. Standard models of yielding, repurposed to describe the dependence of the stress on flow type in steady-state flow and at finite rates, are compared with data
Shear Is Not Always Simple: Rate-Dependent Effects of Flow Type on Granular Rheology.
Despite there being an infinite variety of types of flow, most rheological studies focus on a single type such as simple shear. Using discrete element simulations, we explore bulk granular systems in a wide range of flow types at large strains and characterize invariants of the stress tensor for different inertial numbers and interparticle friction coefficients. We identify a strong dependence on the type of flow, which grows with increasing inertial number or friction. Standard models of yielding, repurposed to describe the dependence of the stress on flow type in steady-state flow and at finite rates, are compared with data
Anisotropic avalanches and critical depinning of three-dimensional magnetic domain walls
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Large-scale frictionless jamming with power-law particle size distributions.
Due to significant computational expense, discrete element method simulations of jammed packings of size-dispersed spheres with size ratios greater than 1:10 have remained elusive, limiting the correspondence between simulations and real-world granular materials with large size dispersity. Invoking a recently developed neighbor binning algorithm, we generate mechanically stable jammed packings of frictionless spheres with power-law size distributions containing up to nearly 4 000 000 particles with size ratios up to 1:100. By systematically varying the width and exponent of the underlying power laws, we analyze the role of particle size distributions on the structure of jammed packings. The densest packings are obtained for size distributions that balance the relative abundance of large-large and small-small particle contacts. Although the proportion of rattler particles and mean coordination number strongly depend on the size distribution, the mean coordination of nonrattler particles attains the frictionless isostatic value of six in all cases. The size distribution of nonrattler particles that participate in the load-bearing network exhibits no dependence on the width of the total particle size distribution beyond a critical particle size for low-magnitude exponent power laws. This signifies that only particles with sizes greater than the critical particle size contribute to the mechanical stability. However, for high-magnitude exponent power laws, all particle sizes participate in the mechanical stability of the packing