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Effect of shape and friction on the packing and flow of granular materials

Physical Review E

Salerno, K.M.; Bolintineanu, Dan S.; Grest, Gary S.; Lechman, Jeremy B.; Plimpton, Steven J.; Srivastava, Ishan S.; Silbert, Leonardo E.

The packing and flow of aspherical frictional particles are studied using discrete element simulations. Particles are superballs with shape |x|s+|y|s+|z|s=1 that varies from sphere (s=2) to cube (s=), constructed with an overlapping-sphere model. Both packing fraction, φ, and coordination number, z, decrease monotonically with microscopic friction μ, for all shapes. However, this decrease is more dramatic for larger s due to a reduction in the fraction of face-face contacts with increasing friction. For flowing grains, the dynamic friction μ - the ratio of shear to normal stresses - depends on shape, microscopic friction, and inertial number I. For all shapes, μ grows from its quasistatic value μ0 as (μ-μ0)=dIα, with different universal behavior for frictional and frictionless shapes. For frictionless shapes the exponent α≈0.5 and prefactor d≈5μ0 while for frictional shapes α≈1 and d varies only slightly. The results highlight that the flow exponents are universal and are consistent for all the shapes simulated here.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Deformation and Fracture in Complex-Shaped Energetic Particles

Cooper, Marcia A.; Bufford, Daniel C.; Barr, Christopher M.; Lechman, Jeremy B.

A new technical basis on the mechanics of energetic materials at the individual particle scale has been developed. Despite these particles being in most of our Sandia non-nuclear explosive components, we have historically lacked any understanding of particle behavior. Through the novel application of nanoidentation methods to single crystal films and single particles of energetic materials with complex shapes, discovery data has been collected elucidating phenomena of particle strength, elastic and plastic deformation, and fracture. This work specifically developed the experimental techniques and analysis methodologies to distill data into relationships suitable for future integration into particle level simulations of particle reassembly. This project utilized experimental facilities at CINT and the Explosive Components Facility to perform ex-situ and in-situ nanoidentation experiments with simultaneous scanning electron microscope (SEM) imaging. Data collected by an applied axial compressive load in either force-control or displacement-control was well represented by Hertzian contact theory for linear elastic materials. Particle fracture phenomenology was effectively modeled by an empirical damage model.

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TYPE Other Report YEAR 2018
DOIOSTI

Letter: Modeling reactive shock waves in heterogeneous solids at the continuum level with stochastic differential equations

Physics of Fluids

Kittell, David E.; Yarrington, Cole Y.; Lechman, Jeremy B.; Baer, Melvin B.

A new paradigm is introduced for modeling reactive shock waves in heterogeneous solids at the continuum level. Inspired by the probability density function methods from turbulent reactive flows, it is hypothesized that the unreacted material microstructures lead to a distribution of heat release rates from chemical reaction. Fluctuations in heat release, rather than velocity, are coupled to the reactive Euler equations which are then solved via the Riemann problem. A numerically efficient, one-dimensional hydrocode is used to demonstrate this new approach, and simulation results of a representative impact calculation (inert flyer into explosive target) are discussed.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus
Results 51–75 of 184
Results 51–75 of 184