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Granular packings with sliding, rolling, and twisting friction

Physical Review E

Santos, Andrew P.; Bolintineanu, Dan S.; Grest, Gary S.; Lechman, Jeremy B.; Plimpton, Steven J.; Srivastava, Ishan; Silbert, Leonardo E.

Intuition tells us that a rolling or spinning sphere will eventually stop due to the presence of friction and other dissipative interactions. The resistance to rolling and spinning or twisting torque that stops a sphere also changes the microstructure of a granular packing of frictional spheres by increasing the number of constraints on the degrees of freedom of motion. We perform discrete element modeling simulations to construct sphere packings implementing a range of frictional constraints under a pressure-controlled protocol. Mechanically stable packings are achievable at volume fractions and average coordination numbers as low as 0.53 and 2.5, respectively, when the particles experience high resistance to sliding, rolling, and twisting. Only when the particle model includes rolling and twisting friction were experimental volume fractions reproduced.

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TYPE Journal Article YEAR 2020
ScopusOSTIDOI

Exploring Microstructural Descriptors in Elastomeric Foams Using Digital Image Correlation and Statistical Analysis

Conference Proceedings of the Society for Experimental Mechanics Series

Waymel, Robert W.; Kramer, Sharlotte L.; Bolintineanu, Dan S.; Quintana, Enrico C.; Long, Kevin N.

In this work, we investigated microstructural features of elastomeric foam with the goal of identifying descriptors other than porosity that have a significant effect on the macroscale mechanical response. X-ray computed tomography (XCT) provided three-dimensional images of several flexible polyurethane foam samples prior to mechanical testing. The samples were then compressed to approximately 80% engineering strain. Stereo digital image correlation was used to measure the three-dimensional surface displacement data, from which strain was determined. The strain data, which were calculated with respect to the undeformed coordinates, were then overlaid on the corresponding surface generated from XCT. Heterogeneities in the strain-field were cross-correlated with topological quantities such as pore size distribution. A statistically significant correlation was identified between the distance transform of the pore phase and strain fluctuations.

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TYPE Conference Poster YEAR 2020
ScopusOSTIDOI

Random walks on jammed networks: Spectral properties

Physical Review E

Lechman, Jeremy B.; Bond, Stephen D.; Bolintineanu, Dan S.; Grest, Gary S.; Yarrington, Cole Y.; Silbert, Leonardo E.

Using random walk analyses we explore diffusive transport on networks obtained from contacts between isotropically compressed, monodisperse, frictionless sphere packings generated over a range of pressures in the vicinity of the jamming transition p→0. For conductive particles in an insulating medium, conduction is determined by the particle contact network with nodes representing particle centers and edges contacts between particles. The transition rate is not homogeneous, but is distributed inhomogeneously due to the randomness of packing and concomitant disorder of the contact network, e.g., the distribution of the coordination number. A narrow escape time scale is used to write a Markov process for random walks on the particle contact network. This stochastic process is analyzed in terms of spectral density of the random, sparse, Euclidean and real, symmetric, positive, semidefinite transition rate matrix. Results show network structures derived from jammed particles have properties similar to ordered, euclidean lattices but also some unique properties that distinguish them from other structures that are in some sense more homogeneous. In particular, the distribution of eigenvalues of the transition rate matrix follow a power law with spectral dimension 3. However, quantitative details of the statistics of the eigenvectors show subtle differences with homogeneous lattices and allow us to distinguish between topological and geometric sources of disorder in the network.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI
Results 26–50 of 120
Results 26–50 of 120