Session Y7: Particulate Matter VI: Compaction

Probing Dynamics of 2-D Granular Media via X-Ray Imaging

Granular systems are ever present in our everyday world and influence many dynamic scientific problems including mine blasting, projectile penetration, astrophysical collisions, and dynamic compaction. Despite its significance, a fundamental understanding of granular media's behavior falls well short of its solid counterpart, limiting predictive capabilities. The kinematics of granular media is complex in part to the intricate interplay between numerous degrees of freedom not present in its solid equivalent. Previous dynamic studies in granular media primarily use VISAR or PDV, macro-scale diagnostics that only focus on the aggregate effect of the many degrees of freedom leaving the principal interactions of these multiple degrees of freedom too entangled to elucidate. To isolate the significance of individualized grain-to-grain interactions, this study uses in-situ X-ray imaging to probe a 2-D array of granular media subjected to high strain rate gas gun loading. Analyses include evaluating displacement fields and grain fracture as a function of both saturation and impactor velocity. X-ray imaging analyses feed directly into our concurrent granular media modeling efforts to enhance our predictive capabilities. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.   

Characterization of the Dynamic Consolidation Behavior of Cerium Dioxide Powders as a Function of Green Density

The uniaxial strain dynamic consolidation behavior of cerium dioxide powders as a function of particle morphology and powder compact green density is investigated in this work. Cerium dioxide is a lanthanide metal oxide powder. It is often used for the study of brittle powders exposed to extreme conditions, such as high velocity impact and shock loading. In this study, cerium dioxide powders of two particle sizes (nominally 1 and 10 $\mu $m) and two green densities (55{\%} and 63{\%} TMD) are shock compressed using gas gun impact and their particle and shock wave velocities are measured using optical velocimetry techniques. The velocity data collected is used to describe the Hugoniot of the shocked cerium dioxide powders and develop an improved P-$\alpha $ compaction model, building upon prior studies at Los Alamos National Laboratory [D. A. Fredenburg, et al, J. Appl. Phys. 115, 123511 (2014)]. In this presentation, the preliminary results regarding the suitability of the P-$\alpha $ compaction model to describe the experimentally determined Hugoniot response of cerium dioxide powders will be discussed.   

Impact Compaction of a Granular Material

The dynamic behavior of granular materials has importance to a variety of engineering applications. Although, the mechanical behavior of granular materials have been studied extensively for several decades, the dynamic behavior of these materials remains poorly understood. High-quality experimental data are needed to improve our general understanding of granular material compaction physics. This paper describes how an instrumented plunger impact system can be used to measure the compaction process for granular materials at high and controlled strain rates and subsequently used for computational modelling. The experimental technique relies on a gas-gun driven plunger system to generate a compaction wave through a volume of granular material. This volume of material has been redundantly instrumented along the bed length to track the progression of the compaction wave, and the piston displacement is measured with Photon Doppler Velocimetry (PDV). Using the gathered experimental data along with the initial material tap density, a granular material equation of state can be determined.   

The Effect of High Energy Ball Milling on the Dynamic Response of Aluminum Powders

Ball milling is an effective method to enhance the reactivity of intermetallic reactives by reducing characteristic diffusions distances. During this process, ductile reactants are mixed into a lamellar material with nanoscale features, resulting in significant strain hardening. Plate impact experiments using a single stage light gas gun have been performed to evaluate the effect of high energy ball milling (HEBM) on the mechanical properties and dynamic response of cold pressed aluminum compacts. The average grain size of the milled material is evaluate and suggested as a method of correlating the measured response to the properties of milled composites.   

Dynamic characterization of anisotropy effects in 3-D printed materials for high-G survivability.

The behavior of dedicated 3-D printed structures for survivability of encapsulated electronic components subject to high-G impact is currently being investigated. Understanding the material characteristics, based on printing layout and build orientation is especially important when considering structural application of 3-D printed parts. While 3 D printing allows fabrication of intricate geometries not amenable to traditional machining or molding methods, prediction of its damping characteristics becomes impossible without modeling and simulations. Accurate modeling parameters need both static and dynamic characterization of 3-D printed materials. A combination of experiments conducted for characterization of Vero White Plus (acrylic), Tango Black (rubber) and mixtures of these (Vero rich and Tango rich) materials used conventional tensile and compression tests, Hopkinson bar, dynamic material analyzer (DMA) and a non-conventional accelerometer based resonance test with spectrum analysis method of obtaining high frequency data. In this paper, experimental results of parent materials and their mixtures in context of 3-D printing orientation and print build direction (layers) of the material and their influence of modeling parameter generation are presented.   

Thermal Runaway in Jammed Networks

The study of thermal explosion has a long history. Names such as Semenov and Frank-Kamenetskii are associated with classical model descriptions under particular assumptions. In this talk we revisit this problem with particular focus on the latter's model for conduction dominated thermal transport and Arrenhius-type reaction chemistry. We extend this description to the case of inhomogeneous microstructure generated by packing mono-sized spheres via a well-defined ``Jamming'' protocol. With these material structures in hand, we recast the Frank-Kamenetskii problem into a reduced-order network form for conduction in particle packs. With this model we can efficiently investigate the variability of the time to ignition due to the random microstructure. Additionally, we propose a modal decomposition and stability analysis of the model akin to stability of linear systems. We highlight the physical insights this approach can give with respect to questions of material dependent performance variability. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.