Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E23: Materials in Extremes: Reactive MaterialsFocus Live
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Sponsoring Units: GSCCM Chair: Nir Goldman, Lawrence Livermore Natl Lab |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E23.00001: Shock-induced consolidation of tungsten nanoparticles-a molecular dynamics approach Jianrui Feng, Chen Pengwan Shock-induced consolidation of tungsten nanoparticles to form a bulk material was modeled using molecular dynamics simulation. By arranging the nanoparticles in a three-dimensional model of BCC super-lattice, the calculated shock velocity-particle velocity Hugoniot data is in good agreement with the experiments. Three states, including solid-undensified, solid-densified and liquid-densified can be sequentially obtained with the increase of impact velocity. It is due to the flow deformation at the particle surface that densifies the cavity, and the high pressure and temperature that join the particles together. Melting is not a necessary factor for shock consolidation. Based on whether or not melting takes place, the consolidation mechanism are liquid-diffusion welding or solid-pressure welding. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E23.00002: Molecular Dynamics Simulation Research on the Transport, Breakup and Reaction Dynamics of Shock-induced Ejecta in Gas Environment Bao Wu, FengChao Wu, HengAn Wu The metal-gases interface instability evolution and subsequent transport process of micro-ejecta in gases has recently begun to attract attention and research interest. Here, we have conducted a series of studies on shock-induced ejection with molecular dynamics simulation, including ejecta transport, breakup and reaction dynamics in gases. We find that ejected microjets experience progressively aggravated deceleration with increasing gas density, and particle flows ahead of jet tips are suppressed. Further, with the presence of gases, the size distribution of ejected particles is altered with an outstanding feature of enhanced formation of atomic particles. Further simulations of ejecta transport in reactive gases revealed that the reactions will quickly increase the temperature of the mixing zone, followed by the deceleration of spikes and a greater shock intensity in the compressed gases, compared with the ejection in inert gases. When ejecta transport in reactive gases, the chemical interactions cause higher temperature in mixed zone and more metal atoms to evaporate from the surface of larger particles, thus forming smaller fragments and more atomic particles. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E23.00003: Hugoniostat, direct shock simulations and viscoelastic modeling in polymer melts Gautier Lecoutre, Nicolas Pineau, Laurent Soulard, Claire Lemarchand The interest for the behavior of polymers under shock loading is increasing because of applications such as car equipment, sport gear and plastic-bonded explosives. Molecular dynamics (MD) simulations are a powerful tool to explore the molecular and mechanical properties of polymers under shock loading but they require long simulation times to relax the polymer chains and large simulation boxes to study the stationary state of the shock wave propagation. The Hugoniostat method has been widely used on atomic and molecular crystals to reproduce the shocked state of materials far from the shock front using much smaller simulation boxes. In this work, we show that the Hugoniot curve of the cis-1,4-polybutadiene melt is correctly predicted by the Hugoniostat method and compare well with direct shock simulations and previous results. However, the shear stress is very different in direct shock simulations, where it is large and decays slowly away from the shock front, and in the Hugoniostat method where they are nearly zero. In order to account for this difference, we use a Prony series model, usual for viscoelastic liquids, which reproduces the slow decay of the normal stress differences with several relaxation times. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E23.00004: Shock compression through different media: air, water and their interface Nilanjan Mitra As the shock wave passes through air and/or water media, various physical and/or chemical changes occurs in the media which eventually alters the equation of state of the media leading to changes in the fluid-structure interaction as well as the impulse transmitted to that of the structure. This presentation summarizes the authors work in the area (held over multiple years) in which molecular dynamics study of shock compression has been conducted for water, air (dry air consisting of 78.08% of Nitrogen, 20.95% of Oxygen and 0.97% of Carbon-dioxide as well as moisture laden air and air at high altitudes) as well as air-water interface. For the case of water, phase transition is observed from liquid water to ice VII “like” structure (rotational diffusion studies indicate the presence of plastic crystal phase at the liquid water-ice VII boundary region). For the case of air, new chemical species are observed to form as a result of shock induced chemical reactions. In the case of air-water interface, interesting observations will be presented for Richtmeyer-Meshkov instability as well as chemical reactions observed at the interface. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E23.00005: Probing High Pressure Structural Evolution in Polyurea with in situ Energy Dispersive X-Ray Diffraction and Molecular Dynamics Simulations Tyler Eastmond, Vahidreza Alizadeh, Rostislav Hrubiak, Jay Oswald, Alireza amirkhizi, Pedro Peralta Polyurea has been proven as an effective coating in defense applications due to its unique mechanical properties. To gain a more complete understanding of the high-pressure atomic-level morphology of these phases and to validate molecular dynamics (MD) simulations, multi-angle energy dispersive x-ray diffraction experiments were performed in situ up to pressures ~6 GPa at room and elevated temperatures. Structure factors were obtained and compared to MD simulations with an average error of less than 5% between major peak positions at room temperature, which indicated that the first sharp diffraction peak shifted from 4.56 Å to lower d-spacing with pressure, indicating compression between hard segments. This was further supported by the behavior of a peak at ~3.86 Å from the pair distribution function, suspected to represent π-stacking and separation between soft segments. Compression within hard domains themselves is minimal at room temperature. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E23.00006: Study of equation of state and deviatoric response in polyurea elastomers via hydrodynamic instability experiments. Elizabeth V Fortin, Vahidreza Alizadeh, Tyler Eastmond, Benjamin Shaffer, Jay Oswald, Alireza amirkhizi, Pedro Peralta Polyurea has shown potential as a protective coating in body and vehicle armor, due to reductions in damage and fragmentation when coated plates are exposed to blasts and ballistic impacts. Hence, the behavior of polyurea at high pressures and strain rates needs to be better understood to design protective coatings. Laser-driven shock experiments were performed to monitor perturbed shock fronts in polyurea at pressures ~ 60 GPa. Changes on the wavelength of the surface perturbations that generated the rippled shocks were used to probe effects of equation of state (EOS) and strength on the propagation of these perturbed shocks, the amplitude of which was measured via spatially resolved laser velocity at the breakout surface. Experimental results were compared to hydrocodes simulations, and they indicate that a decrease of wavelength reduced the amplitude of the shock perturbation. This is consistent with EOS and strength effects, as opposed to viscosity effects. In addition, the EOS at high pressures was consistent with an extrapolation of lower pressures results, which allowed obtaining synamic strength estimates for the material. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E23.00007: Ignition and Combustion Mechanisms of Explosively-Dispersed Reactive Powder Ryan Houim, Jacob Posey, Aaron Knudtson A numerical study was conducted to explore the ignition and combustion of aluminum powder dispersed by a TNT charge. The simulations used a high-order numerical method for a compressible reactive gas that is coupled to a kinetic-theory-based granular multiphase model that is valid up to the packing limit. Scenarios where an annular shell of highly-packed monodisperse Al powder surrounding the TNT charge were considered with varying thickness, particle diameter, and particle packing. The results qualitatively show two different ignition and combustion modes of the explosively-dispersed powder observed in experiments. Prompt ignition, where the particles ignite almost immediately on the outer edge of the particle cloud, was observed if the particle layer is thin or loosely packed. The particles continue to burn in a non-premixed mode of combustion as they disperse outward. Delayed ignition was observed in scenarios where the particle layer is thick or the packing is high. The Al particles on the inner edge of the dispersing cloud ignite when they interact with the TNT fireball and secondary shocks. The Al-dust flame continues burns in a turbulent premixed mode of combustion from the inside towards the outside. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E23.00008: Ballistic Studies with Intermetallic and Thermite Projectiles in Oxidizing and Inert Environments Colton Cagle, Charles Luke Croessmann, Joseph Abraham, Liang Wei, Pascal Dube, Michelle L. Pantoya A High-velocity Impact-ignition Testing System (HITS) was developed to study the dynamic response of thermite and intermetallic projectiles under high strain impact. Projectiles were launched up to 1300 m/s from a .410 caliber powder gun into test chambers filled with air or argon atmospheres. Projectiles entering the test chambers impacted a steel witness plate after either penetrating a 1.6 mm thick steel plate, penetrating two 3.2 mm thick aluminum plates, or experiencing no penetration. Penetration, impact, and reaction were recorded using two high-speed cameras and pressure transducers captured quasi-static pressure curves. Several key results include the following: intermetallic projectiles produced significantly lower quasi-static pressure in argon environments than thermite projectiles. Across all tests, intermetallic projectiles were less sensitive to ignition than the thermite, however both projectiles generated similar quasi-static pressures at 1300 m/s impact. For both intermetallic and thermite projectiles, when impacting without penetration, reaction mechanisms depend more on the fragmentation behavior than the projectile’s material composition. |
Tuesday, March 16, 2021 9:36AM - 10:12AM Live |
E23.00009: Safety and performance characteristics of thermite systems: from powders to 3D printed lattices Invited Speaker: Kyle Sullivan The reaction in thermite powders is a highly complex process. Developing a full understanding of this process involves a detailed understanding of the various length and time scales, as well as the non-equilibrium and equilibrium processes as fuel and oxide particles react to form mixed-phase products on a rapid time scale. In this work, we present an overview of our work, which ranges from loose-powder combustion testing to 3D printed lattices of thermite. Specifically, we explored the dynamic formation of mesoparticles and the resultant multi-phase expansion of these particles as they are entrained in a gas stream. Additive manufacturing (AM) was then used to probe how the printed architecture can be used to manipulate the reactivity, by affecting the forward energy transport through design of the structure. A materials design plot (i.e., an "Ashby Diagram") was constructed to quantify the control AM offers for these materials. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E23.00010: Behavior of phenolic resins shocked to chemistry-relevant pressures Keith Jones, J Matthew Lane, Nathan Moore We study the shock response of phenolic polymers from 0.3 GPa up to 66.5 GPa using classical molecular dynamics (MD). Using the ReaxFF potential in combination with the constant stress Hugoniostat approach, we compare phenolic systems with molecular structures representative of phenolics at different stages in the curing process. We find that the shoulder or “cusp” in the Hugoniot in density-pressure space, also observed by Carter and Marsh, appears over a finite period of time on the order of 10s to 100s of picoseconds above 40 GPa in our simulations. The cusp is associated with finite rate chemistry that ultimately leads to a dense, highly crosslinked, carbonaceous solid. Chemical mechanisms that lead to this state will be explored and compared to cases where the cusp does not form. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E23.00011: Shock Hugoniot and High Strain-Rate Viscoelastic Behavior of a Phenolic Polymer Nathan Moore, Keith Jones, Jack LeRoy Wise, Darren G Talley, J Matthew Lane We investigate the shock behavior of a phenolic polymer using experiments, finite element and classical molecular dynamics (MD) simulation. Plate impact experiments are used to produce transient pressure states up to ~1.2 GPa. The dynamic stress equalization on plate impact is fit to a viscoelastic model in the CTH hydrocode that accounts for the temperature dependence of the phenolic β-transition, which is determined by dynamic mechanical analysis (DMA) based on experimental measurements of shear modulus as a function of temperature and strain rate. This model is used to refine an estimate of the dynamic spall strength for the phenolic and to validate the shock Hugoniot measurement. The results are compared to MD simulations of crosslinked phenolic and found to be in reasonable agreement when a ReaxFF potential is used with a constant stress Hugoniostat, establishing a baseline for investigating higher-pressure shock behavior of phenolic polymers. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Not Participating |
E23.00012: Modeling Burning Metal Streamers in Pyrotechnic Explosions Allen Kuhl, David Grote We have developed a hydrodynamic model of the flow field created by pyrotechnic explosions. The model is based on a 3-phase version of our AMR code: MAUI. It contains the following elements: (i) a gas-dynamic model: GD of the expansion and mixing in the fireball, (ii) a Discrete Lagrangian Particles model: DLP of the projectiles, and (iii) a heterogeneous continuum model: HC of the burning particle wakes. Adaptive Mesh Refinement (AMR) is used to capture turbulent mixing and combustion on the grid. The grid was initialized with similarity solutions for: (i) the detonation products gases, and (ii) the particles. Results compare well with the photography of pyrotechnic explosions. Proposed here is a Model of the burning metal projectiles and their associated wakes. The projectiles are assumed to be Aluminum droplets, formed by shock-heating Al to the liquid state at 933 K. The droplets loose mass according to an empirical burning law that is proportional to the droplet diameter squared. Mass is conserved, so the droplet mass loss is put into the mass of an ultra-fine droplet mist. The mist is then burned instantaneously in stoichiometric proportions with air. We assume a high-Damköhler limit for the combustion rate which is consistent with the MILES theory of Boris. |
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