Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session H6: Particulate/Porous Materials I: Foams |
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Chair: Ken Jordan, Marquette University Room: Grand Ballroom VI |
Tuesday, June 28, 2011 9:15AM - 9:45AM |
H6.00001: Time resolved small angle x-ray scattering measurements in foams and metals loaded in high rate compression Invited Speaker: Nanofoams are valuable for high energy density physics experiments because they provide a convenient method to vary density without changing atomic number. Characterizing the performance of low-density materials under extreme conditions provides crucial feedback concerning the reliability of existing models and insight to develop materials with optimal properties. The significant momentum present in these dynamic compaction events make it difficult to study the evolution of such systems ex-situ and experimental information is lacking. Likewise, the early stages of void formation in dynamically driven spall are difficult to observe experimentally. We have developed the capability to measure small angle x-ray scattering using a single x-ray pulse at the Advanced Photon Source. Two areas of keen interest, considered in this work, are the shock-induced collapse of the void structure in highly porous solids and shock-induced nucleation and growth of microvoids in metals. In solid density metal foils we have seen changes in scattering corresponding to the passage of the compression wave, subsequent formation of a tensile region in the material and eventual return to the uncompressed lattice. The small induced scattering signals seen indicate that, for the low compressive stresses and pure foils investigated here, few voids nucleate. The data support the notion that the void formation and growth is rapid. In contrast, carbon based foam materials begin with significant levels of scattering and, during compression, a decrease in the total scattering intensity and the average pore diameter are observed which is consistent with a collapse of the pore structure in the nanoporous carbon. Evolution of the foam structure continues during release of the compression wave due to the break up of the nanoporous carbon. [Preview Abstract] |
Tuesday, June 28, 2011 9:45AM - 10:00AM |
H6.00002: Energy balance in strong shock compressed low density SiO2 foam James Hawreliak, Ricky Chau, Jon Eggert, Marina Bastea, Thomas Boehly, Gilbert Collins Using a high intensity laser to drive a strong shock through low density silica aerogel foam we performed a series of impedance matching experiments to study the Hugoniot of low density SiO2 foam. Low density foams are being used and planned to be used as materials in complex integrated experiments to model astrophysical phenomena, particularly for the formation and growth of density driven hydrodynamic instabilities. The shock response of the low density foam is very important to the modeling, developing and interpretation of these experiments. We present recent data from shocks in low density SiO2 in which the shock front temperature exceeds $>$eV where the radiation flux can begin to play an important role in understanding the energy balance of the shock front propagation. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, June 28, 2011 10:00AM - 10:15AM |
H6.00003: Measurements of the shock response of porous structures formed by Selective Laser Melting Ernest Harris, Ron Winter, Matthew Cotton, Mark Swan Studies of the shock loading of porous material, formed by selective laser melting, have the potential to improve our understanding of factors such as density, crush strength and pore size on energy absorbing capability. Samples have been manufactured in which a lattice is formed of rods of stainless steel angled at 45 degrees to the surface of a 6 mm thick x 64.5 mm diameter disc. The cell size is 1 mm and the density is 44.6\% of solid. The effect of the cellular structure of the lattice on the temporal and spatial stress variations in the target were assessed using 3D simulation and found to be small compared with the main features of the computed record. A 70 mm gas gun has been used to impact the porous samples onto solid stainless steel plates backed by PMMA windows. The impact time was measured using piezoelectric probes and Het-V laser interferometry was used to measure the velocity time profile of the transmitted shock. The experimental results were compared with one, two and three dimensional computer predictions. It was found that the 2D simulations provide a good match to the time-averaged velocities but that the individual features in the experimental records are best matched by the 3D calculations. [Preview Abstract] |
Tuesday, June 28, 2011 10:15AM - 10:30AM |
H6.00004: Shock compression of dense polymer and foam systems using molecular dynamics and DFT J. Matthew D. Lane, Gary S. Grest, Aidan P. Thompson, Kyle R. Cochrane, Michael P. Desjarlais, Thomas R. Mattsson Organic polymers and nanocomposites are increasingly being subjected to extreme environments. Molecular scale modeling of these materials offers insight into failure mechanisms and response. Classical molecular dynamics (MD) and density functional theory (DFT) MD simulations of the principal shock Hugoniot will be presented for two hydrocarbon polymers, polyethylene (PE) and poly(4-methyl-1-pentene) (PMP). We studied two reactive and two non-reactive classical MD interaction potentials. We will show the exp-6 interaction of Borodin et al. has much better agreement with experiment than OPLS. Futher, that ReaxFF displayed decidedly better agreement than AIREBO. DFT were in excellent agreement with experiment. NEMD studies of low-density foam materials will be discussed. Qualitative response will be characterized. Quantitative comparison will be made with experiment. [Preview Abstract] |
Tuesday, June 28, 2011 10:30AM - 10:45AM |
H6.00005: Shock Compression and Release of Metal Foam Warren Maines, Christopher Neel, Lalit Chhabildas, John Borg, William Reinhart We report of the results of uniaxial strain experiments and computations to discuss the compressed and isentropic release states of aluminum foam $\sim $50{\%} relative density undergoing high velocity impact at up to 10GPa. The initial geometry of the foam was obtained via computed x-ray tomography (XCT) and imported directly into the CTH hydrodynamic code. Simulations of the dynamic response of the foam are compared to experimental measurements and used to build macro scale constitutive relations. The experimental results were obtained utilizing a reverse ballistic plate reverberation technique that obtained shock compression states of the foam. In these experiments, 6061-T6 aluminum, oxygen free copper and tantalum were used as standard witness plates and were shocked by the metal foam projectile at up to 2.0 km/s. The response of the witness plates was monitored by three different velocity interferometers positioned at three different locations on the witness plate to obtain compaction and release behavior. The simulations captured the heterogeneous Hugoniot and release state of the foam extremely well. The resulting constitutive relations built from mesoscale simulations compare favorably to those built from experimental results. [Preview Abstract] |
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