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 H4: Geophysics and Planetary Science III: Impact Phenomena |
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Chair: Mark Boslough, Sandia National Laboratories Room: Renaissance Ballroom C |
Tuesday, June 28, 2011 9:15AM - 9:30AM |
H4.00001: Structure and Thermal Properties of Porous Geological Materials Simon Kirk, David Williamson Understanding the behaviour of porous geological materials is important for developing models of the explosive loading of rock in mining applications. To this end it is essential to first characterise its complex internal structure. Knowing the structure shows how the properties of the component materials relate to the overall properties of rock. The structure and mineralogy of Gosford sandstone was investigated and this information was used to predict its thermal properties. The thermal properties of the material were measured experimentally and compared against these predictions. [Preview Abstract] |
Tuesday, June 28, 2011 9:30AM - 9:45AM |
H4.00002: High-velocity impacts in regolith: insight from numerical models and experiments Katarina Miljkovic, Gareth Collins, Manish Patel, David Chapman, William Proud High-velocity impacts are common events on planetary surfaces, from a constant micrometeoroid bombardment to infrequent but catastrophic large asteroid impacts that form giant craters. The consequences of such impacts depend, in part, on the properties of the planet surface, such as strength, porosity and surface gravity. The near-surface of many solar system bodies is a loose granular material composed of dust, soil and broken rock, known as regolith. Planetary regolith could have a range of material properties, hence it is difficult to specify its material model. As a result, experimental investigations of impacts on planetary surfaces often use sand as a regolith analogue material and hydrocode simulations of impact often assume a sand-like equation of state and strength model. In this study, we compare iSALE hydrocode simulations of impacts in sand and other porous granular materials with results from laboratory impact experiments to test and refine material models for regolith materials. [Preview Abstract] |
Tuesday, June 28, 2011 9:45AM - 10:00AM |
H4.00003: Impact Chemical Evolution Processes for Biomolecules Formed by Oceanic Impact Toshimori Sekine, Nao Fukunaga, Shunsuke Izumi, Yoshihiro Furukawa, Takeshi Kakegawa, Takamichi Kobayashi, Hiromoto Nakazawa The biomolecules on Earth are thought either to have come from the extraterrestrial parts carried with flying meteorites or to have been formed on Earth from the inorganic carbon through given energy. From the standpoint to address impact energy, we need to know possible process how the simple biomolecules formed at a violent impact have been evolved subsequently through several impacts at the time of the late heavy bombardment. In this study we investigated the simplest amino acid, glycine marked by 13C, in order to understand how it will be evolved chemically when it is subjected to further impacts. The results indicate that some new molecules are formed and others are decomposed, and suggest not only that the impact-induced process is not so simple to proceed just to one way, but also that there are complicated and multi-process ways. It also must be taken into account the heterogeneous distribution of impact energy in an impact that may cause a significant effect on the chemical evolution. We will show experimental results of shock recovery on mineral powders mixed with solutions and air within a metal container. [Preview Abstract] |
Tuesday, June 28, 2011 10:00AM - 10:15AM |
H4.00004: Physics of Intact Capture of Cometary Coma Dust Samples William Anderson In 1986, Tom Ahrens and I developed a simple model for hypervelocity capture in low density foams, aimed in particular at the suggestion that such techniques could be used to capture dust during flyby of an active comet nucleus. While the model was never published in printed form, it became known to many in the cometary dust sampling community. More sophisticated models have been developed since, but our original model still retains superiority for some applications and elucidates the physics of the capture process in a more intuitive way than the more recent models. The model makes use of the small value of the Hugoniot intercept typical of highly distended media to invoke analytic expressions with functional forms common to fluid dynamics. The model successfully describes the deceleration and ablation of a particle that is large enough to see the foam as a low density continuum. I will present that model, updated with improved calculations of the temperature in the shocked foam, and show its continued utility in elucidating the phenomena of hypervelocity penetration of low-density foams. [Preview Abstract] |
Tuesday, June 28, 2011 10:15AM - 10:30AM |
H4.00005: Soft X-ray Shock Loading and Momentum Coupling in Meteorite and Planetary Materials$^1$ J.L. Remo, M.D. Furnish, R.J. Lawrence X-ray momentum coupling coefficients, C$_M$, for planetary materials were determined by measuring stress waveforms produced by impulsive radiation loading from the SNL Z- machine. Targets were iron and stone meteorites, solid and powdered dunite, and Si, Al, and Fe. All samples were $\sim$ 1 mm thick and, except for Si, backed by LiF single-crystal windows. The x-ray spectra included thermal radiation (blackbody 170 to 237 eV) and line emissions from the pinch material (Cu, Ni, Al, or stainless steel). Target fluences of 0.4 to 1.7 kJ/cm$^2$ at intensities 43 to 260 GW/cm$^2$ produced front surface plasma pressures of 2.6 to 12.4 GPa. Stress waves driven into the samples were attenuating due to the short ($\sim$ 5 ns) duration of the drive pulse. C$_M$ was determined using the fact that an attenuating wave impulse is constant, and accounted for the mechanical impedance mismatch between samples and window. Related experiments in the literature are discussed. Values ranged from 0.8 to 3.1 x 10$^{-5}$ s/m. CTH hydrocode modeling of x-ray coupling to porous and fully dense silica supported the experimental measurements and extrapolations to other materials. $^1$ Work supported by Sandia National Labs, operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. DOE's NNSA under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, June 28, 2011 10:30AM - 10:45AM |
H4.00006: Analytic models for pulsed x-ray impulse coupling R.J. Lawrence, M.D. Furnish, J.L. Remo Pulsed x-ray momentum coupling is a promising technology for early deflection of NEOs (Near Earth Objects) that might impact Earth. Analytic models for the interactions can preclude the need for large hydrocodes, and provide many point calculations that reveal important features of the nonlinear phenomena, e.g., thresholds and peak coupling. However, validation is an important element. One such model is used to analyze experiments conducted on the Sandia Z machine. Relevant samples were exposed to 5-ns x-ray pulses of a $\sim$200-eV blackbody at $\sim$1 kJ/cm$^2$. Target momenta were measured. Model calculations give impulse couplings somewhat greater than the data. Possible reasons include inherent target heterogeneities, and uncertain target decomposition energies. The work suggests that extrapolation to conditions inaccessible to laboratory experiments, but appropriate for NEO deflection, is justified, especially for the related parameter studies. [Preview Abstract] |
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