Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session W7: Poster Session II |
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Chair: Clint Hall, Sandia National Laboratories; Gerrit Sutherland, Naval Surface Warfare Center, Indian Head Room: Hyatt Regency MD Suite 4:30-6:00pm, Thr |
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W7.00001: DETONATIONS & SHOCK-INDUCED CHEMISTRY
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W7.00002: Experimental Method to Determine the Detonation Characteristics of Very Non-Ideal High Explosives Gerard Baudin, Christian Le Gallic, Pascal Bouinot Common experimental configurations used to determine HE detonation velocity-curvature are right circular cylinders detonated in air. The steadily propagating detonation front is curved and its velocity depends upon the diameter of the cylinder. This configuration requires several experiments with different diameters and sufficiently long cylinders to assume a steadily propagating detonation front. This last hypothesis is practically not achieved for non-ideal HE using reasonably long cylinders. To elude this problem, a special explosive device called ``logosphere,'' developed by CEA, has been adapted to non ideal HE. It provides a well define spherically diverging detonation wave and allows measurements of the detonation velocity-curvature relationship by means of piezoelectric pins without any perturbation. VISAR and DLI diagnostics record the material velocities at the rear surface of HE through transparent windows. The particle velocity values are used to determine the curved detonation states using the detonation velocity-acceleration-curvature model of Louis Brun. [Preview Abstract] |
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W7.00003: Comparison of Failure Thickness and Critical Diameter of Nitromethane Oren E. Petel, Andrew J. Higgins The critical diameter and failure thickness of liquid nitromethane confined by aluminum are determined experimentally. A comparison of these two parameters provides insight into the failure mechanism in nitromethane. If the failure of detonation in a critical charge diameter (or thickness) experiment is due to reaction quenching resulting from wave curvature, then it is expected that the critical diameter should be half the value of the critical thickness.[1] This has been shown to be the case with gas-phase detonations with nearly laminar reaction zones.[2] By comparing the experimentally determined values of critical diameter and thickness for a homogeneous liquid explosive, the validity of this model of detonation failure can be assessed. References: 1. Ramsay, J.B., 8th Symp. (Int.) on Detonation., 372-379 (1985). 2. Radulescu, M., Lee, J.H.S., Comb. and Flame, 131:29-46 (2002). [Preview Abstract] |
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W7.00004: Optimisation of a laser-driven flyer system for the initiation of energetic materials Jonathan Hird, Martin Greenaway A Q-switched Nd:YAG laser operating at a wavelength of 1.064 mcirons has been used to drive miniature flyer plates capable of inducing a prompt shock-to-detonation transition in secondary explosives. In this paper, we report the effect of flyer composition on performance, as determined by high-speed photography, optical diodes and piezoelectric gauges. Research has shown that flyers may reach velocities in excess of 5000 m/s producing impact pressures of the order 10 GPa. The results will be discussed in terms of the material properties of the launch films used and the effectiveness of laser-driven flyers as initiators in energetic material research. [Preview Abstract] |
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W7.00005: Polydimethylsiloxane Shock Chemistry. Robert Sander, Norm Blais, Ray Engelke, Dana Dattelbaum, Rhonda McInroy, Stephen Sheffield Polydimethylsiloxane, (PDMS) is a common silicone polymer. It consists of methyl side groups on silicon-oxygen-silicon-oxygen chains. Understanding the decomposition product distribution is useful for calculating the equation of state under shock conditions. We have detonated small samples of HMX explosive in contact with the polymer in a high vacuum chamber and used a time-of-flight mass spectrometer to analyze the chemical products of PDMS decomposition. We have used the computer code CTH to model the time history of pressure in the sample. This time scale of a few nanoseconds generates products that are significantly different than the equilibrium products observed in thermal pyrolysis experiments. The mass spectrum under shock conditions predominately shows monomers and the first two oligomers. We compared high molecular weight liqiuid PDMS, crosslinked solid PDMS, and silica filled solid PDMS. Shocks in PDMS filled with silica particles show somewhat greater decomposition, suggesting that the temperatures generated are higher in that case and cause greater decomposition. [Preview Abstract] |
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W7.00006: On the Initiation Mechanism in Exploding Bridgewire and Laser Detonators D. Scott Stewart, K. Thomas, S. Clarke, H. Mallett, M Martinez, A. Munger, J. Saenz Since its invention by Los Alamos during the Manhattan Project era the exploding bridgewire detonator (EBW) has seen tremendous use and study. Recent development of a laser-powered device with detonation properties similar to an EBW is reviving interest in the basic physics of the Deflagration-to-Detonation (DDT) process in both of these devices,[1]. Cutback experiments using both laser interferometry and streak camera observations are providing new insight into the initiation mechanism in EBWs. These measurements are being correlated to a DDT model of compaction to detonation and shock to detonation developed previously by Xu and Stewart, [2]. The DDT model is incorporated into a high-resolution, multi-material model code for simulating the complete process. Model formulation and predictions against the test data will be discussed. REFS. [1] A. Munger, J. Kennedy, A. Akinci, and K. Thomas, “Dev. of a Laser Detonator”, 30th Int. Pyrotechnics Seminar, Fort Collins, CO, (2004). [2] Xu, S. and Stewart, D. S. Deflagration to detonation transition in porous energetic materials: A model study. J. Eng. Math., 31, 143-172 (1997) [Preview Abstract] |
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W7.00007: Molecular dynamics analysis of a liquid explosive reaction zone Laurent Soulard, Blandine Crouzet We present in this work a detailed analysis by molecular dynamics of the reaction zone of a stationary planar detonation. In particular, we look at the influence of chemical characteristics such as the reactions reversibility and endothermicity. So, equilibrium and frozen Hugoniot of the reactive system are calculated by a specific molecular dynamics method. These results can be used to a predict the detonation characteristics such as the thermodynamic properties of ZND spike and the CJ point. We observe in particular the influence of the preliminary endothermic phase on the detonation velocity and its stability. The comparisons between these predictions and non equilibrium molecular dynamics results confirm the results of this first theoretical part. In a second step, the main hypotheses of a ZND model are extracted from the MD simulations (mainly the formalism of the reactive EOS in the reaction zone). The parameters of the corresponding model are then fitted on MD results. The final step is the implementation of the model in an hydrodynamic code. Direct comparisons between molecular dynamics simulations and hydrodynamics calculations for various 1D and 2D (in the hydrodynamics sens) configurations are presented. [Preview Abstract] |
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W7.00008: Modeling a Material's Instantaneous Velocity during Acceleration Driven by a Detonation's Gas-Push Process Joseph E. Backofen This paper will describe both the scientific findings and the model developed in order to quantfy a material's instantaneous velocity versus position, time, or the expansion ratio of an explosive's gaseous products while its gas pressure is accelerating the material. The formula derived to represent this gas-push process for the 2nd stage of the BRIGS Two-Step Detonation Propulsion Model was found to fit very well the published experimental data available for twenty explosives. When the formula's two key parameters (the ratio Vinitial / Vfinal and ExpansionRatioFinal) were adjusted slightly from the average values describing closely many explosives to values representing measured data for a particular explosive, the formula's representation of that explosive's gas-push process was improved. The time derivative of the velocity formula representing acceleration and/or pressure compares favorably to Jones-Wilkins-Lee equation-of-state model calculations performed using published JWL parameters. [Preview Abstract] |
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W7.00009: Numerical Simulation of Superfast Shock-Induced Chemical Reactions in Porous Mixtures Sergey Zelepugin, Vitaly Nikulichev, Oksana Ivanova A phenomenological zeroth-order kinetic model for computations of shock-induced solid-state chemical reactions in porous mixtures is proposed. In the model a porous mixture is considered as a continuous medium whose thermomechanical properties are determined at each time step depending on mass fractions of the components. The kinetic relationships are characterized by a constant rate of chemical transformations under shock wave loading. The heat release due to chemical transformations is introduced in the energy equation. The effect of the dispersity of the mixture components on the reaction rate is taken into account by varying the constants that enter the kinetic model. The results of the numerical computations for porous Ti-C, Ti-Si, and Al-S mixtures reflect the fact that the process can be divided into several stages (dynamic compaction, shock-wave propagation, reaction of synthesis). It is shown that an increase in the chemical-reaction rate gives rise to flow regimes in which the unloading wave almost stops. [Preview Abstract] |
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W7.00010: The Piecewise Linear Reactive Flow Rate Model Peter Vitello, P. Clark Souers For non-ideal explosives a wide range of behavior is observed in experiments dealing with differing sizes and geometries. A good predictive detonation model must be able to reproduce many phenomena including such effects as: variations in the detonation velocity with the radial diameter of rate sticks; slowing of the detonation velocity around gentle corners; production of dead zones for abrupt corner turning; failure of small diameter rate sticks; and failure for rate sticks with sufficiently wide cracks. Most models have been developed to explain one effect at a time. Often, changes are made in the input parameters used to fit each succeeding case with the implication that this is sufficient for the model to be valid over differing regimes. We feel that it is important to develop a model that is able to fit experiments with one set of parameters. To address this we are creating a new generation of models that are able to produce better fitting to individual data sets than prior models and to simultaneous fit distinctly different regimes of experiments. Presented here are details of our new Piecewise Linear Fit reactive flow model applied to LX-17. Auspices Statement: This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
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W7.00011: A comparison of two new approaches for fast and accurate hydrodynamic simulations of HE detonations Olivier Heuze, Boris Khasainov, Sergey Victorov The use of the up-to-date theoretical and semi-empirical equations of state (EOS) in modern thermochemical codes allows one to predict the thermodynamic properties of the detonation products of high explosives (HE) very accurately. However, in most cases the direct incorporation of such EOS into hydrocodes is impossible due to too high computer time expanses. In this work, by the example of NM detonation we demonstrate two new approaches to hydrodynamic simulations that make it possible to gather high predictive abilities of modern thermochemical codes and low expanses of computer time. The first approach employs the pre-calculated EOS in table form. This EOS is generated by means of the TDS thermochemical code of Victorov using the up-to-date theoretical EOS for the fluid detonation products based on thermodynamic perturbation theories and intermolecular potentials, and a semi-empirical model for carbon nanoparticles. The second approach uses the CW2 EOS recently suggested by Heuze. It has a compact analytical form and allows for very fast computations so that it may be probably suitable even for 3-D simulations. The CW2 parameters can be determined from TDS calculations. Both approaches are being investigated and compared to each other using the EFAE hydrocode of Khasainov. [Preview Abstract] |
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W7.00012: On Microscopic Detonation Model Leonid Gatilov, Alexander Selezenev, Alexei Aleinikov, Anzhela Komarevskaya Both computation using the code ``Gaussian'' with DFT b31yp/6-311++g** method and spectrometry using ``Nexus'' device have been performed for infrared spectra of HE, including TNT, RDX, HMX and others. The approach proposed in (\textit{A.V.Pozdnyakov, Fizika gorenia i vzryva}, \textit{2002, V.38, ¹3.}) has been basically used to derive correlations between the detonation velocity of individual HE, the effective diameter of HE molecules and the vibrational frequencies of their functional groups. Statistical significance of the resulting correlations has been evaluated by comparing between computed and experimental detonation velocity values. Similarly, detonation velocity computations have been performed for some HE mixtures. The agreement found between the numerical and experimental values of detonation velocity confirms basic concepts of the microscopic detonation model to be developed. [Preview Abstract] |
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W7.00013: EQUATION OF STATE
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W7.00014: A kinetic approach to the propagation of disturbances in liquids Francesco Teodori, Vincenzo Molinari, Domiziano Mostacci, Marco Sumini Intermolecular forces play a key role in the propagation of disturbances in liquids. The details of interaction are best accounted for in the framework of the Kinetic Theory. In this work, the propagation of disturbances is investigated from the point of view of Kinetic Theory: starting from the Vlasov equation, the self-consistent field is calculated for intermolecular forces and a form of wave equation is obtained, where the dispersion relation depends on the type of intermolecular interaction considered. A criterium is found to establish whether or not a disturbance can propagate, criterium which again depends on the details of the interaction. [Preview Abstract] |
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W7.00015: Helmholtz Free Energy Equation of State Applied to the Carbon at Megabar Pressure Jinkyung Jung, Kyu Soo Jhung, Inho Kim We provide a simple form of Helmholtz free energy equation of state that reproduces the Hugoniot of shock compressed porous carbon at megabar pressure. The equation of state consists of the modified Cowan ion EOS and a correction term related to the free energy that is independent of thermal motion. Analytic parameters in the EOS expression are determined by the room temperature isotherm and the Hugoniot curve of non-porous carbon. We compare our results with recent shock experiments up to 10 Mbar as well as theoretical approaches such as mean-field potential calculation of shock-compressed porous carbon. [Preview Abstract] |
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W7.00016: Two-Phase Equation of State for Cerium and Specificity of its Dynamic Compression Vyacheslav Elkin, Evgenii Kozlov, Elena Kakshina, Y. Moreva The unusual thermodynamic properties of cerium result from specificities in the narrow 4f-zone whose electrons are subdivided into localized and delocalized subsystems. In this paper the model of pseudo-binary solid solutions allowing for two different electronic states is applied to construct the thermodynamically complete two-phase equation of state for cerium. The free energy of phases is written as a sum of the terms describing potential curve, lattice vibrations, and the contribution from thermally excited electrons. The parameters of the model were fitted to describe the thermodynamic data obtained in the static experiments with high-purity cerium. This equation of state was used to analyze wave structures realizing under dynamic compression with the regard for the equilibrium phase ($\gamma $--$\alpha )$--transition. The Hugoniot in the (P,T)-plane shows that due to temperature jump on the line of the ($\gamma $--$\alpha )$--transition the Hugoniot does not cross the complicated area of metastable $\alpha \prime $--, $\alpha \prime \prime $--, and $\varepsilon $ -- phases. This allows assumption that possible ($\alpha $--$\varepsilon )$--transitions of cerium in the shock wave won't be concealed by the lower--temperature ($\alpha $--$\alpha \prime )$-- and ($\alpha \prime $--$\alpha \prime \prime )$--transtions. [Preview Abstract] |
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W7.00017: Equation of state and phase diagram of quartz Alexander Petrovtsev, Vladimir Dremov, Vener Vildanov, Mikhail Gorshkov, Vladimir Zahikin, Yurii Zhugin On the basis of the latest experimental data and ab-initio calculations the multi-phase equation of state of quartz has been constructed. Quartz is a basic rock forming mineral. This fact initiated a comprehensive investigation into its thermodynamic, mechanical and shock-wave properties. Quartz has complicated phase diagram and one of the very interesting problems having fundamental character is the study of the polymorphous and phase transformations in quartz at high pressures and temperatures realizing when dynamic loading. Numerical modeling of these processes requires multi-phase equation of state. Here we present such an equation of state including a-quartz, stishovite and liquid quartz. Calculations carried out with the equation of state are in good agreement with the experimental data on static and shock compression of solid and porous quartz including the temperature measurements along Hugoniots. On the basis of an analysis of the calculated phase diagram and porous quartz Hugoniots the conclusions about what phase the legs of the experimental Hugoniots belong to have been done. [Preview Abstract] |
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W7.00018: Thermal properties of close-packed Fe up to 400 GPa determined using Hugoniot functions Yukio Sano, Tomokazu Sano A quadratic equation for the temperature-independent Gr\"{u}neisen coefficient $\gamma$ was derived by a method in which the Walsh-Christian and Mie-Gr\"{u}neisen equations are combined. Some previously existing \textit{ab initio} temperature Hugoniots for hexagonal closed-packed solid Fe are inaccurate because the constant-volume specific heats on the Hugoniots $C_{VH}$, which are related uniquely to the solutions of the quadratic equation, have values that are too small. A $C_ {VH}$ distribution in the solid phase range was demonstrated to agree approximately with a previous \textit{ab initio} distribution. In contrast, the corresponding $\gamma $ distribution was significantly different from the \textit{ab initio} distribution in the lower pressure region, and the $\gamma $ distribution in the liquid phase range had a considerably larger gradient than the \textit{ab initio} distribution. The causes of these disagreements are clarified. [Ref. Y. Sano and T. Sano, Phys. Rev. B 69, 144201 (2004).] [Preview Abstract] |
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W7.00019: Chemical model compositions of Air and Lexan at intermediate temperatures and densities Ann E. Mattsson, Michael P. Desjarlais The generation of wide range electrical conductivity models requires accurate modeling of the ionization equilibrium. At lower temperatures the free electrons contributing to the conductivity can result from the ionization of molecules, such as NO ionizing into NO+ in Air. At higher temperatures the electrons result from full ionization of single atoms. We will describe a scheme for modeling the composition of a gas, including the number of free electrons. As an example the composition of Air through the ionization part of the principal Hugoniot will be discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energyi's National Nuclear Security Administration under Contract DE- AC04-94AL85000. [Preview Abstract] |
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W7.00020: Low Pressure Equation of State for Polymers Brad Clements Low-pressure equations of state (EOS) are constructed for two representative polymers: polycarbonate and polytetrafluoroethylene. Our method, which is based on well-known EOS procedures, relies on having heat capacity data at zero pressure, specific volume data as a function of temperature and pressure, and phase diagram information. The resulting equations of state incorporate the glass transition observed in polycarbonate and the solid-solid phase transitions observed in polytetrafluoroethylene. We describe how this information can be used in modeling the dynamic response of polymers for which we provide examples. [Preview Abstract] |
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W7.00021: Mie-Gr\"{u}neisen EOS based on second order Birch-Murnaghan isotherm and Steinberg parameters David Hebert, Isabelle Bertron, Herve Garnier This paper presents a way to construct a thermodynamically consistent EOS giving access to the temperature, compatible with hydrodynamic codes requirements and with a material database consisting of parameters for the D(u) relation in the Steinberg form. We use the Mie-Gr\"{u}neisen formalism, which is accurate for condensed matter in low shock regime. The reference curve is a second order Birch-Murnaghan isotherm, which coefficients are derived from Steinberg parameters. Numerical results are presented for aluminium and copper which suggest that all approximations are valid until the Mbar range, where they can lead to 10{\%} errors. [Preview Abstract] |
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W7.00022: A Generalized Finite-Strain Function for Condensed Matters on Shock and Static Compression Kyu Soo Jhung, Jinkyung Jung, Kyung Young Choi, Inho Kim We have generalized the finite-strain function by introducing a noninteger exponent in expansion variables for the cohesive energy of condensed matter. The noninteger value is determined to make the function converge rapidly. The cohesive energy model successfully reproduces the experimental isotherms and Hugoniot curves of various solids. A volume dependent Gruneisen function has been obtained from the truncation condition and compared with recent experimental and theoretical data for condensed matters. [Preview Abstract] |
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W7.00023: Structure of a shock front in a complex (dusty) plasma Dmitry Samsonov, Sergei Zhdanov, Gregor Morfill Shock waves with a Mach number M=3.4 were studied experimentally in a two dimensional complex (dusty) plasma. The structure of the shock was resolved at a kinetic level, i.e. motion of every particle was traced and macroscopic parameters such as dust number density, kinetic temperature and particle flow velocity were determined. We obtained a complex plasma by immersing $8.9~\mu$m sized monodisperse microspheres into a capacitively coupled radio-frequency discharge. The grains formed a monolayer hexagonal lattice levitated in the plasma sheath above the disk electrode. They were illuminated with a laser sheet and imaged with a digital video camera at 1000~frames/s. An excitation pulse was applied to the wire placed below the lattice plane. The disturbance propagated into the lattice apparently melting it. The particles were identified in each frame and tracked from one frame to the next to determine their positions and velocities. Using this data we attempt to reconstruct the equation of state of a Yukawa system at the phase transition. A molecular dynamics simulation reproduced the experimental results. [Preview Abstract] |
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W7.00024: The Response of a Heavy Tungsten Alloy During Shock Loading T.D. Andrews, D.D. Radford, K. Tsembelis Plate impact experiments have been performed to assess the behaviour of a heavy proprietary Tungsten alloy in the longitudinal orientation by means of manganin gauges. The Hugoniot curve is compared and contrasted against published data on pure Tungsten and a number of Tungsten alloys. [Preview Abstract] |
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W7.00025: The Shock Induced Equation of State of Two Ferroelectric Ceramics D. Deas, J.C.F. Millett, N.K. Bourne Manganin stress gauges have been used to determine the Hugoniots of two ferroelectric ceramics, lead zirconium titanate (PZT) and a similar material modified with tin (PSZT). Comparison with previously published data shows close agreement between our results for PZT and previously published results. The transition between elastic and inelastic behaviour has also been determined, and again shows close agreement with previous data. In the case of PSZT, while the Hugoniot in terms of shock stress is similar to PZT, the variation of the wave velocity with particle velocity shows an overall increase in contrast with PZT where the opposite is true. [Preview Abstract] |
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W7.00026: The Behaviour of a Carbon-Fibre Epoxy Composite Under Shock Loading R. Vignejvic, J.C.F. Millett, N.K. Bourne, A. Lukyanov Previous work in a glass-fibre epoxy composite has indicated that damage accumulates behind the shock front, and thus some of the shock-induced mechanical properties are pulse duration dependent. In this paper, we extend this work to a carbon-fibre epoxy composite. The shock response is investigated in terms of its equation of state (shock stress, shock velocity and particle velocity) and release wave speeds. [Preview Abstract] |
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W7.00027: High-speed deformation of soft soils Bragov Anatoly, Lomunov Andrey, Sergeichev Ivan Dynamic properties of soft soils represent significant interest in connection with the decision of some important applied problems, such as a penetration of various bodies into soils, interaction of overground and underground constructions with soils at strong earthquakes and explosions. Last years for decision of similar problems numerical methods and different hydrocodes are widely used. One of important components of these complexes is the state equations adequately describing processes of dynamic deformation of soils. Now it is felt an evident lack of experimental data which are necessary for equipping the state equations by corresponding parameters and constants. The message is devoted to the description of methodical aspects for definition of the basic mechanical properties of soft soils in a wide range of strain rates and loads. The modified Kolsky method together with a plane-wave shock experiment are used for definition of dynamic properties of soils. Total diagrams of uniaxial compression of the tested soils, obtained by two methods, are resulted for sand and clay. There were obtained the uniaxial compression diagrams as well as curves of hydrostatic compression, dependences of shear resistance via pressure, factor of lateral thrust. These data are successfully used at the numerical decision of problems of soil dynamics. [Preview Abstract] |
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W7.00028: FIRST PRINCIPLES & MOLECULAR DYNAMICS CALCULATIONS
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W7.00029: Molecular-dynamics simulation of hot spots in energetic materials Ilya Derbenev, Vladimir Dryomov, Yury Nikitenko To define the role of a microporosity on critical conditions of initiation, numerical simulation was performed by a MD-method with the simlified REBO potential including two types of atoms. The potential includes also long-range van der Waals term providing for stability of a molecular crystal (AB -- are located in lattice points). Obtained results on MD simulation of thermal decomposition are in qualitative agrement with the macroscopic theory. Experiments with planar shock initiation have been simulated for a model set-up containing a gap in HE. The effects of the gap width and the flyer width and velocity have been investigated. The analysis of results has shown for a velocity and width of flyer it is possible to select the range of values alternating the cases of an intensive chemistry and a minor molecular dissociation. For a weak shock wave (without chemistry) the origin of a hot spot on a gap has been researched. The curve subdividing the area with and without reactions after a collaps of a gap has been defined as flyer velocity vs gap width function. The width of flyer was fixed at that. [Preview Abstract] |
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W7.00030: Parameter Optimization for Charge Equilibration Method in Molecular Simulations Emeric Bourasseau, Jean-Bernard Maillet In order to build a complete potential model to perform classical molecular dynamic simulations of dense liquids, a new optimization method is proposed to obtain transferable parameters for charge equilibration method. In order to make sure to obtain parameters which only describe coulombic interactions, the minimization of the error function is performed over data set constituted of pure electrostatic results taken from ab initio calculations. We first applied the new procedure to liquid HF systems. Some accurate ab initio calculations have been performed using the VASP code to completely characterize dense liquid of HF (Maillet et al., accepted to Phys. Rev. B, 2005). Electrostatic potential grids have been calculated for several configurations taken from those simulations, and optimization of parameters used in charge equilibration method has been performed on some points of those grids. The optimized parameters (the electronegativity $\chi $ and the Slater orbital exponent $\zeta $ for H and F atoms) appear able to reproduce the variations of the electrostatic potential calculated from ab initio method for different thermodynamic conditions. It is concluded that the proposed method is general, precise and efficient to obtain transferable and realistic parameters. [Preview Abstract] |
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W7.00031: Atomistic Simulations of Shocks in HMX Crystals. Eugenio Jaramillo, Alejandro Strachan, Thomas D. Sewell We are using large scale molecular dynamics simulations to study HMX crystals under shock compression. The objective is to obtain a fundamental understanding on the molecular scale of the dominant mechanisms of plastic relaxation and other dissipative processes in anisotropic molecular crystals. A fully flexible force field (Smith, G. D. and Bharadwaj, R. K.; \textit{J. Phys. Chem. B} \textbf{1999}, $103$, 3570) used in numerous preceding studies is used without modification in the present work. Initial results indicate that plastic deformation occurs even for weak shocks ($\sim $4GPa) on a time scale that is accessible to atomistic molecular dynamics ($\sim $100 ps for a 66,561 molecule system). [Preview Abstract] |
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W7.00032: Molecular dynamics simulation of shock-induced chemical, mechanical and thermal processes in nanostructured metastable composites Shijin Zhao, Timothy Germann, Alejandro Strachan Nanostructured metastable intermolecular composites (MICs) are a new class of energetic materials with a wide range of applications. MICs can be made to react to form a more stable compound while releasing a large amount of energy and exhibit several unique properties, for example, extremely fast propagation of the chemical reactions when the initial components are intermixed at the nanometer scales. The fundamental molecular-level mechanisms that govern the unique properties of these materials are to a large extent unknown. We use molecular dynamics to characterize the chemical and mechanical response of MICs induced by shock and thermal loading. We use detailed analysis methods such as the short-range topological analysis to characterize the atomic level processes responsible for the initiation and propagation of the chemical reactions. Our simulations are designed to characterize the role of composition and nanostructure on the initiation and subsequent ultra-fast propagation of chemical reactions in nanostructured MICs as well as their mechanical and thermal properties. [Preview Abstract] |
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W7.00033: Surface Stability of Polymeric Phases of Nitrogen James Hooper, Federico Zahariev, Tom Woo, Fan Zhang The polymeric phases of nitrogen have been actively studied, including the prediction of cubic gauche that has recently been observed experimentally under conditions of high pressure. The stability and electronic properties at their surfaces are important for the practical application of these materials. We present a theoretical and computational study of the surface of cubic gauche with or without dopants capping the dangling bonds. Use of various capping groups does stabilize the surface. This study uses ab-initio density functional simulations. [Preview Abstract] |
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W7.00034: Simple potentials of interatomic interaction for simulation of shock wave and quasistatic compression of metals with fcc, bcc and hcp crystal lattices Vladimir Golubev Results on parametrization of the Morse and Buckingham potentials for simulation of conditions of not less than double compression of metals with various types of crystal lattices are presented. Practically all basic metals for which it is not marked obvious polymorphic transformations into the specified range of compression were examined. Zero isotherms of bulk compression of metals were used as the pivotal data, but not their physical properties. Fitting of parameters was carried out with the use of the GULP program. Conditions of one-and-a-half-fold and twofold compression were examined. Accuracy of fitting in the first case is approximately on the order higher, however and in the second case it is enough high. Quality and accuracy of the fitting of potential parameters were examined also depending on a number of atoms interacting with the chosen central atom. As a result it was offered to take into account interaction of the central atom with not less than 136 neighbor atoms located not less than on eight coordination spheres of considered lattices. As examples of use of the obtained potentials the results of molecular dynamic simulation of compression and loss of structural stability for fcc, bcc and hcp crystal lattices of metals in conditions of shock wave and quasistatic loading are quoted. [Preview Abstract] |
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W7.00035: Dynamic properties of silica and Lennard-Jones system subjected to simulated laser irradiation Lianqing Zheng, Sheng-Nian Luo We investigate the dynamic properties of the silica and Lennard-Jones systems subjected to simulated laser irradiation using classical molecular dynamics simulations. Laser energy deposition is approximated by converting photon energy to kinetic energy of the system. Two paradigm systems, silica and the Lennard-Jones system, are examined for understanding structure change, metastable behavior in phase transition, and mechanical properties under ultrafast dynamic loading, and the effects of defects, initial stress--temperature conditions and the loading characteristics of the lasers. [Preview Abstract] |
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W7.00036: Molecular-dynamics investigation into influence of nano-particles in spall Sergey Kraichikov, Vladimir Dremov, Philipp Sapozhnikov Recent experiments seem to find nano-particles at every void at the spall plane of Cu targets. 3D molecular-dynamics simulations of planar shock experiments have been carried out to check for whether the nano-particles act as stress concentrators, decreasing significantly the spall strength. The MD model set-up was constructed of two samples of different length colliding at given velocity. As a result of an interaction of two release waves formed after shock waves reached free surfaces the region of negative pressure was created in the longer sample. This stretching led to fracture of the longer sample. The calculations have been carried out with carbon and lead foreign nano-particles introduced into copper matrix. The effects of the nano-particles average size (1-2 nm and 2-4 nm cases have been considered) and their concentration upon the spall strength and the mechanism of spallation have been studied. [Preview Abstract] |
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W7.00037: Shear stresses in shock compressed covalent solids Ivan Oleynik, Douglas Lovelady, Sergey Zybin, Mark Elert, Carter White Shear stresses are the driving forces for the creation of both point and extended defects in crystals subjected to high pressures and temperatures. We report DFT results appropriate for shear stresses in shock compressed covalent solids such as diamond and silicon for three low-index crystallographic directions, $<$100$>$, $<$110$>$, $<$111$>$. The non-monotonic behavior of shear stresses predicted by first-principles theory will be discussed in connection to dynamics of plastic deformations and the structure of the shock wave front. In particular, the non-monotonic dependence of shear stresses on uniaxial compression might result in a significant delay or even freezing of the plastic response that was recently observed in MD simulations of strong shock waves in covalent solids. [Preview Abstract] |
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W7.00038: Molecular dynamics simulations of the surface instability in a shock loaded copper S.V. Zybin, E.M. Bringa, S.I. Abarzhi, B. Remington We report the preliminary results of the molecular dynamics (MD) simulations of the growth of surface perturbations in copper, which is a subject to impulsive acceleration caused by the shock passage. The simulations indicate the developments of the Richtmyer-Meshkov instability at the interface between two solids in the limiting case of the density of the light solid approaching zero (i.e. the Atwood number A = 1). MD accounts for the physical nonlinearities and as well as non-equilibrium character of the energy and mass transfers typical for the shock compression. At the same time, MD numerical method does not use empirical assumptions of the equation of state, the tensor of elastic constants and the properties of shear stress, in contrast to hydrodynamics simulations with elastic-plastic constitutive model. We apply MD simulations to determine the critical values of the perturbation wavelength and the shock velocity, to study the plastic flow and the dynamics of dislocations at nano-scales, and to find their relations to the von Mises plasticity criterion, material strength, and the time evolution of the perturbation growth. [Preview Abstract] |
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W7.00039: Ab Initio MD Computation of the Vibrational Relaxation Time in HE Molecules. Alexander Selezenev, Alexei Aleinikov Ab Initio MD simulation has been used to compute equilibrium time for the intramolecular vibrational degrees of freedom in molecules of TNT, RDX, HMX and PETN. Computation of intramolecular forces field was done utilizing the code ``Gaussian'' with HF/STO-3G method. Ab Initio MD simulations have been carried out for the decomposition of TNT and RDX molecules as they collide. For the kinetic energy of molecular collisions, its threshold values have been found where decomposition of the molecules should occur before the equilibrium distribution of collision energy into vibrational degrees of freedom. [Preview Abstract] |
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W7.00040: PHASE TRANSITIONS
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W7.00041: Material Properties on a Phase Boundary of a Multiphase Equation of State Christopher Robinson Multiphase equations of state (EoS) may be constructed by determining a separate EoS for each individual solid (or liquid) phase. At a phase transition the two phases generally have a different specific volume, energy and entropy. For specific volumes and energies between the two phases the EoS may be determined by assuming the material consists of a mixture of the two individual phases. This paper determines the material properties (bulk sound speed, specific heat etc.) in the mixed two-phase region along the phase boundary assuming the material consists of a mixture of the two single phases at the same pressure and temperature and in thermodynamic equilibrium. Some general relationships between the thermodynamic properties of the mixed two-phase region compared to the single-phase regions are then determined. The effect of a phase boundary on isentropic compression or release is considered. [Preview Abstract] |
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W7.00042: Modeling rate dependent phase transitions in isentropically compressed Bi and Fe Jave Kane, Raymond Smith, Jon Eggert, Gilbert Collins Experiments are underway at the Janus laser to study phase transitions in isentropically compressed samples of Bi and Fe attached to windows of LiF or sapphire. The target is loaded with a ramped laser ICE drive. The velocity history of the sample-window interface is recorded using line VISAR. The response of the targets is modeled by evolving the 1D Euler equations using a drive deduced by back integration from shots performed with Al samples. Multiphase EOS models are used for the sample, and rate dependence is implemented with the Andrews-Hayes equations. [Preview Abstract] |
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W7.00043: Shock induced alpha-epsilon phase transition in iron: Analysis of MD simulations and experimental data James Hawreliak, K. Rosolankova, J. Sheppard, J.S. Wark, J.F. Belak, G.W. Collins, J.D. Colvin, J.H. Eggert, D.H. Kalantar, H.E. Lorenzana, J.S. Stolken, H.M. Davies, T.C. Germann, K. Kadau, P.S. Lomdahl, M.A. Meyers, M.S. Schneider Multi-million atom non-equilibrium molecular dynamics (MD) simulations for shock compressed iron are analyzed using Fourier methods to determine the long scale ordering of the crystal. By analyzing the location of the maxima in k-space we can determine the crystal structure and compression due to the shock. This poster will present results from different shock pressures and compare them to recent experiments of shock compressed iron where the crystal structure was determined using in-situ wide angle x-ray diffraction. [Preview Abstract] |
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W7.00044: Evolution of damage pattern for tin between 18 and 34 GPa Christophe Voltz, Fran\c{c}ois Buy In order to investigate Tin damage and spall, under release wave, shock compression measurements have been carried out in the vicinity of melting curve, up to 34 GPa peak stress. The Asay window technique has been used to characterize spall layers. Both Tin surface and LiF window velocities have been recorded using visar and Doppler laser interferometry measurements techniques. We aimed to point out the influence of phase transitions on the damage behavior between solid and liquid states. Therefore we performed 4 experiments where Tin is submitted to a Taylor wave loading. According to the shock pressure level in the vicinity of the free surface, the material remains solid, melts partially or totally. This paper presents experimental results. The velocimetry curves recorded at Tin/LiF interface presents profiles with more regular shape according to higher molten fraction. We find a fairly good agreement between velocity profiles measurements and calculations performed on a hydrococde, using a multiphase equation of state in the field of low density domain. [Preview Abstract] |
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W7.00045: Structural -- Phase Transformation in Two-Phase Titanium Alloys at Shock Loading Margarita Skotnikova, Mikail Martynov, Nikolai Krylov, Vladimir Vinogradov, Aleksey Galyshev Plane targets from ($\alpha$ + $\beta$) Titanium alloy VT6 loaded under uniaxial strain conditions at the impact velocities from 400-600 m/s. The investigations were carried out on thickness of sample along the shock wave propagation, both in the central zone, and on distance 4, 7 and 11 mm from the centre. As it have shown results of microhardness, X-ray analysis, REM and TEM investigation, on an input in material of sample the shock loading wave resulting in decomposition of $\beta$-phase and enrichment by vanadium of $\alpha$-phase up to formation soft orthorhombic martensite - phase, braking shock wave was formed. The shock wave was reflected from opposite side on output and the wave of unloading was formed. Here there was a change of the mechanism of plastic deformation from shift to rotational. Thus there was an intensive heat-generating and return phase transformation, at which soft $\beta$-phase enriched with vanadium, inclined to decomposition down to formation of a brittle $\omega$-phase was formed. Than the more the quantity of soft $\beta$-phase, the microhardness of opposite side material was less. From the moment when $\beta$-phase turned in brittle $\omega$-phase, the hardness of sample material was raised. In this place the crack was formed. [Preview Abstract] |
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W7.00046: Influence of temperature upon the a-w transition in titanium Galina S. Bezruchko, Sergey V. Razorenov , Gennady I. Kanel, Vladimir E. Fortov The $\alpha \to \omega $ polymorphic transition in shock-compressed high-purity Ti was studied at normal and elevated temperatures. In the experiments, the velocity histories of the sample free surface or interface between the sample and LiF window were recorded. The shock-wave loads were created by impact of Al flyer plates at the impact velocities of 650 m/s and 1200~m/s. The effect of polymorphic transformations was observed at both peak stresses. The parameters of inflection point in the compression wave profile are not constant and strongly depend on the peak stress and the wave propagation distance that indicates great influence of the kinetics of transformation on the wave dynamics. The transition occurs much faster at $\sim $400\r{ }C than at the $\sim $10\r{ }C. As a result of the kinetic effects, apparent pressure of start of the transition at high impact velocity decreases with heating, whereas at low impact velocity it increases in agreement with the phase diagram. No evidences of reverse $\omega \to \alpha $ transition were recorded. [Preview Abstract] |
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W7.00047: Shock compression of C$_{70}$ fullerite with use of recovery assemblies Sergey Sokolov, Vladimir Milyavskiy, Tatiana Borodina, Andrey Zhuk Shock-induced phase transitions of C$_{70}$ fullerite were studied with use of recovery assemblies of planar geometry. The starting material consisted of two crystalline phases: phase with hexagonal close-packed (hcp) and phase with rhombohedral structure. In the specimens, maximal shock pressures were reached after several reverberations of the waves between the walls of the recovery ampoule (step-like shock-wave compression) and were ranged from 9 to 52 GPa. We have found that C$_{70}$ fullerite undergoes a series of shock-induced polymorphic phase transitions. In the samples, recovered from 9, 14 and 19 GPa, a dominant phase was fullerite C$_{70}$ with cubic structure. Also, some amount of C$_{70}$ with hcp structure was observed. The quantity of hcp phase was decreasing with increasing of intensity of shock compression. With further growth of shock pressure, destruction of C$_{70}$ molecules occurs. In the specimens recovered after shock compression up to pressures over 19 GPa, the main phase was graphite with a low degree of three-dimensional regularity. [Preview Abstract] |
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W7.00048: Alkali metals conductivity at multistep dynamic compression Victor I. Postnov, Denis V. Shakhray, Vladimir E. Fortov This work is devoted to studying of phase and structural transitions, in alkaline metals (lithium, sodium, potassium and calcium) at dynamic compression. Experiments were carried out at a room temperature and at temperature of liquid nitrogen with application of smooth shock wave technique. As a result for calcium almost tenfold increase in electrical resistance was observed at the maximal pressure 60GPa. Similar electrical resistance changing was fixed in sodium experiments. In experiments with lithium the range of pressure has been expanded up to 210GPa. The break on pressure-resistivity dependence at 160Gpa was found [1]. The fixed electrical resistance changing of samples at 120GPa makes about 70 times. Character of pressure-resistivity dependence for potassium samples qualitatively coincides with fixed for sodium and lithium. In unloading electrical resistance of all samples came back to the initial value. This phenomenon testified about convertibility of occurring processes. This work was supported by RFBR N03-02-16322, grant of the President of Russia N NS 1938.2003.2, program of basic researches of the Russian Academy of Science ``Thermophysics and mechanics of intensive energy influences'' and Russian Science Support Foundation. 1. V E Fortov, V V Yakushev, K l Kagan et al // J.Phys.: Condens Matter 14 (2002) 10809-10816 [Preview Abstract] |
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W7.00049: GEOPHYSICS AND PLANETARY SCIENCE
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W7.00050: The Response of Silica Gel under Shock Loading Conditions E.A. Taylor, K. Tsembelis, C.S. Cockell, W.G. Proud A series of plate impact experiments has been performed to assess the dynamic behaviour of silica gel in the longitudinal orientation by means of manganin gauges and VISAR using the Cavendish facility. This series is part of a preliminary program to assess the survivability of biological materials during a terrestrial impact event. [Preview Abstract] |
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W7.00051: Chemical Reactions Between Iron and (Mg$_{0.92}$, Fe$_{0.08}$)SiO$_{3}$ Perovskite under Shock Compression Xiufang Chen, Zizheng Gong, Li Zhang, Liwei Deng, Yingwei Fei, Fuqian Jing The possible chemical reactions between liquid iron and (Mg$_{0.92}$, Fe$_{0.08})$SiO$_{3}^{ }$perovskite was checked up to 115GPa shock pressure (the corresponding temperature is estimated about 4950K). The XRD observations showed the main composition of the recovered samples is Fe and (Mg, Fe)$_{2}$SiO$_{4}$, and no evidence for the existence of (Mg$_{0.92}$, Fe$_{0.08})$SiO$_{3}$ perovskite. We inferred that the chemical reactions between iron and perovskite happened during shock compression. It suggest that reactions between liquid iron and (Mg$_{0.92}$,Fe$_{0.08})$SiO$_{3}^{ }$perovskite should occur at the core-mantle boundary conditions, creating a very heterogeneous zone at the base of the mantle. [Preview Abstract] |
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W7.00052: Peculiarities of biotite, quartz and garnet transformations in conditions of step-like shock compression of crystal slate Andrey Zhuk, Vladimir Milyavskiy, Tatiana Borodina, Sergey Sokolov, Vilen Fel'dman, Ludmila Sazonova A character of shock metamorphism of the crystal slate, which consists of a garnet, plagioclase, biotite and quartz has been studied with use of recovery assemblies of planar geometry. In the specimens, maximal shock pressures were reached after several reverberations of the waves between the walls of the recovery ampoule and were ranged from 19 to 52 GPa. In biotite, the mechanical deformations (fractures and kink bands of various crystallographic orientation) in the whole range of pressures were observed. The melt of biotite begins from $\sim $30 GPa along fractures and on contacts with other minerals. At shock pressure 52 GPa about 70{\%} of biotite grains transform to glass. From biotite melt formed at 52 GPa, after pressure and temperature drop crystallization of new phases begins. One of them corresponds to alumina ringwoodite (Al$_{2}$O$_{3}$ content up to 16{\%}). The composition of the second phase is essentially close to that of grossular garnet. Shock-induced transformations of quartz and garnet were studied in the present work, too. The results of experiments were compared to the literature data and natural metamorphism of rocks in impact craters. [Preview Abstract] |
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W7.00053: Measurements of sound velocity of laser-irradiated iron foils relevant to earth inner core condition K. Shigemori, T. Irifune, T. Shiota, K. Otani, T. Sakaiya, H. Azechi We have demonstrated an experiment for the measurement of the sound speed of high-temperature (6000 - 8000°C), high-pressure (350 GPa) iron relevant to earth inner core with intense laser. When the iron target is irradiated by laser, the shock wave passes through the iron. After the shock front reaches the rear surface, the rarefaction wave moves back to the laser-irradiated surface. When the rarefaction wave (sound wave) reaches the laser-irradiated surface, the laser-irradiated surface starts to accelerate. From the measurement of the shock breakout timing and the rarefaction breakout timing with the radiograph, it is possible to obtain the sound velocity. The experiments were done on the HIPER laser facility at ILE, Osaka Univ. In order to avoid the preheating, we employed three-layered target (CH - Au - Fe). The pulse shape of the irradiated laser was foot pulse (2$\omega $, 4 ns, 2$\times $10$^{12}$ W/cm$^{2})$ followed by main pulse (3$\omega $, 7.5 ns, 2$\times $10$^{13}$ W/cm$^{2})$. We measured the sound velocity of shock-compressed Fe foils with side-on x-ray backlighting technique. We also measured the shock velocity and the shocked temperature from the rear-surface emission spectrum to characterize pressure and temperature of the laser-compressed iron. [Preview Abstract] |
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W7.00054: The Shock Hugoniot Properties of Various Geological Materials C.H. Braithwaite, W.G. Proud, J.E. Field A series of plate impact experiments was performed to determine the principal Hugoniot curves of various geological materials. The experiments were carried out using the plate impact facility at the Cavendish Laboratory, Cambridge University. Samples were fired in both conventional and reverse configurations, at a variety of impact velocities from 256 m/s to 957 m/s, and stresses of up to 11 GPa. Data from the samples was collected by a number of methods including calibrated manganin stress gauges, high speed photography and laser velocity Interferometry. [Preview Abstract] |
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W7.00055: EXPERIMENTAL DEVELOPMENTS
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W7.00056: Temperature Controller System for Gas Gun Targets Scott Bucholtz, Ted Rupp, Russell Gehr, Stephen Sheffield, David Robbins A temperature controller system capable of heating and cooling gas gun targets over the range -75\r{ }C to +200\r{ }C was designed and tested. The system uses cold nitrogen gas from a liquid nitrogen Dewar for cooling and compressed air for heating. Two gas flow heaters control the gas temperature for both heating and cooling. One heater controls the temperature of the target mounting plate and the other the temperature of a copper tubing coil surrounding the target. Each heater is separately adjustable, so the target material will achieve a uniform temperature throughout its volume. A magnetic gauge with integrated thermocouples was developed to measure the internal temperature of the target. Using this system shock experiments, including equation-of-state measurements and shock initiation of high explosives, can be performed over a range of initial temperatures. Successful tests were completed on Teflon samples. This work was supported by the NNSA Enhanced Surveillance Campaign through contract DE-ACO4-01AL66850. [Preview Abstract] |
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W7.00057: The Study of Shock Waves and Laser Excited Lattice Dynamics using Ultrafast X-ray Diffraction David J. Funk, G.L. Fisher, D.E. Hof, H.J. Lee, D. Lim, Q. McCulloch, C.A. Meserole, D.S. Moore, J. Roberts, J.B. Workman, A.J. Taylor, N. Hur, S.-W. Cheong, J. Wark We have studied the picosecond lattice dynamics of optically pumped hexagonal manganite LuMnO3 using ultrafast x-ray diffraction. The results show a shift and broadening of the diffraction curve due to the stimulated lattice expansion. To understand the transient response of the lattice, the measured time- and angle-resolved diffraction curves are compared with a theoretical calculation based on dynamical diffraction theory modified for the hexagonal crystal structure of LuMnO3. Our simulations reveal that a large coupling coefficient between the a-b plane and the c-axis (c13) is required to the data. We compare this result to our previous coherent phonon studies of LuMnO3 using optical pump-probe spectroscopy. We have also performed preliminary experiments of shock waves traversing thin (approximately one micron) metal single-crystals, characterizing the shock wave using ultrafast spatial interferometry and with ultrafast x-ray diffraction. A summary of our current results will be presented. [Preview Abstract] |
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W7.00058: Shock Velocity Detection using Photonic Doppler Velocimetry Palakkal Asoka-Kumar, Ricky Chau, Neil C. Holmes Photonic Doppler Velocimetry (PDV) using Doppler-shifted coherent laser light offers a novel way to access the instantaneous of a moving surface. Light scattered from a moving surface is shifted in frequency and when allowed to superpose with the original light will result in intensity modulation at the beat frequency of the two light fields. Such a system is capable of recording the velocities of moving surfaces in a gas gun experiment as demonstrated by O.T. Strand et al.\footnote{O.T. Strand, L.V. Berzins, D.R. Goosman, W.W. Kuhlow, P.R. Sargis, and T.L. Whitworth, $\textit{Velocimetry using Heterodyne Techniques}$, 26th Int. Congress on High-Speed Photography and Photonics, Alexandria, VA, Sept 19-24, (2004).} We describe a Photonic Doppler Velocimetry (PDV) System that measures shock arrival times in materials to a wide range of pressure values. The response time for shock arrival detection is similar to or better than the conventional pin recording system. We describe several examples of obtaining dynamic EOS data, sound velocity, and free surface velocity profiles. This work was performed under auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
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W7.00059: OTHER TOPICS
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W7.00060: Evolution of Shock Waves in Silicon Carbide Rods Igor Balagansky, Alexey Balagansky, Sergey Razorenov, Alexander Utkin Evolution of shock waves in square rods made of silicon carbide has been investigated. Several experiments were conducted to measure shock wave profiles in ceramic rods. Square rods made of self-bonded silicon carbide were used; rod thickness was 20 x 20 mm, rod length -- 20.0, 40.0, 77.5 mm. Density of the samples was 3.08 g/cm$^{3}$, porosity -- less than 2{\%}. The value of Hugoniot elastic limit was estimated at 10 GPa. Shock waves in the rods were initiated by detonating a stabilized RDX high explosive charge 40 mm in height, 40 mm in diameter, and density of 1.60 g/cm$^{3}$. Manganin gauges were used to measure the pressure profiles. Propagation of shock wave along the ceramic rod was also investigated using a rotating mirror camera. Analysis of the results allows drawing the following conclusions. It has been observed that the propagation velocity of compressed impulse is constant along the length of ceramic rod, and amounts to 11.0 km/s, which equals to elastic wave velocity in the rod. Strong fuzziness of the wave front is observed, which conforms to theoretical conception of impossibility of shock wave existence in a finite size elastic body. The phenomenon of fuzziness of the wave front may be used for desensitization of heterogeneous high explosives. [Preview Abstract] |
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W7.00061: Pressure Measurements for Tungsten Wire Explosions in Water V.N. Afanas'ev, I.V. Glazyrin, V.B. Bychkov, E.I. Karnaykhov, D.N. Kazakov, O.N. Pan'shina, A.N. Grigoriev, G.I. Shuranova Successful wire array implosion experiments carried out on PBFA- Z accelerator [1], in which a record-breaking soft x-ray yield of more than 1.5 MJ was observed, stimulated interest in research of electric explosion of thin metal wires. The results of pressure measurements micron's tungsten wire explosion, which carried out in deionized water. Thin tungsten wire explosion was investigated experimentally at current pulse 100 ns duration. The shock waves from the 70 $\mu $m tungsten wire explosion were measured by the piezoceramic pressure gauge. The gauges were placed at a range from 3 to 15 mm of wire. The piezoceramic gauges were calibrated on the stable electron beams generator with nanoseconds duration. Experiments were carried out for verifying the tungsten plasma equation of state parameters under different values of the deposited energy. [1] R. B. Spielman, C. Deeney, G. A. Chandler \textit{et al.}, Phys.Plasmas {\#}5, ð. 2105, 1998. The work was supported by ISTC {\#} 1826 [Preview Abstract] |
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W7.00062: PHYSICS AND CHEMISTRY AT HIGH STATIC PRESSURE
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W7.00063: Strength and Deformation Modes of Strong Covalent Solids Changfeng Chen We present results of first-principles studies on the atomistic deformation modes and the ideal strength of several strong covalent solids, including diamond, cubic boron nitride and recently synthesized cubic B-C-N ternary compounds. We show that the widely used empirical relationship between the elastic moduli and material strength leads to a significant overestimate for the strength of the ternary compounds. The nonelastic stress response at large strains makes it necessary to examine the stress-strain relation up to the breaking point for an accurate determination of the strength and the structural failure mode. Implications for other similar materials will be discussed. [Preview Abstract] |
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