Session F1: Poster Session I (5:30 - 7:00PM)

Raman Spectroscopy of Tin Monoxide under High Pressure

Under ambient conditions, tin monoxide crystallizes in litharge structure which consists of tetragonal \textit{P4/nmm} symmetry. An orthorhombic distortion of this compound at high pressure is assumed to be driven by softening of the unobserved $B_{1g}$ phonon, which results in a spontaneous strain in the \textit{xy} plane of the tetragonal unit cell. In this case, a reduction of the symmetry into \textit{Pm2}$_{1}n$ occurs. The correlation between the tetragonal and orthorhombic symmetries shows a splitting of the degenerated $E_{g}$ phonon into a superposition of $A_{1}$ and $B_{1}$ phonons in the lower symmetry. This splitting was observed in our pressure dependent Raman scattering measurements. The changes in the pressure induced Raman spectrum of tin monoxide can be quantitatively obtained by first order perturbation theory. The frequency of this phonon under stress is obtained by diagonalizing the relevant matrix. This procedure gives a frequency shift and splitting of $E_{g}$ phonon as a function of pressure induced strain. By means of Landau's classical free energy theory this order parameter gives a critical pressure value of 1.03 GPa for the phase transition.   

Attempts in PTTT diagram of pressure induced phase transformations

Temperature-time-transition (TTT) diagram is widely applied for understanding the kinetic behavior of temperature induced phase transition. In contrast to it, kinetic behavior of pressure induced phase transitions is still not effectively researched, although many equilibrium phase diagrams have been found up to very high pressure. In fact, behavior of diamond nucleation and growth from C-H-O system could be well known through characterization of recovered samples. The results suggest time-dependent conditions of pressures and temperature. A notional kinetic phase diagram is established by previous experimental and geological data. In recent years, we made a pressure-jump apparatus with the compression rate from several to 500GPa/s within 10GPa, such rate range lies in the gap between conventional static and dynamic high pressure experiments. By using it, some novel metastable phases were solidified through rapid compressing their melts, including alloys, non-metallic elements and polymers. Comparing characterization of recovered phases with the experimental conditions, dependence of phase transition on the compression rates could be clearly demonstrated, furthermore, combining with heating or cooling rates at high pressure, the kinetic phase diagram with three dimensions, pressure, temperature and time, (PTTT diagram) could be established.   

Observation of electrical and magnetic property of CaIrO$_{3}$ and CaRhO$_{3}$ post-perovskite by electrical resistivity measurement under high pressure

Since discovery of MgSiO$_{3}$ post-perovskite (PPv) phase, high-pressure polymorph of MgSiO$_{3}$ perovskite (Pv), there are extensive studies regarding physical properties of various PPv materials. It is well known that the crystal structure of high-$T_{c}$ cuprates is based on Pv structure. Material with PPv structure is thus expected to show superconducting behavior with high $T_{c}$. Here we investigated electrical properties of CaIrO$_{3}$ and CaRhO$_{3}$ PPv. These PPv materials are quenchable to ambient condition, and known as a quasi-2D Mott Insulator showing antiferromagnetic transition at low temperature [1,2]. We performed electrical resistivity measurements on the samples under high pressure and low temperature conditions up to 191 GPa, and found that the energy gap of both samples came close to zero with applying pressure. On CaIrO$_{3}$ PPv, we observed an abrupt increase in sample resistivity at low temperature, which is likely to correspond to antiferromagnetic transition in the sample. The N\'{e}el temperature decreased with applying pressure. In the experiments on CaRhO$_{3}$ PPv, we could not observe such resistivity jump likely caused by the magnetic transition.\\[4pt] [1] Yamaura et al., J. AM. CHEM. SOC. 131 2722-2726 (2009)\\[0pt] [2] Ohgushi et al., Physica B 404 3261-3263 (2009)   

Presence of parimagnetism in HoCo$_{2}$ under hydrostatic pressure

HoCo$_{2}$ belongs to a group of RECo$_{2}$ compounds (RE $=$ rare earth metal) which were previously studied mostly due to presence of two types of magnetism - the localized RE magnetic moment and the Co moment originating in the splitting of the Co 3d subbands. The corresponding RE and Co magnetic sublattices are both ferromagnetic and antiparallel to each other for RE $\in $~(Gd..Tm) below $T_{C}$. In 2007 Herrero-Albillos et al. published experimental evidences of the Co moments surviving in paramagnetic state above $T_{C}$ in ErCo$_{2}$. The surviving Co magnetic moments form small (ferromagnetic) clusters coupled antiparallel to the nearest RE magnetic moments in the paramagnetic state. These antiparallel short-range Co-Er moment correlations at $T$ \textgreater $T_{C}$ are denoted as parimagnetism. Above a characteristic temperature $T_{f}$ (observed in the AC magnetic susceptibility data as a tiny anomaly) the Co magnetic moment turns to the same direction as Er magnetic moment. The phenomenon of parimagnetism has been recently confirmed for HoCo$_{2}$. In 2011 Bonilla at al. presented results from $\mu$ SR experiment on ErCo$_{2}$. Results of the $\mu$ SR experiment show the presence of Co magnetic clusters up to temperature $T^{\ast } $\textgreater $T_{f}$. We present experimental results AC susceptibility measurements for HoCo$_{2}$ under hydrostatic pressure up to 3 GPa and $\mu$ SR data under hydrostatic pressure up to 2 GPa. The results will be discussed in terms of corresponding variations of the hierarchy inter- and intra-sublattice exchange interactions.   

Vibrational properties of Ba$_{8}$Ga$_{16}$Sn$_{30}$ under high pressure

Semiconductor clathrates consist of host cages made by group-14 (13 and 15) atoms with sp$^{3}$ network, and guest atoms encapsulated into the host cages. Ba$_{8}$Ga$_{16}$Sn$_{30}$ clathrate are well known to provide a typical rattling vibration of the guest. Because of the cage size much lager than guest ion size, the guest ions are located not at the center of the cage, leading to so-called off-center rattling vibration. The sizes of guest ion and/or host cage are important for the rattling nature. It is straightforward to apply the pressure for investigate the rattling vibration which is expected to be highly sensitive to the host cage size. In this paper, we provide the dependence of the rattling vibration of Ba$_{8}$Ga$_{16}$Sn$_{30}$ on the pressure.   

High pressure melting of Tellurium

The melting curve of Tellurium was measured in a laser heated diamond anvil cell (LHDAC). Using our IR pyrometer we were able to measure melting temperatures as low as 600 K. Melting at high-pressure was identified by image analysis of an auxiliary laser light scattering images, taken from the surface of the hot spot, and designed to detect changes in the sample surface due to melting. Our data is consistent with previous measurements performed in a large volume press and go to higher pressure.   

Application of the shock reverberation technique to determine Gr\"{u}neisen gamma for float glass

Determination of high strain-rate material properties following loading from a non-principle Hugoniot ground state requires detailed knowledge of the shape of a materials equation-of-state. The material-specific variable Gr\"{u}neisen gamma, $\gamma $(v), defines the shape of ``off-Hugoniot'' points in energy-volume-pressure space. Comparison between experimental and simulated results of ``ring-up'' experiments, where shock reflection allows a material to be loaded successively into a series of off-Hugoniot states, has the potential to allow ready access to values of gamma. However, previous attempts to determine $\gamma_{1}$ via comparison to ANSYS Autodyn$^{\textregistered}$ simulations for the temperature-resistant polymer polyether ether ketone (PEEK) only produced a partial success, due to the highly non-linear nature and poorly defined residual deviatoric (strength) effects inherent in the material response. Consequently, in this study an attempt is made using a similar approach to calculate $\gamma_{1}$ for the well-defined material float glass (whose high elastic limit should also minimise deviatoric effects).   

Modeling Dynamic Compaction of Porous Materials with the Overstress Approach

To model compaction of a porous material (PM) we need 1) an equation of state (EOS) of the PM in terms of the EOS of its matrix, and 2) a compaction law. For the EOS it is common to use Herrmann's suggestion, as in his P$\alpha $ model. For a compaction law it is common to use a quasi-static compaction relation obtained from 1) a mezzo-scale model (as in Carroll and Holt's spherical shell model), or from 2) quasi-static tests. Here we are interested in dynamic compaction, like in a planar impact test. In dynamic compaction, the state may change too fast for the state point to follow the quasi-static compaction curve. We therefore get an overstress situation. The state point moves out of the quasi-static compaction boundary, and only with time collapses back towards it at a certain rate. In this way the dynamic compaction event becomes rate dependent. In the paper we first write down the rate equations for dynamic compaction according to this overstress approach. We then implement these equations in a hydro-code, and run some examples. We show how the overstress rate parameter can be calibrated from tests.   

Shock-recovery studies on InSb single crystals up to 24 GPa

A series of shock-recovery experiments on InSb single crystals along the (100) or (111)-axis up to 24 GPa were performed using a flyer plate impact. The structures of recovered samples were characterized by X-ray diffraction (XRD) analysis. According to calculated peak pressures and temperatures, and phase diagram for InSb, the sample could undergo phase transitions from zinc-blende structure to high-pressure phases. However, the XRD trace of each sample revealed the absence of additional constituents including metastable phases and high-pressure phases of InSb except for 15 and 16 GPa. The XRD trace of each sample corresponded to powder pattern of InSb with zinc-blende structure. At 16 GPa, in addition to zinc-blende structure, additional peaks were obtained. One of these peaks may correspond to the \textit{Cmcm }or \textit{Immm} phase of InSb, and the other peaks were not identified.   

The evolution of bulk strength behind a shock propagating in metals with controlled flaw populations

Plastic deformation in metals in the ``weak shock'' regime occurs by slip in the metals crystalline structure. However, such atomic motions take a finite time. Consequently, coalesce of inherent flaws leading to a macroscopic compressive strain will not occur immediately on shock arrival. In this study the effect of artificially induced flaws in the well-characterised FCC metal Al on strength behind the shock was interrogated. Cold-pressing of two differing particle size/morphology plasma-spray powders to close to bulk density allowed generation of microstructures with inherent flaws on the initial powder-size scale. Inclusion of longitudinal and lateral Manganin stress gauges then allowed the temporal evolution of material shear strength to be monitored at different distances from the impact face. Comparison to the response of bulk material subsequently allowed de-convolution of the influence of the induced flaws in the pressed structures.   

Plate impact experiments and simulation on porous graphite

We present some plate impact experiments on a commercial grade of graphite. The dynamic loadings range between 0.4 and 15 GPa under shock, and reach 25 GPa under reshock in the samples, which were approximately 20{\%} porous and macroscopically isotropic. Material velocity at the sample rear surface is measured and recorded optically with Visar or Perrot-Fabry interferometers. These experimental results are then compared to hydrodynamic simulations. The model for graphite takes porosity into account, and the parameter fitting will be presented. Our model is also compared to previously published experimental data. The overall agreement is good.   

The $\alpha \rho \lambda $-model of Operational EoS

The operational EoS concept can be traced back to fundamental principles of thermodynamics. From the one hand, the operational EoS is nothing else but the complete EOS, i.e., one of the thermodynamic potentials referred to their canonically adjoint thermodynamic variables. On the other hand, the operational EoS is the operator (typically, integro-differential operator) of the measured series of experimental data. Thus, from the one hand, the operational EoS is thermodynamically consistent, and, from the other hand, it explicitly indicates the measurements required for obtaining the usable EoS. Making some plausible physical conjectures the amount of required experimental measurements can be diminished. Such conjectures can be formulated, for instance, in terms of the structure of the heat capacity function. For instance, the assumption of constant heat capacity leads to the model of the Dulong-Petit model, the assumption of that the heat capacity is function of the entropy density leads to the Mie-Gruneisen EoS. etc. In the paper, we suggest one more model, having three functional degrees of freedom, which is based on the assumption about the heat capacity function dictated by hydrocode modeling approach.   

Effect of Pressure on Some Optical Properties of Ga$_{x}$In$_{1-x}$P Semiconductors

A theoretical procedure is presented for the study of optical properties of ternary alloy Ga$_{x}$In$_{1-x}$P. The calculations are based on the pseudopotential formalism in which local potential coupled with the virtual crystal approximation (VCA) is applied to evaluate the effect of pressure on the optical properties like refractive index, electronic polarizability, plasmon energy, dielectric constant and equation of state for gallium concentration $x =$ 0, 0.25, 0.50, 0.75 and 1 of the ternary alloy Ga$_{x}$In$_{1-x}$P. To incorporate the screening effect, local field correction functions due to Hartree, Taylor, Ichimaru et al. and Nagy are employed. The refractive index, electronic polarizability and dielectric constant computed for the parent binary compounds GaP and InP are found to be satisfactorily agreeing with the experimental report. It is seen that the refractive index of Ga$_{x}$In$_{1-x}$P decreases nonlinearly with the increase in pressure. The results obtained using Hartree's screening functions are not very close to the experimental data as it does not include any exchange and correlation effects. Overall good agreement with the experimental and other theoretical findings confirms the application.   

Structural, electronic and phase transition properties of ytterbium monopnictides under high pressure: A LSDA$+$U study

In present paper, we have investigated the structural, electronic properties of ytterbium monopnictides (YbX $=$ N, P) and its phase transition behaviour under high pressure by using the full potential linear augmented plane wave plus local orbitals approach within the framework of density functional theory. In the study the generalized gradient approximation (GGA) is chosen for the exchange-correlation functional energy. The equilibrium properties \textit{viz}., equilibrium lattice constants, bulk modulus, its pressure derivative and total energy are calculated in four different phases $i.e.$ B1, B2, B3 (zinc blende), and BCT phases and compared with previous calculations and available experimental data. The local spin-density approximation along with Hubbard-U corrections and spin--orbit coupling has been used for correct prediction of electronic properties. The LSDA $+$ U strategy shows significant impact on the energy levels of the occupied and unoccupied 4$f $states in the electronic structure of both the compounds. The calculation shows YbX to be semi-metallic. The LSDA $+$ U method provides better description of crystal properties of present system. At ambient conditions YbX (X $=$ N, P) stabilize in NaCl (B1) structure characterized by the space group \textit{Fm-3m}. Under compression, both YbN and YbP undergo first-order structural transition from \textit{Fm-3m} (B1) to Pm\textit{-3}m (B2) at 164.0 and 31.0 GPa, respectively.   

The dehydration of potassium alum induced by shock loading

Shock-induced dehydration and structural change on potassium alum, KAl(SO$_{4}$)$_{2}$ $\cdot$ 12H$_{2}$O, has been studied up to a peak pressure of 8 GPa. The shock-recovered samples have been characterized using Raman spectroscopy, x-ray diffraction (XRD), and a scanning electron microscopy (SEM). Although the sample shocked at 5 GPa are consolidated and recovered, no evidence for structural change or dehydration is obtained. However, prominent change of texture and color of the recovered sample shocked at 8 GPa is observed. The XRD results reveal that the recovered sample shocked at 8 GPa consists of anhydrous potassium alum crystals with amorphous. This structure differs from that of dehydrated alum caused by heat. The critical pressure for the shock-induced phase transition is close to the transition pressure from alum crystal to amorphous phase, which is obtained by static pressure loading.   

Magnetoresistance and electrical properties of multi-component copper chalcogenides at pressures up to 50 GPa

Multi-component chalcogenides based on layered semiconductors A$^{3}$B$^{6}$ (such as InS, InSe, GaS, GaSe, etc) are new objects of study, they have interesting physical properties and undergo temperature and baric phase transitions. This paper presents the results of a study of the electrical properties and magnetoresistance of CuInS$_{2}$, CuInSe$_{2}$, CuInAsS$_{3}$, CuInAsSe$_{3}$, CuInSbS$_{3}$ at pressures up to 50 GPa. High pressures have been generated in the cell with synthetic carbonado-type diamond anvils that can be used as electric contacts [1]. Electric properties at high pressure have been investigated on dc current and by means of impedance spectroscopy. Magnetoresistance has been measured in transverse magnetic field. The pressure ranges of noticeable changes in a behavior of magnetoresistance, of impedance and admittance, tangent of loss angle, relaxation time upon a pressure increase and a pressure decrease are established. This behavior of physical parameters can be due to structural transitions and due to a change of electron structure. This work was supported in part by the Russian Foundation for Basic Research, project no. 13-02-00633.\\[4pt] [1] A.N. Babushkin. High Press. Res. 1992, 6. P 349.   

High-pressure studies of cycloheptane up to 30 GPa

High-pressure synchrotron angle dispersive x-ray diffraction, Raman scattering and infrared absorption studies have been performed on cycloheptane (C$_{\mathrm{7}}$H$_{\mathrm{14}})$ up to 30 GPa at room temperature by using diamond anvil cell techniques. The synchrotron x-ray diffraction results indicate that the liquid cyclopentane undergoes two phase transitions at around 0.5 and 1.0 GPa, respectively. Then, it gradually turns into glass state starting from 3.0 GPa. The features of the Raman scattering and infrared absorption show no significant changes with increasing pressure below 3 GPa. This implies that the two phases observed by the x-ray diffraction can be attributed to plastic phases in which the cycloheptane molecules are held in an ordered structure while the molecular orientation is disordered. Up on further compression, all Raman and infrared bands begin broadening around 3.0 GPa that provide further evidence on the transition to glass state. Our results also suggest different paths on phase transitions under isothermal compression at room temperature compare to that previously reported under isobaric cooling at ambient pressure.   

Phase transition criterion under pressure and shear loading

Does the shear stress affect the transition pressure threshold? It is a question in shock dynamics field. We established the criterions for both ``stress induced'' and ``strain induced'' phase transitions under pressure and shear loading. The critical surface in the principal stress space is in-symmetric to the tension and compression and appears to be a conic surface. The effects of pressure, shear stress and temperature on the phase transition are discussed. Since the cylindrical yield surface may intersect with the conic critical surface of phase transition in the principal stress space, it means a ``strain induced'' phase transition might become a ``stress induced'' phase transition at certain condition. The prediction is in good agreement with the experiment results.   

Recording of Phase Transition in Tin in Shock and Release Waves Using Laser Interferometer

In this paper the authors present results of experiments, concerning the recording of free surface velocity and particle velocity of tin/LiF window interface of tin sample at the dynamic pressure in the range 10~to~70~GPa, using laser interferometry methods Fabry-Perot and PDV. The features of recorded velocity histories interpreted the polymorphous transitions (the direct $\beta ~-~\gamma $ phase transition, the reverse $\gamma ~-~\beta $ phase transition) and some points on tin melting curve. The tin samples were loaded by impactor accelerated by explosion products of HE cartridge (the wave with the rectangular profile) or by direct detonation wave of HE layer (the wave with the decaying profile). With the help of PDV method, velocity of particles cloud was recorded with the free surface velocity at the moment when the shock wave front arrived to the tin free surface with the pressure amplitude of P~$\ge $~19~GPa. This could is corresponded to appearing of the liquid-solid phase at the release wave. The tin melting in the shock wave is recorded at the loading pressure of P~$\ge $~51~GPa. The pressure and temperature numerical simulations were performed for shock compression and the further releasing of tin.   

Boron and aluminum halides under pressure - polymerization and chemical transformations

High-pressure phase transitions of boron and aluminum halides have been theoretically studied. At low pressure, crystals of the familiar monomers (BX$_{\mathrm{3}})$ and dimers (Al$_{\mathrm{2}}$X$_{\mathrm{6}})$ are the structures of choice. While the higher oligomers as well as three dimensional infinite polymers are unstable at ambient pressure, they are stabilized by application of external pressure, taking advantage of the extra orbitals made accessible by the increased coordination. Several new crystal structures of boron and aluminum halides have been predicted at high pressures. Calculated x-ray diffraction patterns and Raman spectra of these phases are in good agreement with available experimental data.   

A reversible pressure-induced phase transition in sulfamide

Sulfamide is a good case of hydrogen bonding networks with the molecular structure H$_{\mathrm{2}}$NSO$_{\mathrm{2}}$NH$_{\mathrm{2}}$. At ambient conditions, sulfamide crystallizes into an orthorhombic structure with the \textit{Fdd}2 space group. In this work, powder samples of sulfamide have been studied by Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell up to pressures of 16 GPa. The abrupt changes in Raman spectra around 5 GPa have provided convincing evidence for pressure-induced structural phase transition. This phase transition was confirmed by angle dispersive X-ray diffraction (ADXRD) experiments. On release of pressure, the observed transition was completely reversible with pronounced hysteresis. We propose that this phase transition was due to the rearrangements brought about by changes in the hydrogen bonding networks.   

Particle Velocity Fluctuations and Pressure Induced Phase Transitions in Bismuth

The dynamical behavior of a pressure induced phase transitions at high pressures is of current interest in high-pressure physics. It is known that hysteresis plays a major role in most rate driven phase transitions. The area and amplitude of the hysteretic cycle typically exhibit well defined scaling. We have studied the particle velocity correlations in Bismuth samples that have been shock loaded in plate impact experiments with pressures ranging from 3.1 - 14.4 GPa. The data show both global scaling of transition times with pressure as well as local scaling of fluctuation frequency with local average pressure. Using wavelet analysis and temporal autocorrelation functions, the analysis suggests that the phase transition proceeds by a sequence of hysteretic cycles. The onset of the new phase occurs when enough hysteretic cycles result in a sufficiently high phase fraction. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 Lawrence Livermore National Security, LLC.   

Toward a Multi-scale Phase Transition Kinetics Methodology: From Non-Equilibrium Statistical Mechanics to Hydrodynamics

Shock and ramp compression experiments are allowing us to probe condensed matter under extreme conditions where phase transitions and other non-equilibrium aspects can now be directly observed, but first principles simulation of kinetics remains a challenge. A multi-scale approach is presented here, with non-equilibrium statistical mechanical quantities calculated by molecular dynamics (MD) and then leveraged to inform a classical nucleation and growth kinetics model at the hydrodynamic scale. Of central interest is the free energy barrier for the formation of a critical nucleus, with direct NEMD presenting the challenge of relatively long timescales necessary to resolve nucleation. Rather than attempt to resolve the time-dependent nucleation sequence directly, the methodology derived here is built upon the non-equilibrium work theorem [Jarzynski, \emph{Phys. Rev. Lett.}, 78:2690 (1997)] in order to bias the formation of a critical nucleus and thus construct the nucleation and growth rates. Having determined these kinetic terms from MD, a hydrodynamics implementation of Kolmogorov-Johnson-Mehl-Avrami (KJMA) kinetics and metastabilty is applied to the dynamic compressive freezing of water and compared with recent ramp compression experiments [Dolan \emph{et al., Nature} (2007)]   

Cold compressed graphite -- A revisit

Phase transition in cold compressed graphite has been a paradox for several decades. Although a pressure-induced phase change is certainly supported by several lines of experimental evidence, the nature of the change as well as the pressure range of the transition remain unsettled. X-ray diffraction studies have revealed a graphite to hexagonal diamond transition in the pressures from 11 to 25 GPa [1] and recently a graphite to M-carbon transition from 19 to 37 GPa [2]. A transition from graphite-like carbon to an amorphous state was reported based on Raman observations [3]. Several post-graphite structures have also been predicted in recent theoretical studies [4,5]. Here we report x-ray diffraction studies on cold compressed polycrystalline and single crystal graphite samples to above 30 GPa. Instead of the transformation to the hexagonal diamond or M-carbon, we observed a transition from graphite to an amorphous carbon. Our results together with the previous studies point to the importance of the starting material characterization, as well as pressure environment control in the study of phase transition in cold-compressed graphite.\\[4pt] [1] T. Yagi et al. (1992)\\[0pt] [2] Y Wang et al. (2012)\\[0pt] [3] AF Goncharov (1991)\\[0pt] [4] H. Niu et al. (2012)\\[0pt] [5] Amsler et al. (2012)   

High Pressure Studies on (111)-Terminated CeO$_{2}$ Nano-Octahedrons: The Major Effect of Non-Hydrostatic Conditions

The effect of nonhydrostatic conditions on high pressure phase transition on (111)-terminated CeO$_{2}$ nano-octahedrons were studied using in situ high-pressure Raman spectroscopy. Under non-hydrostatic conditions (with no pressure medium) the CeO$_{2}$ nano-octahedrons underwent a reversible phase transition from fluorite phase to $\alpha $-PbCl$_{2}$ phase at 26 GPa, which is lower than the bulk counterpart. In contrast, in our previous research, the CeO$_{2}$ nano-octahedrons under hydrostatic conditions are shown to be more stable than the bulk, which is driven by lower compressibility of the exposed (111) planes. The transition pressure from cubic to orthorhombic phase is approximately 3 GPa higher than bulk materials. Further analysis shows that lager stress existing in the grain boundaries is believed to major factor to reduce the phase transition under non-hydrostatic conditions.   

A possible existence of phase change of deuterated ice VII at about11 GPa by X-ray and Raman studies

Ice exhibits a wide variety of forms because of polarity of water molecules. More than fifteen forms including crystalline and amorphous phase have been reported so far. Among them ice VII and iceVIII have been known to have wide stability region, however, recent experimental and theoretical studies have suggested possible phase change and property change at around 10 to 15 GPa. The change has not yet sufficiently been explained. To obtain a clue for understanding the phase change, high pressure experiments were performed with deuterated and light water using DAC at room temperature. Raman spectroscopy showed that the peak width of OD vibrational mode became sharper at about 11 GPa with increasing pressure, and then it became broader again above the pressure. The squared vinrational frequency changed linearly with pressure, and the slope evidently change at about 14 GPa, indicating existence of phase change. In-situ X-ray diffractmetry revealed splitting of diffraction line of cubit ice VII above 11GPa, which were indexed a tetragonal structure. The Similar result was reported previously for light water. The tetragonal structure survived at least up to 60 GPa. All experimental results showed existence of phase change at around 11 GPa.   

Freezing of liquid water under combined compression and electric fields

The melt curves of materials hold rich information concerning phase stability, coexistence, and other kinetics, typically studied through heating and cooling. Compression-induced solidification exposes new kinetics, yet is a practical challenge due to adiabatic heating. Water has a large heat capacity and many solid phases, making it a good candidate for compression freezing. Optical transmission measurements and high-speed imaging have demonstrated that water can freeze on nanosecond time scales. Being highly polar, freezing in water is strongly influenced by electric fields at atmospheric pressure. However, the role of external electric fields in freezing has yet to be determined at high pressure. We present experimental and theoretical results from our attempts to transform liquid water into solid ice under rapid compression. To minimize heating, samples are quasi-isentropically compressed via multiple shock or ramp wave compression. An external electric field applied to the sample imparts local order to the system, influencing solidification onset and growth. Classical molecular dynamic simulations show significant ordering effects at V/nm field strength, well above the dielectric strength of water. We present work that to address this issue.   

Raman scattering analysis of the structural phase transformations of III-V semiconductors induced by mechanical impact

In the present work we report a Raman scattering study on the structural phase transitions of indium antimonide submitted to high non-hydrostatic pressure applied by mechanical impact, which induces several transformations, leading to very rich Raman spectra. We are able to observe the normal disordered zinc blende structure with a Raman spectrum displaying two broadened peaks at 180 and 190 cm$^2$, an amorphous phase with a Raman spectrum displaying only a broad band centered at about 175 cm$^2$, the optical band, that reflects the vibrational density of optical states, the wurtzite structure with Raman peaks at 145, 175 and 180 cm$^2$ and a completely new and intense Raman spectrum presenting fourteen lines. Similar results for GaAs and GaSb were also obtained.   

Resistivity and equations of state of warmed gallium melt in megabar pressure range

The electrical conductivity of gallium melt was measured under step shock compression up to $\approx $100 GPa. The semiempirical equation of state (EOS) are constructed in the shock pressure range 30-300 GPa. The EOS was used for reconstruction of thermodynamic history of the sample in the experiments and for the subsequent definition of volume-temperature dependence of gallium melt resistivity. It was shown the volume-temperature dependence of gallium melt resistivity is proportionally to temperature and inversely to the square of characteristic temperature in the shock pressure range 30-80 GPa and temperatures 1000-2000 K. Thus the warmed high pressure gallium phase melt possesses metal conductivity.   

Phase transition and electrical resistivities of PrBa$_2$Cu$_4$O$_8$ under high pressures

PrBa$_2$Cu$_4$O$_8$(Pr124) dose not exhibit superconductivity but its resistivity shows a metallic behavior below 170 K. This behavior is a sharp contrast to semiconducting one of PrBa$_2$Cu$_3$O$_7$(Pr123). In this work, we have measured is the temperature dependence of the electrical resistivities in the Pr124 under pressures up to 13 GPa by using a modified Bridgman anvil type cell. The metallic region is found to be extended toward high temperatures with increasing pressure up to 5 GPa. The pressure dependence of the resistivity in room temperature is positive up to 10 GPa while that is negative above 10 GPa. We have also studied the crystal structure of Pr124 means of the synchrotron radiation X-ray powder experiment under high pressure. High-pressure X-ray powder diffraction was performed at PF, BL-18C beamlines at room temperature using a diamond anvil cell (DAC). Up to 10 GPa, the diffraction patterns were fitted using the tetragonal $Ammm$ symmetry model. The continuous change of lattice parameters as a function of pressure was observed. Futhermore, we were confirmed the phase transition in Pr124 over 10 GPa. More detail results will be reported in this conference.   

Transport properties of Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta}$ under high pressures

Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta}$ (Pr247) was found to exhibit superconductivity in 2004 by introducing oxygen deficiencies.\footnote{Matsukawa et al., Physica C, 411,101(2004).} Superconducting transition temperature (T$_{\mbox{c}}$) varies from zero to about 20 K depending on the oxygen deficiency $\delta$. This high-T$_{\mbox{c}}$ cuprate consists of three structural units, i.e., CuO$_{2}$ planes, CuO single chain and CuO double chains. The CuO$_{2}$ planes are insulating in this compound and therefore, the superconductivity is believed to occur in the CuO double chains. Interestingly, the electrical resistivity was found to show T$^\alpha$ dependence at low temperatures under high magnetic fields.\footnote{Matsushita et al., Sci. Tech. Adv. Mater., 8,477(2007).} This temperature dependence is known as the characteristic property of Tomonaga-Luttinger liquid and suggests a possibility that the CuO double chains have one-dimensional property. In this study we report the pressure dependence of the transport properties for Pr247 with various oxygen deficiency $\delta$'s.   

Electrical resistance of dysprosium and titanium under pressure

The electrical resistances of metallic dysprosium and titanium have been measured in the temperature range 80-700 K and under hydrostatic pressure in silicone oil up to 1.2 GPa. For both metals, the measured temperature and pressure dependence of resistance are in good agreement with available literature data near room temperature and atmospheric pressure. For titanium, the temperature dependence of the electrical resistivity can be very well described by standard Bloch-Gr\"{u}neisen theory if a correction for the density of states is applied, although saturation effects are observed at the highest temperatures. The pressure dependence is practically independent of temperature over the range 300 to 700 K, as expcted from simple theory. For dysprosium, the low temperature data show the well known antiferromagnetic-to-paramagnetic transformation near 174 K. The pressure coefficient of resistance at room temperature is somewhat larger than found by Bridgman, probably reflecting a higher purity of the material. The pressure coefficient is observed to decrease with increasing temperature.   

Current Work to Improve Precision in Measurements of Helium Fine Structure

With the recent improvement on the 2$^{\mathrm{3}}$P Helium fine structure calculation by Pachucki and the quest for finding the most precise value for $\alpha $, spectroscopic measurement of the helium atom has a great advantage to find this primary constant. Distinctively, the 32 GHz atomic fine structure of 2$^{\mathrm{3}}$P J2 to J0 interval with uncertainty of 100Hz leads a factor of three better than the best current value of $\alpha $ and an impulsion to the theory to evaluate the largest term of order m$\alpha^{\mathrm{8}}$ is our ambition. This measurement not only tests the quantum electrodynamics, but also establishes the fine structure constant $\alpha $ with uncertainty of 1.6 ppb. The electron g-factor measurement of $\alpha $, even though, is by far more accurate at 0.37 ppb, our end result would be a examination to the best alternative atom recoil measurements with different approach. To reach on this level of accuracy, we implement our frequency selector with precision better than 1 to 100 along with laser cooling mechanism to enhance the signal to noise ratio by increasing the signal strength.   

Calculation of thermodynamic functions for hydrocarbons and their mixtures

Knowledge of thermodynamic parameters of oil components in their pure forms and in mixtures is vital to understanding the properties of petroleum. The fact that hydrocarbons, thermodynamically unstable at ambient conditions, are formed spontaneously at geochemical conditions from a variety of precursors, ranging from kerogen to carbon, suggests that the thermodynamic stability of hydrocarbons increases dramatically with increasing pressure and temperature. Better grasp of their thermodynamic properties at extreme conditions is therefore crucially important both for our understanding of the processes of oil formation and for our ability to design and engineer new methods of synthetic oil production. Unfortunately, with a very few exceptions of the simplest compounds, such as e.g. methane, ethane, or ethene, these properties are tabulated for rather narrow ranges of pressures and temperatures, and in most cases are listed only for standard conditions at 25$^{\circ}$C. We propose a new computational methodology, based on classical molecular dynamics simulations, for obtaining accurate thermodynamic functions, such as Gibbs energies, entropies, and enthalpies, of oil components and their mixtures at elevated and extreme temperatures and pressures.   

Calculation of High Pressure Effects in Reactions of Hydrogen Transfer from Substituted Toluenes to Bromine Atom

A given reaction may proceed through several different mechanisms, each with its own transition state (TS). These TSs may have similar energies but different geometries and, as a result, different volumes. According to transition state theory, the activation volume ($\Delta $V$^{\ne })$ is the difference between the volume of the TS and the reactants. Experimentally, activation volumes can be obtained from the pressure dependences of the rate constants: \begin{center} -RT($\partial $ln k/$\partial $P)$_{T}=\Delta $V$^{\ne }=$ V$^{\ne }$ - V$^{R}$ \end{center} By comparing the calculated and experimental activation volumes, one can pick a TS of the right ``size'' and thus elucidate the reaction mechanism by identifying the most likely reaction pathway. It has recently been shown by our research group that molecular dynamics simulations provide a suitable tool for theoretical calculations of activation volumes. In this project we focus on the calculation of the activation volumes for a series of reactions in which an alpha-hydrogen is abstracted from a substituted aromatic hydrocarbon by bromine radical.   

High-pressure phase diagram of O2 and N2 binary system: formation of the kagome-lattice of O2

Recently, in the mixture of oxygen and nitrogen molecules, the appearance of a new solid phase, which does not occur for either pure component, has been reported under high pressure. We consider that the magnetic interaction of oxygen molecules would play a main role of the formation of the phase. In this paper, the high-pressure phase diagram of the binary system has been investigated by examining the x-ray diffraction patterns of the polycrystalline or powder samples. The solid phase was stable in a rather wide pressure and concentration range than previous report. From the Reitveld refinement the structure of the phase was identified to be a hexagonal structure with seven molecules in the unit cell. The results of x-ray diffraction, Raman scattering and magnetization measurements have suggested a magnetic order of oxygen molecules on the Kagome-lattice.   

Identification of TS structures by a combination of high pressure kinetics and MD volume calculations

In order to use transition state theory (TST) to describe the kinetics of conformational changes in large macromolecules, such as proteins, the transition state (TS) for the process must be well defined. However, the extremely long timescales and high dimensionality of such processes make identification of the TS difficult using traditional molecular dynamics (MD) techniques. We propose to identify TS structures using their volumetric properties. The effect of pressure on reaction rates is traditionally expressed in terms of logarithmic pressure derivatives, known as activation volumes. According to TST, activation volumes can be identified as the difference in volume between the TS and reactant species: -RT($\partial $lnk/$\partial $P)$_{T}=\Delta $V$^{\ne }=$V$^{\ne }$-V$_{R}$. Recently, a method was developed\footnote{H. Wiebe et al, J. Phys. Chem. C, 2012, 116, 2240--2245; J. Spooner et al, Phys. Chem. Chem. Phys., 2012, 14, 2264-2277.} which uses MD simulations for calculation of accurate theoretical volumes of activation. MD volumes can also be calculated for any transient structure along reaction coordinate, y, to produce theoretical volume profiles $\Delta $V$_{MD}$(y). If the position y$^{\ne }$ of the TS along the reaction coordinate is unknown, it can be found by locating $\Delta $V$^{\ne }$ on the MD-generated volume profile: $\Delta $V$_{MD}$(y$^{\ne })=\Delta $V$^{\ne }$. In this work we present a successful test of our methodology for two model systems: isomerization in a bistable diatomic and conformational changes in a long chain with strongly interacting termini.   

Elastic properties of methane-propane mixed gas hydrate under high pressure

Methane hydrate (MH) is widely observed in Earth's environment such as permafrost and deep sea floors. At low temperature and low pressure conditions, pure MH crystallizes a cubic structure I (sI) which consists of hydrogen-bonded two small and six medium water cages which enclathrate methane molecules as guests. However, actual MH in deep sea deposits contains not only methane molecules but also ethane and propane molecules. Therefore, the estimation of elastic properties and mechanical stability for both sI and structure II (sII) are required for the safe extraction of methane gas from the deep sea floors. The purpose of this study is to determine the elastic properties of methane-propane mixed gas hydrate (MPH) with sII by applying the high-pressure Brillouin spectroscopy to a single crystal of MPH-sII grown in a diamond anvil cell. The obtained elastic constant $C_{11}$ of MPH-sII showing independent of pressure is obviously different from that of pure MH-sI. On the other hand, the $C_{12}$ and $C_{44}$ are similar to MH-sI. The present results suggest that a variety of gas hydrates have the individual elastic properties and stability depending on the gas hydrate structures.   

Energetic Lanthanide Complexes: Coordination Chemistry and Explosives Applications

Metals are generally added to organic molecular explosives in a heterogeneous composite to improve overall heat and energy release. In order to avoid creating a mixture that can vary in homogeneity, energetic organic molecules can be directly bonded to high molecular weight metals, forming a single metal complex with Angstrom-scale separation between the metal and the explosive. To probe the relationship between the structural properties of metal complexes and explosive performance, a new series of energetic lanthanide complexes has been prepared using energetic ligands such as NTO (5-nitro-2,4-dihydro-1,2,4-triazole-3-one). These are the first examples of lanthanide NTO complexes where no water is coordinated to the metal, demonstrating novel control of the coordination environment. The complexes have been characterized by X-ray crystallography, NMR and IR spectroscopies, photoluminescence, and sensitivity testing. The structural and energetic properties are discussed in the context of enhanced blast effects and detection. Cheetah calculations have been performed to fine-tune physical properties, creating a systematic method for producing explosives with ``tailor made'' characteristics. These new complexes will be benchmarks for further study in the field of metalized high explosives.   

New high-pressure perovskite-like phases ACu$_{3}$V$_{4}$O$_{12}$ (A-Sm, Gd, Tb, Dy, Er and Tm): synthesis and electrical properties

The aim of this work was to investigate the effect of high pressures on the electrical properties of the new high-pressure perovskite-like phases ACu$_{3}$V$_{4}$O$_{12}$ (A-Sm, Gd, Tb, Dy, Er and Tm). The X-ray and microstructural studies of the synthesized by barothermal compression compounds were carried out. The electrical properties of the compounds were studied in the wide ranges of frequencies of the electric field, temperatures and pressures.   

Single walled carbon nanotubes at ultra-high pressure/stress

We report on the first study of single walled nanotubes (SWCNTs) synthesized by HiPCO method under pressure/stress up to 70 GPa aimed at probing structural stability of small diameter SWCNTs and synthesis of new nanostructured carbon phases. Firstly, the material has been exposed to 25 GPa. Raman spectra of the recovered of material exhibited extremely high defect density and evident recovery of the radial breathing mode (RBM) band with some intensity profile alteration. Secondly, the material was pressurized subsequently to 70 GPa followed by a relatively fast pressure release. Raman characterization provides indications of a transformation of the material to a new structural state as the result of the second pressure cycle. We discuss the structural evolution of the system en-route the final structure which is presumably comprised of deformed graphene nanoribbons and/or polymerized CNTs in addition to the smallest diameter SWCNTs which survived ultra-high pressure/stress.   

High-pressure high-temperature behavior of polymer derived amorphous B-C-N

Dense diamond-like BCN compounds are of interest due to their extreme hardness and predicted exceptional thermal and chemical stability superior to diamond and c-BN. Here, we report on high-pressure high-temperature (HP-HT) behavior of amorphous BC$_{2}$N and BC$_{4}$N -- potential precursors for HP-HT synthesis of diamond-like BCN. Prepared via hydroboration reaction of piperazine borane and pyridine borane, respectively,\footnote{R. Riedel, J.Bill, and G. Passing, Adv. Mater. 3 (1991) 551.} amorphous BC$_{2}$N and BC$_{4}$N are characterized by well-mixed B-N, C-C and C-N bonds, confirmed by XPS analysis. These BCN compositions were subjected to pressures between 5-24 GPa and temperatures up to 2000$^{\circ}$C using multi anvil press, toroid press and laser-heated diamond anvil cell (LH-DAC). In- and ex-situ X-ray diffraction reveals decomposition of BC$_{4}$N to graphite and h-BN between 5 to 12 GPa above 700$^{\circ}$C, in contrast to BC$_{2}$N which remains amorphous up to 1600$^{\circ}$C. Examination of the recovered LH-DAC samples using HR-TEM, EELS and EDS, indicates a tendency of BC$_{2}$N to transform into a mixture of c-BN (micron size) and nanocrystalline diamond between 20-24 GPa and 1500-2000$^{\circ}$C.   

Diamond Anvils Using Nano-polycrystalline Diamonds for the High-pressure Generation

Diamond-anvil cell (DAC) technique with natural single crystal diamonds (SCD) as anvils is widely used for high-pressure experiments. High-purity nano-polycrystalline diamond (NPD) consists of very fine diamond grains of several 10s of nanometer oriented in random directions, and has extremely high hardness comparable to or even harder than SCD[1]. The NPD has neither the cleavage feature nor the anisotropy of hardness peculiar to SCD, and has high fracture toughness [2]. We have examined some pressure generation pilot tests using the diamond anvils prepared from the NPD [3][4]. The pressures were determined by the EOS of Pt. A powder X-ray diffraction experiment of Pt was carried out using a synchrotron radiation on BL10XU at SPring-8. Some high-pressure generating tests were performed using diamond anvils of various shapes prepared from NPDs. The achievable pressure value of an NPD anvil with a culet size of more than 0.3 mm is about 1.5 to 2 times higher than that of SCD anvils, indicating that NPD anvils have considerable potential for large-volume diamond anvils with large culet sizes. Furthermore, we consider about beveled culet and lateral supported bottom shape on NPD anvil. It was found that the generated pressure is increased 2.5 times higher than the SCD anvil with normal anvil shape. [1] T. Irifune \textit{et al}., Nature, \textbf{421}, 599(2003). [2] H. Sumiya and T. Irifune, J. Mater. Res., \textbf{22}, 2345(2007). [3] Y. Nakamoto\textit{ et al}., Jpn. J. Appl. Phys. \textbf{46,} L640 (2007). [4] Y. Nakamoto\textit{ et al}., Rev. Sci. Inst. \textbf{82}, 066104 (2011).   

Measurements of Residual Stress in Shocked Samples

Study of meteorites not only indicates the place of origin but also carry precious secrets about the formation of the solar systems. Impact chronology of Howardite-eucrite -diogenite (HED) meteorites derived from vesta-4 asteroid indicates occurrence of many significant collisions-the major impact between 4.1 and 3.5 Ga as recorded by $^{40}$Ar- $^{39}$Ar shock ages of HED. Howardite meteorite which fell at Lohawat village in Jodhpur district (Rajasthan) was studied under up to 9 GPa using diamond anvil cell through in-situ x-ray diffraction and M\"{o}ssbauer spectroscopy supported by electrical conductivity measurements using WC anvil cell. EPMA analysis indicated the presence of orthopyroxene (Fs$_{64.91}$En$_{34.13}$Wo$_{0.96}$) and plagioclase (An$_{94.63}$ Ab$_{5.37})$. All the three techniques showed pressure induced structural variation at 2.8 GPa and 5.6 GPa representing irreversible amorphization and reversible crystallization respectively which could be explained based on the high pressure behaviour of anorthite and orthopyroxene. The lower value of phase transition for the meteorite sample to that of pure end members indicate preservation of residual stress. High pressure studies, therefore would be useful in estimating the residual peak shock pressure experienced by the parent body.   

Shock behavior of carbon nanotubes at pressures up to 100 GPa

Recent experiments in a diamond anvil cell demonstrate high structural stability of double walled carbon nanotubes (DWNTs) exposed to a static pressure of 35 GPa. Here we report on the study of DWNTs after application of stepwise shock compression in a recovery assembly. Peak shock pressures in the specimens were achieved by several reverberations of waves between the walls of the recovery ampoules and were 14, 19, 26, 36, 52 and 98 GPa. The recovered samples were characterized by Raman, XPS and HRTEM and revealed outer wall disruption along with shortening of the DWNTs and unzipping of the DWNTs accompanying by the formation of gpaphene sheets. Structural damage of the DWNTs increases with the shock pressure. Simultaneously, the Raman data exhibit a steep increase of D/G-band intensity ratio.   

Atmospheric breakup of meteoroids

When meteoroids enter a planetary atmosphere, breakup is governed by the Rayleigh-Taylor instability, mitigated by the strength of the meteoritic material. Particle sizes in the breakup cascade depend on the perturbation length scales exhibiting growth. The physics of meteoroid entry is thus related closely to experiments where strength at high pressure is inferred from the Rayleigh-Taylor growth of perturbations. There are significant discrepancies between predicted and observed breakup altitudes of meteoroids, which in turn reduce the accuracy of assessments of the impact threat from asteroids. Simulations, validated by laboratory experiments of instability growth, can play a role in understanding the breakup of meteoroids and thus the threat from asteroids. Continuum dynamics simulations provide more rigorous stress distribution than are usually used in breakup analyses, and can be used to calibrate compact expressions describing the breakup conditions. We have measured the strength of samples from Fe-rich meteorites using indentation and shock-loading experiments, and found them to be significantly stronger than was previously realized. This, together with the more accurate stress analysis, removes the altitude discrepancy for Fe-rich meteorites.   

Low- and high-temperature single crystal X-ray diffraction study of CaGeO$_{3}$ perovskite synthesized at 12 GPa and 1253 K

The perovskite (pv) phase of CaGeO$_{3}$ has the \textit{Pbnm} structure (orthorhombic) at ambient condition and is the best analogue of MgSiO$_{3}$ pv, a major constituent of the earth's lower mantle. The CaGeO$_{3}$ pv was previously reported to undergo the phase transition to the \textit{Cmcm} structure (orthorhombic) at 520 K. However, there is some doubt as for the existence of this high-$T$ phase, and the structural behavior of the \textit{Pbnm} phase at high-$T$ is also unclear. Clarifying these is important to help the crystal chemical understanding of MgSiO$_{3}$ pv in the lower mantle. For this purpose, we have conducted the single crystal X-ray diffraction study of CaGeO$_{3}$ pv in the range from 98 to 873 K. The crystal structures were successfully refined in the \textit{Pbnm} structure up to 873 K, and the $R$-factors reached $R =$ 0.0142$-$0.0229 and \textit{wR} $=$ 0.0117$-$0.0184 for each temperature. The structural parameters, such as lattice constants and volume, varied monotonously with temperature. No phase transition was thus observed in the investigated temperature range. The further detailed structural properties of CaGeO$_{3}$ pv at high-$T$ will be discussed.   

A view on the functioning mechanism of EBW detonation - Part 3: Explosive Initiation Characterisation

This paper is the third of three looking at the initiation of PETN in an exploding bridgewire detonator. The energy flow from the fireset through the bridgewire has been characterised and the probable input to the low density PETN determined. These earlier studies showed that shock initiation remained a credible mechanism for an exploding bridgewire detonator. This final set of experiments was designed to compare and contrast the shock initiation of low density PETN, by both a slapper detonator and a shock sensitivity test, with exploding bridgewire initiation. The shock sensitivity of low density PETN has been studied and the run distance for low pressure input shocks examined. The function and lost times of slapper and EBW detonators were compared to one another to allow the credibility of a shock initiation mechanism to be further assessed. The results of the experimental work will be presented, together with a potential step-by-step initiation mechanism for a PETN exploding bridgewire detonator. The proposed mechanism is based on the energy flow through the detonator system and the affect of varying the input energy on the detonator function time.   

The shock sensitivity of nitromethane/methanol mixtures

The dilution of liquid explosives has multiple effects on detonation properties including an increase in critical diameter, spatiotemporal lengthening of the chemical reaction zone, and the development of propagating wave instabilities. Earlier detonation studies of NM/methanol mixtures have shown several effects of increasing dilution, including: 1) a continual increase in the critical diameter, 2) lowering of the Chapman-Jouguet detonation pressure, and 3) slowing of the steady detonation velocity (Koldunov, et al. Comb. Expl. Shock Waves). Here, we present the results of a series of gas gun-driven plate-impact experiments to study the shock-to-detonation transition in NM/methanol mixtures. Embedded electromagnetic gauges were used to obtain in situ particle velocity wave profiles at multiple Lagrangian positions in the initiating explosive mixture. From the wave profiles obtained in each experiment, an unreacted Hugoniot locus, the initiation mechanism, and the overtake-time-to-detonation were obtained as a function of shock input condition for mixture concentrations from 100{\%} NM to 50 wt{\%}/50 wt{\%} NM/methanol. Desensitization with dilution is less than expected. For example, little change in overtake time occurs in 80 wt{\%}/20 wt{\%} NM/methanol when compared with neat NM. Furthermore, the shock wave profiles from the gauges indicate that wave instabilities grow in as the overdriven detonation wave settles down following the shock-to-detonation transition.   

Using laser-driven flyer plates to study the shock initiation of nanoenergetic materials

A tabletop system has been developed to launch aluminum laser-driven flyer plates at speeds up to 4 km/s. The flyer plates are used to initiate a variety of nanoenergetic materials including aluminum/iron oxide particles produced by arrested ball milling, and multi-layer nano-thermites produced by sputtering. The initiation process is probed by a variety of high-speed diagnostics including time-resolved emission spectroscopy. Impact velocity initiation thresholds for different thickness flyer plates, producing different duration shocks, were determined. The durations of the emission bursts and the effects of nanostructure and microstructure on these bursts were used to investigate the fundamental mechanisms of impact initiation.   

Impact Initiated Combustion of Aluminum Exposed to Mechanical Pre-Activation

The impact initiation of as-received and mechanically activated aluminum powder compacts is investigated using uniaxial stress rod-on-anvil impact experiments. The compacts reveal light emission due to combustion reaction at velocities greater than 320m/s. Mechanical pre-activation, such as that achieved via high-energy ball milling (HEBM) or high strain machining, strain hardens the starting materials, affecting their combustion initiation behavior. The starting materials are characterized by their lattice strain, hardness, and quasi-static compaction behavior. High speed imaging reveals that the ``threshold'' velocity (minimum velocity necessary for reaction initiation) changes as function of the mechanical pre-activation. Meso-scale simulations performed in CTH are used to correlate the effects of material properties within the powder compact with the crush up, deformation, and reaction behavior.   

Pressure-induced transformations of bis(tetrazolyl)amine and cyanuric triazide probed by vibrational spectroscopy and X-ray diffraction

As promising high energetic materials, bis(tetrazolyl)amine (BTA) and cyanuric triazide (CTA) have been studied extensively due to their high nitrogen content. Here we report the first in situ high-pressure study of BTA and CTA using vibrational spectroscopy and synchrotron X-ray diffraction. A reversible phase transformation of BTA was observed in the compression-decompression cycle. For CTA, we observed an interesting phase transformation as evidenced by the color change of the sample as well as the change in the Raman profile and X-Ray diffraction patterns. The transformations of BTA and CTA provide more understanding of the high-pressure behavior of nitrogen-rich materials and guidance for the further developments of energetic materials.   

Tilt Correction of High Explosive Test Data with Examples

Many high-explosive experiments view a nominally-axially-symmetric detonation wave breaking through a charge surface. Emerging waves virtually always exhibit a degree of tilt, which one generally wants to excise from the data whilst quantifying its direction and magnitude. In some cases, such as front-curvature rate sticks and Onionskin (OS)-type tests, the diagnostic is a single-slit streak camera (1D correction). In other cases, such as a Plane-Wave Lens characterization test or a Furball test, multiple slits or fibers provide sparse data over a surface (2D correction). We demonstrate both 1D and 2D corrections, the latter of which is the more challenging. In 2D, we represent the breakout time as the sum of a symmetric component and an asymmetric component (a tilted plane). The two tilt angle components are found that minimize the data scatter associated with the symmetric component. The most compelling example is the Furball test, an OS-variant for which the breakout time over the hemispherical observation surface is measured at many points using optical fibers. Unlike the OS test that looks in one (random) direction, we are able to construct OS-type data in the direction of maximum tilt, even though there are generally no fibers at that direction.   

Shock initiation of the TATB-based explosive PBX 9502 cooled to 77 Kelvin

Recently we reported on shock initiation of PBX 9502 (95 wt.\% tri-amino-trinitro-benzene, 5 wt.\% Kel-F800 binder) cooled to -55$^{\circ}$C or 218K (J. Appl. Phys., 112, 74909 (2012)). Shock waves were generated by gas-gun driven plate impacts and reactive flow in the cooled PBX 9502 was measured with embedded electromagnetic gauges. Here we describe methods to cool the explosive below -55$^{\circ}$C; down to liquid nitrogen temperature of -196$^{\circ}$C or 77K. We start cooling by flowing chilled nitrogen (N$_2$) gas through channels in a sample mounting plate and a copper tubing coil. Temperature in the sample is monitored using type-E thermocouples; samples are cooled at $\approx$ 1-2$^{\circ}$C/min. After minimum temperature is reached using N$_2$ gas, we flow liquid nitrogen (LN$_2$) through the channels. Minimum temperatures of 77K were reached. Preliminary results show continued reductions in temperature cause continued reductions in shock sensitivity. Reducing the temperature below -55$^{\circ}$C further reduces the sensitivity. Wave profiles were also obtained during the shock-to-detonation transition and will be presented.   

Explosive acceleration of plates using nonconventional explosives heavily loaded with inert and reactive materials

The detonation behavior of high explosives containing dispersed quantities or packed beds of dense additives has been previously investigated with the observation that such systems depart from the ``gamma law'' behavior typical of homogeneous explosives due to momentum transfer and thermalization between particles and detonation products. However, the influence of this non-ideal detonation behavior on the divergence speed of plates has been far less rigorously studied and existing literature suggests that the effect of dense additives cannot be explained solely through the straightforward application of the Gurney method with energy and density averaging of the explosive. In the current study, the acceleration history and terminal velocity of aluminum flyers launched by packed beds of granular material saturated by amine-sensitized nitromethane is reported. Two experimental configurations are used to study acceleration either by a purely grazing detonation in a finite thickness slab of explosive or by a normal detonation from an effectively infinite thickness of explosive. Flyer acceleration and velocity is measured via Photonic Doppler Velocimetry. Packed beds of plastic, aluminum, glass, iron, and bismuth are considered and the data is compared to Gurney velocity predictions.   

Small-Scale Tunnel Tests for Blast Performance

The data reported here provides a validation of a small-scale tunnel test as a tool to guide the optimization of new explosives for blast performance in tunnels. The small-scale arrangement consisted of a 2-g booster and 10-g sample mounted at the closed end of a 127-mm diameter by 4.6-m long steel tube with pressure transducers along its length. The three performance characteristics considered were peak pressure, initial energy release, and impulse. The relative performance from six explosives was compared to that from a 1.16-m diameter by 30-m long tunnel that used 2.27-kg samples. The peak pressure and impulse vs. distance did not scale between the small and larger scale tests but the relative ranking was preserved. The initial energy release was determined from a one-dimensional point-source analysis, which tracked with peak pressure vs. distance results but not with impulse suggesting additional energy released further down the tunnel for some explosives. This test is a viable tool for optimizing compositional variations for blast performance in target scenarios of similar form factor.   

Small-Scale Chamber Test for Internal Blast Performance

The data reported here provides a validation of the use of a small-scale internal-blast test to predict the energy release of explosives in larger scale. The small-scale arrangement consisted of a 2-g booster and 10-g sample mounted in a holder attached at one end of a closed chamber. The internal volume of the chamber was 89 liters not including the charge holder. The design of the charge holder served two purposes. One was to provide confinement around the charge to avoid degradation of performance from explosives with critical diameters larger than that of the sample. The second was to provide a separate space from that of the chamber that retained the fragments from the confinement to minimize the absorption of heat from the products. The energy release was determined from measurements of the peak quasi-static overpressure and the ideal gas law. The results from six different explosives were compared to larger scale tests involving a bombproof chamber (180,000 liters) with bare charges between 1 and 16 kg. The energy release between small and large scale compared favorably with regard to relative ranking of each explosive. The energy release measured in the small chamber was lower than the large chamber analogs, possibly due to heat losses to the holder. Despite these differences, the small-scale chamber test appears to provide a ranking of explosives based on their energy release that correlates with larger scale tests. Hence, this test is a viable tool for optimizing compositional variations for internal blast performance in target scenarios of similar form factor.   

High and Low Velocity Detonation in a Highly Insensitive Explosive

TBD   

Modified Reaction Detection Methods on the Drop Weight Impact Machine

High explosives small-scale sensitivity testing has been a hallmark of safety screening since WWII. Sensitivity testing was once as crude as using the end of a broom stick to scrape explosives on the floor, looking, listening, and smelling for signs of reaction. Since then, a wide variety of testing apparatus have been developed to explore the effects of different stimuli on explosives. In concert with the development of the machines themselves the reaction detection methods have also evolved. Some modern detection devices include sound level meters, high speed cameras, and light detection sensors to name a few. For this paper, the viability of new and modified reaction detection methods employed on the LANL Explosives Research Laboratory (ERL) Type 12 Drop Weight Impact Machine is explored. A large bandwidth microphone and a series of strain gauges were installed on the machine and, with an oscilloscope, were able to capture the acoustic and mechanical wave forms during an impact event. These data were then used as a metric for developing reaction criteria for explosives on drop weight impact.   

Reactivity of Ti-B, Cr-S, and Mn-S powder systems during explosively-driven collapse

Metal-metal and metal-sulfur reactive powder mixtures have been previously tested for initiation of reaction via planar, normal-shock loading. In addition to reacting under shock, such powder mixtures may undergo exothermic reaction under other types of mechanical loading. The thick-walled cylinder (TWC) technique was performed on samples of Ti-B (1:2 molar ratio), Cr-S (1.15:1 molar ratio), and Mn-S (1:1 molar ratio). These experiments were performed to determine the effect of large shear strains exerted on reactive metal powder mixtures and to establish the relative effectiveness of shear loading in comparison to shock loading in initiating reaction. Recovered samples were analyzed via SEM and XRD to determine the degree of reaction.   

The effect of hydrostatic vs. shock pressure treatment on plant seeds

The hydrostatic pressure and shock response of plant seeds have both been previously investigated (primarily driven by an interest in reducing bacterial contamination of crops and the theory of panspermia respectively). However, comparisons have not previously been made between these two methods of applying pressure to plant seeds. Here such a comparison has been undertaken based on the premise that any correlations in such data may provide a route to inform understanding of damage mechanisms in the seeds under test. In this work two varieties of plant seeds were subjected to hydrostatic pressure via a non-end-loaded piston cylinder set-up and shock compression via employment of a 50-mm bore, single stage gas gun using the flyer-plate technique. Results from germination tests of recovered seed samples have been compared and contrasted, and initial conclusions made regarding causes of trends in the resultant data-set.   

Development of Experimental Tissue Models for Blast Injury

There is a pressing need to better understand the relationship between the intensity of a blast wave and the clinical consequences for victims of an explosion. In order to quantitatively study how these factors correlate with one another, blast injury tissue models are being developed. Sections of larynx, trachea and pulmonary tissue were excised from a recently sacrificed pig and maintained on ice prior to testing. The samples were subjected to strain rates of between 0.001 s$^{-1}$ and 1000 s$^{-1}$ in the laboratory by using a Split Hopkinson Pressure Bar and quasi-static testing apparatus. During high strain rate testing, samples were housed in a polycarbonate chamber which permitted experimentation on tissue held in fluid. Data were analysed using 1, 2 and 3 wave analysis software in Matlab to yield information about the material properties of both undamaged and damaged tissues. In addition, macroscopic changes in tissue organization were also visualized using histopathological techniques. This work is being extended to cellular and animal models to derive more detailed information about the underlying molecular changes relating to blast-induced damage and repair.   

Ultrafine particle generation by high-velocity impact of metal projectiles

In the present work, size distributions and total concentrations of ultrafine particles generated during high velocity impacts of metals are shown in order to estimate the possible exposure of survival personnel to ultrafine metallic particles in the event of kinetic energy penetrator impact. Taylor cylinder impact tests were designed and performed using a light gas-gun facility investigating both high purity copper and aluminum cylinders impacting against a steel anvil in impact chamber. Moreover, in order to deepen the possible particle formation mechanisms, ballistic impact tests without metal-on-metal sliding contacts were also performed. In particular, symmetrical Taylor impacts of copper cylinders tests (rod-on-rod tests) were designed. High-resolution time measurements of particle distributions and total concentrations were performed through Fast Mobility Particle Sizer spectrometer and Condensation Particle Counters. Particle number emission factors were also evaluated. High particle generation in the ultrafine range were detected in classic Taylor cylinder impact tests: particle number distributions with a mode of 10 nm were detected. Moreover, number emission factors comparable to the ones typical of combustion phenomena were recognized.   

Femtosecond laser-driven shock-induced lattice defects in iron

We found high-density lattice defects such as microbands and twins in the femtosecond laser-driven shocked-pure iron. We used two kinds of femtosecond laser pulses of 1.5$\times $10$^{14}$ W/cm$^{2}$ and 9.8$\times $10$^{14}$ W/cm$^{2}$ to drive a weaker shock wave for multiple shots and a stronger one for single shot, respectively. TEM images and EBSD analysis showed that the former created microbands organized by high-density dislocations and the latter twins. We suggest that microbands are formed by pile-up of dislocations which is promoted by their interactions in multiple shots and that the twinning occurs owing to the high-strain rate which is strong enough to induce high-pressure phase. The process of lattice defects formation will be addressed in the presentation.   

Correlating Computationally Derived Particle Surface Stress-Strain States to Mesoscale Shock Response

The results of 2D and 3D FE simulations are presented, correlating the in-situ mesoscale shock response at the particle level to their surface observable stresses-strains for possible future experimental measurements. The ongoing work is an attempt to address a yet unresolved question; how a complex non-uniaxial thermomechanical shock response at the mesoscale, which may be a precursor to more complex phenomena, correlates to the average continuum uniaxial shock response. The objective of this work is to gain insight into how the complex responses at the meso/sub-mesoscale manifest to quantities that could be experimentally measured without perturbing the material. The simulations consider a 60 micron spherical sand particle mounted with a 1.8 micron thick epoxy coupon impacted by a 60 micron aluminum ball at 500 m/s. The impact is considered for the particle alone (direct impact) as well as embedded within an ensemble of 100 particles of the same size (indirect impact). Particle contact is modeled with and without friction. The spatial and temporal average stresses and strains at the particle-coupon interface are compared with the in-situ shock response of the particle. The results obtained to date indicate that in spite of the wave reflections and reverberations within the coupon, the particle-coupon interface response can be statistically correlated to the in-situ shock response.   

Mechanoluminescence of nylon under high velocity impact

The light emissions produced during deformation of solids induced by any mechanical action is called mechanoluminescence (ML). This phenomenon was reported mostly in hypervelocity impact. Using high speed video-recording, the authors found evidence of ML for nylon at much lower impact velocity (of the order of 10$^2$ m/s). In order to understand the mechanism responsible for ML, Taylor impact experiments were planned and performed. Several impact configurations were investigated: Taylor anvil impact, Taylor impact on nylon anvil and rod on rod impact experiment. During the tests, the emitted light was measured using a wide-spectrum visible-to-infrared photodiode with promptness below 1 microsecond, and the signals were analyzed. The existence of a limit velocity impact below which ML is no longer observed seems to be indicative of the fact that ML is controlled by the high pressure that generates under uniaxial strain loading conditions. This result is consistent with the fact that, as soon as the compressive stress wave travels longitudinally in the Taylor sample and the pressure drops as a result of the arrival of the release waves, the ML no longer occurs.   

Three-dimensional characterisation and simulation of deformation and damage during Taylor impact in PTFE

Aerospace, defence and automotive applications of polymers and polymer matrix composites have placed these materials under increasingly more extreme conditions. It is therefore important to understand the mechanical response of these multi-phase materials under high pressures and strain rates. Crucial to this is knowledge of the physical damage response in association with the phase transformations during the loading and the ability to predict this via multi-phase simulation taking the thermodynamical non-equilibrium and strain rate sensitivity into account. The current work presents Taylor impact experiments interrogating the effect of dynamic, high-pressure loading on polytetrafluoroethylene (PTFE). In particular, X-ray microtomography has been used to characterise the damage imparted to cylindrical samples due to impact at different velocities. Distinct regions of deformation are present and controlled by fracture within the polymer, with the extent of the deformed region and increasing propagation of the fractures from the impact face showing a clear trend with increase in impact velocity. The experimental observations are discussed with respect to parallel multi-phase model predictions by CTH hydrocode of the shock response from Taylor impact simulations.   

The effect of fibre orientation on a TWCP composite

Multiple authors have shown that orientation can greatly affect the shock profiles seen in composites. Carbon fibre composites are employed in multiple sectors, with their use in the aerospace industry becoming more prevalent. An angle of 20$^{\circ}$ between the outer surface and the weave direction provides a good compromise between strength and ablation. Using a single stage gas gun with manganin pressure gauges the shock response of both a 90$^{\circ}$ and 45$^{\circ}$ layup TWCP composite were investigated up to a particle velocity of c.a. 1 mm$\mu$s$^{-1}$, in both the U$_S$-u$_p$ and pressure-volume plane. Comparisons in terms of shock propagation were also made with previously investigated TWCP orientations of 0$^{\circ}$ and 20$^{\circ}$ as well as other carbon fibre based composites from the literature. This allowed a detailed interrogation of the effects of weave orientation in this important TWCP composite to be made.   

High strain rate fracture behavior of fused silica

Fused silica is a high purity synthetic amorphous silicon dioxide characterized by low thermal expansion coefficient, excellent optical qualities and exceptional transmittance over a wide spectral range. Because of its wide use in the military industry as window material, it may be subjected to high-energy ballistic impacts. Under such dynamic conditions, post-yield response of the ceramic as well as the strain rate related effects become significant and should be accounted for in the constitutive modeling. In this study, the procedure for constitutive model validation and model parameters identification, is presented. Taylor impact tests and drop weight tests were designed and performed at different impact velocities, from 1 to 100 m/s, and strain rates, from 10$^{\mathrm{2}}$ up to 10$^{\mathrm{4}}$ s$^{\mathrm{-1}}$. Numerical simulation of both tests was performed with IMPETUS-FEA, a general non-linear finite element software which offers NURBS finite element technology for the simulation of large deformation and fracture in materials. Model parameters were identified by optimization using multiple validation metrics. The validity of the parameters set determined with the proposed procedure was verified comparing numerical predictions and experimental results for an independent designed test consisting in a fused silica tile impacted at prescribed velocity by a steel sphere.   

Deformation and Fracture Behavior of Steel Projectiles Impact AD95 Ceramic Targets-Experimental Investigation

The deformation and fracture behavior of steel projectile impacting ceramic target is an interesting investigation topic. The deformation and failure behavior of projectile and target was investigated experimentally in the normal impact by different velocities. Lab-scale ballistic tests of AD95 ceramic targets with 20 mm thickness against two different hardness 38CrSi steel projectiles with 7.62 mm diameter have been conducted at a range of velocities from 100 to 1000 m/s. Experimental results show that, with the impact velocity increasing, for the soft projectiles, the deformation and fracture modes were mushrooming, shear cracking, petalling and fragmentation(with large fragments and less number), respectively; for the hard projectiles there are three deformation and fracture modes: mushrooming, shearing cracking and fragmentation(with small fragments and large number). All projectiles were rebound after impact. But, with the velocity change, the target failure modes have changed. At low velocity, only radial cracks were found; then circumferential cracks appeared with the increasing velocity; the ceramic cone occurred when the velocity reached 400 m/s above, and manifested in two forms: front surface intact at lower velocity and perforated at higher velocity. The higher velocity, the fragment size is smaller and more uniform distribution. The difference of ceramic target damage is not obvious after impacted by two kinds of projectiles with different hardness at the same velocity.   

The preheating effect on the dynamic strength of aluminum containing helium bubbles

The influence of helium bubbles or boron inclusions in an aluminum target is studied by plane impact experiments with a gas gun and VISAR diagnostic. The experiments were done for targets with initial temperatures of 25 $^{\circ}$C and near melting at 600 $^{\circ}$C. The Hugoniot elastic limit y$_{HEL}$ for all targets becomes substantially higher at 600 $^{\circ}$C, related to the phonon drag mechanism at high strain rates and high temperatures. The y$_{HEL}$ and the elastic strain rate of the preheated samples with helium are lower than these without helium, therefore it is suggested that the helium is slowing down the mobile dislocation velocity. The spall strength for all targets becomes substantially lower at 600 $^{\circ}$C. The spall strength of Al-$^{10}$B with helium bubbles is significantly reduced in comparison to Al-$^{10}$B without helium, while at 25 $^{\circ}$C the spall strength is the same for both cases. The experiments are analyzed by using a one dimensional hydrodynamic simulation coupled to a spall model. The model applies an inertial Rayleigh type equation of motion for the void expansion with a viscosity term presenting the high strain rate plastic flow. The simulation results indicate that at room temperature the growing voids around boron inclusions are causing the spallation while the spall in the preheated target with helium is dominated by growing helium bubbles.   

Dynamic properties of a magnetic alloy Fe-Cr-Co

The high-strain-rate methods of materials were developed for dynamic strength investigations under microsecond durations of shock loads on the base of electrical explosion of conductors. The experimental investigations of dynamic properties for magnetic alloy Fe-Cr-Co under shock loads of microsecond duration (4-8) mks in the pressure range up to 20 GPa were carried out. The values of HEL and spall strength for these amorphous alloys were received. The results of microstructure analysis of saved specimens revealed essential differences in deformation mechanisms determining fracture and plasticity in these alloys under high-strain-rate.   

Orientation-dependent response of nanovoids in Tantalum

Defective BCC Tantalum monocrystals are expected to display a particularly rich behavior when stressed along different directions. Using molecular dynamics simulations, we model Ta monocrystals containing a single spherical void of different sizes, under uniaxial compression, for two different empirical potentials. Differences on the yield point, dislocation generation and plastic heating are observed depending on the void size and stress direction, as distinct slip systems are activated, resulting in a variety of dislocation structures and mobilities. We calculate plastic heating and dislocation densities, and compare results for different interatomic potentials.   

Spall strength, dynamic elastic limit and fracture of ittrya dopped tetragonal zirconia

Specimens of the ceramics based on zirconia partially stabilized by yttrium oxide of the composition of 97 mol {\%} ZrO$_{2} +$3 mol {\%} Y$_{2}$O$_{3}$ were prepared. The densities of the specimens were 5.79 and 6.01 g/cc. The ceramics mainly have the tetragonal structure (93-98 wt. {\%} of t-ZrO$_{2})$. The mechanical action on the ceramic activates the transformation of the tetragonal phase into the monoclinic one: at the abrasive cutting or at the fracture by hammer shock, the content of the monoclinic phase is increasing. The same trend was observed in the specimens, recovered after stepwise shock compression up to 36, 52 and 99 GPa. It was found that shock compression do not initiates tetragonal-monoclinic phase transition directly, and this transition is caused by the destruction. Recovered specimens do not reveal any traces of the phase change which was observed by Mashimo et al. under the pressures 30-35 GPa (J. Appl. Phys. 1995. V. 77. P. 5069). Recording of the profiles of the free surface velocity of the specimens during single-stage shock compression allowed us to determine the dynamic elastic limit, as well as spall strength of the material versus maximal shock stress. In addition, the ceramics were subjected to the action of low temperatures. There were no significant changes in the specimens recovered after storage in liquid nitrogen and helium.   

Effcts of the grain size on the spall damage of copper

The void nucleation equation of the NAG model is modified in the spall damage model for ductile metals, by considering the corresponding relation between grain size and potential nucleated void number. The simulation shows the influence of grain size on free-surface velocity profile, qualitatively producing the consistent results determined experimentally by Escobedo (JAP,110,033513,2011).   

The Influence of Grain-size on Dynamic Shear Localization in Thick Walled Copper Cylinders

Thick-Walled Cylinder collapse experiments were carried out on copper specimens to explore the influence of grain size on their spontaneous dynamic shear localization behavior. Average grain sizes of 20, 75, 200, and 300 $\mu $m, were achieved by means of heat treatments. Measuring the stress strain curve for the different coppers on the Kolsky-Bar apparatus showed no significant differences between the strength of these materials. This enabled us to pinpoint the microstructural influence on shear localization, excluding the possible effect of strength differences between the specimens. Experiments were conducted on a pulsed current generator using magnetic pressure as the driving force. Large plastic strains, of up to 1, were reached, for which preliminary results show the formation of intense twinning together with faint signs of localized shear bands in both fine and coarse grained specimens. We found at the inner surface of the specimens, where shear strains are the highest, a substantial layer of very fine grains followed by a layer with a very high density of twins. The weak appearance of shear bands in our copper specimens might be attributed to this fine grained layer, where shear bands initiate in this geometry, which we have not seen in other materials we tested such as Ti, Ti64 or stainless steel.   

Multi-step Kolsky bar loading of metals which fail by adiabatic shear banding

In a previous work we showed that thermal softening of materials in Kolsky bar tests can be eliminated by multiple step loading. Specimens made of metals which tend to undergo adiabatic shear banding fail at relatively low strains, due to local heating which enhances local reduction in strength. In this paper we present results from multi-step loading tests performed in our interferometry-based Kolsky bar, with specimens made of titanium and magnesium alloys and stainless steel. Multi-step loading should prevent the local heating of the specimen and, consequently, move the occurrence of shear banding to higher strains. However, our experiments showed that these specimens fail at about the same strains under multi-step and single loadings. Thus, the mechanism which is responsible to shear banding cannot be related to local heating and a new approach is needed to explain this phenomenon.   

Two-dimensional Imaging Velocimetry of High-Strain Rate Deformation in Silicon

The novel 2D-VISAR diagnostic that has been developed over the past few years has provided an unprecedented view into the details of material deformation during shock compression. Utilizing a two interferometer system with quadrature phase recording and an ultrashort illumination pulse, a snapshot of the 2D velocity field of a shocked sample was obtained and the elastic and plastic breakout patterns were extracted. This diagnostic was used to measure the 2D velocity map of shock compressed single crystal silicon in three orientations, \textless 100\textgreater , \textless 110\textgreater \space and \textless 111\textgreater . Varying the probe delay allowed us to track the evolution of complex deformation dynamics at the silicon interface. Characteristic breakout structures were found for each of the three orientations. The elastic breakout shapes demonstrated a dependence on the anisotropic wave speeds in the crystal and the plasticity was found to depend on the crystallographic slip planes.   

Compaction model of damaged medium

At the present time difficulties emerge in the course of numerical simulation of high-rate strain of materials, accompanied by damage and compaction of defects (pores) under the action of compression waves. Compaction of defects formed by the action of pulsed tensile stresses is studied not sufficiently presently, and simplified mathematical models are used in calculations. The available compaction models are too complicated for their use in numerical procedures or they do not show all phenomena occurring at closing pores. A compaction model of a damaged medium is proposed in the present paper, which was based on the description of collapse of a single pore by taking into account elastic-plastic properties of a medium. To describe convergence of pores distributed with substance volume, a motion of one spherical cell was considered in an ideal-plastic incompressible medium. The analytical solution was obtained for the dependence of integral damage on pressure, shear strength and initial damage in this approximation. The equations were derived describing kinetics of compaction for the case of arbitrary pressure dependence on time and variable yield strength.   

Experimental Comparison of Tantalum Material Strength between Single Crystal [100] and [111] Samples at High Pressure and Strain Rates

Experiments were performed using the OMEGA laser to investigate the strength difference between single crystal [100] and [111] Ta samples at high pressure (1 Mbar), and high strain rates (10$^{6}$- 10$^{8}$ s$^{-1})$. To achieve these pressures and strain rates in experiment without melting the sample, a quasi-isentropic drive [1] was employed to drive the growth of pre-imposed sinusoidal perturbations on the surface of the Ta samples, via the Rayleigh-Taylor (RT) instability. By measuring the ripple amplitude using face-on high energy ($\sim$22 KeV) radiography [2], the strength of the Ta sample is inferred from the amount of RT growth observed [1]. Under these experimental conditions, the Ta material strength can be modeled by the Multiscale (MS) model [3], developed at LLNL. The value of the ``Taylor Factor'' (a MS model parameter), is thought to vary for [100] and [111] crystal orientations. To investigate this difference under these conditions, a comparison of the ripple growth was performed on the two samples for the same shot and drive conditions. [1] Park, H.S., \textit{et al}., PRL \textbf{104}, 135504 (2010). [2] Barnes, J. F., \textit{et al}., JAP \textbf{45}, 727, (1974). [3] N. Barton \textit{et al.}, JAP \textbf{109}, 073501 (2011).   

Multi-scale modeling of deformation and fracture of ceramic materials under dynamic loading

The multi-scale approach to dynamic analysis of deformation and fracture, taking place in structured condensed matter show a great promise in prediction of the mechanical response for new materials. In present work the results of two-level simulations on deformation and fracture mechanisms for brittle materials subjected to impulse and shock-wave loadings are demonstrated. The dynamic effects occurring in structured representative volumes of the ceramics and the processes relating to damage and fracture of the ceramic materials with porous structures, ceramic composites and nanocomposites were modeled using the SPH methods. The grain, phase and porous structures were simulated in an explicit form. The presence of dispersed inclusions, dislocation substructures, nano - and micro-voids at the lower structural level were taking into account in an implicit form. The two-level model allows taking into account different relaxation and fracturing characteristic times at the different structural levels. This approach suggest to describe the relaxation process at the higher structural level in terms of integrated effect of the lower level processes. It is found that clusters of nano-voids in ceramic materials are the centers of damage nucleation. The presence of the clusters of nano-voids in ceramic materials subjected to dynamic loadings results in decrease of the Hugoniot elastic limit value.   

A Lagrangian scheme based on characteristics theory for simulating two-dimensional flow on unstructured grids

The paper presents a second order cell-centered finite volume method of 2D Lagrangian hydrodynamics based on semi-discrete framework. The velocity and pressure on the vertex of a cell are computed on the basis of the characteristics theory. Then, the two variables are used to compute the numerical flux through the cell interface by the trapezoidal integration rule. By combining with some reconstruction procedure, the method is extended to second order. An entropy modification strategy is proposed for simulating complex compressible flow. Several numerical experiments confirm good properties of convergence and symmetry of the method. The method permits large CFL number and can be applied on the structured and unstructured grids. It is also very robust in the multi-materials flow simulation.   

Excitation energies of electrons in molecules {\&} crystals of PETN, RDX, HMX, and TATB

The key role in the model of detonation based on metallization of explosive plays the fundamental band gap of molecular crystal. For determining it in shocked crystal we performed prerequisite calculations for ideal PETN, RDX, HMX and TATB at ambient conditions. Density of states for these explosives was obtained and fundamental gap was determined. Calculations were done within the framework of Density Functional Theory and its planewave and pseudopotential implementation in the ABINIT package [1]. Beside we determined excitation energies of electrons for isolated molecules of these explosives and compared it with fundamental gaps for crystals. [1] ABINIT : First-principles approach of materials and nanosystem properties. X. Gonze, B. Amadon, P.-M. Anglade, J.-M. Beuken, F. Bottin, P. Boulanger, F. Bruneval, D. Caliste, R. Caracas, M. Cote, T. Deutsch, L. Genovese, Ph. Ghosez, M. Giantomassi S. Goedecker, D.R. Hamann, P. Hermet, F. Jollet, G. Jomard, S. Leroux, M. Mancini, S. Mazevet, M.J.T. Oliveira, G. Onida, Y. Pouillon, T. Rangel, G.-M. Rignanese, D. Sangalli, R. Shaltaf, M. Torrent, M.J. Verstraete, G. Zerah, J.W. Zwanziger Computer Phys. Comm. 180, 2582-2615 (2009).   

CO$_2$ and CH$_4$ clathrate hydrate under pressure

DFT first principles calculations have been performed to study the response to hydrostatic pressure of sI-type CO2 and CH4 clathrate hydrates. Two kinds of simulations were carried out i) periodic crystalline structures were considered to optimize unit cell geometries, determine static equation of state parameters, and investigate the energetic stability of clathrates. Dispersion interactions have been accounted for by the exchange-hole dipole moment model recently implemented for solid state calculations. It is found that, gas filling is a stabilization process independent on the guest molecule. However, while CH4 shows no preference for the size of the cage, the effect of stabilization is more pronounced when CO2 is in 5$^{12}$6$^2$ cages. Pressure also favors stabilization of both molecules, with CO2 being more sensitive than methane. ii) Molecular calculations using finite clusters were also carried out. At selected geometries, vibrational frequencies and intensities have been computed for all the gas-cage combinations. A change in the vibrational modes due to the confinement of the guest molecules is revealed. However, pressure barely affects the Raman/IR spectrum of the clathrate. These theoretical findings will be compared with experimental data already in progress   

Patterning in stress: a new insight into the deformation behavior of polycrystalline materials

The distribution of stress and strain in plastically deforming polycrystalline materials is widely observed to be heterogeneous and has so far evaded simple characterization. While elastic plastic and visco plastic self-consistent models (which assume that the Schmid factor governs slip) enjoy some success in predicting macroscopic behavior, the distribution of strain between constituent grains is not well predicted by the Schmid factor. This lack of correlation is caused by differences between the macroscopic stress state and the local stress state around each crystal due to the mechanical interactions of neighboring grains. Using 2D plane strain finite element models of large ensembles of grains, I show that the distribution of stress in a polycrystal forms patterns that are broadly reminiscent of those associated with phenomena that are governed by percolation theory. The pattern of stress transmission is related to the degree of heterogeneity in and statistical distribution of the elastic and plastic properties of the constituent grains in the aggregate. For a highly heterogeneous polycrystals, the patterns are similar to force chains observed in granular materials. For a more homogeneous polycrystal, the density of force chains is greater and the degree of stress concentration in them is less. Understanding stress patterning will be critical for linking the macroscopic rheology of polycrystalline materials to the single crystal elastic and plastic properties of their constituent crystals.   

Effect of pressure on electronic {\&} optical properties of Cadmium Chalocogenides

We report effect of pressure on electronic {\&} optical properties of Cadmium Chalcogenide. The theoretical computational studies of Cadmium Chalcogenide are carried out using the full-potential linear augmented plane wave (FP-LAPW) method. In this approach the Generalized-gradient-approximation (GGA) is used for the exchange--correlation (XC) potential. We have calculated the equilibrium lattice constant, electronic band structure dispersion, total {\&} partial density of electron states, band gap, bulk modulus, and its pressure derivative. The calculated parameters are found in good agreement with experiment and other theoretical results. Furthermore, optical constants such as dielectric functions, refractive indices, reflectivity, absorption coefficient, optical conductivitity, loss functions of stable Cadmium chalcogende S were calculated for photon energies at ambient {\&} high pressure.   

Refractive index of K9 Glass under Shock Loading

We study K9 glass refraction index under shock loading conducted on powder gun,all experimental tests are plate impact loading. The impact veceloty range from 300m/s to 1200m/s, and the measure method is laser interferometer Photon Doppler Velocimetry(PDV) to measure the particle velocity both at the impact interface and free surface, The shock pressure from 2GPa to 8GPa, values for refraction are found from velocity corrections that must be made to account for refraction-index changes in the K9 glass due to shock wave motion. Experiment results show that refraction-index of K9 glass changes with the shock pressure in line relations, it can be as measure window to study the interesting materials under 10GPa during the shock loading.   

XMCD investigation of Rare Earth Metal at high pressure conditions

The X-ray Magnetic Circular Dichroism is a selective magnetic probe for high pressure studies. Nowadays, XMCD under pressure is usually employed, mainly on 3d and 5d metal systems. We will present new results on Rare Earth metals. Up to now, most of the pressure works are devoted to the structural properties of RE. However, only a few works deal with the pressure effect on their magnetic properties. RE, having high magnetic moment and large anisotropy, are commonly used for practical applications. Nevertheless, their magnetic ordering temperature is below RT. Adding transition metals solves this limitation: the alloys then present the advantages of RE and the high magnetic ordering temperature of TM. To optimize the properties of these systems, a pressure study may be a better way than an empirical investigation. Interpreting the XMCD signal at the L$_{2,3}$ edges of RE is very difficult since many contributions are involved. The important role of the 4f-5d interactions has to be taken into account and the quadrupolar transitions cannot be neglected. The quadrupolar transitions can be of the same order than the dipolar ones, since the 4f orbitals carry a much larger spin and orbital moments than the 5d. Under compression, each orbital may not been affected in the same way, thus giving rise to a separation of the dipolar and quadrupolar contributions and a better understanding of these signals. Among the few works dedicated to the magnetic properties of RE under pressure, it has been shown that metallic Dysprosium is no more magnetic above 7.5 GPa. Our XMCD measurements contradict this result since a signal is still observed.   

The Bactericidal Effect of Shock Waves

There are a variety of theories relating to the origins of life on our home planet, some of which discuss the possibility that life may have been spread via inter-planetary impacts. There have been a number of investigations into the ability of life to withstand the likely conditions generated by asteroid impact (both contained in the impactor and buried beneath the planet surface). Previously published data regarding the ability of bacteria to survive such applied shock waves has produced conflicting conclusions. The work presented here used an established technique, in combination with a single stage gas gun to shock load and subsequently recover Escherichia coli populations suspended in a phosphate buffered saline solution. Peak pressure across the sample region was calculated via numerical modelling, validated via Heterodyne velocimetry measurements. Survival data against peak sample pressure for recovered samples is presented alongside control tests.   

Imaging velocity interferometer system for any reflector based on Shen Guang-III prototype laser facility

The imaging velocity interferometer system for any reflector (VISAR) has been introduced in this report for shock-timing experiment in inertia confined fusion (ICF). Some important technique has been provided, including the probe laser with single mode and shaped capability, imaging technique with high resolution and calibration character. The new target design can be used widely after analyzing the interaction of laser and target. Then the blanking effect on the signal can be avoided. Without the quartz window effect, the new target concept with the reflected design can be provided to do the Deuterium-tritium (DT) material experiment. After using this concept, the fourth shock can be diagnosis easily in shock-timing experiment. Since the one dimension Fourier transform method (FTM) may occur the data loss, the new unwrap algorithm should be developed. The new flood algorithm with high confidence has been programmed. Although the fringe contrast of VISAR is very low, the unwrapping phase map can be satisfied. The space resolution of imaging VISAR is 5$\mu $m , and the time resolution is 10ps $\sim$ 30ps. The uncertainty is less than 2{\%}, which has reached the international level.   

FUZZYICS$=$CATEGORYICS$=$PRAGMATYICS(``Son of `TRIZ''')/CATEGORY-SEMANTICS COGNITION (FCP/CSC) of Plato-Aristotle ``SQUARE-of-OPPOSITION''(SoO): LINGUISTICS: ANTONYMS VS ``SYNONYMS'' VS ANALOGY/ METAPHOR: COARSEST-POSSIBLE TOPOLOGY: Shocks/High-Pressures Applications

Siegel[MRS Fall-Mtgs,:Symp.Fractals(89)-5-papers!!!;Symp.Scaling(90)] FCP/CSC \textbraceleft aka SPD\textbraceright (Tic-Tac-Toe-Matrix/Tabular List-Format) ``COMMON-FUNCTIONING-PRINCIPLE'' DI/TRI-CHOTOMY GENERIC ``INEVITABILITY\textunderscore -WEB'' PURPOSEFUL PARSIMONY-of-DI/TRI-CHOTOMY STRATEGY REdiscovery of SoO automatically/optimality is in NON-list-format/matrix: DIMENSIONALITY-DOMINATION --INEVIT-ABILITY ROOT-CAUSE(RC) ULTIMATE-ORIGIN(UO): (level-0.-logic) DIMENSIONALITY (level-0. logic): [d$^{\mathrm{st}} \quad =$ODD-Z]$\leftrightarrow $\textbraceleft D$^{\mathrm{st=FRACTAL}}$-UNcertainty FLUCTUATIONS\textbraceright $\leftrightarrow $(d$^{\mathrm{st}} \quad =$EVEN-Z): \textbf{CAUSES}: (level- I.-logic): EXTENT/SCALE/RADIUS: (\underline {relative})-[LOCALITY]$\leftrightarrow $ (\underline {relative})-(...GLOBALITY...) {\&} (level-II.-logic): POWER-SPECTRUM\textbraceleft noise$\cong $generalized-susceptibility\textbraceright : [``l''/$\omega ^{\mathrm{0}}$-White]$\leftrightarrow $(...-''l''/$\omega ^{\mathrm{1.000...-}}$ \underline {HYPERBOLICITY}...) {\&} (level-III.-logic) CRITICAL-EXPONENT:n$=$0$\leftrightarrow $n$=$ 1.000... ; BUT ALL 3 ALSO CAUSED BY ANOTHER INdependent RCUO (level-IV.-logic):   

Underwater Shock Response of Air-Backed Thin Aluminum Alloy Plates: An Experimental and Numerical Study

Studies on dynamic response of structures subjected to underwater explosion shock loading are of interest to ship designers. Understanding the deformation and failure mechanism of simple structures plays an important role in designing of a reliable structure under this kind of loading. The objective of this combined experimental and numerical study is to analyze the deformation and failure characteristics of 5A06 aluminum alloy plates under underwater shock loading. Some non-explosive underwater blast loading experiments were carried out on air backed circular plates of 2mm thickness. The deformation history of the clamped circular plate was recorded using a high speed camera and the deflections of specimens at different radii were measured in order to identify deformation and failure modes. In the finite element simulations, the strength model of 5A06 aluminum alloy is considered using the slightly modified Johnson-cook mode to describe structure deformation. Good agreement between the numerical simulations and the experimental results is found. Detailed computational results of each scenario are offered to understand the deformation and failure mechanism.   

Mesoscale Probing of Local Perturbations in PBX-driven Liners

Efforts are aimed on experimental studies of how to improve a dynamic performance of the shaped charge jet. We postulated four basic elements to the problem: (1) The fluctuations in properties inherent in PBXs cause kinetic localizations in the detonation reaction zone (DRZ) structure, which cause (2) perturbations in the detonation products velocity and pressure, which induce (3) Perturbations in the response of the PBX-driven liner; and (4) Local perturbations/instabilities in liner are amplified during its collapse phase causing micro-fragmentations and ejected debris from the cumulative jet at initial stage, and then the incoherence and premature breakup of the resulting shaped charge jet. Spatially-resolved scenarios of each of phenomena (1-4) were obtained in experiments with copper-liners and HMX-based PBXs fabricated on maximum packing density of crystalline constituents, in which the DRZ-induced perturbations were recorded and quantitatively measured in the mesoscale range with application of the 96-channel optical analyzer MCOA-UC. Obtained experimental evidence is indicative that ejecta from the DRZ and ejecta-driven detonation cells are dominating in wide spectrum perturbations translated to a PBX-driven liner.   

Table-top Generation and Spectroscopic Study of $\sim$10 TPa High-Energy Density Materials with C$_{60}^{+}$ Hypervelocity (v $\sim$ 100 km/s) Impact

Intense bursts of soft x-rays were discovered by Bae et al. in hypervelocity (v $\sim$ 100 km/s) impact of bio and water nanoparticles at the Brookhaven National Lab (BNL) in 1994. In the experiment, the nanoparticles were directly impacted on and detected by Si particle detectors that also detected the soft x-rays. Energy deposition measurements through thin films revealed that the impact generated pressures were $\sim$10 TPa, and the photon energies in the range of 75-100 eV for Si targets. The conversion efficiency from the kinetic energy to the radiation energy was unexpectedly high, $\sim$38\%, which was attributed to Dicke Superradiance of collective quantum states in High-Energy Density Materials (HEDM), Metastable Innershell Molecular States (MIMS). This talk presents recent experimental results obtained in a table-top apparatus completely different from and orders of magnitude smaller than that at BNL. In the new setup, hypervelocity (v~100 km/s) C60+ ions impacted on Al targets, and the impact generated soft x-rays were detected off-axis and analyzed using three Si photodiode detectors with selective energy response curves. The photon energy was determined to be $\sim$70 eV with the kinetic-energy to photon-energy conversion efficiency of $\sim$35\% in confirmation of the results by Bae et al. at BNL. The present results demonstrate a new way of generation and spectroscopic study of HEDM with pressures exceeding 10 TPa, and show the pathway to scaling up the soft x-ray generation method for a wide range of applications from lithography to inertial fusion.   

Characterization of Viscoelastic Materials for Low-Magnitude Blast Mitigation

Recent preliminary research indicates that exposure to low amplitude blast waves, such as from IED detonation or multiple firings of a weapon, causes damage to brain tissue resulting in Traumatic Brain Injury (TBI) and Post Traumatic Stress Disorder (PTSD). Current combat helmets are not sufficiently protecting warfighters from this danger and the effects are debilitating, costly, and long-lasting. The objective of this research is to evaluate the blast mitigating behavior of current helmet materials and new materials designed for blast mitigation using a test fixture recently developed at the Naval Surface Warfare Center Dahlgren Division for use with an existing gas gun. A 40-mm-bore gas gun is used as a shock tube to generate blast waves (ranging from 5 to 30 psi) in a test fixture mounted at the gun muzzle. A fast opening valve is used to release helium gas from a breech which forms into a blast wave and impacts instrumented targets in the test fixture. Blast attenuation of selected materials is determined through the measurement of pressure and accelerometer data in front of and behind the target. Materials evaluated in this research include 6061-T6 aluminum, polyurea 1000, Styrofoam, and Sorbothane (durometer 50, shore 00). The experimental technique, calibration and checkout procedures, and results will be presented.   

Measuring Three-Dimensional Deformation with Surface-Imaging ORVIS

With growing interest in understanding heterogeneous material phenomena under shock compression and the advancement of computational methods, three-dimensional data suitable for model validation and scientific pursuit is needed. The optically recording velocity interferometer system (ORVIS) is a velocity interferometer that measures the apparent motion of a set of parallel interference fringes. Initially demonstrated for collecting one-dimensional data at a point using a streak camera and a focused laser spot, line-imaging ORVIS is a useful extension for the collection of two-dimensional data using a streak camera and a laser light sheet. We extend ORVIS operation further to a surface-imaging mode for collecting three-dimensional data using a framing camera and an expanded region of laser illumination. In surface-imaging mode, snapshots of surface velocity across a cross-sectional area are collected at regular time intervals and combined to yield the surface velocity history. Data collected with surface-imaging ORVIS applied to several model problems will be presented along with a discussion of the analysis methodology and some experimental challenges.   

VISAR `cross-hairs': Simultaneous perpendicular line-imaging VISAR

Often the velocity measured at the rear surface of a dynamic compression target varies spatially, caused for instance by the tilt/curvature of a gas gun flyer, asymmetries in the magnetic field on a pulsed power driven experiment, or mesoscale heterogeneous targets. One way to monitor this in an experiment is to employ multiple point velocimetry techniques, but even with multiplexing this can become expensive in terms of hardware, in particular high speed sensors and scope channels. We report on the development of a multi-axis line-imaging VISAR system, which records the spatial velocity along two orthogonal directions. Cylindrical optics are used to project a set of cross-hairs onto the target, maximising the use of input laser light. We describe the image relay and interferometer configuration, along with an evaluation of system resolution. This `quasi' two dimensional system will become one of the principal diagnostics on the MACH (Mega Ampere Compression and Hydrodynamics) facility, where the multi-axis measurement will help optimise strip-line design to achieve uniform ramp compression of targets.   

Single-Shot Ellipsometry for the Z-Machine

We have developed a single-shot ellipsometry diagnostic capable of taking time-resolved measurements. A comparison of dielectric constants obtained using this method with those from a standard spectroscopic ellipsometry technique showed good agreement when used to measure a static Au sample. The ellipsometer is being designed for use on the Z-machine at Sandia National Laboratories to measure the conductivity of Fe at pressures and temperatures of the Earth's core.   

Termination and hydration of ultramafic mineral surfaces: Forsterite (010) and Diopside (010) surfaces

The weathering and hydrous alteration processes of ultramafic rocks (Serpentinization) are known to contribute to abiotic hydrocarbon generation in near surface region of the planet. Atomic level characterization of the interface between water and mineral surface, which plays crucial roles in mineral weathering and dissolution, is highly demanded to better describe the processes in molecular scale. We use in-situ high-resolution X-ray reflectivity to examine the natural forsteritic olivine (010) surface and diopside (010) surface in aqueous conditions. By modeling the electron density profile in surface normal direction and fitting the measured data with least-square method, the atomic structures of hydrated mineral surfaces are depicted. We found, for alumina polished forsterite surface under acidic environment, a homogeneous termination with about half of the magnesium depleted and replaced with possibly the hydronium ions. In contrast, the silica polished forsterite does not show such homogenous surface, as confirmed by ex-situ Atomic Force Microscopy measurements. In comparison, the diopside (010) surface is naturally grown without any polishing but, interestingly, it shows qualitatively identical features to forsterite (010) in terms of the termination and the first adsorbed water structures. These results indicate a common chemical characteristic of these mineral surfaces interacting with water, despite the distinguishing silica ratios and silicate structures they have.   

Deformation of an Iron-based bulk metallic glass at high strain-rates

Bulk metallic glasses (BMG) are multi-component, amorphous alloys that have garnered recent interest due to their high strength and hardness. Although extensive work on their response to quasi-static, uniaxial loading exists, the behavior of BMG, especially Iron-based ones, under dynamic shock loading has not been fully explored. In this work, we conduct reverse-Taylor plate impact experiments of an iron-based alloy commonly known as SAM2X5 at impact velocities up to 300 m/s using a gas gun, and at higher velocities of up to 2000 m/s using a powder gun, in order to determine its response to high strain-rate loading. Resulting deformation is observed under a Scanning Electron Microscope. Experiments at higher velocities are instrumented using a Velocity Interferometer System for Any Reflector. In addition, a Zr-based BMG commonly known as Vitreloy 106a will be also subjected to the same impact conditions, in order to compare its dynamic response with that SAM2X5. Since Iron alloys have higher densities than Zr ones (7.6 g/cc compared with 6.7 g/cc), it is expected to result in more superior strength properties for the former. A comparison of fracture morphologies and differences in spall strengths, Hugoniot elastic limits, magnitudes of strain-to-failure etc are studied.   

The effect of varying aspect ratios on the low strain rate behaviour of metals and polymers

This poster looks at the effect of varying aspect ratios, from 1:4 to 3:1, on a number of different materials, including aluminium and polycarbonate. A range of strain rates (10$^{\mathrm{-4}}$ s$^{\mathrm{-1}}$ to 10$^{\mathrm{+3}}$ s$^{\mathrm{-1}})$ is achieved using quasi-static Instron equipment, drop weight machines and Split Hopkinson Pressure Bars. The mechanical behaviour is discussed, and high-speed video used to further the analysis.   

Lateral stress evolution in Chromium Sulfide

In this paper the shock response of chromium sulfide, a cermet of potential interest as a matrix material for ballistic applications, has been investigated. Compacts with a Chromium:Sulfur ratio of 1.15:1 were investigated via the plate-impact technique. These experiments allowed the material to be loaded under a one-dimensional state of strain. Embedded manganin stress gauges were employed to monitor the temporal evolution of longitudinal and lateral components of stress. Comparison of these two components has allowed assessment of the variation of material shear strength both with impact pressure/strain-rate and time. Interestingly tentative evidence of what appeared to be an elastic-plastic transition was noted on the lateral traces, despite the absence of a lateral shock.   

Shock response of 7068 aluminium alloy

Aluminium alloys are widely employed throughout the aerospace and defence industries due to their high specific strength. Aluminium alloy 7068, often described as the ultimate aluminium alloy was developed by Kasier Aluminium in the mid-1990s and is the strongest aluminium commercially produced. There remains little published data on the response of this micro-structurally anisotropic alloy to dynamic loading. As part of an investigation of the high-rate mechanical properties of Al 7068, a series of plate-impact experiments using a novel meso-scale planar impact facility and a more conventional large bore gas gun were undertaken. The evolution of the elastic-plastic shock wave and spall strength as a function of sample thickness and specimen orientation were investigated using optical velocimetry (line-VISAR, PDV) techniques. Planar shock wave experiments were conducted on specimens several 100 microns to several millimetres thick cut from either parallel or perpendicular to the extrusion direction.   

Hugoniot-based equations of state for two filled EPDM rubbers

The shock response of silica filled and Kevlar filled ethylene-propylene-diene (EPDM) rubbers was studied using gas gun-driven plate impact experiments. Both materials are proprietary formulations made by Kirkhill-TA, Brea CA USA, and are used for ablative internal rocket motor insulation. Two types of experiments were performed. In the first, the filled-EPDM sample was mounted on the front of the projectile and impacted a Lithium Fluoride (LiF) window. The Hugoniot state was determined from the measured projectile velocity, the EPDM/LiF interface velocity (measured using VISAR) and impedance matching to LiF. In the second type of experiment, electromagnetic particle velocity gauges were embedded between layers of filled-EPDM. These provided in situ particle velocity and shock velocity measurements. Experiments covered a pressure range of 0.34 -- 14 GPa. Hugoniot-based equations of state were obtained for both materials, and will be compared to those of other filled elastomers such as silica-filled polydimethylsiloxane and adiprene.   

Tuning the Electrical and Optical Properties of MoS$_2$ under High Pressure

Transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS$_2$), has been of recent interest to many theoretical and experimental studies. MoS$_2$ has served as a potential material for optoelectronic and field-effect-transistors (FETs) with high on/off ratios (up to 10$^8$). MoS$_2$ is composed of quasi-two-dimensional sheets that are stacked on top of one another where each monolayer is tri-layered with a transition metal, molybdenum, in the middle that is covalently bonded to a chalcogen atom, sulfur, located on the top and bottom of the layers. These layers are separated by weak van der Waals (vdW) forces along the c-axis which makes the properties of MoS$_2$ anisotropic. Having control over the electronic properties, and therefore, the band-gap of MoS$_2$, allows for a wide range of applications from electrochemical devices to tunable photo-detectors to be adopted. We demonstrate the electronic phase transition of MoS$_2$ from semiconducting to a metallic state at $\sim$15GPa. The electronic transport properties in the semiconducting region (lower pressures) exhibits a shockley-like behavior while in the metallic region (higher pressures), we observe ohmic transport. We also examine the light-induced electronic properties by creating optical switches under pressure in greater detail. This photo-current behavior of MoS$_2$ allows for optical switches with three order decrease in turn-on time. We examine the change in the activation energy, optical Raman, XRD, and resistance, by inducing pressure to MoS$_2$ up to 35 GPa.   

Three-dimensional constitutive model for shock-induced phase transition with N transforming phases

Phase transitions are commonly controlled by pressure, shear and temperature. In this paper we established 3D incremental constitutive equations for both ``stress-induced'' and ``strain-induced'' phase transitions with N transforming phases based on the Gibbs free energy of each phase, which can describe the dynamic deformation behavior of mixed phase. An evolution equation was established considering the over driving force and the growing space in the transition process. The critical criteria, the constitutive equation of mixed phase and the evolution equation constitute the whole constitutive model. The $\alpha$-$\varepsilon$ transition simulation of iron with the present model coincides qualitatively with the experimental result.