摘要:

The equation of state (EOS) for TATB‐based explosives has been built using complex information — the experimental data (Hugoniots of PBX9502 for different initial temperatures) as well as the results ofab initioand molecular dynamic calculations of the thermodynamic parameters (heat capacity at constant volume and isochoric pressure coefficient). The main features of these thermodynamic coefficients were identified, namely the strong temperature dependence of heat capacity and the strong volume dependence of isochoric pressure coefficient. Shock wave heating calculations for explosive with different initial temperatures and densities were performed. The analysis of calculated dependences T(P) was done. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780203

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present new data on the unreacted approximate isentrope of the HMX‐based explosive LX‐04, measured to 170 kbar, using newly developed long pulse isentropic compression techniques at the Sandia National Laboratories Z Machine facility. This study extends in pressure by 70&percent; the previous state of the art on unreacted LX‐04 using this technique. This isentrope will give the unreacted Hugoniot from thermodynamic relations using a Gruneisen equation of state model. The unreacted Hugoniot of LX‐04 is important in understanding the structure of the reaction front in the detonating explosive. We find that a Hugoniot given byUS= 2.95 km/s + 1.69uPyields for an isentrope a curve which fits our LX‐04 ICE data well. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780204

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A perturbation technique is used to calculate the thermodynamic properties of nitromethane for high pressures. The intermolecular interaction is described by a spherically symmetric, exponential‐6 potential and an angular dependent, multipolar contribution. Isothermal compression and the shock Hugoniot for nitromethane are well characterized by the theory. Molecular dynamics calculations, with the intermolecular forces constructed from interatomic interactions, also describe the experimental observations under consideration. There is a considerable difference in the predicted shock temperatures from the two methods. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780205

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The objective of the present study is the evaluation of cv, the constant volume heat capacity along a locus of CJ states of nitromethane. Nitromethane (NM) was chosen because reliable measurements of its TCJare available, and there are requisite other data at varied initial densities &rgr;0. Acquisition of the latter is accomplished by changing the initial temperature, but this also changes the initial internal energy E0and creates some problems. An equation for cvwas developed which contains the experimental TCJ, assumed to be constant over the rather narrow range of &rgr;0of the other input data, and &ggr; =cP/cv, which still needs to be evaluated. Thus only provisional values of cvare presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780206

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A thermodynamically consistent equation of state for &bgr;‐HMX, the stable ambient polymorph of HMX, is developed that fits isothermal compression data and the temperature dependence of the specific heat computed from molecular dynamics. The equation of state is used to assess hot‐spot conditions that would result from hydrodynamic pore collapse in a shock‐to‐detonation transition. The hot‐spot temperature is determined as a function of shock strength by solving two Riemann problems in sequence: first for the velocity and density of the jet formed when the shock overtakes the pore, and second for the stagnation state when the jet impacts the far side of the pore. For a shock pressure below 5 GPa, the stagnation temperature from the jet is below the melt temperature at ambient pressure and hence insufficient for rapid reaction. Consequently, for weak shocks a dissipation mechanism in addition to shock heating is needed to generate hot spots. When the stagnation temperature is sufficiently high for rapid reaction, the shock emanating from the hot spot is computed, assuming a constant volume burn. For initial shocks below 20 GPa, the temperature behind the second shock is below 1000 K and would not propagate a detonation wave. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780207

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Isentropic compression experiments were performed on molten tin (initial temperature 500–600 K), using the Sandia Z Accelerator to generate magnetically driven, planar ramp waves compressing the tin across the equilibrium liquid‐solid phase boundary. Velocity interferometry measured time‐resolved wave profiles at the tin/window interface. The experiments exhibit a departure from expected liquid response, time‐dependent behavior above 8 GPa, and, at higher pressure, reduced wave speed relative to calculations using a nonequilibrium phase‐mixture model. These phenomena may be due to a nonequilibrium solidification process, but verification of this conjecture will require further work. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780208

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Using shock wave reverberation experiments, water samples were quasi‐isentropically compressed between silica and sapphire plates to peak pressures of 1–5 GPa on nanosecond time scales. Real time optical transmission measurements were used to examine changes in the compressed samples. Although the ice VII phase is thermodynamically favored above 2 GPa, the liquid state was initially preserved and subsequent freezing occurred over hundreds of nanoseconds only for the silica cells. Images detailing the formation and growth of the solid phase were obtained. These results provide unambiguous evidence of bulk water freezing on such short time scales. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780209

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Theories on superheating‐melting mostly involve vibrational and mechanical instabilities, catastrophes of entropy, volume and rigidity, and nucleation‐based kinetic models. The maximum achievable superheating is dictated by nucleation process of melt in crystals, which in turn depends on material properties and heating rates. We have established the systematics for maximum superheating by incorporating a dimensionless nucleation barrier parameter and heating rate, with which systematic molecular dynamics simulations and dynamic experiments are consistent. Detailed microscopic investigation with large‐scale molecular dynamics simulations of the superheating‐melting process, and structure‐resolved ultrafast dynamic experiments are necessary to establish the connection between the kinetic limit of superheating and vibrational and mechanical instabilities, and catastrophe theories. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780210

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The mixed perovskite oxides KTa1−xNbxO3, or KTN, are a model system for studying ferroelectric behavior and phase transitions under pressure. Crystals withx> 0.1 exhibit ferroelectric soft‐mode behavior and a sequence of phase transitions, while forx⩽ 0.02 a pressure‐induced ferroelectric‐to‐relaxor crossover occurs. The system also exhibits a pressure‐induced crossover from classical‐to‐quantum behavior ultimately leading to the complete suppression of the phase transition and the formation of a quantum paraelectric state. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780211

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Shock‐induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in pulsed power devices. The bulk density and corresponding porous microstructure can be varied by adding different types and quantities of organic pore formers prior to bisque firing and sintering. In previous studies, a baseline material having a particular microstructure was examined in detail. Comparative experiments with a second material having a common density but a very different porous microstructure showed only subtle differences in mechanical and electrical shock properties. However, large differences in these properties were observed using materials prepared over a range of bulk densities. Recent studies have examined three new materials that were prepared at a common density matching that of the baseline material. Each was made using spherical pore formers having diameters within a narrow range, with nominal diameters varying from 15 &mgr;m to 140 &mgr;m. Normally poled samples of each material were used in identical planar impact experiments that produced peak stresses of 2.5 GPa under high‐field conditions, or 4.5 GPa under short‐circuit conditions. Unlike previous comparisons of common‐density materials, consistent trends were evident in depoling currents, wave rise times and amplitudes, and yielding thresholds. Overall differences between two of these materials and the baseline material were relatively small, but the material made with the smallest pore former showed significant differences. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780212

出版商:AIP    

年代:1904

数据来源: AIP