摘要:

Wave structure methods have played an important role in probing mechanical and physical states of matter under dynamic loading. Applications cover a broad spectrum of research, including dynamic yielding; shock‐induced phase transformations; energetic reactions, tensile and compressive strength; and viscoplastic deformation. A large variety of experimental configurations have been developed to explore these phenomena using an extensive range of time‐resolved diagnostics. These methods were developed on single‐stage light gas guns for the most part, but extended to higher‐pressure capabilities, including explosive loading, propellant guns and two‐stage light gas guns. More recently, peak pressures accessible with these methods have been extended to even higher impact velocities and pressures through novel experimental platforms, including a modified two‐stage light gas gun that increases impact velocities to about 15 km/s, magnetically driven flyer plates that extend the velocities above 20 km/s, and laser‐induced shock loading which increases peak pressures even further. In addition to shock compression studies, magnetic loading enables a new application of wave structure studies using large amplitude ramp waves to probe shockless, or nearly isentropic compression, to pressures exceeding 3 Mbar. Furthermore, the use of time‐resolved diagnostics to measure the structure of magnetically induced ramp waves provides off‐Hugoniot data unachievable with other methods. In this presentation, I will give a brief summary of wave structure techniques for studying thermomechanical and physical properties and discuss several examples from the research that my colleagues and I have performed using these methods. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780173

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Modeling dynamic fracture and fragmentation has many applications ranging from space debris impact to armor penetration. Modeling scales range from microscopic descriptions at the grain level, to mesomechanical models that average the microprocesses over many grains, to standard continuum models, and up to engineering models at the structural scale. Designers and interpreters of experiments prefer to work at the highest scale possible to minimize computational time, but the higher scale models often have weak links to the underlying physics. This paper discusses current activity to tie the various scale models together by computationally simulating selected experiments at various scales and comparing the “knob settings,” thereby linking the higher scale models to the lower scale ones. Examples are given from the community working on shrapnel hazards in large laser and pulsed power facilities and from the community working on earthquake propagation in the earth’s crust. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780174

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Recent static highP‐Texperiments using diamond anvil cell techniques reveal an array of phenomena and provide new links to dynamic compression experiments. Selected recent developments are reviewed, including new findings in hot dense hydrogen, the creation of new metals and superconductors, new transitions in molecular and other low‐Zsystems, the behavior of iron and transition metals, chemical changes of importance in geoscience and planetary science, and the creation of new classes of high‐pressure devices based on CVD diamond. These advances have set the stage for the next set of developments in this rapidly growing area. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780175

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In the paper we present the results of measurements of sound speed in zinc single crystals with orientation ⟨0001⟩ at initial temperatures 17°C and 322°C over the stress range from 13 GPa of shock compression down to −2 GPa of tension. Within this stress range zinc of given orientation is elastic. The method is based on the measurement and analysis of wave reverberation in a plate, one surface of which is free whereas other surface contacts with a high‐impedance material (molybdenum). The results were confirmed by computer simulation. Nonlinearity of longitudinal compressibility of zinc exceeds that of the bulk compressibility. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780176

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Hugoniot data and shock temperatures of gaseous helium were measured in the pressure range 500–700MPa and temperature 6.7–10.8kK generated by flyer accelerated up to ∼6km/s with a two‐stage light‐gas gun. Gaseous specimens were shocked from initial pressure 5MPa at 285K. Spectral radiance histories from the shocked helium sample were studied experimental by using pyrometer. Shock velocity was measured and particle velocity was determined by the shock impedance matching method. The equation of state and degree of ionization has been calculated by applying the Saha model with Debye‐Hu¨chel correction. In comparison of the experiment with theoretical results, we found that shock pressure versus particle velocity is in agreement with each other, but for the shock temperatures. It implies that the theoretical degree of ionization should be lower than that of the experiments due to their lower values of shock temperature, and thus the ionization energies and level populations of the compressed atoms are also changed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780177

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Cerium, a member of the rare earth metals, has been studied up to 300 kilobars in a diamond‐anvil cell using energy‐ and angular‐dispersive x‐ray diffraction with a synchrotron source. The purpose of this experiment was to examine the electronic and structural behavior of cerium and to examine the effects of deviatoric stress due to non‐hydrostatic conditions within the sample environment. Using the standard sample orientation and data from various orientations, the effects of deviatoric stress are shown. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780178

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have developed a technique for constructing two‐phase EOS for simple metals using lattice dynamics, liquid dynamics, and electronic structure theory, and we have tested this technique by constructing an EOS for Aluminum valid up to compressions over two and temperatures up to five times melting temperature [Chisolm, Crockett, and Wallace, to appear in Phys. Rev. B]. Here we investigate the predictions of this EOS for the pressure, energy, and entropy along the Hugoniot up to roughly 5 Mbar, showing the relative contributions of the cold curve (T= 0 isotherm) and thermal part of the EOS to each function. We also comment on the possibility of taking data from different regions of the Hugoniot as tests of different terms in the EOS. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780179

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We compute the bulk sound speed along the Hugoniot using a new solid‐liquid two‐phase equation of state (EOS) for aluminum [Chisolm, Crockett, and Wallace, to appear in Phys. Rev. B] and compare with experimental sound speeds from various sources. The experiment extends from the crystal through the entire solid‐liquid two‐phase region. The EOS and data closely agree on where the Hugoniot passes through the two‐phase region, which corresponds to where aluminum melts. The bulk sound speed in the crystal region is consistent with the data, given the uncertainty in the experimental procedure. We also estimate shear moduli by using the experimental longitudinal sound speed data and the calculated bulk modulus. The shear modulus satisfies the approximationGS/BS=constant, within experimental error bars, throughout the crystal region on the Hugoniot. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780180

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Here we present new wide range equation of state for water. It has been constructed by sewing together a number of local models describing the matter in different regions of the phase diagram. At the temperatures under dissociation and moderate densities semiempirical equations of state describing water with high accuracy and taking evaporation into account have been used. To construct thermodynamic model describing properties of water in the region covered by shock data Variational Perturbation Theory has been applied. Dissociation reactions have also been introduced in the model. In this region water is considered as a mixture of molecular fluids. Some peculiarities of intermolecular potential for water and their effect upon parameters of shock compression have been investigated. Results of calculation have been compared with experimental data on shock compression of porous ice and snow. At high densities the matter is considered as homogeneous mixture of atoms and Thomas‐Fermi model with quantum corrections and nuclei treatment by Kopyshev is applied. At low densities and high temperatures the model of weakly non‐perfect dissociating gas and Saha model of ionized gas have been used. The EOS has been converted into tabular form to make it efficient when using in hydrodynamic codes. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780181

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Plasma phase transitions in dense hydrogen and electron‐hole plasmas are investigated by direct path integral Monte Carlo (DPIMC) method. The results are compared with existing theoretical and experimental data. The phase boundary of the electron‐hole liquid in germanium is calculated in agreement with the known experimental results. High‐density hydrogen exhibits similar behavior. In both cases the phase transition is accompanied by the conductivity rise and the internal energy is lowered due to the formation of droplets. The high‐density part of the deuterium shock Hugoniot is computed using the simulation results. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780182

出版商:AIP    

年代:1904

数据来源: AIP