摘要:

The dynamic compression of molten metals including Sn is of current interest. In particular, experiments on the compression of molten Sn by Davis and Hayes will be described at this conference. Supporting calculations of the equation of state and structure of molten Sn as a function of temperature and pressure are in progress. The calculations presented are ab initio molecular dynamics simulations based on electronic density functional theory within the local density approximation. The equation of state and liquid structure factors for zero pressure are compared with existing experimental results. The good agreement in this case provides validation of the calculations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780183

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A new material parameter &bgr;:&bgr; = (&rgr;0 − &rgr;00 pH/PH′)/&rgr;0&rgr;00 (1 − PH/PH′), where &rgr; is density and subscript 0 and 00 represent different initial density, andPHandPH′represent Hugoniot pressure of &rgr;0and &rgr;00which compressed to the same density &rgr;, was find out to keep in constant along Hugoniot. For metal&bgr;metal=1.217&rgr;0−0.884, where &rgr;0is the ideal crystal density. By using of &bgr;, Hugoniot data of different initial density samples can be simply converted by:PH = PH′ &rgr;0 (&bgr;&rgr;00 − 1)/&rgr;00 (&bgr;&rgr;0 − 1), and a new empirical Equation to express Hugoniot State was obtained:pHVn = p0V0n, wherenis constant. The properties and limitation of this empirical material parameter to be constant with variations of pressure and porosity were discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780184

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The lattice vibrations are determined in the quasi‐harmonic approximation for elemental Au and Cu to twice their normal density by first‐principles electronic band‐structure calculations. It is found for these materials that the important moments of the phonon density of states can be obtained to high accuracy from short‐ranged force constant models. We discuss the implications for the Gru¨neisen parameters on the basis of calculated phonon moments and their approximations by using bulk moduli and Debye‐Waller factors. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780185

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Wave propagation in a granular bed is a complicated, highly nonlinear phenomenon. Yet studies of wave propagation provide important information on the characteristics of these materials. Fundamental nonlinearities of the bed include those in the particle contact model and the fact that there exists zero applied force when grains are out of contact. The experimental work of Liu and Nagel showed the strong dependence of wave propagation on the forming and breaking of particle chains. As a result of the nonlinearities, anomalous behavior such as solitary waves and sonic vacuum have been predicted by Nesterenko. In the present work we examine wave propagation in a granular bed subjected to vertical agitation. The agitation produces continual adjustment of force chains in the bed. Wave propagation speed and attenuation measurements were made for such a system for a range of frequencies considerably higher than that used for the agitation. Both laboratory experiments and simulations (using a two‐dimensional, discrete soft‐particle model) have been used. The present paper is progress report on the simulations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780186

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The authors discuss results of experiments with measurement of compression of gaseous deuterium at initial pressure of 25MPa in the pressure range up to 300GPa in cylindrical steel chambers capable to transform shock compression into quasi‐isentropic compression. To record time trajectories of motion of steel shells compressing gas, two independently‐operating sources of hard gamma‐radiation with beams crossed at angle of 135° were used. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780187

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Hugoniot measurements of the high‐pressure phase stability of titanium‐silicon carbide (Ti3SiC2) were performed in this study. Ti3SiC2is a unique ceramic having high stiffness, but low hardness. Time‐resolved measurements employing plate‐impact geometry were conducted on Ti3SiC2samples in the pressure range of 50 to 120 GPa using the NIMS two‐stage light‐gas‐gun. Experiments performed in the lower pressure range followed the continuous pressure‐volume compressibility trend reported by Onodera, et al. in static high‐pressure experiments. At pressures around 80–120 GPa, deviation in pressure‐volume compressibility to a more compressed state was observed indicating evidence of a possible phase change. Streak camera records of the free surface velocity measured using the inclined mirror method also showed discontinuous slope, indicating a possible pressure‐induced phase transformation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780188

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Using intense magnetic pressure, a method was developed to launch flyer plates to velocities in excess of 20 km/s. This technique was used to perform plate‐impact, shock wave experiments on cryogenic liquid deuterium (LD2) to examine its high‐pressure equation of state (EOS). Using an impedance matching method, Hugoniot measurements were obtained in the pressure range of 22–100 GPa. The results of these experiments disagree with previously reported Hugoniot measurements ofLD2in the pressure range above ∼40 GPa, but are in good agreement with first principles,ab‐initiomodels for hydrogen and its isotopes. Additionally, a novel approach was developed using a wave reverberation technique to probe density compression ofLD2along the principal Hugoniot. Relative transit times of shock waves reverberating within the sample are shown to be sensitive to the compression due to the first shock. Results in the range of 22–75 GPa corroborate the ∼4 fold density compression inferred from the impedance matching Hugoniot measurements, and provide data to differentiate between proposed theories for hydrogen and its isotopes. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780189

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The information on thermodynamic properties of matter at extremely high pressures and temperatures is very important both for fundamental researches and applications. We have collected about 14000 experimental points on shock compression, adiabatic and isobaric expansion and measurements of sound velocities behind the shock front for more than 400 substances. The database with graphical user interface containing experimental data, approximation modules, and caloric equations of state models has been worked out. One can search the information in the database in two different ways and obtain the experimental points in tabular or plain text formats directly via the Internet using common browsers. Registered users can remotely add new data into the database. It is also possible to draw the experimental points on graphs in comparison with different approximations and results of equation‐of‐state calculations. Recently we have added an ability to make calculations of shock Hugoniots, isentropes, isobars, and other curves using semiempirical equations of state for more than 100 substances via the Internet. One can present the results of calculations in text or graphical forms and compare them with any experimental data available in the database. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780190

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Shock adiabats of metals with different initial volume and pressure have been calculated with the use of multi‐phase equation of state. The stability of shock wave has been investigated with the use of known criteria. We found two types of instabilities occurring in the vicinity and inside two‐phase liquid‐gas region. They are the specific sound instability arising as a spontaneous sound emission from the shock discontinuity and two‐wave configuration. The position of the instability region and its dependence on initial pressure and volume has been analyzed. Discussed are general regularities obtained on the base of the analysis for 30 metals. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780191

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The maximum superheating of a solid prior to melting depends on the effective dimensionless nucleation energy barrier, heterogeneities such as free surfaces and defects, and heating rates. Superheating is rarely achieved with conventional slow heating due to the dominant effect of heterogeneous nucleation. In present work, we investigate the superheating‐melting behavior of crystals utilizing ultrafast heating techniques such as exploding wire and laser irradiation, and diagnostics such as time‐resolved X‐ray diffraction combined with simultaneous measurements on voltage and current (for exploding wire) and particle velocity (for laser irradiation). Experimental designs and preliminary results are presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780192

出版商:AIP    

年代:1904

数据来源: AIP