摘要:

The response of polymers to shock loading is becoming of increasing importance, both as binder systems in plastic‐bonded explosives (PBXs) and as structural materials in their own right. In this paper, we report on the shock Hugoniot of hydroxy‐terminated polybutadiene (HTPB), which is commonly used as a binder system in PBXs, but whose shock response has yet to be presented in the open literature. Results indicate that the shock velocity — particle velocity relationship is linear, similar to some but not all polymer‐based materials. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780193

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Based on an optical or a gauge‐and‐optical method, shock Hugoniot curves for two kinds of polyethylene (PE) specimens, i.e., high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE), have been measured in the shock stress region up to 1 GPa. It is found that the shock‐versus‐particle velocity Hugoniot curves for these PE specimens are non‐linear in this shock stress region. As one of the reasons for this non‐linearity, it is plausible that the molecular chains of polymers have anharmonic potential in the direction of intermolecular motion and intramolecular motion. The Gru¨neisen parameter of representing the anharmonic properties of the potential has been calculated from the obtained Hugoniot curves for these PE specimens. Calculated values of the parameter change rapidly from large to small values with shock compression up to 1 GPa shock stress. Large values of the parameter correspond to the selective excitation of the intermolecular vibrational modes of with lower phonon frequency. It is revealed that the non‐linearity of the Hugoniot curves for the PE specimens results from the drastic increase of the number of the excited vibrational modes of intramolecular motion in case the value of shock stress exceeds some level. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780194

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper considers a multi‐phase equation of state for solid and liquid lead. The thermodynamically consistent equation of state is constructed by calculating separate equations of state for the solid and liquid phases. The melt curve is the curve in the pressure, temperature plane where the Gibb’s free energy of the solid and liquid phases are equal. In each phase a complete equation of state is obtained using the assumptions that the specific heat capacity is constant and that the Gru¨neisen parameter is proportional to the specific volume. The parameters for the equation of state are obtained from experimental data. In particular they are chosen to match melt curve and principal Hugoniot data. Predictions are made for the shock pressure required for melt to occur on shock and release. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780195

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Shock waves and solitons were obtained in 2D complex plasmas i.e. plasmas mixed with micron‐sized particles. These particles acquire large (1000 – 50000e) negative charges and strongly interact with each other. The particle cloud can form ordered structures and exist in a solid, liquid, or gaseous state. A monolayer hexagonal lattice was formed from monodisperse plastic micro‐spheres in the sheath of an rf discharge and excited with an electrostatic pulse. It was found that weak pulses produced solitons, which did not change the phase state of the lattice. Stronger excitation created shock waves. The lattice melted behind the shock front and later recrystallized. Two shock regimes were distinguished. One had a stable, thin, well defined front, the other had an unstable front. The shocks were analyzed by tracking individual particles with a video camera and calculating their velocity, number density, kinetic temperature, and defect density. Molecular dynamics simulation reproduced the experimental results. Shock waves were also observed in a 3D complex plasma on board of the International Space Station. Those shocks were accompanied by a potential drop across the front. In this case not only the dust component but also ions, electrons and neutrals had to be considered. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780196

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

It is of great interest to planetary science to understand how the current experimental uncertainty on the hydrogen EOS affects the inferred structure of Jupiter. In particular, the mass of a core of heavy elements (other than H and He) and the total amount and distribution of heavy elements are very sensitive to the EOS of hydrogen and constitute important clues to its formation process. We present a study of the range of structures allowed by the current uncertainty in the hydrogen EOS. We show that an improved experimental understanding of hydrogen at Mbar pressures is necessary to put firm limits on the internal structure of Jupiter. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780197

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The dynamic response of beryllium on nanosecond time scales is important for controlling symmetry during the implosion of the fuel capsule in inertial confinement fusion. Particularly important is the behavior up to about 200 GPa, covering the foot of the implosion drive. We have performed experiments to measure the equation of state (EOS) and flow stress of beryllium, and to investigate solid‐solid phase transitions and melting, using flyer impact and isentropic compression by pulsed electromagnetic fields at Z, and shocks induced by direct laser irradiation at TRIDENT. The principal diagnostic was VISAR velocimetry; transient x‐ray diffraction was also used on some TRIDENT experiments. The Hugoniot and isentrope data were consistent with previously‐reported EOS. The flow stress was inferred from elastic precursor waves to be about 6 GPa in the (0001) direction on these time scales, with significant sensitivity to orientation. Possible evidence was observed of the hex‐bcc transition and of melting. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780198

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The 0 K isotherm for the organic molecular crystal 1,1‐diamino‐2,2‐dinitroethylene is calculated reasonably accurately using the Hartree‐Fock approximation to the solutions of the many‐body Schro¨dinger equation for a periodic system as implemented in the computer program CRYSTAL. The equilibrium lattice parameters are predicted to within one percent of the values reported by Bemm and O¨stmark. Pressure values on the isotherm agree extremely well with the values measured by Peiris and co‐workers. The key to obtaining such accuracy is the relaxation of all the molecular coordinates as well as the lattice parameters under a fixed volume constraint. It was found that Density Functional Theory (DFT) calculations gave much poorer results, but optimizations were not as extensively investigated in this case. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780199

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Gadolinium gallium garnet (Gd3Ga5O12: GGG) is expected to have very high shock‐impedance compared with sapphire (Al2O3), etc., and thus to be used as a potential new anvil material in shock reverberation experiments on hydrogen and other low‐Z materials. In this study, the Hugoniot‐measurement experiments were performed using both a powder gun and two‐stage gas guns in the pressure range to 100 GPa by means of the inclined‐mirror method. The HEL stress was measured to be larger than 30 GPa. A kink was observed on the Hugoniot in the pressure range higher than 60 GPa, which might be caused by structural phase transition or decomposition. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780200

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Using generator of shock waves of the hemispherical geometry, densities of liquid xenon were measured at pressure of shock compression of 175 GPa in direct shock wave and at pressure of ∼350 GPa in shock wave reflected from a sapphire window. High‐velocity four‐channel pyrometer was used to measure temperatures up to ∼ 33000 K in pressure range up to 230 GPa at wavelengths of 406, 498, 550 and 600 nm. The photochronographic method was used to measure temperature of ∼ 20000 K of shock‐compressed liquid xenon in plane‐wave devices in pressure range up to 95 GPa at wavelength of 430 nm. The obtained results were compared to available experimental and calculated data. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780201

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Physical properties of hot dense matter at megabar pressures are considered. The new experimental results on pressure ionization of hot matter generated by multiple shock compression of hydrogen and noble gases are presented. The low‐frequency electrical conductivity of shock compressed hydrogen, helium and xenon plasmas was measured in the megabar range of pressures. To reduce effects of irreversible heating and to implement a quasi‐isentropic regime strongly compressed matter was generated by the method of multiple shock compression in planar and cylindrical geometries. As a result, plasma states at pressures of the megabar range were realized, where the electron concentration could be as highne∼ 2×1023cM−3, which may correspond to either a degenerate or a Boltzmann plasma characterized by a strong Coulomb and a strong inter‐atomic interaction. A sharp increase (by three to five orders of magnitude) in the electrical conductivity of a strongly nonideal plasma due to pressure ionization was recorded, and theoretical models were invoked to describe this increase. Opposite effect was observed for lithium compressed by multiple shock up to pressures ∼ 200 GPa, where electrical conductivity was sharply decreased as pressure increased. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780202

出版商:AIP    

年代:1904

数据来源: AIP