摘要:

The term “overdriven detonation” refers to detonation process in which the main detonation parameters, such as detonation pressure and propagating velocity, exceed the corresponding Chapman-Jouguet (C-J) values. This kind of detonation state can be realized by the impingement of a high velocity object upon the explosive. This paper presents our initial survey on the occurrence of overdriven detonation in high explosive. The HMX-based PBX is used to accelerate the metal plate being used as the impactor. The target explosive is the so-called SEP, simplified from the term of the ‘safety explosive,’ with the composition of PETN wt.65&percent; and paraffin 35 wt.&percent;. By changing the thickness of the metal plate under an unvaried amount of donor explosive, the different impinging velocities are yielded. The propagation of the detonation wave grown from the impingement of metal plate is recorded by the high-speed streak camera owing to the self-luminosity of detonation. The higher detonation velocity is found from the experimental results. Meanwhile, the impacting velocities of the metal plate are determined by one-dimensional Lagrangian numerical method enabling to estimate the initial input pressure into the target explosive by the impedance matching method. The obtained input pressures are of larger values than the C-J pressure. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303462

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A thermodynamically consistent equation of state (EOS) was developed for unreacted, single-crystal ammonium perchlorate (AP) for shock compression along the [210] and [001] directions. The specific heat,cv,the pressure-temperature coefficient,(∂P/∂T)v,and the isothermal bulk modulus,BT,were determined from Hugoniot and isothermal compression curves, along with available data at atmospheric pressure. The mechanical response of each orientation of the AP crystal was modeled as an isotropic elastic-plastic solid. Above the HEL, the rate dependent yielding of AP was described with a simple overstress model. Time-resolved Raman spectroscopy experiments were carried out to obtain temperatures in the shocked state. These temperature measurements were used to constrain the values of various EOS parameters. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303463

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A theoretical equation of state for detonation products is described and compared with various data. A perturbation theory approach is used for the mixture of molecular fluids that is based on Monte Carlo simulations. The solid carbon is characterized as small clusters rather than as a bulk material. The free energy of the clusters is modeled as primarily additive contributions such as vibrational modes, bond strengths, and effective volumes. Up to 30&percent; of the atoms in a diamond cluster are on the surface with dangling bonds capped by various groups composed of C, H, N, and O from the background fluid. A counting term similar to ideal entropy of mixing is also found for the surface composition. Competition between the U, TS, and PV terms in the Gibbs free energy leads to dramatic shifts in the surface composition in some regions. This in turn leads to shifts in the background fluid mixture composition and anomalous behavior in the total EOS. This behavior in PBX 9502 is in good agreement with recent data on release isentropes from overdriven states (1). ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303464

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In shock-wave physics, emphasis has changed from obtaining Hugoniot states to examining the properties of those states. States prepared by initial shocks can be probed by second waves. The overtaking wave experiments use this idea to obtain sound speeds in shocked states. Such a study(1) was done on PBX 9501. The diagnostic technique in the overtake experiments uses the radiation from a shock front in a covering material. In addition, explosive/window release measurements have been done with the VISAR technique. When one applies these techniques to a less ideal explosive such as PBX 9502, one finds initial transient effects and structures in release curves. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303465

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The paper presents review of techniques and results of experimental studies of structural transitions in solids under shock-wave loading. The developed explosion-proof containers allow to save studied samples after explosive loading up to pressures exceeding 100 GPa. The authors present results obtained by studies of solid structures of various types (metals, chemical compounds, etc.) after compression of them by shock waves. The studies were carried out with use of the methods for metallographic, X-ray structural, and electron-microscopic analyses. It is shown that in majority of the considered cases the phase transitions of solids in shock waves occur in accordance with the martensite type. For determination of the fact of melting at shock-wave compression, the method for loading of composite sample is suggested. The composite sample consists of studied sample and more fusible one that is a melting indicator capable to form solid solutions or intermetallic compounds with material under study. Results of study of Bi, Sn, Pb, Cd, Zn with the help of this method are presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303466

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

It was shown by authors that if there exists pressure-induced phase transition of ceramic material at the critical stressPcso thatPc<H(H is the material hardness) the phase transition takes place during indentation in the thin layer under indenter. During kinetic energy projectile penetration into ceramics the stress must be of the same level as during indentation or more. X-Ray investigation of the powder from the crater of self-bounded silicon carbide destroyed by kinetic projectile has been carried out. In the initial specimen silicon carbide had the structure of the most abundant 6H hexagonal polytype with 6 layers in the lattice cell. But in the powder from crater there was the 33R rhombohedron polytype with 33 layers in the lattice cell together with initial 6H polytype. By this way phase transition6H→33Rwas observed in the thin surface layer of silicon carbide. This transformation is usually connected with sharp increase in dislocation density and can be an effective mode of energy absorption. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303467

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The pressure-induced phase transition in CdS was investigated using picosecond time-resolved electronic spectroscopy in plate impact shock wave experiments. Real-time changes in the electronic spectra were observed, with 100 ps time resolution, in single crystals of CdS shocked along thecandaaxes to peak stresses between 35 and 90 kbar (above the phase transition stress of approximately 30 kbar measured in continuum studies). When shocked to stresses above approximately 50 kbar along the crystalcaxis and 60 to 70 kbar along the crystalaaxis, the crystals undergo a very rapid change in electronic structure, indicating that significant structural changes occur within the first 100 ps. These results, along with previous ns continuum measurements, make a strong case for a metastable state during the phase transition in shocked CdS.Ab-initioperiodic Hartree-Fock calculations (with DFT correlation corrections) were employed to examine the compression of CdS and to determine a possible lattice structure for the proposed metastable structure. These results, along with details of the transformation kinetics and orientational dependence, will be discussed. Work supported by ONR. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303468

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In many technological and scientific applications it is desirable to accurately determine the off-Hugoniot isentropic response of materials at ultra-high pressures. Although unloading isentropes can be determined from unloading profiles, experimental techniques for measuring compressive isentropic response have been extremely limited. A brief summary is presented of the various techniques that have been developed for isentropically compressing materials to high pressure. A new technique is also discussed, which shows considerable promise for performing isentropic compression experiments with smooth ramp waves to multi-Mbar pressures. This approach uses the high current densities produced with fast pulsed power accelerators to create continuous magnetic loading to a few hundred kbar in the present study over time intervals of 100 ns. The method has been successfully applied on copper and iron to determine the isentropic compression curve in copper and evaluation of the kinetic properties of the alpha-epsilon phase transition in iron. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303469

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Pressure-shear plate impact experiments have been used to study the kinetics of martensitic phase transformations in polycrystalline NiTi—a shape-memory alloy. From symmetric impact experiments the limiting shear stress at which the transformation occurs is found to be46&hthinsp;MPa.From experiments in which a thin NiTi foil is sandwiched between two hard plates, The transformation process appears to involve the propagation of a diffuse boundary, resulting in a gradual increase in the shear stress transmitted through the specimen. Full transformation of160&hthinsp;&mgr;mfoils occurs in approximately0.8&hthinsp;&mgr;sunder the impact conditions of the experiments. Time dependent Landau-Ginzburg equations are introduced to model the volume fraction transformed to each of the variants in each of the grains. Comparison of theory and experiment allows the kinetic coefficient in the equations to be determined. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303470

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The propagation of macroscopic phase boundary in material with CdS-type phase transition constitutive relation is investigated. The phase boundary is consisted of two segments corresponding to the new phase and mixed phase, respectively. The step by step approximation method can be applied to the new phase segment, however, the mixed phase segment can only be solved by numerical method. A sample problem is calculated of which the results of the step by step approximation method and numerical method fit to each other quite well. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303471

出版商:AIP    

年代:1900

数据来源: AIP