Reflection of a bubble-detonation wave from a rigid obstacle

The process of detonation-wave reflection from a rigid obstacle in mono- and polydisperse bubble media is studied experimentally. The evolution of the reflected wave formed upon interaction of the detonation wave with the butt-end of a shock tube is traced. The structure of the detonation and reflected waves is studied and the wave pressures are measured at various parameters of the bubble media. The damping constants of the reflected waves are determined. In addition, the velocities of the detonation and reflected waves are measured. The effect of the gas-bubble size on the characteristics of these waves is investigated. The energy-dissipation mechanisms in the detonation and reflected waves in the bubble media are analyzed qualitatively. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 107–113, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32325).     

Explosive compaction of aluminum powder and the structure of compacts

Macrodefects of the structure of samples produced by explosive compaction of an aluminum powder were examined. The areas of the new contact particle surfaces produced by high-rate deformation were measured by stereological methods. The eddy current method was used to measure the macroscopic electric conductivity of the compacts. From these data, the mean sizes and number of macrodefects per unit volume of a compact were calculated. The techniques employed can be useful for an analysis of the structure of composite materials produced by various methods. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 105–109, March–April, 2000. The present work was supported by the Russian Foundation for Fundamental Research (Grant No. 99-01-00572) and the Federal target program “State Support of the Integration of Higher Education and Basic Research for 1997–2000” (Grant No. 274 in the direction “Basic Research in the Field of Physics and Advanced Technologies).     

Generation and transfer of an electric charge in self-propagating high-temperature synthesis using the Co-S system as an example

Based on experimental studies, it is shown that the propagation of a combustion wave in a Co-S powder mixture is accompanied by a complex of physical phenomena including acoustic noise, generation of the constant, pulse, and variable electromotive force in a frequency range greater than 1 MHz, and superequilibrium emission of electric-charge carriers. The volt-ampere characteristic of the emission current in the combustion wave, which has a negative-resistance site, is obtained. Combustion occurs under conditions of mutual influence of the physical phenomena observed. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 130–133, September–October, 2000. This work was supported by the Russian Foundation of Fundamental Research (Grant No. 99-03-32465) and the Program of the Ministry of General and Professional Education of the Russian Federation.     

The dynamic behavior of polytetrafluoroethylene in reshock and unloading waves

The behavior of polytetrafluoroethylene under loading by a shock wave and a wave of a complicated structure that consists of a shock wave, subsequent loading, and a rarefaction wave is studied. The front structure that includes a stress jump up to 0.92-0.95 of the equilibrium amplitude and a stress-relaxation zone whose duration is up to 0.5 μsec was recorded. The velocity measurements for the selected points with constant levels of stress in the wavefront show that the reshock wave moves over the shock-compressed polymer in a stationary regime. The phase trajectories of change in the polytetrafluoroethylene state in the coordinates of gauges on the “stress-specific volume” diagrams, which were obtained using the Lagrangian analysis of the stress profiles, show the marked effect of the hysteresis upon variation of the direction of loading of the sample. Depending on the magnitude of the hysteresis, the shear stresses were estimated to be (0.6±0.3) and (0.3+0.15) GPa at dynamic stresses of 18.5 and 32.5 GPa, respectively. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 109–118, September–October, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant Nos. 99-01-00516 and 96-15-96264).     

Preexplosion phenomena in heavy metal azides

The paper reports results of investigation of the explosive decomposition of heavy metal azides in real time. The characteristics of the detected predetonation effects — the preexplosion conductance and luminescence of heavy metal azides — are described. The obtained value of the preexplosion conductivity of silver azide indicates that the process is of a chain nature. A model for the development of explosion of heavy metal azides is developed including multiplication of active particles (holes) by a first-order reaction and chain termination by a second-order reaction. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 78–89, September–October, 2000. This work was supported by the Russian Foundation of Fundamental Research (Grant No. 98-03-32001a) and the Foundation of the Ministry of General and Professional Education of the Russian Federation.     

Nonequilibrium magnesium-related processes in the wake behind a model moving with hypersonic speed in air

Changes in the wake flow characteristics behind a body made of an aluminum-magnesium alloy and flying in air with a hypersonic speed are analyzed. It is shown that, as a result of afterburning of magnesium vapor in the wake, first, MgO forms in the gas phase, and then it condense to drops, which thermoionically emit electrons. The latter leads to accumulation of a positive charge on the drops and to a noticeable increase in the electron concentration in the wake. Calculations that illustrate the time dependence of the magnesium concentration and a substantial temperature rise in the wake, caused by magnesium afterburning, are described. Translated from Fizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 72–81, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-01-00630) and by the Federal Supporting Center “Integration” (Grant No. K0575).     

Flame spread over liquid fuel films on metallic substrates

New experimental studies of parametric dependences of the flame spread velocity and limits for liquid fuel films on metallic substrates confirmed the main features of the physical model proposed previously. For thermally thin layered systems “fuel-substrate,” a steady-state regime of flame spread is possible. It is shown that the flame velocity depends on the effective thermal diffusivity of the layer system, and its value is determined mainly by the volumetric heat capacities of the components of the system and, to a lesser degree, by their thermal conductivities. The mechanism of flame spread includes a series of interrelated elementary processes: heat conduction over the substrate from the combustion zone to the preflame zone, heating and evaporation of the fuel by the substrate, formation of a combustible mixture, and heating of the metallic substrate by the combustion products. The flame edge is located at the liquid surface, where the temperature corresponds to the formation of a stoichiometric mixture under equilibrium conditions. The liquid fuel is completely evaporated from the substrate at temperatures below the boiling point. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 25–30, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32308) and the INTAS Fund (Grant No. 96-1173).     

New method for estimating the time of chemical transformation upon shock compression

The distribution of the components of an inert mixture and the expansion products of a chemical compound upon shock compression in recovery ampoules is studied. Its character is explained by the cumulative action of the heavy component of the mixture. The identity of the distribution of the components in the inert and reacting media allows one to estimate the time of chemical transformation. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 131–132, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32142).     

Gas combustion in a narrow tube

A simplified model of flame propagation over a single capillary in the low-velocity regime is proposed. The model is based on the concept that the main features of flame propagation in the low-velocity regime are determined by the heat flux along the tube wall from the combustion products to the fresh mixture. Qualitative agreement with experimental results is obtained. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 22–26, March–April, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 99-03-32309).     

Numerical analysis of combustion kinetics for hydrogen—air mixtures with NH3, CH4, and C2H6 additives behind shock waves

The possibility of reducing the concentration of nitrogen oxides and HNO_x-group components with simultaneous shortening of the reaction-zone length during combustion of hydrogen-air mixtures in a supersonic flow behind an oblique shock wave by introducing NH₃, CH₄, and C₂H₆ additives into the mixture is analyzed. A numerical study shows that a small (up to 5%) amount of these additives substantially changes the combustion kinetics behind the shock-wave front, shortens the flame length, and diminishes the NO and NO₂ content in the combustion products. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 31–38, May–June, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 96-02-18377).     

Filtration combustion of a gas in a semiinfinite porous medium

An asymptotic analysis of the combustion of a gas moving in a semiinfinite porous medium is performed for large values of the Zel’dovich parameter. The case of a highly porous medium with high gas permeability is considered. The basic terms of asymptotic expansions of the main parameters of the process for combustion and separation regimes are obtained by the method of joined asymptotic expansions. The effect of the rate of motion of the gas and heat transfer from the surface of the skeleton into the ambient medium on the combustion parameters is analyzed. The critical conditions of failure of stationary combustion at the external surface of the layer and the conditions of transition of the process to the separation and induction regimes are determined. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 3–14. July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-01-03009).     

Reflection of a shock wave from a rigid wall in a mixture of a liquid metal and solid particles

The problem of reflection of shock waves and expansion waves from a rigid wall in a mixture of liquid iron and small molybdenum crystals is considered. The study is performed within the framework of equilibrium and nonequilibrium approximations of mechanics of heterogeneous media with different pressures of the components. The mathematical model is verified by fitting the dependence of the equilibrium-frozen velocity of sound on the initial pressure in the mixture with available experimental data. In the equilibrium approach, the dependence of the type of the reflected wave on the type of the incident wave is determined. Direct numerical calculations within the framework of the nonequilibrium model of mechanics of heterogeneous media confirmed the validity of the reflection chart obtained. The possibility of significant compacting of molybdenum particles in reflected waves is revealed. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 97–107, July–August, 2000. This work was performed within the framework of the Integration Project No. 97-24 of the Siberian Division of the Russian Academy of Sciences.     

Combustion regimes of magnesium in carbon oxides. 2. Combustion in CO

The oxidation and combustion of solitary magnesium particles in a CO medium in the range of ambient temperatures 898–1323 K are studied experimentally. Various regimes of interaction between magnesium and CO are revealed: low- and high-temperature regimes of slow heterogeneous combustion, low- and high-temperature regimes of vapor-phase combustion, and pulse combustion. The possible reasons for the existence of various regimes are discussed on the basis of an analysis of the processes in the surface film and in the gas phase with allowance for the thermodynamic features of the Mg CO system. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 67–73, March–April, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 95-03-09829).     

Combustion of titanium plates

The lower combustion limit is determined depending on the pressure of plates made of OT-4 titanium alloy in an O₂-Ar medium. The values of this limit decrease monotonically as the concentration of oxygen in O₂-Ar mixtures grows and increase with the sample thickness. The velocity of combustion propagation over the surface of the samples in a 75% O₂+25% Ar mixture at a pressure of ≦3.1 MPa is found. It is shown that, for titanium, the dependence of the combustion rate on the sample thickness is much weaker and, in contrast, it is much stronger on the pressure compared to similar dependences for cylindrical soft-steel samples known from the literature. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 60–65, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 96-03-32039a).     

A study of the interaction between the components of heterogeneous explosives by the electrical-conductivity method

The detonation of TNT/RDX alloys is studied by the electrical-conductivity method. The measurement technique is developed with correction for the deformation of electrodes in the explosion. The maximum electrical conductivity of pure TNT was ≈25 Ω⁻¹·cm⁻¹. The addition of RDX decreases the electrical conductivity and width of the conducting zone, which, is, apparently, connected with the formation of diamond. It is shown that the RDX particle size plays an important role. With equal mass fraction, the conductivity of the sample is several times smaller for micron particles than for millimeter particles. This fact is explained by the different degree of mixing of the detonation products of the heterogeneous-explosive components. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 97–108, September–October, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant Nos. 99-03-32336 and 96-15-96264).     

Detonation of pressed HMX charges

The pressure-profile measurement results obtained in the shock-wave front in bromoform upon detonation of HMX charges of diameter 40 mm and length 22–110 mm are reported. The initial density of the charges was 1.81 g/cm³. In all the experiments, a monotonic decrease in pressure occurred, and a chemical peak was not observed. With increase in the charge length, the maximum pressure values first increase and then decrease. An analysis of the pressure measurement results shows that, for the given charge size and the initiation system used, the process of HMX detonation occurs in a nonstationary regime. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 83–86, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 97-03-32000).