Secondary sites of fire in an explosion of organic dust

Formulas for the pressure, momentum, and time of impact of a shock as functions of the energy of a spherical explosion in air and the distance to the center of the explosion are used to calculate parameters of the incident and reflected (from a rigid obstacle) shock waves produced by an explosion of a concentrated mass of organic dust. The distances from the explosion center are determined within which the temperature in the incident or reflected shock waves exceeds the ignition temperature of the particles suspended in air and secondary sites of fire can be initiated by the shock passing through the dusty space. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 60–64, May–June, 2000.     

Modeling the action of X-ray radiation on the walls of explosion chambers of pulsed nuclear power plants

Computational and experimental methods are developed to model (using explosion and impact) shock-wave processes in the walls of the explosion chamber of pulsed nuclear power plants exposed to powerful X-ray radiation. A comparison shows that experimental and calculated parameters of shock waves produced by explosive and shock loading of various materials are in good agreement with each other. The methods developed were used to study the behavior of a Li₁₇Pb₈₃ cooling liquid film on the explosion-chamber wall when the recoil momentum caused by vaporization is the major loading factor. The possibilities of reducing the explosive loads on the walls are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 117–122, September–October, 2008.     

Decreasing the parameters of an air shock wave using an air-water curtain

The efficiency of using an air-water drop curtain for protection from the force and noise action of an air shock wave generated by an open explosion is studied experimentally. It is shown that the curtain generated by outburst of sprayed water after an advanced underwater explosion of a demolition cord is a reliable means of pressure decrease at the shock-wave front. The dependence of the “effective coefficient of charge-mass reduction” on the position of the curtain relative to the point of explosion, its length, time of evolution, and other conditions was studied. Zones with local pressure increase or decrease in the shock wave were found, which is explained by imposition of secondary compression and expansion waves on the shock wave. Possible physical mechanisms that ensure the protective effect are considered. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 120–130, May–June, 2000.     

Calculation of the intensity of air shock waves in the near range of the explosion

The results of the studies dealing with the air shock-wave parameters are analyzed and the parameters obtained in the authors’ studies are reported. Generalized empirical dependences are obtained to calculate the wave intensity in the near range of the explosion of open concentrated and linear charges of large extent which consist of various shell-free explosives in a broad range of initial densities. The explosion fields of a full torus-like charge and linear and partially torus-like charges of finite length are considered theoretically. Formulas are derived to calculate the intensity of air shock waves of these charges, which agree with experiment. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 6, pp. 77–84, November–December 1998.     

Shear strength of aluminum in shock waves

Two series of experiments are conducted for determining the shear strength of shockcompressed aluminum (type AD1) at pressures of 4–16 GPa, including in loading and release waves. A saturated water solution of ZnCl₂ serves as a control material. Previous data on the shear strength of materials based on measuring the two principal stresses are refined. It is confirmed that tangential stresses in aluminum and its alloys relax in the shock front for shock amplitudes exceeding 10 GPa. The reasons for discrepancies in previous determinations of the shear strength of metals in shock waves are clarified. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 102–107, January–February 1999.     

In the theory of blast waves

The behavior of the blast wave from an exploding spherical volume is investigated mathematically over the entire range of blast-wave propagation. The computational method uses analytical results for a similar problem for a point explosion with counter pressure and the theory of an asymptotically equivalent point explosion. The asymptotic solution of the gas-dynamic equations away from the explosion site is matched to the initial conditions of blast-wave formation due to the disintegration of the detonation shock upon its arrival at the boundary of the exploding volume. The spatial distribution of the blast-front pressure is found for combustible gaseous systems and solid explosives. The theoretical results obtained agree quantitatively with available experimental measurements. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 93–99, July–August, 2006.     

Heat of explosion of commercial and brisant high explosives

Methods for determining the heat of explosion of high explosives (HEs) with ideal and nonideal processes of explosive decomposition are considered. It is shown that the heat of explosion is of significance for estimating the efficiency of commercial HEs and is used in the energetic characterization of the working capacity. The heat of explosion of brisant HEs is only part of the blast heat of explosion and is the heat content of gaseous detonation products during their isentropic expansion from the initial state to a certain expansion ratio (determined by experimental conditions). The heat of explosion can be obtained by thermodynamic calculations based on physically justified equations of state for fluids (gaseous detonation products in the chemical-reaction zone of the detonation wave in the supercritical state) and condensed nanocarbon phases (nanographite, nanodiamond, and liquid carbon). Experimental and calculated values of the heat of explosion are given. The thermodynamic calculation is inapplicable to commercial HEs because of the nonideal nature of their detonation. The heat of explosion of commercial HEs can be calculated using the Hess law. The heat of explosion of brisant HEs is not a measure of power. The power of HEs is characterized by the propellant performance. It is shown that even detonation velocity cannot be a measure of the power of HEs. The power and detonation parameters of brisant HEs are determined by the energy release density in unit volume of the chemical-reaction zone of the detonation wave and by the rate of energy release from the shock front rather than by the heat of explosion, which cannot be considered a universal characteristic. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 100–107, March–April, 2007.     

Motion of a shaped-charge jet in a porous medium

The problem of the motion of a shaped-charge jet in a porous medium is equivalent to the problem of a blunt cylinder in a hypersonic flow whose velocity at infinity is equal to the jet velocity in the porous medium. The flow pattern of the medium is the same as in the case of propagation of a blast wave generated by a point explosion of a cylindrical charge. The approximate theory of a strong explosion is used to obtain the basic relations for the shock wave and the expanding cavity in the hypersonic flow of a porous medium around the blunt cylinder. A comparison with experiments on the motion of a copper shaped-charge jet in porous aluminum is performed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 119–124, November–December 1999.     

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).     

Impact sensitivity of binary compositions of ground solid propellants and coal

Ram-impact machine tests of the impact explosion excitation behavior of binary mixtures of coal with ballistite powder and blended propellant are conducted. It is found that, as the coal content in the mixtures is raised, their mechanical sensitivity decreases. The effect of moisture on the impact sensitivity of the mixtures is analyzed. A recommendation is given for the safest way to load the components in a mixer during the stage of preparing propellant formulas of the required composition. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 113–116, July–August 1998.     

Detonation of ammonium nitrate and dynammons with and without inert additives

The detonation velocities of 10–60 mm thick, flat charges of ammonium nitrate and mixtures of it with various liquid and solid fuels plus added inert components in varied amounts and dispersions are determined experimentally. These explosives have been used for cladding of flat metal stock with areas of up to 12 mm ² by explosion welding with thicknesses of the cladding layer ranging from 1 to 30 mm and of the base layer, from 4 to 120 mm. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 114–119, May–June 1999.     

Conditions of detonation initiation by focusing shock waves in a combustible gas mixture

Based on experiments on focusing shock waves in hydrogen-air mixtures and available publications, the critical shock-wave Mach number at which detonation is initiated near the apex of a concave reflector is analyzed as a function of the reflector size and reactivity of the mixture. The effect of the reflector shape and size on the value of this Mach number is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 84–89, November–December, 2007.     

Shock synthesis and microstructure of Ti-Al alloy

High-temperature solid-state synthesis was for the first time performed with the use of explosion energy combined with shock compression. The composition and structure of the alloy obtained by synthesis of the stoichiometric Ti+Al mixture using this method are studied. The microstructure of the double-phase (γ + α ₂) intermetallic alloy differs from the structure of the alloys produced by hot explosive pressing at close temperatures of preheating and shock pressure and from the structures produced by powder metallurgy methods. A considerable increase in the yield of the γ phase is obtained. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 117–124, January–February, 2009.     

Basic self-ignition regimes and conditions for their realization in combustible gas mixtures

Self-ignition of hydrogen-air mixtures has been studied experimentally. This process was initiated behind a reflected shock wave at an initial pressure of up to0.5 MPa and with hydrogen volume contents ranging from9.5–20 and40–60%. Simultaneous recording of pressure and temperature profiles near the end of a shock tube made it possible to reveal the specific features of various self-ignition regimes and the regions of their existence. The peculiarities of the realization and evolution of mild and strong self-ignition processes are discussed, and a comparison with self-ignition of carbon-air mixtures is done. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow 117977. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 3–10, March–April, 1997.     

Interaction of weak shock waves with a layer of a powdered medium

Results of analytical and numerical studies of the interaction of linear and weakly nonlinear air shock waves with an infinite layer of a powdered medium and with a finite-thickness layer are presented. Approximate analytical expressions for phase-pressure distributions in the powdered medium are obtained. It is found that the gas pressure at the “gas-powder” interface is continuous for linear waves and experiences a sudden change for nonlinear waves. The dependences of phase pressures on a shielded solid wall obtained by solving a general nonlinear system of equations of motion of a powdered medium and an approximate analytical solution of linear equations are compared. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 131–140, March–April, 2000.     

Radiographic study of interaction of shock and detonation waves in a high explosive

Collisions of shock and detonation waves in an HMX-based high explosive are experimentally studied with the use of flash radiography. Based on X-ray patterns, specific features of the wave-interaction process are identified, and qualitative differences are found in detonation formation and evolution in an explosive precompressed by a weak shock wave and in an undisturbed explosive. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 132–138, May–June, 2007.     

Eulerian Monte Carlo method for the joint velocity and mass-fraction probability density function in turbulent reactive gas flows

A new Eulerian (field) Monte Carlo method for solving an equation that describes the one-time one-point probability density of species mass fractions in turbulent reactive gas flows has been proposed in a previous article. In the present paper, this method is extended to an equation for the joint velocity and mass-fraction probability density function. The method is based on passing from Lagrangian variables used in Lagrangian Monte Carlo methods to Eulerian variables. In this manner, stochastic ordinary differential equations for the Lagrangian trajectories of fluid particles are transformed to partial stochastic equations. As compared to the classical hydrodynamics, the stochastic velocity field satisfies only the mean continuity constraint and not the instantaneous one. As a consequence, one has to introduce a stochastic density, which differs from the physical density but has the same mean value. The case of the mass-fraction probability density is revised. The equations differ from those derived previously: they can be written in divergent form. Both formulations, however, are statistically equivalent. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 144–155, November–December, 2006.     

Hydrodynamic effect of an electrical explosion on the ignition of condensed materials

The ignition of condensed materials by an electrical explosion is studied numerically. The effect of the wave process in the sample on its ignition characteristics is analyzed. Calculated values of the ignition time are given for various sample layouts, sample dimensions, and parameters of the initiating pulse. The effect of the hydrodynamic process caused by an electrical explosion in a condensed reactive material on the ignition period is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 15–22, January–February, 2007.     

Transformation of shock waves at the interface of bubble media

The transition of shock waves from a bubble medium into a liquid or into another bubble medium with different properties is considered experimentally. Data on the structure, velocity, and pressure in the shock wave incident onto the interface, transmitted wave, and reflected wave are obtained. Experimental results are compared with numerical data. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 97–104, March–April, 2006.