Effect of porosity on shaped-charge flow

It is shown that for shaped charges with porous liners, shaped-charge flow of two types is possible: dispersed jet flow, which fills the entire shaped-charge cavity, and monolithic jet flow. Conditions for transition from one type of flow to the other are estimated, and it is shown that by changing the initial porosity, it is possible to control the physicomechanical characteristics of the liner material during compression of the liner by the detonation products of the explosive charge. For monolithic jet flow, it is shown experimentally that shaped charges with porous liners can have greater penetrating capability into steel targets than charges with monolithic liners of similar design. Dispersed jet flow is used to apply coatings on substrate targets and to synthesize new compounds. Experiments are described in which shaped-charge liners made of a mechanical mixture of W or Ti powders with carbon are used to produce layers containing the carbides of the indicated metals on steel or titanium substrate. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 122–132, March–April, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant Nos. 97-01-00826 and 98-03-32328).     

Formation of a shaped-charge jet upon nonsymmetric compression of a shell

The effect of technological errors on the formation and displacement of components of a shaped-charge jet is studied numerically. The linear character of the dependence of the radial center-of-mass velocity of the transverse cross section of a linear on the magnitude of the variation in the wall thickness of shells and a layer of an explosive substance, and the variation in its charge along the circumferential coordinate is clarified. Computations have shown that, for a shaped-charge jet, the magnitude of the radial velocity can be considerably larger compared to the entire liner. This is due to a conversion of only a part of the linear material to the jet, with large values of the radial velocity. The different values of the radial velocity along the liner length lead to distortion of the jet shape, and, hence, to a decrease in the effectiveness of its action. Estimation of the degree of influence of each technological error on the curving of a shaped-charge jet makes it possible to give concrete recommendations concerning the increase in the precision of treatment and assembling of the corresponding members of an explosive system. Institute of Applied Mathematics and Mechanics at Tomsk State University, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 6, pp. 121–126, November–December, 1997.     

Optical methods of studying the explosion of shaped charges

This article describes a group of optical methods for studying the explosion of shaped charges, including modifications of established methods (slit photorecording, the luminous points method, laser probing) and two new methods — measurement of wave velocities with transducers based on optical fibers and laser visualization of the shaped-charge jet. Optical methods are used to study such jets under laboratory conditions. Characteristic distortions of the symmetry of the detonation front and their effect on the jet are discussed, the probable character of breakup of the jet is established, and the distribution of the jet particles with respect to size is determined along with the maximum values of average limiting tension for copper. Scientific-Research Institute of Machine Design, 125212 Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 6, pp. 147–154, November–December, 1995.     

Effect of the strain rate on the tensile strength of a copper shaped-charge jet

The data on the penetration depth of a rotating shaped-charge jet were used to estimate the strength of the material of a copper jet formed from a “low” conical linear with an apex angle of120° under the action of centrifugal forces. The estimates0.07–0.15 GPa obtained are close to the static yield point of deformed copper. The jet strength, which is estimated using the length of the fragments formed upon breakup of a rotation-free jet owing to the axial velocity gradient, attains1–1.5 GPa at a strain rate of ≌2·10⁴ sec⁻¹. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 111–118, January–February, 1997.     

Propagation of spherical gas filtration combustion waves in inert porous media

The behavior of spherical combustion waves of gases in inert porous media is described in terms of one- and two-temperature models. Parametric dependences are obtained for the wave velocity and acceleration and for the temperature of the gas and porous medium in the wave. It is shown that in a diverging spherical gas flow, combustion waves initiated at different radii of the sphere converge to the standing wave coordinater ^*, and in a converging flow, on the other hand, they diverge from it. The experimentally observed propagation behavior of spherical combustion waves is well described by the proposed models. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 60–66, January–February 1999     

Numerical simulation of the characteristics of turbulent Taylor vortex flow

Turbulent Taylor vortex flow, which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends, is simulated by applying the development in Reynolds stress equations mold (RSM) of the micro-perturbation. This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations. Based on the numerical simulation results of the turbulent Taylor vortex flow, its characteristics such as the fluctuation of the flow field, the precipitous drop of azimuthal velocity, the jet flow of radial velocity, the periodicity of axial velocity, the wave periodicity of pressure distribution, the polarization of shear stress on the walls, and the turbulence intensity in the jet region, are discussed. Comparing the pilot results measured by previous methods, the relative error of the characteristics predicted by simulation is less than 30%. Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2006, 32(5), 617–622 [译自: 华东理工大学学报 (自然科学版)]     

Disruption of Shaped-Charge Jets by a Current

In our previous experiments on disruption of metal shaped-charge jets by a capacitor-bank current, we attained almost complete disruption of the entire jet. In those experiments, the distance between the shaped charge and the current electrodes was approximately equal to the diameter of the shaped-charge cavity. Physically, jet disruption by a high current consisted of initial development of MHD instability of the jet in the form of growth of necks and subsequent electric explosion of the necks. The present paper describes similar experiments in which the distance between the shaped charge and electrodes was increased. It is shown that this can worsen results of jet disruption because the change in the initial state of the jet changes the physical picture of the process of jet disruption by a current. Key words: shaped-charge effect, shaped-charge jet, capacitor bank, MHD instability, electric explosion of a conductor, electric-current pulse.     

Stabilized gas combustion wave in an inert porous medium

A stabilized gas combustion wave in an inert porous medium with intense internal interphase heat exchange (at low velocities) is considered to elucidate the mechanism underlying the increase in the burning velocity of the homogeneous gas mixture due to the porous medium. It is shown that the major factor of the increase in the burning velocity is conductive heat recuperation from the postflame zone to the region of the fresh mixture through the solid skeleton of the porous medium. Analytical dependences of the degree of increase in the burning velocity of the mixture in the stabilized wave on the determining parameters are obtained. The possibilities and restrictions of the use of the results to analyze the operation of porous burners are discussed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 8–15, September–October, 2008.     

Effect of macroscopic heterogeneity of the medium on the solid-state combustion wave characteristics in thermally and chemically heterogeneous media

A macroscopically heterogeneous medium is modeled by a set of cylinders (rods) pressed from a mixture of solid reagents, which have coaxial cylindrical cores made from an inert material. A three-dimensional mathematical model describing propagation of combustion waves over one cylinder is studied by numerical methods. The influence of the distance between the centerlines of the neighboring cylinders and transverse sizes of the cylinders on characteristics of combustion waves propagating over a heterogeneous medium is considered. It is demonstrated that there exists an optimal distance between the inert rods, which ensures a much higher velocity of the combustion wave along the specimen than the theoretically predicted velocity of the classical combustion wave propagating over a solid specimen. New types of spinning waves are described, whose motion makes the high-temperature spot move inside the charge mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 39–49, May–June, 2008.     

Numerical study of the transfer of shock-wave loading to a screened flat wall through a layer of a powdered medium and a subsequent air gap

The two-velocity, two-temperature model with two stresses in a mixture of a gas and solid particles contacting each other is used to numerically study the dynamic effect of an air shock wave incoming onto a solid wall with a screening layer of a porous powdered medium at some distance from the wall. The process is described for the case of one-dimensional planar motion of the gaseous and disperse phases under the assumption of a viscoelastic behavior of the powder skeleton. The effect of stepwise shock waves onto the porous powdered screen is considered. The influence of parameters of the screening layer and the air gap on the dynamics of loading of the screened solid wall is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 132–142, January–February, 2007.     

Two-dimensional numerical simulation of deflagration-to-detonation transition for a porous explosive using a model of a multivelocity heterogeneous medium

The model of a multivelocity heterogeneous medium is used for one- and two-dimensional numerical calculations of the deflagration-to-detonation transition for charges of a porous explosive enclosed in a casing. Calculation results are compared with experimental data. Depending on the charge diameter, different explosion regimes — detonation and low-velocity explosive transformation — are registered in both the two-dimensional calculations and experiments. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 97–106, May–June, 2000.     

Flame propagation in porous media wetted with fuel

Some specific features of flame propagation over a gas mixture with a very low value of enthalpy have been studied experimentally in an evaporative-diffusive regime in various porous media. The combustion wave is shown to propagate steadily in a high-porosity medium wetted withn-octane at velocities of3–10 cm/sec. We have also studied the effect of the volumetric heat capacity and thermal conductivity of the material of a porous medium on the velocity and characteristics of flame propagation both in a high-velocity regime for high-enthalpy gas mixtures and in a low-velocity regime for low-enthalpy ones. The existence conditions of an evaporative-diffusive regime have been considered. Institute of Chemical Kinetics and Combustion, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 3, pp. 76–85, May–June, 1997.     

Effect of the permeability of a rigid wall on the energy recovery factor in a Lagrangian problem

A study is made of the effect of the permeability of a rigid wall on limiting propulsive velocity and the explosion energy recovery factor in a Lagrangian problem. The gasdynamic features of the flow of explosion products are examined and analytic expressions are obtained for the determining parameters of the problem. NII Spetsmash, N. é. Bauman Moscow State Technical College. Moscow 107005. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 5, pp. 84–90, September–October, 1994.     

Modeling of low-speed combustion of a methane-air-coal dust suspension

A plane one-dimensional problem of the propagation of slow-speed combustion in methane-air-coal dust suspensions is solved. Methane contained originally in the gas is assumed to burn-up completely in the flame front. The front velocity relative to the gas is calculated from relations derived in analysis of the stationary problem using the theory of thermal explosion. The gas suspension is regarded as a two-temperature and two-velocity medium. Heterogeneous reactions of carbon (coke) combustion and carbon monoxide reduction, and the yield of volatile components and their gas-phase combustion together with carbon monoxide are taken into account. Based on numerical calculations, the coal dust is shown to affect unambiguously the flame velocity, with moderate content of the dust. In lean mixtures, with a moderate content of the dust the intensity of the combustion wave increases and decreases under conditions close to stoichiometric ones. Institute of Mechanics at Moscow State University, 119899 Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 46–54, July–August, 1997.     

Detonation waves in a reactive supersonic flow

A supersonic hydrogen—air flow is studied in detail, in particular, the fields of gas-dynamic parameters and chemical homogeneity of the mixture in various cross sections of the duct. The processes of excitation and propagation of a detonation wave in the downstream and upstream directions are considered. The detonation-wave velocity with respect to the mixture flow is found to differ from the nominal Chapman—Jouguet velocity for a quiescent mixture: the detonation-wave velocity is higher if the wave moves upstream and lower if the wave moves downstream. Some hypotheses on the reasons for these deviations of the experimentally measured velocity from the nominal value are given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 85–100, September–October, 2006.     

Resistance of the medium during high-velocity penetration of long rods and shaped-charge jets

We consider the high-velocity penetration of long rods and shaped-charge jets into semi-infinite targets with initial impact velocities of 2–4 km/sec. At these velocities, the mechanical characteristics of the target materials makes a great contribution to the final parameters of the process: penetration depth and critical velocity of the impactor (jet). The dynamic compressive stability threshold of the material, obtained in experiments with uniaxial dynamic loading of flat targets, is proposed as a parameter that determines the properties of the target in the penetration process.     

Numerical simulation of the formation of shaped-charge jets from hemispherical liners of degressive thickness

The formation of shaped-charge jets from hemispherical copper liners of degressive thickness (decreasing from apex to bottom) is analyzed by numerical simulation of a twodimensional axisymmetric problem of continuum mechanics. The comparison was based on the parameters of the jet formed from a modern standard shaped charge with a conical liner which provides penetration of a steel target to a depth equal to 10 charge diameters. The comparative analysis was performed using calculated mass–velocity distributions and the ultimate jet length–velocity distributions obtained on their basis, from which the potential penetrability of jets was evaluated. It is shown that the shaped-charge jets formed by hemispherical shaped-charge liners of degressive thickness are comparable in head velocity and penetrability to the jets from conical liners.     

Calculation of the acceleration of a cylindrical body by an unsteady two-phase flow

Calculations are performed for the acceleration of a cylindrical body by the unsteady flow of a two-velocity two-temperature gas-disperse medium taking into account the following two mechanisms of interparticle interaction: collisions of randomly moving dispersed particles in a rarefied state or deformation of a porous skeleton in closepacked particles. It is established that there are regimes of acceleration of the body in which its velocity exceeds the maximum velocity of the particles at the duct exit. The possibility of using simplified calculation schemes in modeling the acceleration of the body is shown. Calculation and experimental results are compared. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 138–145, September–October 1999.     

Rotational components of deformation in metal bodies under dynamic loading

The plane problem of an initially quiescent cylinder subjected to a gradient flow of a highly viscous fluid is solved. It is shown that the cylinder is brought into rotation with angular velocity ω=−εé, where εé in the shear-strain rate of the medium. The solution is used to analyze flows under high-rate loading of metallic bodies that occurs at the level of the microstructure. The appearance of rotation is associated with the presence of fragments in the structure of the substance (grains, fragments, cells, and inclusions) that are unable to change their shape under the given loading conditions and, consequently, begin to rotate in the process of shear strain. Rotations that occur at the microlevel during joint deformation of solid bodies lead to transfer of oxide, hydroxide, and other surface films into the depth of the material, and this contributes to formation of a bond. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 129–133, March–April, 1998.     

Formation of a specific layer on the surface of a metallic target interacting with a shaped-charge jet of boron-containing liners

Coatings on titanium targets are obtained under conditions of a shaped-charge explosion; the maximum microhardness of the coatings at certain segments of the target can reach 4000 kg/mm². A conical liner with a cone angle of 20° prepared from a mixture of fine powders of amorphous boron and ammonium nitrate is used in the experiments. A comparative quantitative X-ray powder diffraction analysis of various segments of the coating is performed. The values of the unit cell parameters indicate the formation of complex phases. The dynamics of the results of the X-ray study with the cone angle of the liner decreasing from 45 to 20° is demonstrated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 121–127, March–April, 2006.