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).     

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.     

Dynamic Behavior of a Shear-Formed Shaped-Charge Liner

A high-resolution, multi-frame, image-converter camera developed for high speed photography is applied to study the dynamic behavior of shear-formed shaped-charge liners. Grid lines applied to the inner liner surface allow the precise quantification of liner collapse, early jet formation, and jet development for comparison with two-dimensional hydrocode simulations. The technique affords the first direct measurement of the angular velocity of jets formed from shear-formed shaped-charge liners.     

The Behavior of Shaped Charges with open-poled hemispherical liners

This paper discusses the effect of an opening at the pole of a hemispherical shaped-charge liner. An experimental study was performed in which various diameter holes were made in otherwise similar shaped-charge liners. Flash radiographs were taken to observe changes in the liner collapse and the jet characteristics. The collapse process and jet characteristics of a hemispherical liner are significantly altered for a hole diameter which is 10% or more of the outer liner diameter. The jet tip velocity is increased by 26% for a hole diameter-to-liner diameter ratio of 0.25. Explanations are presented for the behavior of the tip region of the shaped-charge jet.     

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.     

Magnetic-field amplification in metal shaped-charge jets during their inertial elongation

This paper considers magnetic-field amplification in inertially elongating metal shaped-charge jets formed by explosion of a shaped charge with an axial field previously produced in the charge liner. The amplification is related to the effect of magnetic-field freezing in a conducting material and is due to the deformation of the jet material with particle elongation along the magnetic lines. The model of a uniformly elongating, conducting, incompressible, cylindrical rod was used to determine the nature of the field variation in the jet elements versus the magnetic Reynolds number determined by the electrical resistance of the material, the initial axial-strain rate, and the element radius. In high-gradient copper shaped-charge jets, the magnetic field can be amplified by more than a factor of five during elongation. It is shown that the joint action of the force and thermal factors accompanying field amplification in the jet material can lead to jet breakup with radial scattering of the material particles.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 120–128, January–February, 2005.     

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.     

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.     

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.     

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.     

一种截顶线性聚能装药射流特性的数值模拟

为了得到特性更好的线性聚能射流,设计了一种截顶线性药型罩加矩形辅助药型罩的新型装药结构,利用ANSYS/LS-DYNA3D有限元程序对6组新型装药结构及传统装药结构进行了模拟计算,分析了矩形辅助药型罩宽度和截顶间隙长度对线性射流特性的影响。结果表明,该新型结构形成的线性射流的头部最大速度总体较传统线性聚能射流高,形成的线性射流形态更细更长,并且杵体相对较少,药型罩质量利用率较高。在6组方案中,矩形辅助药型罩宽度为1.0cm、截顶间隙为0.4cm时,该结构形成的线性聚能射流头部速度最大,为3.58km/s,连续性较好,有效宽度最大。     

Method for calculating the combustion efficiency of aluminum in explosion products from a metallized composition

A method is proposed for calculating the dynamics of energy production in metallized explosive compositions based on constructing plots of the velocity and acceleration of radial expansion of a cylindrical shell and can be used to estimate the effective fraction of reacted aluminum. Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 99–101, September–October, 1993.     

On the inconsistency of the asymmetric-sandwich gurney formula when used to model thin plate propulsion

The asymmetric sandwich Gurney formula is used extensively worldwide during explosive reactive armor and shaped-charge war-head design, in either its original form^(1,2) or its extended form used to model implosion configurations^(3–5). It is therefore very important to realize that calculations may contradict physical observations when the formula is used to calculate the velocity of thin plates having mass which is smaller than half the explosive mass per unit area. This inconsistency between calculation and experimental results is explained as resulting from the failure of the assumption made in deriving all the Gurney formulas that the velocity distribution of the explosive products is a linear function of the expansion coordinate.     

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.     

The Initiation of Covered Composition B by a Metal Jet

The initiation and build-up to detonation of Composition B covered by steel barrier plates and impacted by a shaped-charge jet has been studied. Two different barrier thicknesses were used representing strong and weak shock initiating systems. The results showed that, in both cases, a shock (designated the precursor shock) that travelled ahead of the penetrating jet and entered the explosive was roduced when the jet impacted the steel surface. The strong precursor shock from the thin barrier system produced initiation close to the explosive surface while for the weak precursor shock from the thick barrier system there was a long run to detonation (40 mm, 11 μs). In the latter case, close to the onset of detonation, a retonation was observed moving back through the previously shocked explosive which was expanding radially. These observations are used to discuss and explain some of the apparent anomalies in previously reported work. The effect of the precursor shock on the classical jet penetration theory was estimated.     

Methodology for simulation of the jet formation process in an elongated shaped charge

The performance of linear shaped charges depends on several different parameters. The density, the detonation velocity of the explosive, the shape of the detonation wave, the shape and wall thickness of the liner, and the distance of the shaped charge from the target are among the parameters that can be optimized by using computer simulation methods. In this paper, the jet formation process in a linear shaped charge and its action on an obstacle are simulated by using the LS-DYNA software. The results obtained are compared with experimental data.     

On the limits of flame propagation in a dusty gas

The limits of flame propagation in a gas with suspended inert particles in the presence of external heat removal have been studied. The mathematical model used is based on an unsteady heat-diffusion two-temperature model of gas combustion in the presence of inert particles. The problem is solved by a numerical method. A parametric analysis was performed, and critical values of the parameter that characterizes external heat removal are obtained. Dispersed-phase parameters are determined for which the two-temperature nature of the medium is insignificant. For this case, an analytic estimate for the critical parameters of flame quenching was obtained. At the moment of flame quenching, the normal flame-propagation velocity in a dusty, gas decreases by a factor of compared with the flame velocity in the dusty gas under adiabatic conditions. Tomsk State University, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 14–20, July–August, 1997.     

On the possibility of physicochemical transformation of substances upon shaped-charge application of coats

Experiments on shaped-charge application of coats made of a mechanical mixture of tungsten or titanium with carbon have been performed. Carbides of these metals have been shown to form steadily. This supports the fundamental possibility of synthesis of systems in a shaped-charge device. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 6, pp. 127–130, November–December, 1997.     

Improved formulas for velocity,acceleration, and projection angle of explosively driven liners

Improved one-dimensional formulas for both the direction and magnitude of the velocity of explosively driven liners are developed. First, an analytical formula for the direction of motion of the liner under unsteady conditions is derived. This new formula is compared with both two-dimensional calculations and experimental data for both shaped-charge and exploding cylinder geometries. The new formula is more accurate than the classical steady-state Taylor-angle formula for these cases. Next, for implosive geometries, a new formula for the fully accelerated liner velocity is given. Since the standard Gurney approach does not apply to imploding geometries, a modified approach was adopted. Results agree well with two-dimensional code results for a wide range of explosives and geometries. Also, the velocity history is shown to follow an exponential law, and a useful formula for characteristic metal acceleration time was developed.     

Generation of Hypervelocity Particle Flows by Explosive Compression of Ceramic Tubes

The compression of ceramic (corundum) tubes by the detonation products of explosives have been studied experimentally and numerically. The formation of the shaped-charge jet of ceramic particles and its effect on steel witnesses targets has been investigated. The tubes were produced by detonation spraying. Ceramic particles were deposited on copper tubes, which were then dissolved in a solution of ferric chloride. In the experiments, a considerable penetration of the flow of ceramic particles was observed. During the interaction of the flow with the target, the target material was partially evaporated, as shown by metallographic analysis. Numerical analysis of the formation of the discrete shaped-charge jet showed that the maximum velocity of the jet head was about 23 km/s, and the velocity of the main part of the jet was about 14 km/s.