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.     

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.     

Interaction of a shaped-charge jet with moving reactive armor plates

The mechanisms of the stationary and nonstationary interaction between a metal shaped charge jet and the front reactive armor plate (moving toward the jet) and rear (moving behind the jet) reactive armor plate. The range of interaction parameters in which these mechanisms take place was determined. The interaction of the shaped-charge jet with the front plate is mainly stationary and leads to the wearing of the jet in the transverse direction (reduction in the diameter of the jet) and its deflection by a small angle. The interaction of the shaped-charge jet with the rear plate is mainly of a nonstationary discrete nature and forms unilateral transverse perturbations in the jet, which, developing, lead to its bending and subsequent destruction.     

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.     

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).     

Influence of Drift Velocity and Distance Between Jet Particles on the Penetration Depth of Shaped Charges

The penetration depth of shaped charge jet into target is strongly affected by the stand‐off. The penetration process terminates even when the jet velocity is still high, and the penetration capability of jet particles degrades after jet breakup at a large stand‐off. This work presents an analytical model to describe the radial drift velocity and distance between jet particles, which leads to decreased penetration depth. The results show that jet particles with low drift velocity impact the crater wall easily. Furthermore, the jet particles cannot reach the crater bottom to increase depth because the crater diameter generated by the jet is quite small. Moreover, the distances between jet particles also play an important role in penetration depth under the influences of strain hardening of target, as well as tumbling and dispersion of jet particles. The radial drift velocity and distance between jet particles are investigated by applying the model to non‐precision charge and precision charge penetrations into target at different stand‐offs. The cutoff jet velocity and cutoff penetration velocity also are determined based on the analytical model. With increased stand‐off, the cutoff jet velocity increases, and the cutoff penetration velocity is almost constant. This result is proven by a number of experiments. The stand‐off curves of two charges are also calculated, and results are in good agreement with experiments. The stand‐off curve can be determined with only two or three experiments using the proposed method. Notably, jet particles should have a slow drift velocity and great penetration capability after breakup for suitable shaped charge.     

An Analytical Model for the Particulation of a Jet from a shaped charge liner

A new model is presented to predict the cumulative breakup time of the jet from a shaped charge liner. The model invokes a plastic instability criterion, kinematic considerations, and a material constitutive equation. Very good agreement of the cumulative breakup time and jet length with experimental data for several copper liner geometries is shown. The results are dependent on the initial strain rate and jet temperature distribution.     

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.     

Studies of shaped charges with built-in asymmetries. Part II: Modelling

A well-characterized shaped charge was used to study the influence of asymmetrical initiation on the jet. An experimental study yielded flash radiographs of the jets from charges fired with the initiation point offset 2, 4, 6, 8 and 10 mm, respectively, from the central axis. The axial and lateral velocities of the jet particles were determined from the sets of radiographs. In a previous paper it was hypothesized that a simple relationship might exist between the departure vectors of the jet particles and the geometry of the impingement of the detonation front on the liner. Any part of the jet from an asymmetrically initiated shaped charge departs at an angle determined by the difference between the current angle between the actual detonation wave where it contacts the liner, and that which would have arisen had the initiation been perfectly axial. We set up a simple computer code which evaluates, for any given initiation offset distance, the instantaneous angles between the detonation front and the successive elements of the liner which are encountered as the wave sweeps along it. Since it is possible to map particle velocities in the jet on to those regions of the liner where they originated, simulated sets of axial and lateral jet velocities were readily generated. Agreement between theory and experiment is sufficiently close to suggest that our approximation is useful and can assist in understanding the jet dynamics of asymmetrically initiated shaped charges.     

The experimental and theoretical study on the spatial-temporal distribution of electromagnetic radiation from JO-8 explosions.

The detonating fuse in the multistage warhead will be subjected to strong electromagnetic interference, derived from electromagnetic radiation generated by explosion of the shaped charge warhead, which may cause premature detonation or misfire. In order to explore the possible electromagnetic environment surrounded the detonating fuse, the spatial-temporal distribution of electromagnetic radiation after the explosion of JO-8 explosive was investigated in this paper. The electromagnetic radiation signal was collected and its frequency coverage was analyzed in the far-field area by the field blast test. Moreover, based on electromagnetic theory, a theoretical model of electromagnetic radiation generated by the explosion of JO-8 explosive was established, and the spatial-temporal distribution of the electric field intensity was illustrated in detail for several typical positions after the explosion. The better agreement between experimental and theoretical results indicates that the proposed theoretical model and computational method are reasonable. On this basis, the distributions of electric field intensity for different positions and various explosive weights were predicted respectively by using distance and explosive weight as variables. This study is expected to provide a reference for the research on the electromagnetic radiation for explosive explosion and anti-explosive electromagnetic interference.     

A relation between the liner kinetic energy and the distance reached by the shaped charge jet at the moment of particulation

It is shown that distance from the virtual origin reached by the shaped charge jet at the moment of particulation is proportional to the square root of the kinetic energy per unit directrix length which is delivered to the liner by the explosive. This relation helps in better understanding some basic shaped charge design problems. It also points at the possible existence of a convenient way for comparing the yield strength in the jet, between different materials.     

起爆方式对线性聚能装药射流形成的影响

以工程中常用的柔性切割器为研究对象,在不考虑端部效应的前提下,对3种起爆方式下线性聚能装药射流的形成过程进行了理论分析和数值模拟。结果表明,不同起爆方式下射流头部速度以端部面起爆最大,线起爆次之,端部点起爆在端面附近处形成的最低,但在距端面一定距离处,射流头部速度又能增大到与端部面起爆的速度相近。在射流内部,端部面起爆形成的射流在内部各点处的速度都是3种起爆方式中最大的,而端部点起爆时,则是随着距起爆点距离的增加由处处小于线起爆的射流速度分布转变到与端部面起爆相同的射流速度分布。在此基础上进一步提出3种起爆方式下线性聚能装药切割目标的数值模拟方法。     

Shaped charge jet interaction with Highly Effective Passive Sandwich Systems - experiments and analysis

The development and investigation of reactive sandwich targets and their interaction with shaped charge jets is one of the many research areas, where important contributions were made by Manfred Held. Such reactive sandwiches are known to be extremely effective against jets, but have a number of disadvantages. In this work, the interaction of the copper jet from a shaped charge calibre 136 mm with a double sandwich system, each sandwich consisting of a non-reacting layer between outer steel plates, is investigated. In 10 experiments with identical geometrical setup, only the material of the non-reacting layer is changed. Using flash X-ray pictures, the interaction of the jet with the sandwich system is investigated. Evaluation of these pictures as well as the comparison of the measured residual penetrations behind the sandwich target clearly demonstrate the influence of the material of the inner sandwich layer. The deformation and movement of the steel plates, caused by the penetrating jet, can be seen in the X-ray pictures. It is shown that it is possible to distort a shaped charge jet so that its penetration capability behind the target is reduced to a minimum. A fully three-dimensional hydrocode simulation of the experiments enabled the jet/sandwich interaction and steel plate deformation and rupture to be studied in detail.     

Effect of Moving Plate on Jet-Penetration

Effect of a moving plate between a shaped charge jet and the target on jet-penetration has been investigated theoretically. It has been assumed that the plate moves undeformed with uniform velocity, and jet-penetration in the plate or the target occurs hydrodynamically so that the impact of the jet produces a hole in the plate whose diameter is bigger than that of the jet. The free passage of the jet through this hole is intercepted when the jet touches the wall of the hole due to its transverse motion. The presence of a moving plate between the jet and the target has been found many times more effective than that of a stationary plate in reducing the jet penetration in the target. The effect of angle of attack, velocity of the plate and initial distance between the plate and the target on penetration, produced by the jet going out of the plate, has been investigated for a typical set of arbitrarily selected values of jet and plate parameters.     

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.     

Theoretical and Experimental Study on the Effects of Impact Angle on the Performance of Kevlar Woven Fabric Rubber Composite Armor against Shaped Charge Jet Impact

Kevlar woven fabric rubber composite armor (WFRCA) is a type of add‐on armor that usually consists of two steel plates with two Kevlar woven fabrics and a rubber layer in between. In this study, a theoretical model was developed to analyze the effect of the impact angles on the performance of the Kevlar WFRCA against the shaped charge jet impact. The calculation of the precursor length was discussed in detail. A series of X‐ray experiments were conducted to analyze the disturbance mechanism and precursor length of the Kevlar WFECA against the shaped charge jet under different impact angles. Theoretical and experimental analyses showed that the greater the impact angle, the higher the tip velocity of the precursor and the shorter the precursor length. A microscopic study of the edge of the Kevlar woven fabric, rubber, and steel plates after the shaped charge jet impact was also conducted to evaluate the structure and composition. Several broken Kevlar fibers were embedded in the steel plate and the moving jet. This phenomenon can be used to further investigate the disturbance mechanism of the Kevlar WFRCA against the shaped charge impact.     

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.     

Discussion of the Experimental Findings from the initiation of covered,but unconfined high explosive charges with shaped charge jets

The results of experiments on the initiation of covered, but unconfined high explosive charges with shaped charge jets from Chick and Hatt, which have been diagnosed by the flash X-ray technique, as well as the author's own experiments in which the build-up distances and the run-up times have been recorded by means of a rotating-mirror camera in the framing and streak modes, are analyzed and explained in detail in this paper. Build-up distances and run-up times versus the residual jet velocity, or versus the dynamic pressure, are in fairly good agreement, despite the somewhat different shaped charges and acceptor charges that have been used in the two approaches. The greater initiability of an acceptor charge behind a barrier, but with an air gap between, is attributed less to a precursor shock that desensitizes the high explosive charge which is in contact with a barrier, but rather to the higher velocity of the free shaped charge jet and, particularly, to the area loading on a high explosive charge with an air gap in front.     

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.     

Energy storage density and efficiency of polyetherimide nanocomposites diminished by the temperature dependent charge hopping

The utilization of renewable energies requires extensive use of energy storage equipment such as dielectric capacitor. Polyetherimide nanocomposites (PEI PNCs) have high energy storage performance, and become the next generation advanced dielectric s However, the quantitative relation between the charge transport and energy storage of PEI PNCs is not very clear, restricting further improvement of their performance. Considering the charge injection from electrodes and the charge hopping transport inside the dielectric, the energy storage and release model of capacitors was established. Firstly, the conductivities of PEI PNCs were simulated, and the charge transport parameters were determined by comparing with the experiments. Then, the electric displacement-electric field (D-E) loops of PEI PNCs were simulated, and the discharged energy density and energy efficiency were calculated from them. The simulation results are consistent with the experiments, and the quantitative relationship between charge injection and transport parameters and energy storage performance is established. In addition, it is found that the energy storage density and efficiency are diminished by the increase of hopping distance at high temperatures. Increasing the hopping barrier, reducing the hopping distance and its temperature dependence through nano-doping can significantly improve the energy storage performance under high temperatures and high electric fields.