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.     

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.     

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.     

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.     

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.     

Characteristics of Shaped Charges with Hemispherical Liners

During the last 10 years shaped charges with spherical liners have arosed great interest in research and development because their application in special munition results in an increase of performance. The present report presents measured characteristics of shaped charges with hemispherical liners. A short explanation of the jet formation process and the typical jet characteristics as a function of charge geometries are given, and the effect of liner materials is described. Additionally, the influence of various explosives and wave shapers have been studied. The important feature of such shaped charges is that the projectiles are associated with a high terminal ballistic effective part of the liner mass, which is of particular interest for application.     

Formation of Phases upon Collision of a Shaped-Charge Flow of Particles with a Titanium Target

It is shown that chemical interaction between a carbon-containing shaped-charge flow and titanium target is possible. The upper layers of the targets tested are examined by x-ray diffractometry. The dependence of the phase composition on the experimental conditions and composition of the initial porous liner is studied.     

Shaped Charge Optimisation against Bulging Targets

Equivalent to the results against explosive reactive armour sandwiches also bulging armours can be better defeated by high performance precision shaped charges compared to so‐called robust shaped charges. The shaped charges with larger liner angles or thicker liners have less jet tip velocities which results in less residual penetration capabilities.     

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.     

Limits of Increasing the Penetration of Shaped‐Charge Jets by Pulsed Thermal Action on Shaped‐Charge Liners

The effect of preheating of liners on the penetration capability of shaped charges is considered theoretically. It is shown that for a plastically fractured shapedcharge jet, preheating of the liner generally increases the effective jet length and shapedcharge jet penetration. Restrictions on the parameters of preheating of shapedcharge liners due to the possible thermal initiation of the explosive are established. It is noted that excessive weakening of a shapedcharge jet can lead to transition from plastic to volume fracture with a corresponding decrease in shapedcharge jet penetration. The ultimate possibilities of the thermal method for increasing the penetration capability of shaped charges are estimated. Calculation results are compared with available experimental data.     

Mechanical effect of shaped charges with porous liners

This paper presents experimental data on the penetration of shaped charges with porous liners into metal targets located at distances smaller than or comparable to the diameter of the charge and some experimental data on the velocity of the jets from the investigated charges with liners of metal powders.     

药型罩切分方式对射流形成影响的数值模拟

为了研究药型罩切分方式对其形成射流性能的影响,利用数值模拟软件ANSYS/LS-DYNA对横向切分和纵向切分的药型罩以及未切分药型罩在爆轰波作用下形成射流的过程以及对45号板的侵彻能力进行了数值模拟,比较了不同切分方式的药型罩在爆轰波作用下形成射流的形状、头尾部速度、拉伸长度和抗拉伸性能及其对45号钢板的侵彻能力。结果表明,在相同装药条件下,横向切分药型罩相比纵向切分药型罩的头部速度提高约220m/s,且抗拉伸性能更好,对45号钢板的侵彻深度提高约3.26cm;横向切分药型罩相比未切分药型罩的头部速度提高约360m/s,对45号钢板的侵彻能力提高约5.62cm。     

Three–Dimensional Simulation of Shaped Charges with a Star–Shaped Liner

Results of the three–dimensional simulation of the formation of a shaped–charge jet and the piercing of a steel target by a charge with a star–shaped liner are reported. The calculation results show the efficiency of the three–dimensional numerical technique TRÉK–UP used and the possibility of its applications to direct simulation of the problem considered. In addition, it is shown that one can optimize star–shaped charges significantly with a view to reaching higher efficiency.     

Shaped Charge Optimization against ERA Targets

Shaped charges with different angles or/and different liner wall thicknesses have been tested against an explosive reactive armor sandwich. The reason was to find out if more robust shaped charges give more residual penetration against an ERA sandwich, compared to shaped charges with more penetration performance in RHA targets. It was thought, that the latter ones are more sensitive against disturbances. But the shaped charges with the higher perforation capability have typically higher jet tip velocities and this gives more residual penetration also against ERA targets. In other words the so‐called more robust charges gave less performance against the ERA sandwiches than the shaped charges which have higher performance in RHA targets.     

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.     

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.     

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.     

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.     

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.     

Demolition Mechanism and Behavior of Shaped Charge with Reactive Liner

The application of reactive materials on shaped charge liners has received much attention. Herein, the demolition mechanism and behavior of reactive materials based shaped charge liner are investigated by experiment, numerical simulation, and theoretical analysis. Three reactive shaped charge liners, composed of a mixture of Al/PTFE (26.5/73.5 wt‐%) powders, are fabricated by pressing and sintering. The damage effects of the multi‐layered target against reactive materials based shaped charge are investigated. The results show that the reactive liners create excellent collateral damage due to the release of chemical energy contained in reactive materials. An Eulerian computational model is developed to investigate penetration behavior of the reactive jet formed by shaped charge liner. In addition, a theoretical model based on cavity expansion is derived to predict the initiated location of reactive materials. Comprehensive analysis indicates that the TNT equivalence factor for these powder mixtures used in this work is 3.41–7.77 and that the self‐delay time is about 0.8 ms. This work will provide guidance and reference for the design of reactive shaped charge liner.