Charge Jet Research Articles

Physical and numerical assessments of the penetration behavior of coplanar linear shape charges

In this study, we aimed to demolish irregular constructions that are usually composed of convex, concave, and straight structures based on the shaped charge jet. Accordingly, the penetration behaviour of convergent, divergent, and straight linear shaped charges (LSCs) have been detected with numerical and physical methods. For comparison purposes, numerical models for all three types of LSCs with identical cross-sections have been established to investigate the impacts of structural features. It is found that the shaped charge structure not only determines the kinematic consumption during the penetration process but also influences the initial value of the jet velocity. Additionally, because of the interactions between the previous and subsequent jets, the jet velocity of the convergent LSC shows an obvious undulation during the penetration process. Furthermore, quantitative analyses of the kinematic consumption and initial velocity differences for three types of LSCs are conducted with physical models. A kinematic consumption difference is revealed, and the mass of the charge that determines the initial jet velocity as a function of the geometric parameters in three types of LSCs is deduced. Finally, we combined the numerical and physical models and conducted integral analyses to assess the penetration behaviours of the three LSC types.

High Strain Rate Effect on Tensile and Compressive Property of Carbon Fiber Reinforced Composites

With high strength and stiffness-to-weight ratios, Carbon-Fiber-Reinforced Polymer (CFRP) composite has been applied to the separation device of the rocket by shaped charge jet. But dynamic tensile and compressive properties of CFRP under high rate strain are still unclear. In the article, tensile testing along transverse direction are conducted. The quasi-static tests (10-3 s-1) use a universal testing machine and high dynamic loadings of 800 s-1 and 1600 s-1 tests adopt a high-speed tensile testing machine. Meanwhile, dynamic compressive tests of unidirectional and cross-ply laminated specimen under the thickness direction loading are implemented by a Split Hopkinson Pressure Bar (SHPB) from dynamic loading 500 s-1 to 2500 s-1. Test results show that compared with static tests data, both transverse tensile modulus and strength of CFRP composites materials at dynamic loadings are sensitive to tensile tests. The compressive peak stress and stiffness of specimens also have an increasing tendency with the increases of the strain rate. Furthermore, for failure mode of tensile specimens, the crack propagation of the specimen fracture is along the interface of the fiber/matrix under all loading conditions. The failure modes of compressive specimens are different as the strain rate changes. The higher the strain rate, the more severe the crushing.

Simple flash screens for shaped charge jet and flyer velocity measurements

The paper describes a novel technique for measuring the velocity of fast flying objects. The technique utilises a series of simple single-use screens which are placed along the expected flight path. The projectile interaction with the screen generates a flash of light which is captured by an optical fibre connected to the light detecting device. The velocities are calculated from the signal arrival times and screen positions. The flash screens were tested using copper shaped charge jets and flyer discs accelerated by explosive charges made of sensitised nitromethane. In addition to the simple time of arrival measurement with VOD-815, the light signals were recorded using an OPTIMEX-64 light analyser which enabled checking their intensity and reproducibility. Some of the experiments were also carried out using a UHSi 12/24 high-speed camera. The flyer plate velocities measured were compared with empirical calculations from a Gurney model.

Experimental and numerical investigation of zirconium jet performance with different liner shapes design

This paper studies the shaped charge jet performance in terms of different liner shapes including conical, bell, hemispherical and bi-conical liners. The critical angles and the relevant flow velocities for the zirconium liner material were calculated analytically and numerically using Autodyn hydro-code. The relationship between the critical collapse angle and the flow velocity was determined for the conditions of jet formation and coherency. Penetration tests according to the standard testing procedures of API-RP34 (Section-II) were performed to validate the numerical predictions of the jet performance of the studied liners. It was found that the four shaped charge liners all produced coherent jets with different performances. The penetration depth of the shaped charges with the bell and the bi-conical liner shapes increased by 10.3% and 22%, respectively, while the crater diameter of shaped charge with hemispherical liner increased by 85% representing the formation of an explosively-formed-projectile (EFP), when they are compared with the corresponding jet characteristics of a conical liner shaped charge.

The inhibitor effect on the shaped charge jet penetration

A submunition is one of the small shaped charges and has a severe penetration capability when it is dispensed in large numbers from the sky. Neutralizing it is one of the major interests in military science. An inhibitor which can be formed inside of shaped charge liner when a submunition impacts soft material target plays an important role to the penetration performance. A silicone rubber material that shows suitable inhibitor character of being dug deep by submunition impact in penetration mechanism was selected. The penetration performance of a shaped charge adopted inhibitors was investigated through ballistic experiments and numerical simulations. A remarkable reduction of jet penetration capability was obtained from the experiment. Numerical simulation using LS-DYNA, which is a non-linear finite element analysis code, was also carried out to reconstruct the experimental results. The simulation results showed good agreement with the experimental results, providing insights into the noticeable reduction of jet penetration performance due to a silicone rubber inhibitor.

Kinematics of the shaped charge jet formation process

Based on the review of scientific and technical literature, an analysis is made of the problems of the modern theory of formation, extension and destruction of the shaped jet. The focus of the research is on the kinematics of the formation of a shaped jet based on the approach of operating with the characteristics of a real metal when the velocity vector of the cumulative jet is the result of three vectors: strain, strain and displacement of the shaped jet’s material. The numerical experiment of the functioning of the shaped charge is carried out, and the procedure for evaluating the calculation results is proposed. The obtained data correlate with existing knowledge about the physics of the cumulation process.

Investigate the effects of magnetic fields on the penetration ability of a shaped charge jet at different standoffs

The influence of a magnetic field on the stability of a shaped charge jet is experimentally investigated at standoffs of 490, 650 and 800 mm. The experimental results without and with the magnetic field are compared in terms of the shaped charge jet form, stability and penetration ability. A theoretical model based on one-dimension fluid dynamics is then developed to assess the depth of penetration of the shaped charge at those three standoffs and magnetic conditions. The results show that the penetration capability can be enhanced in more than 70% by the magnetic field. The theoretical calculations are compared with the experimental results with reasonably good correlation. In addition, the parameters introduced in the theory are discussed together with the experiments at three standoffs studied.

A semi-empirical study of penetration of shaped charge jet into high and ultra-high strength reactive powder concrete targets

In this study, a semi-empirical model was proposed to calculate the penetration depth and cavity diameters generated by shaped charge jet into high and ultra-high strength concrete (H&UHSC) targets. A recently proposed axial penetration equation and the two-step mechanism of cavity growth were employed to determine the analysis. The predictions were validated with reference to the experiments conducted using a kind of H&UHSC named reactive powder concrete (RPC). Furthermore, the influences of the RPC compressive strength and the jet velocity on the penetration were analyzed. The results showed that the RPC targets had good protection efficiency for both penetration depth and cavity diameters as the compressive strength approaches approximately 250∼280MPa. Moreover, the radial cavity growth efficiency increased linearly with the increase of the jet velocity, while the axial penetration efficiency increased rapidly when the jet velocity was 1.0∼4.0km/s and reached the maximum at 4.0∼7.0km/s and tended to be stable as the jet velocity increased to greater than about 7.0km/s.

Study on Plastic Deformation Behavior of Mo-10Ta under Ultra-High Strain Rate

This study investigated the deformation behavior of the Mo-10Ta alloy with a strain rate range of 102–105 s−1. The Split Hopkinson pressure bar (SHPB) experiments were conducted to investigate the influence of deformation conditions on the stress-strain relationship and strain rate sensitivity of the material within a strain rate range of 0.001–4500 s−1. The Shaped Charge Jet (SCJ) forming experiments under detonation loading was conducted to clarify the dynamic response and microstructure evolution of the material within an ultra-high strain rates range of 104–105 s−1. Based on the stress-strain relationship of Mo-10Ta alloy at high temperature (286–873 K) and high strain rate (460–4500 s−1), the influence of temperature and strain rate on the activation energy Q was analyzed. The results indicate that the material strain rate sensitivity increased with the increase in strain rate and strain. Meanwhile, the activation energy Q decreased as the temperature and strain rate increased. The plasticity of the Mo-10Ta alloy under the condition of SCJ forming was substantially enhanced compared with that under quasi-static deformation. The material grain was also refined under ultra-high strain rate, as reflected by the reduction in grain size from 232 μm to less than 10 μm.

Determination of Delay in Detonation of a Sandwiched Explosive Impacted by a Shaped Charge Jet

A simple analytical model has been developed to determine delay in detonation of an explosive sandwiched between two metal plates and impacted by a shaped charge jet. The analytical model consists of a relation between detonation delay and depth of jet penetration in a target kept in contact across the explosive sandwich. This relation is derived by expressing depth of jet penetration P as a function of detonation delay Tdx and duration Tw of free passage of the jet through the hole in the top plate of the sandwich. One more relation between Tdx and Tw has been obtained from the theory of expansion of hole produced in a metal plate by jet impact. These two relations have been solved simultaneously to get values of both these parameters as a function of jet penetration. It is proposed that this analytical model can be used in two ways. First, this model can be used to calculate detonation delay by experimental measurement of jet penetration in a target. The detonation delay thus determined can be used to calculate insensitivity constant Aj of an explosive. Second, this model can be used to theoretically calculate jet penetrations obtained by different shaped charge warheads when using a sandwich of explosive with a given insensitivity. Both uses of this analytical model are illustrated using numerical examples.

Initiation of shaped charge into booster devices

ABSTRACT In this paper, the initiation capacity of shaped charges against booster devices is carefully examined using both experimental and simulation method. A booster device, which consists of insensitive charges, is investigated by shaped charge jet impact test. The results show that the response degree of the booster device with insensitive charge is detonation reaction. The numerical simulation results of jet initiation into booster devices are also compared with the witness board deformation performance. Furthermore, based on the validated numerical models and the corresponding parameters, a series of numerical simulations are performed to investigate the influence of the explosive types of booster devices, the locations of booster devices and the shell materials of booster devices. By assessing the peak pressure, maximum reaction degree and jet velocity, the influences of the key parameters on the booster device initiation are numerically discussed. The results indicate that, compared with traditional charge, the insensitive charge booster device has low jet initiation insensitivity. As the location of booster device changes, the anti-initiation performance of booster device changes. At the angle of 45°, the minimal initiation performance of the booster device is obtained. It is found that the density and strength of shell material have a slight effect on the jet initiation performance under the given thickness booster device. However, variations in the shell material property are found to impart significant effect on the jet penetration velocity, while variations in the strength impart a significant influence on the low-speed jet.

Reaction characteristics of polymer expansive jet impact on explosive reactive armour

Abstract In this study, a new damage mode for the explosive reactive armour (ERA) of a shaped charge jet was proposed. The response characteristics of polytetrafluoroethylene (PTFE) and polyamide (PA) polymer jet impact on the ERA were analysed. The expansion degree and the diameter of the PTFE jet are larger than those of the PA jet, but the compactness of the PTFE jet head is lower than that of the PA jet, resulting in different impact pressures of the different polymer expansive jets on the target. The PTFE jet achieved the penetration without initiation of the ERA at different standoffs, while the PA jet directly detonated the sandwich charge when impacting the ERA vertically and failed to penetrate the front plate when impacting the ERA at 68°. With the increase of standoff, the reaction degree of the PTFE jet to the ERA decreased gradually, and the aperture of the front plate did not change.

Finite element modeling of the shaped charge jet and design of the reusable perforating gun

Finite element method is used to study the formations of the penetration jet, the bulge, and the burr in the designed reusable perforating gun. The attached layer of the soft metal on the perforator is studied for the controlling of the bulge height on the casing of the reusable perforating gun. Results indicate that the shaped charge jet is initially formed in the center of the shaped charge liner and then the material of the liner is driven to the centerline of the liner by the detonation wave. The attachment of the soft metal layer to the cartridge of the perforator can be beneficial to control the bulge height. The design on the blind holes on the casing can affect the burr height formed by the collision between the jet and the casing. With the increase in the liner angle, the penetration width on the cement wall of the wellbore is increased.

Phase transitions effect on interaction of aluminum alloys at velocities exceeding 9 km/s

The authors investigate aluminum shaped charge jet (SCJ) penetration into an aluminum alloy target at 8–11 km/s velocities. The analysis of kinetics, penetration parameters and structures of cavern surfaces formed after the penetration show that at velocities exceeding 9–11 km/s, the hydrodynamic character of the penetration changes due to the melting of the interacting materials. When during the penetration process SCJ velocity exceed 9 km/s, porous layer of aluminum nanospheres with 20–100 nm in diameter form in the penetration region. The results obtained are appropriate for developing spacecraft shield protections against most dangerous space fragments.

Penetration of annular and general jets into underwater plates

Underwater structures can be seriously damaged by a metal jet associated with underwater explosion. Three main modes—Shaped Charge Jet, Jetting Projectile Charge and Explosive Formed Projectile—are included for traditional metal jets. Compared with the traditional ones, an annular jet may cause more serious damage into a target. Hence, a comparison for the entire process of annular and general jets penetration into underwater plates was analysed in this paper. Since Smoothed Particle Hydrodynamics (SPH) method has advantages of solving problems of large deformations, a modified scheme for approximating kernel gradient is used in simulation of processes of shaped charge detonation, jet formation and its penetration into underwater plates. An SPH model of an annular jet penetration into a steel target was first developed, and its numerical results were compared with experimental data. Then, models of annular and general jets associated with underwater explosion penetrating a plate were built. After that, the wave propagation in the detonation process and the formation of annular and general jets were analysed. Finally, damage characteristics of plates subjected to these two metal jets were compared.

Influence of a liquid-filled compartment structure on the incoming shaped charge jet stability

Liquid-filled compartment structure consists of a bulk steel plate with matrix blind holes which are filled with liquid and a steel front plate to seal up the liquid with rings and bolts. The liquid-filled compartment structure can resist the shaped charge warhead effectively. This paper presents experimental and theoretical investigations of the penetration ability of the residual shaped charge jet emerging from the liquid-filled compartment structure after the penetration process at different impact angles. On the basis of shock wave propagation theory, the influence of the liquid-filled compartment structure on jet stability is analysed. The interferences of the liquid backflow caused by a reflected shock wave and a back plate on jet stability under different impact angles are also examined. In addition, the range of the disturbed velocity segments of the jet at different impact angles and the penetration ability of the residual jet are obtained. A theoretical model is validated against the experimental penetration depths.

Simulation study on the influence of liquid level on anti-jet penetration ability of single-cell composite structure

The liquid composite armour produces transverse interference to the sharped charge jet through the backflow of liquid in the inner cavity, which affects the subsequent penetration ability of the jet. Within this article, a single-cell structure filled with water is take as the research target. Through numerical simulation, the process of shaped charge jet penetrating the single-cell structure at different liquid level is reproducing, and the parameters of the remaining jet after penetration, the interference of jet, and the deformation and energy absorption of shell are obtained. The results showed that the liquid level of liquid-filled single-cell structure has a significant influence on the anti-jet penetration ability of the single cell structure. When the liquid level was 60mm to 65mm, the water-filled single-cell structure has the best interference effect on the incoming shaped charge jet.

Study on the influencing factors of underwater unexploded ordnance destruction based on shaped charged jet

In order to study the influence of the stand-off distance and the waterproofness on the penetration effect of liner shaped charge (LSC) jet to destroy underwater unexploded ordnance, the LS-DYNA finite element program was applied to simulate the process of the metal jet formation and penetration into steel plate under different stand-off distances and waterproof condition. On the basis, the model experiment was carried out. And combing the experimental and numerical result, it can be found that, if no waterproof measures is adopted the metal jet will directly get contact with the water, the unexploded ordnance will not be successfully destructed, moreover, with the increase of the stand-off distance, the shaped charge jet works more ineffectively.

Formation Regularity of Annular Shaped Charge Jet by Numerical Simulation

Formation process of an annular-shpere liner driven by shaped charge has been studied using AUTODYN numerical simulation software. Research works of factors, including length to diameter ratio of charge, detonation radius and distance between liner and shell, that affect the jet head velocity, deflection angle, and head diameter have been implemented. The results show that the liner driven by shaped charge initiated annularly will be shaped into a annular jet which can form a large-diemeter hole on the target, while the liner forms a converged jet when shaped charge is centrally initiated. As the ratio and the initiation radius increase, the jet diverges; as the distance between the liner and the shell increases, the jet converges.

Numerical simulation to determine the shaped charge jet-slug interface

In order to determine the interface of shaped charge jet-slug, numerical simulation of the shaped charge jet forming process is carried out by non-liner finite element numerical simulation. A plurality of gauge points is arranged in the thickness of the liner, and the velocity and pressure time history of different gauge points is obtained in the jet forming stage. The result show that in the process of shaped charge jet formation, obvious velocity and pressure difference in gauge point is observed. By dividing the boundary between the slug and jet of different sets of gauge points, the corresponding area of jet and slug can be determined on the liner. The numerical simulation to determine the shaped charge jet-slug interface can be used to evaluate the performance of different shaped charge design and provide guidance for shaped charge design.