Explosively Formed Projectile Research Articles

Microstructure evolution and deformation mechanism with comparison of Ta-2.5 W and Cu under detonation load

The comparison of microstructure evolution of Cu and Ta-2.5 W liner during explosively formed projectile (EFP) formation was studied. The electron backscatter diffraction method (EBSD) was used to statistically characterize the microstructure of the liner before and after deformation. Both recycled EFPs show strong fiber texture and different degrees of recrystallization. The center of the recycled Cu EFP has strong <001> and <111> preferred orientations along the EFP axis, and the density of the texture changes with the deformation strain. Cu EFP has extensive dynamic recrystallization, up to 88%, which is considered to be a traditional dynamic recrystallization mechanism, the temperature is the main controlling factor in the refinement process. On the contrary, the recycled Ta-2.5 W EFP has a strong <101> fiber preferred orientation, and almost no dynamic recrystallization occurs, large strain deformation is the main factor for the microstructure fragment.

Study on ballistic performance of metal matrix ceramic ball composite

Different metal matrix ceramic composite plates were manufactured using different diameter ceramic balls. The ballistic resistance of these composite plates were investigated by firing 12.7mm, 25mm armor-piercing incendiary (API), and 200 standard explosively formed projectile(EFP). The tests results showed that these ceramic balls with higher mechanical properties performed better ballistic resistance, in the meantime, there was a correlation between diameters of the ceramic balls with projectile caliber. The quality protection factor of composite plate using 2mm diameter ceramic ball against 12.7mm armor-piercing incendiary (API) is better than 2.2; The mass effectiveness factor of composite plate using 6mm diameter ceramic ball against 25 mm armor-piercing incendiary (API) is better than 1.7; The quality protection factor of composite plate using 6mm diameter ceramic ball against 200 standard explosively formed projectile(EFP) is better than 3.5.

Research on the formation behavior of PTFE/Al reactive explosively formed projectile

Based on AUTODYN-3D finite element analysis platform, the SPH algorithm is used to simulate the forming characteristics of Al/PTFE reactive Explosively Formed Projectile (EFP). The evolution behaviors and distribution of morphology, velocity, density, and temperature field during the reactive EFP were analyzed. Numerical simulation results show that Al/PTFE reactive shaped charge can form stable reactive EFP, and the overall density of reactive EFP decreases with the extension of the forming time, and the density of reactive EFP is much lower than the initial density of reactive liner. When the reactive EFP is in the state of freely flying, the high temperature region mainly concentrates on the tail of the reactive EFP, the bottom of the reactive liner and the fracture flying zone, and the high temperature region proportion is significantly affected by the explosive type, the curvature radius of the reactive liner and the wall thickness of the reactive liner.

Energy Spatial Distribution of Behind-Armor Debris Generated by Penetration of Explosively Formed Projectiles with Different Length–Diameter Ratio

To understand the influence of the length–diameter ratio (L/D) of explosively formed projectiles (EFPs) on the energy spatial distribution of behind-armor debris (BAD), three EFPs with different L/Ds were designed in this study. The scattering characteristics of the BAD formed by the EFP penetrating a steel target were investigated. High-speed photography was used to observe the shape of the BAD cloud. Fiber and foam plates were sequentially stacked to recover the fragments. The three-dimensional damaged area by the BAD was obtained based on the spatial position information of a large amount of BAD. Finally, the energy spatial distribution characteristics of the EFP and target material fragments were analyzed. The results showed that a large EFP L/D increased the total energy of the BAD, and the proportion of the energy of projectile fragments increased. The difference in the energy spatial distribution between EFPs with varying L/Ds was mainly in the scattering angle range of 3–17°. The total energy of fragments within 17° of scattering angle accounted for 85% of the total energy of all fragments. The BAD energy of the EFP with a large L/D (L/D = 3.86) was concentrated in a small scattering angle range in which the residual projectile was located. The average projectile fragment energy of the EFP with a moderate L/D (L/D = 2.4) was evenly distributed in the scattering angle range of 5–20°. As a result, the energy distribution of the BAD from EFP (L/D = 2.4) shifted towards the large scattering angle, thus leading to a uniform radial distribution of the striking area within the range of 500–1100 mm behind the target. However, with the increase in the distance behind the target, the radial direction of the striking area of the other two EFPs was gradually reduced. The reason was explained according to the force analysis of the fragments resulting from the bulge fracture of target. The spatial energy distribution of BAD is closely related to the damage ability of EFP in relation to the armored target. Thus, it is necessary to design EFPs with appropriate L/Ds in order to maximize the damaging effect behind the armor.

Damage Effects of Shaped Charges on Concrete Piles

Concrete piles are a common obstacle in an antilanding obstacle field. To research the damage ability of concrete piles with different shaped charges, penetration tests of concrete piles with different standoff distances (SODs) were carried out with explosively formed projectiles (EFPs) and jetting projectile charges (JPCs). The pressure was measured at different positions inside the concrete piles during the penetration process, and the failure mechanism and damage characteristics of the concrete piles were analyzed. The penetration velocity of the JPC was measured by placing reticular targets inside the concrete pile. The results show that the damage ability of JPCs to concrete piles is stronger than that of EFPs. When the SOD is in the range of 20∼50 cm, an EFP causes slight damage to a concrete pile. With the increase in SOD, the penetration capacity of JPCs increases, but the damage ability of JPCs decreases. When the SOD is 15 cm, a JPC causes severe damage to a concrete pile, and when the SOD is in the range of 20∼40 cm, a JPC causes moderate damage. When attacking targets with obvious side boundary effects, such as concrete piles, the SOD that results in the strongest damage is not the SOD that results in the strongest penetration ability.

Formation Behaviors of Coated Reactive Explosively Formed Projectile.

The formation behavior of coated reactive explosively formed projectiles (EFP) is studied by the combination of experiments and simulations. The results show that the coated EFP can be obtained by explosively crushing the double-layer liners, and the simulation agrees with the experiment well. Then, the interaction process between the two liners is discussed in detail, and the formation and coating mechanism are revealed. It can be found that there are three phases in the formation process, including the impact, closing and stretching phases. During the impact phase, the velocities of two liners rise in turns with the kinetic energy exchange. In the closing phase, the copper liner is collapsed forward to the axis and completely coats the reactive liner. It is mentioned that the edge of the copper liner begins to form a metal precursor penetrator in this stage. During the stretching phase, the coated reactive EFP is further stretched and fractured, resulting in the separation of the metal precursor penetrator and the following coated reactive projectile. Further studies show both the edge thickness and the curvature radius of the copper liner have significant influences on formation behaviors. By decreasing the edge thickness or the curvature radius, the difficulty of closing decreases, but the tip velocity and the length of precursor penetrator increases. As the thickness and diameter of the reactive liner decrease, the coating velocity increases slightly, but the total length of coated reactive EFP tends to decrease.

Orthogonal optimization design and experiments on explosively formed projectiles with fins

In this study, a polygonal shell is used to produce an explosively formed projectile (EFP) with fins for good flight stability. The forming characteristics of an EFP with fins produced by a polygonal shell are studied numerically using the LS-DYNA 3D finite element code. Orthogonal design method combined with range analysis is applied to optimize the EFP with fins. The orthogonal test schemes are established with 5 levels under plane initiation of 0.2 times the charge diameter and point initiation, respectively. The influence rankings of the EFP length-to-head diameter ratio, compactness, velocity, kinetic energy and length of fin-to-tail radius ratio are determined. Furthermore, the EFPs of the optimized design are tested for forming and recycling. Subsequently, the EFPs recovered from the tests are reconstructed. Finally, an EFP penetration performance test is conducted. When ignoring the influence of EFP initial state on target penetration, Steinberg and Johnson-Cook (J-C) constitutive models are used for the formation and penetration processes, respectively. The results show that the forming effects of EFPs with fins are coupled by the structure of liner, charge arrangement and shell structure. The ranges of the various structural parameters of the EFPs are obtained. The numerical simulation results of EFP with fins designed by orthogonal optimization method are in good agreement with the experimental results. The effectiveness of Steinberg algorithm and J-C algorithm in EFP forming and penetration process is verified.

Damage of a large-scale reinforced concrete wall caused by an explosively formed projectile (EFP)

To quickly break through a reinforced concrete wall and meet the damage range requirements of rescuers entering the building, the combined damage characteristics of the reinforced concrete wall caused by EFP penetration and explosion shock wave were studied. Based on LS-DYNA finite element software and RHT model with modified parameters, a 3D large-scale numerical model was established for simulation analysis, and the rationality of the material model parameters and numerical simulation algorithm were verified. On this basis, the combined damage effect of EFP penetration and explosion shock wave on reinforced concrete wall was studied, the effect of steel bars on the penetration of EFP was highlighted, and the effect of impact positions on the damage of the reinforced concrete wall was also examined. The results reveal that the designed shaped charge can form a crater with a large diameter and high depth on the reinforced concrete wall. The average crater diameter is greater than 67 cm (5.58 times of charge diameter), and crater depth is greater than 22 cm (1.83 times of charge diameter). The failure of the reinforced concrete wall is mainly caused by EFP penetration. When only EFP penetration is considered, the average diameter and depth of the crater are 54.0 cm (4.50 times of charge diameter) and 23.7 cm (1.98 times of charge diameter), respectively. The effect of explosion shock wave on crater depth is not significant, resulting in a slight increase in crater depth. The average crater depth is 24.5 cm (2.04 times of charge diameter) when the explosion shock wave is considered. The effect of explosion shock wave on the crater diameter is obvious, which can aggravate the damage range of the crater, and the effect gradually decreases with the increase of standoff distance. Compared with the results for a plain concrete wall, the crater diameter and crater depth of the reinforced concrete wall are reduced by 5.94% and 9.96%, respectively. Compared to the case in which the steel bar is not hit, when the EFP hit one steel bar and the intersection of two steel bars, the crater diameter decreases by 1.36% and 5.45% respectively, the crater depth decreases by 4.92% and 14.02% respectively. The EFP will be split by steel bar during the penetration process, resulting in an irregular trajectory.

Formation of Shaped Charge Projectile in Air and Water.

With the improvement of the antiknock performance of warships, shaped charge warheads have been focused on and widely used to design underwater weapons. In order to cause efficient damage to warships, it is of great significance to study the formation of shaped charge projectiles in air and water. This paper uses Euler governing equations to establish numerical models of shaped charges subjected to air and underwater explosions. The formation and the movement of Explosively Formed Projectiles (EFPs) in different media for three cases: air explosion and underwater explosions with and without air cavities are discussed. First, the velocity distributions of EFPs in the formation process are discussed. Then, the empirical coefficient of the maximum head velocity of EFPs in air is obtained by simulations of air explosions of shaped charges with different types of explosives. The obtained results agree well with the practical solution, which validates the numerical model. Further, this empirical coefficient in water is deduced. After that, the evolutions of the head velocity of EFPs in different media for the above three cases are further compared and analyzed. The fitting formulas of velocity attenuation of EFPs, which form and move in different media, are gained. The obtained results can provide a theoretical basis and numerical support for the design of underwater weapons.

Research on Numerical Simulation of Tantalum Explosively Formed Projectile Forming Driven by Detonation

In order to study the formation characteristics of tantalum explosively formed projectile (EFP), based on LS-DYNA finite-element software, this article analyzes the influence of mesh size on tantalum EFP forming, compares the accuracy of JC constitutive parameters in different literature on the characterization of tantalum EFP forming, calculates the effective action time of detonation that drives EFP formation, and carries out experimental verification. The results show that the EFP forming velocity was less sensitive to grid size; however, the EFP shape was highly sensitive to grid size, among which the liner had the greatest influence. Besides, for the same density and different constitutive parameters, the velocity of the stabilized EFP was the same, but the change trend of velocity was different, which led to the difference in morphology. The verification test showed that a selection of appropriate JC constitutive parameters could simulate tantalum EFP forming. Finally, the effect of detonation products on EFP forming was reflected mainly in the axial acceleration and radial contraction of the tail skirt. The influence of explosives and detonation products on EFP forming can be ignored 80 μs after the charge detonates. In this work, the numerical simulation method of tantalum EFP forming was studied, which provides guidance for the design and engineering application of tantalum EFP.

Microstructure Evolution and Deformation Mechanism of Tantalum-Tungsten Alloy Liner under Ultra-High Strain Rate by Explosive Detonation.

The microstructure evolution and plastic deformation mechanism of a Ta-2.5W liner under the ultra-high-strain-rate conditions generated by the explosive detonation were investigated in this study. For this purpose, a modular soft-recovery apparatus was designed to non-destructively recover the Ta-2.5W explosively formed projectile (EFP) in the ballistic endpoint. The electron backscattered diffraction (EBSD) method was employed to examine the microstructure of the Ta-2.5W liner before and after deformation. The microstructure of the recovered EFP exhibited significant grain refinement with preferred fiber texture. The theoretical computation results showed that the temperature of the EFP was in the range of 0.27–0.65 Tm. The deformation mechanism of the Ta-2.5W liner forming EFP driven by the detonation is the continuous dynamic recrystallization (CDRX) induced by high strain deformation, rather than the conventional dynamic recrystallization of nucleation and growth. The new grain structures evolve when the low-angle grain boundaries are transformed into the high-angle grain boundaries, and the specific grain refinement mechanism is the progressive rotation of subgrains near pre-existing grain boundaries.

Explosively Formed Projectile from Stepped Casing Shaped Charge: Formation Mechanism of Canted Fins

ABSTRACT Canted fins can significantly improve the flight stability and the on-target accuracy of Explosively Formed Projectiles (EFP). The current work uses the effective charge theory to derive the formation of periodic tails from shaped charge with stepped casing by considering the detonation impulse. According to the established model, the distribution of velocity along the circumference of the liner increases linearly with the square root of the casing thickness. There are two stages in the formation of canted fins influenced by the stepped casing: (1) the distribution of velocity along the circumference of the liner upon initiation, and (2) the torsion and folding of the liner edge during deformation. Numerical simulation was carried out with LS-DYNA for shaped charge (56 mm in diameter) with regular and stepped casing. The expansion of the casing and the deformation of the liner with velocity distribution at initial times were compared between the regular and the stepped casing. The distribution regularities and the final velocity of the canted fin EFP from the simulation agree well the established velocity distribution model. Soft recovery experiments were also carried out to prove the feasibility of using shaped charge with stepped casing.

Effect of material characteristics of explosive on formation of collinear explosively formed projectile from warhead with double layer liners

In order to obtain the effect of material characteristics of explosive on the formation of collinear explosively formed projectile (EFP)from warhead with dosuble liners, the LS-DYNA simulation software was used to simulate and analyze the forming process of collinear EFP from warhead with five explosive materials including pe4booster, PETN, TNT, C4 and B explosives. The results indicate that with the increase of density, detonation velocity, and detonation pressure, the velocity and the length diameter ratio of the front EFP and rear EFP increase with different laws. With the increase of explosive material density, the velocity and the length diameter ratio of EFPs increase gradually, but the increasing rate decreases gradually. As the detonation velocity increases, the velocity of EFPs increase gradually, but the increasing rate decreases gradually. The length diameter ratio of EFPs decreases first and then increases gradually, showing an "s"-shaped change law. With the increase of explosive detonation pressure, the velocity of EFPs increase gradually, but the increasing rate decrease gradually. The length diameter ratio of the front EFP shows a parabolic growth law with the increase of detonation pressure, and the length diameter ratio of the rear EFP shows an "s"-shaped change law with the detonation pressure.

Dynamic Response and Numerical Interpretation of Three Kinds of Metals for EFP Liner under Explosive Loading

In order to study the dynamic response of tungsten heavy alloy materials under explosive loading, two kinds of typical tungsten alloys for explosively formed projectile (EFP) liner and one kind of existing EFP liner were tested in a flash X-ray experiment, with copper liner as a reference. Results showed that copper liner could form a coherent EFP, while 90W–9Ni–Co and W–25Re liners fractured to different extents. The microscopic features of the three kinds of metals were examined and compared with the original liner, and the microstructure evolutions under explosive loading were analyzed with the fracture model and mechanism of the two kinds of tungsten alloys’ fracture determined. Associated with the stress and strain conditions by numerical simulation, the fracture mechanism of tungsten heavy alloys can be analyzed. The crack-tip plastic zones of 90W–9Ni–Co and W–25Re are much smaller than copper, and due to the severe stress concentration at the tip of cracks, it is easy for cracks to propagate and trigger the cleavage in tungsten alloys. The value of a crack-tip plastic zone r(θ) can be used to explain the fracture phenomenon in explosive loading, which can be an alternative guideline for the material selection criteria of the EFP liner. The research results are significant in understanding the dynamic forming, microstructure evolution, and fracture mechanism of tungsten heavy alloys.

Numerical simulations of the formation behavior of explosively formed projectiles

Explosively formed projectile (EFP) is a self-forging shape charged structure having very high penetration ability compared to conventional kinetic energy projectile. The penetration capability of an EFP is strongly dependent on various design parameters. The main parameters can be roughly divided into geometric and material parameters used in the warhead configuration.&#x0D; The present research is an effort to study the effect of metal casing thickness, type of metal used for casing, explosive type, liner thickness, type and configuration on the formation of EFP. Effectivness of an EFP is studied in terms of final velocity and shape of formed penetrator. The study is carried out by performing a number of simulations by using explicit finite element (FE) hydrocode ANSYS/Autodyn.

Mechanism analysis and prediction of explosive formed projectile’s axial fracture

To explain the axial fracture phenomenon of Explosively Formed Projectile (EFP), the fracture mechanism of long rod EFP during the forming phase is analyzed by the stress wave theory. When the velocity gradient [Formula: see text] between the head and tail parts exceeds the critical value [Formula: see text], the EFP would fracture in the axial direction. Based on the Johnson–Cook constitutive model parameters and the special conditions in the forming phase of EFP, the critical velocity gradient [Formula: see text] can be determined by theoretical calculation and then validated by experimental results for both copper and tantalum EFPs. The experimental results for EFP’s fracture agree well with the prediction of the theoretical analysis. The theoretical analysis method can be applied as an important measure to determine the critical velocity gradient and predict the fracture of long rod EFP, providing reference for the application of new kinds of high density materials in the EFP research area.

Numerical simulation study on collinear EFP from warhead with double layer liners penetrating into target

In order to improve the penetration efficiency of the traditional explosively formed projectile (EFP) warhead, a new warhead with double layer liners formed collinear EFP was designed. In order to get the law of its formation and penetration into different type target, the process of the collinear EFP from warhead with double layer liners forming and penetrating into targets was simulated by using LS-DYNA software. It is obtained that the double layer liners formed two EFPs with different axial velocities under the action of detonation wave, and the velocity of the front EFP is higher than that of the rear EFP, which makes the front EFP and rear EFP separation during the flight, so it can effectively attack the reactive armor. For finite thickness target, the front EFP can effectively penetrate the hole on the target, and the rear EFP will enlarge the hole. For infinite thickness target, the collinear EFP can effectively increase the penetration depth. Compared with the single EFP, the collinear EFP from warhead with double layer liners can increase the penetration depth by 36 %.

Research advances in circumferential multiple linear explosively-formed projectile technology

The traditional fragmental warhead used in air defense and antimissile can not effectively destroy the incoming insensitive ammunition due to the weak fragmentations, which limits its development. After explosion of the circumferential multiple linear explosively-formed projectile (MLEFP) warhead, a number of folded linear explosively formed projectiles (LEFP) are produced in the circumferential direction with high speed, large mass and large length to diameter ratio. These projectiles can penetrate thick cases and ignite insensitive ammunitions, so the MLEFP warhead has a great application prospect in the medium-short range air defense and anti-missile system. Based on the development of linear projectile and the forming method of new LEFPs, the influences of charge and liner are focused on. Theories, merits and demerits of three initial velocity models are compared. The results of penetration tests using folded LEFPs in recent years are summarized. Finally, the future development direction of circumferential MLEFP warhead and linear projectile is analyzed.

Numerical Simulation of Tantalum-Tungsten Alloy for Forming Characteristics of EFP with Liner of Different Tungsten Contents

By LS-DYNA hydrocode, the EFP (Explosively Formed Projectile) forming characteristics of tantalum tungsten alloy are simulated. The EFP forming characteristics of tantalum tungsten alloy with different W contents under typical charge structure are obtained. The curvature range of the liner required for forming solid rod shaped EFP with large aspect ratio is determined, and the influence of tantalum tungsten alloy material’s constitution parameters on EFP forming is analyzed. The forming patterns of tantalum tungsten EFP with different tungsten contents are similar, but the range of outer curvature required for forming a solid EFP is different. The research results can provide references for EFP design and lay foundation for the application of high density tantalum tungsten alloy in the intelligent and smart ammunition.

Numerical Simulation of Multiple Explosively Formed Projectile Warhead Forming Characteristics considering Various Materials

To study the influence of different liner structures and materials (copper, steel, and tungsten) on the forming characteristics of multiple explosively formed projectile (MEFP) with integrated liner and shell designs, three types of liners with different structures were designed. LS-DYNA was used for numerical simulation, and the results show that the thickness change at the center of the liner has no obvious influence on the shape of the explosively formed projectile (EFP). However, the curvature radius of the liner has a significant influence on the shape of the EFP. When the liner material is copper and the curvature radius of the liner is greater than 8 mm, the EFP shape approximates an ellipsoidal or hemispherical shape and the EFP forming speed is between 1900 m/s and 2400 m/s. When the material of the liner is steel or tungsten and the curvature radius of the liner is thicker than 8 mm, the liner is not able to form projectiles in the shape of a sphere, ellipsoid, or long rod. By comparing the forming speed from 1#EFP to 4#EFP, it can be said that MEFP with integrated liner and shell design displays a certain pressurization effect. Research results show that, for small-caliber MEFP warheads, subject to the size of the warhead, when the liner is steel or tungsten, the detonation energy generated by the limited charge does not result in the liner forming an effective EFP. However, when the liner material is selected as copper, the EFP forming shape and speed are more appropriate.