Copper Shaped Charge Jets Research Articles

Explosively Formed Penetrators Inflight Heating Compared to Hemispherical Copper Shaped Charge Jet

Explosively Formed Penetrators Inflight Heating Compared to Hemispherical Copper Shaped Charge Jet

Jet formation and penetration performance of a double-layer charge liner with chemically-deposited tungsten as the inner liner

This paper proposes a type of double-layer charge liner fabricated using chemical vapor deposition (CVD) that has tungsten as its inner liner. The feasibility of this design was evaluated through penetration tests. Double-layer charge liners were fabricated by using CVD to deposit tungsten layers on the inner surfaces of pure T2 copper liners. The microstructures of the tungsten layers were analyzed using a scanning electron microscope (SEM). The feasibility analysis was carried out by pulsed X-rays, slug-retrieval test and static penetration tests. The shaped charge jet forming and penetration law of inner tungsten-coated double-layer liner were studied by numerical simulation method. The results showed that the double-layer liners could form well-shaped jets. The errors between the X-ray test results and the numerical results were within 11.07%. A slug-retrieval test was found that the retrieved slug was similar to a numerically simulated slug. Compared with the traditional pure copper shaped charge jet, the penetration depth of the double-layer shaped charge liner increased by 11.4% and >10.8% respectively. In summary, the test results are good, and the numerical simulation is in good agreement with the test, which verified the feasibility of using the CVD method to fabricate double-layer charge liners with a high-density and high-strength refractory metal as the inner liner.

Investigation on the grain size effect on the copper shaped charge jet stretching behavior

The grain size effect on the shaped charge jet (SCJ) stretching process was analytically formulated and experimentally verified by penetration tests. The present analytical model predicts an optimum grain size for the SCJ performance, deduced from the concurrent effect of grain size on flow stress, strain rate sensitivity, and surface roughness. Specifically, reducing the grain size will improve the initial surface roughness and decrease the initial perturbation amplitude, favoring the SCJ stretching. On the other hand, the strain rate sensitivity and flow stress for copper increase with the decrease of grain size, facilitating the perturbation growth and leading to a premature breakup. Thus, the present analytical model predicts that the optimum grain size of the SCJ is about 1–5 μm. The penetration test verified that the shaped charge liner with an average grain size of about 3.6 ± 2.5 μm exhibited the largest penetration depth. The consistent results from the analytical model and the penetration experiments certify the feasibility of the present analytical model on the SCJ performance.

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.

Deformation and acceleration of Zn and Cu liners under explosive shock loading

Both zinc and copper shaped charge jets (SCJs) generated from conical liners under explosive shock loading were observed using soft flash x-ray radiography. The goal was to ascertain the effect of the liner material melting point on the jet features and density. An analytical method termed in situ mass analysis from x-ray image processing (i-MAX) was utilized to estimate the mass and apparent density of each SCJ in this study. The masses determined for the zinc and copper leading jets were (34 ± 2) mg and (68 ± 3) mg, respectively. The overall mass distributions of both the zinc and copper SCJs showed the same tendency to decrease toward the tip of the jet, with the exception of the leading jet. The density distribution of the zinc SCJ gradually decreased toward the leading jet as it stretched. In contrast, the density distribution of the copper SCJ varied depending on the appearance of a necking region, and the minimum apparent density was observed 30 mm from the leading jet. These results demonstrate that the occurring of cavitation or vacancy avalanches in metal jet depend on the melting point of the liner material.

Effects of equations of state and constitutive models on simulating copper shaped charge jets in ALEGRA

We investigate the effects of copper equations of state and constitutive models on simulations of shaped charge jets using the Sandia National Laboratories’ multiphysics hydrocode, ALEGRA. Specifically, we compare (1) the 3320, 3325, 3331, and 3337 SESAME copper equations of state (EOS), and (2) Johnson–Cook, Zerilli–Armstrong, Preston–Tonks–Wallace, Steinberg–Guinan–Lund, and Mechanical Threshold Stress constitutive models. Several of these cases are also compared against photon Doppler velocimetry measurements of the tip velocity. Lagrangian tracer particles are used to follow a part of the jet's evolution in state space for the various models. We monitored the jet topology and found that the various EOS produce similar results, although the 3325 model generates a cavity near the jet tip whose size decreases with increasing mesh resolution. Constitutive models generated more noticeable differences. We found the SGL and PTW models produced higher temperatures while the MTS and JC models returned very similar results at lower temperatures. The SGL model was the only strength model that reported a liquid region along the axis of the jet. For all material models, we found similar results for the velocity history of the jet tip as measured against experiment using photon Doppler velocimetry.

In-flight Conductivity and Temperature Measurements of Hypervelocity Projectiles

The conductivity and temperature of hypervelocity projectiles were studied using a novel magnetic diffusion analysis technique and five color radiometry. A copper shaped charge jet was fired through an electromagnetic coil to saturate the tip with a magnetic field. After leaving the coil, the tip passed through a series of sensing coils that are used to detect the magnetic field's decay rate, which depends on the geometry of the tip and its electrical conductivity. A mathematical model was then used to calculate the decay rate of the magnetic field from the tip and the signals produced by the sensing coils to determine the electrical conductivity. The resulting conductivity indicated that the tip of the shaped charge jet has a bulk temperature on the order of 1200K. The experimental data were directly compared to temperature distributions generated by hydrocodes using both the Johnson-Cook and Steinberg-Guinan-Lund strength models. Because the magnetic diffusion technique is extremely versatile, various projectiles over a broad dynamic range can be investigated. Thus, this measurement is compared to radiometry and diffusion measurements of explosively formed penetrators.

Specific features of interaction of a shaped-charge jet with a target

Coaxial interaction of a copper shaped-charge jet with a thin tungsten rod is considered. A theoretical model of spraying of the shaped-charge jet on the rod and results of experiments performed are presented.

Rebounding of a shaped-charge jet

The phenomenon of rebounding of a shaped-charge jet from the armour surface with small angles between the jet axis and the target surface is considered. Rebounding angles as a function of jet velocity are obtained in experiments for a copper shaped-charge jet. An engineering calculation technique is developed. The results calculated with the use of this technique are in reasonable agreement with experimental data.

Re-examination of the evidence for a failure wave in SiC penetration experiments

Previous work suggested the possibility that the effects of a failure wave, evidenced through a change in the slope of the penetration velocity vs. impact velocity ( u– v p) curve resulting from an increase in target penetration resistance, could be observed in penetration experiments of SiC. However, the previous work had to combine two different sets of experimental data, one using long tungsten rods and the other copper shaped-charge jets. A new set of experiments was conducted to address the uncertainties associated with combining the two disparate data sets. Analysis of the new experiments showed no evidence of a distinct change in the slope of the u– v p response of SiC, up to an impact velocity of 6.2 km/s. We re-examine the original data and analysis in light of the new experiments to understand the origins of the original misinterpretation.

Effects of liner grain size on shaped – charge jet performance: A combined experimental/numerical/analytical approach

Experimental data on the fragmentation of copper shaped-charge jets are presented. A combined numerical/analytical analysis is designed to describe shaped-charge jet break-up. The method overcomes drawbacks from exclusively numerical or analytical analyses, such as mesh sensitivity or oversimplified description. It yields predictions for break-up time, total number and cumulative length of fragments in fairly good agreement with the experimental data. The dependence of fragmentation characteristics in the liner grain size is well predicted, except for the leveling out of performances at very large grain size. A discussion is provided.

Breakup of Copper shaped-charge jets: Experiment, numerical simulations, and analytical modeling

Experimental data on the fragmentation of copper shaped-charge jets are presented and the techniques used for data processing are described. A combined numerical/analytical analysis is designed to describe shaped-charge jet breakup. The method overcomes drawbacks from exclusively numerical or analytical analyses, such as mesh sensitivity or oversimplified description. It yields predictions for break-up time, total number, and cumulative length of fragments in fairly good agreement with the experimental data. The dependence of fragmentation characteristics on the grain size in the liner is also well predicted.

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.

Experimental investigation of fast shaped-charge jets

The effect of various methods for producing a fast shaped-charge jet on the jet velocity is studied. Experimental results allow one to optimize the process of formation of fast shapedcharge jets. Spectra of a copper jet are obtained, and its temperature is determined. It is shown that fast copper shaped-charge jets can be used for quasi-cw lasing.

Possible detection of failure wave velocity using hypervelocity penetration experiments

Data for projectile penetration of silicon carbide (SiC) from two types of experiments are combined. For impact velocities, v, in the range 1.5 – 4.6 km/s the data are from reverse ballistic two-stage light-gas gun experiments with long tungsten rods. For impact velocities of about 5 – 7 km/s copper shaped charge jets are the projectile. The data exhibit an apparent inflection in the penetration velocity, u, versus impact velocity curve at u ≈ 3 km/s, corresponding to v ≈ 4.5 km/s. The apparent decrease in the slope of u versus v for u = 3 km/s, and the consequent rapid increase in the Alekseevskii and Tate target resistance term Rt with v is tentatively interpreted in terms of a failure wave in SiC. With this interpretation the propagation speed of the failure wave in SiC is about 3 km/s or 1 3 of the compressional wave speed.

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.

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.

Microtextural zones in a copper shaped charge particle

The microtexture of a soft-caught copper shaped charge jet particle is characterized using point specific measurements of crystallographic orientation. The results show a radial variation in preferred orientation that can be correlated to radial variations in grain size.

Experimental Evidence For Sulfur Induced Loss Of Ductility In Copper Shaped-Charge Jets

AbstractWe have observed that a change in the bulk sulfur content of oxygen-free electronic copper markedly affects its high temperature (400–1000°C), high strain-rate (> 103 s−1) deformation and fracture behavior. These conditions are typical of those found in "jets" formed from the explosive deformation of copper shaped-charge liners. Specifically, an increase in the bulk sulfur concentration from 4 ppm to 8 ppm shortens the breakup time, tb, of the copper jets by nearly 20% as measured using flash x-ray radiographs recorded during breakup of the jets. At bulk concentrations of 4 ppm, the jet was observed to be uniform and axisymmetric with a breakup time of 186 µs. Jet particles exhibited length-to-diameter ratios of roughly 8:1. The addition of sulfur transformed the jet breakup behavior to non-uniform, non-axisymmetric rupture and reduced the breakup time to 147 µs. The length-to-diameter ratios decreased to roughly 5:1 in the sulfurdoped samples. Previously measured sulfur solubilities and diffusivities in copper at the temperatures where this material was processed indicates nearly all of the sulfur was localized to grain boundaries. Therefore, we infer that the increase in sulfur content at grain boundaries is directly responsible for the change in breakup performance of the shaped-charge jets.

Analysis of Strains, Strain Rates and Temperatures during the early stages of shaped charge liner collapse

AbstractIn trying to understand the extraordinarily high dynamic ductility of a copper shaped charge jet, prior work by the authors has utilized the Eulerian MESA 2D code with a novel form of the LaGrangean tracer particle technique as well as the experimental “soft recovery” and metallurgical examination of partially collapsed copper liners.This work had indicated that localized material processing occurs during the earliest stages of liner collapse and causes dramatic visible grain size refinement, evident in the photomicrographs. Further computational analysis shows that the localized plastic flow is accompanied by very high localized engineering strains (>200), extremely high (>4 × 107 s−1) localized strain rates, as well as elevated temperatures, all of which favor a dynamic recrystallization process.In this paper, the focus is on a detailed quantitative analysis of strain, strain rate and temperature distribution history within the collapsing liner, in the region of the inner liner apex and the early location of the moving collision zone, where the early material conditioning first occurs. Correlations are sought between the computed, time‐dependent values of these three paremeters and the microstructures observed in the interiors of the partially collapsed liners, in those regions where the grain size changes are observed. This data may ultimately permit quantitative comparisons with the predictions of dynamic recrystallization models.