Solid Projectile Research Articles

Theoretical and Experimental Modeling of Real Projectile Flight Heating

A projectile with a conical nose e ying at Mach number M1 >1 in the atmosphere develops a bow shock around its nose by which the incoming aire ow is turned parallel to the projectile surface. Across the shock wave, the air is compressed,heated,andacceleratedfromupstreamairpressure p1 ,upstreamairtemperature T1 ,andu1 ,which is equal to the projectile e ight velocity up, to the downstream parameters pe, Te, and ue. Consequently, a heat e ux develops from the hot aire ow along the projectile surface which is directed into the projectile material. This heat e ux causes a temperature increasethat depends on the projectile speed, the e ight time, thestructure of the surface material, and its geometry. A boundary-layer model is applied, and the gas heat e ux into the projectile nose cone is analytically determined. To predict the heating of the solid projectile cone, an analytical solution, coming from the heat conduction equation, is used to obtain thesurface temperature distribution. Experimentally theprojectile e ight in the atmosphere is modeled in a worldwide unique aerothermoballistic high-pressure facility built at the French‐German Research Instituteof Saint-Louis, where the heating during several seconds of atmospheric e ight is duplicated with a e ight in compressed gas resulting in the same heat e ux for a e ight time of some milliseconds. In this facility the cone surface temperature is measured by detecting the intensity of the infrared emission coming from the cone surface.

Numerical and experimental study on the shaped charge for space debris assessment

This paper proposes a numerical analysis method to simulate jet formation and penetration process by the ‘low-velocity’ (6∼7 km/sec-class) inhibited shaped charge launcher, in order to assess the protection capability of the bumper structure against orbital space debris impacts on the spacecraft. The present simulations by a two-dimensional hydrocode (AUTODYN-2D), which was performed by an improved method on the basis of our former works, were compared with the test results based upon the experimental method that we had proposed in our another work. The both results were in fairly good agreement, and the feasibility was ascertained of the calibration between the inhibited CSC jet and solid spherical projectile by the numerical method. Consequently, the accuracy of the ballistic limit curve at 10∼15 km/sec is expected to be enhanced by making use of the present method hereafter.

A Laboratory Impact Study of Simulated Edgeworth–Kuiper Belt Objects

This paper reports on a series of laboratory impact experiments designed to provide basic data on how simulated Edgeworth–Kuiper belt objects (EKOs) fragment in an impact event. In September–October 1997 we carried out 20 low-velocity airgun shots at the Ames Vertical Gun Range into porous and homogeneous ice spheres using aluminum, fractured ice, and solid ice projectiles. We found that the porous ice targets behaved as strongly as solid ice in collision. Energy is apparently well dissipated by the void spaces within the target, such that these fragile ice structures respond as if they were strong in impacts. Therefore, it would appear that if EKOs are porous, they are not collisionally weak. Also, our data show that collisional outcomes for low-velocity impacts into ice targets depend on the type of projectile used as well as the properties of the target. We observed that the degree of fragmentation for a given type of target increases as the strength of the projectile increases. Aluminum projectiles are far more damaging to the target at the same collisional energy than are solid ice projectiles, which, in turn, are more damaging than fractured ice projectiles. One possible explanation for this behavior is the variable depth of penetration of the projectile for the different cases—stronger projectiles penetrate more deeply and couple more energy into the target than do weak projectiles. Based on this, if we assume that there has not been significant heating or differentiation in the Edgeworth–Kuiper (E–K) belt, the most applicable impact strength for the low-velocity E–K belt collisions is likely to be that derived from similar target/projectile materials impacting each other. The laboratory data from this analysis indicate that a value for impact strength>5×10 5 erg/cm 3 is appropriate for porous ice targets impacted with solid/porous ice projectiles.

Core and Rydberg State Populations for HCI Projectiles in Solids

Complete experimental studies of the production and transport of core and Rydberg nl states have been performed for Ar17+ at high velocity (v = 23 a.u.) on different carbon targets; a range of target thicknesses from single collision condition to equilibrium has been investigated. Considering the collision system chosen, two models, based on a collisional approach—a rate-equation model and a classical Monte Carlo simulation—can be applied and compared. Our calculations show that they both represent well the experimental Rydberg l state populations but fail to describe the core states (n = 2,3,4). The observed l-mixing for these states is much larger and faster than predicted. This discrepancy could possibly be explained by the Stark mixing induced by the projectile polarization of the medium, and neglected, thus far, in these two models.

Constrained local plasma density approximation for the calculation of the stopping power for slow ions in solids

A constrained local plasma density approximation is presented for the calculation of the stopping power of solids for slow ions. Using the density-functional theory with the local density approximation for exchangecorrelation in the scattering potential and the constrained local plasma density approximation for averaging over effective solid-state electron densities, the stopping power for slow hydrogen and helium projectiles in different solids are calculated. The obtained results of the stopping powers for slow H and He projectiles, and the stopping power ratio R5( 1 )@(2dE/dx)He /(2dE/dx)H# in some solids are in agreement with recent experimental predictions. @S0163-1829~98!02330-3#

Nonlinear calculations of the stopping power for slow hydrogen and helium projectiles in solids

The stopping powers for slow H and He projectiles in different solids are calculated using density-functional theory with local density approximation for exchange correlations in the scattering potential and the concept of local plasma density approximation for excitation channels. The calculated results for the stopping power ratio $R=(1/4)[(\ensuremath{-}{dE/dx)}_{\mathrm{He}}/(\ensuremath{-}{dE/dx)}_{\mathrm{H}}]$ in some solids are in agreement with recent experimental predictions.

A Study on the Large Ductile Deformations and Perforation of Mild Steel Plates Struck by a Mass—Part I: Experimental Results

An experimental study is reported on the ductile deformation and perforation of plates struck at the center by solid cylindrical projectiles having the longitudinal axis normal to the plate surface. The plates, which are made from 4 to 8-mm-thick mild steel sheet, are fully clamped around a circular boundary and are struck by projectiles having blunt ends and traveling with impact velocities within the range 7.7–118.9 m/s. Comparisons are made in Part II with the static perforation behavior and with previously published experimental results and several empirical equations for the impact case. A new empirical equation, which retains the influence of the impact velocity on the perforation energy, is also proposed in Part II.

Launching tactically configured solid armature projectiles from large and medium calibre railguns-results from the DRA test programme

One of the main thrusts of the United Kingdom EM gun programme is to prove the feasibility of accurate hypervelocity flight of projectiles launched from an EM gun. Several notable successes have been achieved in pursuit of this goal. To date DRA has carried out almost 70 large and medium calibre solid armature experiments using 40 mm and 90 mm round bore railguns. With one or two exceptions all firings have employed monolithic aluminium alloy armatures, the majority in base-push configuration. So far, approximately half of the shots have been full tactical packages with discarding sabots and long rod sub-projectiles flown over range. This paper presents results from these tactical package firings and observations on armature performance based on analysis of shot data and recovered specimens. Other gun issues that may be important to any future implementation of EML technology in a weapons system are also discussed.

Large calibre armature firings at Green Farm electric gun test facility

The DNA/Maxwell Laboratories SSG 90 mm Rail Gun has been used to fire a number of solid armature projectiles in conjunction with the United Kingdom, (UK) Defence Research Agency, (DRA). These projectiles have been fully tactical, discarding sabots rounds fired at short range into RHA steel targets. This paper gives details of those shots, the diagnostics used to capture the data and some of the design methodology behind the test. Visual recordings have been assisted in the analysis of the results, showing good sabot discard and flight characteristics. Velocities of over 2000 m/s have been achieved with fully discarding tactical packages and typical accelerating lengths. The tests have shown for a limited sample size, that EM projectiles can be launched as accurately as ones from a conventional powder gun, and that the differing launch conditions do not pose a major problem to the shot designers.

The use of a shotgun for the emergency slaughter or euthanasia of large mature pigs

The isolated heads of a Friesian bull and three large, Large White pigs were shot from various aspects with a 12-gauge shotgun using both a single 28 g solid lead projectile and buckshot, the latter consisting of nine individual lead pellets with a combined mass of 28 g. The sites of impact to the skull included the conventional frontal region, an occipital site and immediately behind the ear. A live mature Large White sow was shot with buckshot in the depression just caudal to the right ear, resulting in immediate insensibility and death. The damage caused to the isolated heads indicated that similar effects could be expected if the heads had been part of intact living animals. It is suggested that buckshot (nine lead pellets with a combined mass of 28 g) fired from a 12-gauge shotgun may be suitable for the emergency slaughter or euthanasia of a wide variety of domestic livestock and other species of animal.

Head-on collision opens 15–20 km/s opportunities

Velocity doubling in head-on collision of solid projectiles can practically be achieved with the use of electromagnetic launchers that permit precise synchronization of shots. Most promising for this purpose are so-called “fast” railguns operating in the regime of maximum constant acceleration limited only by strength of the projectile or electrode skin-layer explosion. No light-gas preaccelerator is used. This minimizes the acceleration path and the scatter of shot parameters. Our experimental system uses an augmented magnetic field and compacted plasma armature (PA); it launches two lexan cubes of 2 mm size (∼ 10 mg), at 5 km/s each, to head-on collision at relative velocity ∼ 10 km/s.The collision process in air is registered using the shadowgraph Toepler method on static film with high-speed camera with rotating mirror and a multipulse laser. Previously reported velocities of > 7 km/s for “fast” railgun launching 1 g projectiles can be further increased with making use of the compacted PA, which opens new prospects of the head-on-collision method for studying hypervelocity impacts and their applications.

Mid-push plasma armatures for long-rod electromagnetic gun projectiles

Ongoing research is addressing the concept of mid-pushing plasma armatures in large-bore rail guns. Testing began with solid Lexan projectiles which posed finite risk to the gun in the event of launch package breakup. Designs progressed to the launching of actual separating mid-riding aluminum sabots with steel projectiles representative of actual armor-penetrating flight-configured projectiles. The concept of launching mid-pushing sabots with plasma armatures was validated with these tests. A technique for deconvolution of signals from B-dot probes was developed to determine current distributions in the plasma armature. The technique has been applied to B-dot data from several tests. The results indicate a general tendency of the current to move aft of the projectile tail. This is fortunate, as it reduces the likelihood of arc attachment to conducting sabot/projectile structures and reduces the danger of generating extremely high unbalanced lateral pressures on the aft portion of the launch package.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Compressive Strength of Damaged and Repaired Composite Plates

Tests were performed assessing the effectiveness of repair in restoring the mechanical properties of damaged, solid composite plates made either of Fiberite T300/976 graphite-epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, or ICI APC-2 graphite-PEEK. The plate length, the layup and the amount of damage were also varied. Damage was introduced in the plates either by impacting them with a solid projectile or by applying a transverse static load. Some (75 % ) or all (100 % ) of the damaged zone was then cut out, and the plate was repaired by plugging and patching the hole. The effec tiveness of the repair was evaluated by measuring the compressive strengths of undamaged plates, damaged plates with no cutout, damaged plates with a cutout, and repaired plates. The data at an intermediate stage of repair (damaged plates with a cutout) provide informa tion on the effect of each repair step on the compressive strength. The results indicated that for the solid plates used in these tests, the repair methods used herein did not improve the compressive strength of already damaged plates.

Projectile penetration in granular soils : J Geotech Engng Div ASCE V117, N4, April 1991, P658–672

Results from centrifuge and 1-g model tests of projectile penetration into granular soils are described. Solid spherical projectiles in four calibers were fired into uniform samples of dry sand at approximately 305 m/s. Comparison to full-scale test results verified the suitability of the centrifuge testing technique for this type of problem. Power relationships between projectile penetration depth and projectile mass-to-area ratio are developed. Statistical analyses show that these functions describe the combined 1-g and centrifuge test results with a high degree of accuracy. Test results are compared to predictions of penetration depth based on Young’s equation. Suggestions for improvements in Young’s equation are made, including elimination of an arbitrary mass-scaling factor, use of a soil description based on physical properties of the soil, and use of a soil-specific exponent with the projectile mass-to-area ratio.

Magnetohydrodynamic wave drag

A calculation is made of the energy loss by emission of shear-Alfvén and slow magnetoacoustic waves by a perfectly conducting solid spherical projectile moving with uniform velocity through an ideal magnetoplasma.

Projectile Penetration in Granular Soils

Results from centrifuge and 1-g model tests of projectile penetration into granular soils are described. Solid spherical projectiles in four calibers were fired into uniform samples of dry sand at approximately 305 m/s. Comparison to full-scale test results verified the suitability of the centrifuge testing technique for this type of problem. Power relationships between projectile penetration depth and projectile mass-to-area ratio are developed. Statistical analyses show that these functions describe the combined 1-g and centrifuge test results with a high degree of accuracy. Test results are compared to predictions of penetration depth based on Young’s equation. Suggestions for improvements in Young’s equation are made, including elimination of an arbitrary mass-scaling factor, use of a soil description based on physical properties of the soil, and use of a soil-specific exponent with the projectile mass-to-area ratio.

Experimental results from CEM-UT's single shot 9 MJ railgun

A 10-m-long, 90-mm bore railgun has been designed and fabricated. During the test program, a number of solid armatures and projectile packages have been tested in a 50-m-deep vertical test range. The experiments are powered by six homopolar generator (HPG) charged inductive stores, sequentially staged to provide the desired acceleration profile. Prior to testing, computer simulations are run to determine the preferred current profile and predict system performance. During projectile flight, high-speed films, X-rays, muzzle volts, and velocity/acceleration profiles are recorded along with power supply operating parameters. Postshot diagnostics include bore wear analysis and armature and target recovery. Comparisons of predicted and recorded shot performance are also made. On selected tests, an energy balance is performed to determine efficiencies of the various components. A summary of all 90-mm gun shots is presented along the critical data collected from selected tests. >

Testing of a rapid-fire compensated pulsed alternator system

A compensated pulsed alternator (compulsator) has been designed and fabricated to drive a rapid-fire railgun system. Initial testing of the compulsator resulted in the failure of the compensation shield at full speed. An ambitious rebuild effort was undertaken, allowing testing to begin in August 1987. Since then, several rapid-fire shots have been performed, firing two 3 m guns at a 60-Hz repetition rate. A 65-g solid armature projectile was accelerated to 1.8 km/s during the initial tests with the compulsator operating at half-speed and reduced excitation. These preliminary results suggest a high probability that the compulsator rapid-fire system will meet and exceed the design goals.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Explosive-magnetic generators as power sources for railgun accelerators of solid projectiles

As the result of the conducted investigation within the framework of an electrotechnical model, requirements were set up for explosive-magnetic generators intended for use as energy sources for railgun accelerators of solid projectiles. The dependence of the generator inductance on the coordinates was determined such as to provide constant acceleration motion. Construction was completed on single and three-element plane MK generators which are able to provide this acceleration regime. Promising prospects were demonstrated for the use of multielement busbar and coaxial EMG's for supplying energy to railgun accelerators.

Soft acceleration of a metal plate by a rail gun plasma

The following situation is considered: A dense plasma armature which has been accelerated to a high velocity in a rail gun is allowed to impact a stationary metal plate. At impact, a shock wave is transmitted into the plate and a shock wave is reflected back into the plasma. For very high plasma velocities, the subsequent behavior depends primarily on the plasma density profile just prior to impact. The appropriate partial differential equations are analyzed in plane geometry and the conditions required to prevent spallation of the plate are determined. These results are compared with the "plasma only" armature plasma profiles predicted by Sloan, and it is shown that the conditions for not spalling the metal are well satisfied. The typical rail gun makes use of a low mass plasma armature to continuously accelerate a more massive solid projectile down the length of the rails. It has been suggested that substantially higher velocities and energies may be achievable with a "plasma only" rail gun-which has no solid projectile, but which has an armature mass comparable to the mass of a solid projectile. Subsequent to the acceleration, the momentum of this high velocity plasma must be transferred to a solid projectile. One way to do this is to simply allow the plasma to collide with the projectile. For this to be of interest, the projectile should not shatter and the energy transfer should be reasonably efficient. The purpose of the paper is to analyze an idealized model of such a collision.