Hypervelocity impact of rod projectiles with L/D from 1 to 32

Beside a short remark on the “hydrodynamic theory of rod projectiles”, the paper deals with the terminal ballistic behaviour of cylindrical projectiles against semi-infinite targets. Experimental data of EMI, completed by results of some other authors, are presented. Crater parameters like depth, diameter and volume and their dependence on projectile velocity (up to 5000 m/s), projectile and target material properties, as well as L/D-ratios (1–32), will be discussed. Mainly the projectile materials steel and tungsten sinter-alloys are considered. Target materials are mild steel and high strength steel, an Al-alloy and a tungsten sinter-alloy. The results show that the influence of material density on the crater dimensions is considerably greater than the influence of strength. The L/D ratio determines the velocity dependence of crater depth, diameter and volume. At high velocities in the hydrodynamic regime, the crater depth of short cylinders (L/D 1) is approximately proportional to v_p^2/3 (V_p=projectile velocity). With increasing L/D-ratio, the slope of the penetration curves decreases and converges for rods (L/D 1) versus a saturation, i. e. becomes nearly independent on v_p. A consequence of this saturation is the existence of a so-called “tangent velocity”, above which an optimal increase of efficiency is only realized by increasing the projectile mass and not the velocity. Furthermore, ballistic limits of real targets like single plates and symmetric double plates meteorite bumper shield) are taken into account. The expected better performance of “segmented rods” is also discussed.     

Debris clouds behind double-layer targets

It is demonstrated that the impedance mismatch and the order of the layers in two-layer sandwiches strongly influences the crater hole size formed in the target, the down-range debris cloud peak velocity, the fragment number and size, and the angles of downrange and uprange debris. Full and half scale test series with aluminum spheres of 10 mm and 5 mm diameter are performed with two-stage light gas guns against glued sandwiches of two layers at about equal areal density and different as well as equal shock impedances in the velocity range of 3–8 km/s. In the case of the titanium/tungsten plate sequence the transmitted shock wave is much stronger than for the tungsten/titanium target. This leads to a higher degree of fragmentation of the participated materials. For titanium/tungsten the hole diameter formed in the titanium layer is distinctly larger than in the tungsten layer for tungsten/titanium. For the titanium/tungsten target the larger crater diameter on the impact side is in agreement with the lower maximum debris cloud velocity.     

Experiments on the study of effect of microparticles anomalistic penetration into solid bodies

At certain conditions interaction between high velocity (up to 3 km/s) flows of microparticles with dimensions 20–70 μm and solid bodies could result in their super deep penetration (SDP) into those bodies. For SDP-effect to be studied a number of experiments were carried out. The X-ray analysis of microparticles acceleration has shown the advantage of acceleration of microparticles in mixture with the extender (porofor) because it makes it possible to regulate the flow density, its velocity and impact duration by means of the extender concentration variation. Experiments have been performed on the impact of microparticle flows with velocities in the range 1–2.6 km/s on copper and iron substrates. Results of metallographic investigations of cross-sectional and lengthwise grinds of substrates indicate that some tungsten particles penetrate into a target. The diameter of channels in the substrate material, which are formed due to particles penetration, is in the range 2–15 μm.     

The influence of confinement on the penetration of ceramic targets by KE projectiles at 1.8 and 2.6 km/s

This paper presents the results of scale size experiments using a tungsten-alloy long-rod projectile fired against 97.5% Al₂O₃ ceramic targets at 1.8 and 2.6 km/s. Two targets were used, one having lateral steel confinement; the other without. The projectile overmatched the target, and residual projectile length and velocity were recorded using ballistic-syncro photography. Flash radiography was used during penetration of the unconfined target to obtain the penetration velocity. Manganin pressure gauges were also used to obtain additional data on the response of the ceramic target during penetration. Results from the eight experiments indicate that the confinement reduced the residual energy of the projectile at both impact velocities. Expressed in terms of the projectile impact energy, 55–56% was lost in the unconfined target at 2.6 km/s compared with 60% for the confined design. The same trend was found at 1.8 km/s with 68% and 72–73% for the unconfined and confined, respectively. Predictions using the QinetiQ GRIM2D hydrocode and a simplified form of the Johnson–Holmquist ceramic material model agreed well with the experiments for three out of the four test configurations. The predicted projectile erosion and retardation against the confined target at 1.8 km/s was excessively high. Analytical predictions using the Tate modified Bernoulli equation also gave reasonably accurate predictions for three of the tests, but values for the Tate target ‘strength’ extracted from experiments using a different target configuration were not accurate for the target design used in this paper.     

The effect of phase changes on target response

This paper presents the results of two impact studies with lead projectiles and lead targets. Impact velocity varied between 2.65 and 8.3 km/s, a range of velocities that induces a range of response in lead from fragmentation to vaporization. The first study considers the response of a lead target to impact by a 1.5 mm tungsten carbide sphere. Target response measurements included crater parameters and target momentum. Normalized target momentum, i.e. the ratio of target to projectile momentum, was observed to increase non-linearly with impact velocity, obtaining a value of 7.1 at 8.3 km/s. The second study compares the response of a shielded aluminum target to impact by either a lead or molybdenum projectile (the shield material was the same as the projectile). Test variables included shield to target spacing, shield thickness, target orientation and impact velocity. The four test variables affected the two test conditions differently, with the most similar results observed for tests with thick shields, minimal spacing and low impact velocity.     

Measured charge generation by small mass impact at velocities between 1 and 45 km/s

The electrical charge that is generated by the impact of a small mass at velocities between 1 and 45 km/s was investigated using the Electrostatic Dust Accelerator of the Max-Planck-Institut in Heidelberg (MPI) and the Plasma Accelerator of the Lehrstuhl fu¨r Raumfahrttechnik (LRT) of the Technische Universita¨t Mu¨nchen (TUM). Glass beads were accelerated, and the targets were of different materials i.e., (Au, W, Fe, Al). The mass/velocity range of the accelerated small masses was: MPI: 10⁻¹⁵g−10g/ 1km/s−10g−5g/ 2km/s±_total of both polarities can be described by the empirical formula: Q^±_total =Cmv^β[Coulomb], C being a function of the density ratio of target/projectile, is approximately unity and β between 2.92 and 3.77. The charge detector is described and the results that were obtained in test series at both facilities are discussed in relation to the empirical formula.     

High velocity flyer plate launch capability on the Sandia Z accelerator

A method has been developed for launching plates useful for equation of state (EOS) studies to high velocities using fast pulsed power on the Sandia National Laboratories Z Accelerator. The technique employs magnetic pressure developed in an insulating gap between the anode and cathode of the machine to provide smoothly increasing, quasi-isentropic loading to plates of 9 – 12 mm in diameter and hundreds of microns thickness. Successful launches of titanium to 12km/s, aluminum to 13km/s, and copper to 10km/s have been demonstrated. The plates were monitored through the entire launch process with both conventional and spatially resolved velocity interferometry to obtain acceleration histories and impact profiles. Impacts of the flyers into aluminum wedges were also performed to experimentally estimate final plate thickness. Initial indications are that the plates are intact, slightly bowed, and at essentially ambient state.     

A study of damage in composite panels produced by hypervelocity impact

A phenomenological observation of the damage in graphite fiber (AS4/3501-6) composite panels caused by hypervelocity impact was made in this study. The panels have a nominal thickness of 2.54, 4.83, 6.6 and 17 mm. The impacts were made with nylon and aluminum projectiles of dimension 1.75 mm (dia) × 1.88 mm (length) with velocity from 3–7.5 km/sec. It was observed that the damage in the plate was caused by multiple breakage and delamination of the laminae and matrix material. The crater or hole area in all panels are approximately 7 to 9 times the area of projectiles for the velocity range used in the testing. The area of multiple breakage and delamination of layers in the panels are much larger than the corresponding crater or hole area, and they increase with the panel thickness and impact velocity.     

The impact of flat, thin plates on aluminum targets in the 5–10 km/s velocity range

The purpose of the study was to investigate the effect of the impact of a thin membrane on aluminum in the velocity range 6–10 km/s. The impulsive load delivered by a membrane impact will exceed the momentum/area of the membrane because of rebound, blow-off of vaporized membrane material, and ejection of molten and fractured material from the target (impulse gain). One of the objectives of the study was to quantify the impulse gain in the velocity range of interest. Also of interest was the physical damage to the target including spall, melting and fracture. Understanding these damage mechanisms is important for protecting spacecraft from the impact of space debris and meteoroids.

Simple theories account for the flyer rebound, but hydrodynamic modeling is required to treat the blow-off of target material. At lower velocities, the blow-off is negligible, but at10 km/s calculations show it to be equal to the rebound momentum for one-dimensional (1-D) impacts. The modeling of three-dimensional (3-D) experiments revealed large effects at the edge of an impacting membrane, prompting an emphasis on 1-D pressure profile experiments.     

Reverse impact experiments against tungsten rods and results for aluminum penetration between 1.5 and 4.2 km/s

Reverse impact experiments against 0.76 mm diameter L/D = 20 tungsten rods have been conducted with a 38 mm diameter launch tube, two-stage light-gas gun using four 450 kV flash X-rays to measure penetration rates. Techniques for projectile construction, sample placement, alignment, and radiography are described. Data for penetration rate, consumption velocity, and total penetration were obtained for 28 mm diameter 6061-T651 aluminum cylinders at impact velocities between 1.5 and 4.2 km/s. It was found that penetration velocity was a linear function of impact velocity over this velocity range. Above 2 km/s impact velocity, penetration was completely hydrodynamic. There was substantial secondary penetration, and the total penetration increased linearly with impact velocity over the range 1.5 to 2.5 km/s.     

The dependence of penetration velocity on impact velocity

Recent experimental measurements show that eroding long-rod penetration velocity is a linear function of impact velocity over a very wide range of impact velocities and for an interesting range of rod–target material combinations. These experiments all show that U=a+bV, where U and V are the penetration and impact velocity, respectively, and “a” and “b” are constants for given projectile and target materials. Numerical simulations also show that U=a+bV. The accumulation of these results suggests that a linear relationship between penetration and impact velocity may be fundamental over a very large range of impact velocities. A linear relationship between penetration and impact velocity has a number of implications. Some implications of this result for the Tate–Alekseevskii model are briefly examined in this paper.     

Penetration mechanics and performance of segmented rods against metal targets

Terminal ballistic experiments confirm theoretical predictions that a segmented rod will penetrate a semi-infinite metal target deeper than a continuous rod of the same material and having equal mass, diameter and velocity. For copper segmented rods impacting aluminum targets and tantalum segmented rods impacting 4340 (BHN 300) steel, penetration depths of at least 50 percent greater than that for a corresponding continuous rod are measured at impact velocities of 4 to 5 km/s. Spacing between segments of only about 2.5 segment diameters or more are required to achieve these results. Reducing the Li/D of the segments to less than 1 improves the penetration efficiency of a segmented rod. For segmented rods with segment L_i/D < 1, experiments suggest that penetration may increase with impact velocity rate greater than V^2/3.     

Scaling flow fields from the impact of thin plates

A dimensional analysis is performed to obtain velocity scaling relationships for the perforation of thin plates. The approach used is an extension of Dienes and Walsh's “late-stage equivalence” and Holsapple and Schmidt's “coupling parameter” concepts, used to simplify velocity scaling of impact phenomena. The coupling parameter C for plate perforation, is shown to have the form C=dU^μδ^ν for the perforation of thick plates and the form C=dU^μδ^ν f(t/d) for the perforation of thin plates (d is the projectile diameter, t is the plate thickness, U is the impact velocity and δ is the projectile density). It is shown that μ=1/2 for momentum scaling and μ=1 for energy scaling, however, from scaled hydrocode output it is found that, for aluminum impacting aluminum, the value of μ is equal to 0.83±0.03, which is neither energy nor momentum scaling. It is also shown that velocity scaling of thick plate perforation, using the same materials in the model and prototype and the same t/d, is not possible. An example of velocity scaling hydrocode output is given where the radial particle velocity wave profiles from the model calculation at U=55.6km/s and t/d=0.675 are similar to those from the prototype calculation with U=100km/s and t/d=1.08.     

Stress measurements in glass using shaped-charge jets

Stresses were measured in glass targets in the vicinity of a penetrating shaped-charge jet. Stress levels of approximately 0.3 GPa were measured 12–20mm away from a jet formed by a 35mm copper liner. High speed framing camera photographs showed that the penetration velocity in the glass was 2.57 km/s and the glass fracture velocity was 2.10 km/s.     

High-velocity solid ejecta fragments from hypervelocity impacts

The recent discovery of meteorites from the moon and the strong probability that the 8 SNC (Shergottite, Nakhlite and Chassignite) meteorites originated on Mars indicate that large hypervelocity impacts eject some solid debris at very high speed (more than 2.5 and 5 km/sec in the above cases). The standard Hugoniot relation between particle velocity and shock pressure predicts that lunar ejecta should be very heavily shocked (40–50 GPa) and Martian ejecta should be vaporized (100–200 GPa). However, the lunar meteorite ALHA 81005 was in fact subjected to less than 15 GPa, while the most highly shocked SNC meteorite was exposed to ca. 50 GPa, while others showing no detectable shock damage at all.

Theoretical work shows that the normal Hugoniot relation doesn't apply in the vicinity of a free surface. The free surface is, by definition, a pressure-free boundary, so shock pressures on it must be identically zero. On the other hand, the acceleration of debris is proportional to the pressure gradient, so that near-surface material may be accelerated to high speed and still escape compression to correspondingly high pressure. This process occurs only in a restricted zone near the free surface. The thickness of this zone is proportional to the rise time of the stress-wave pulse generated by the impact.

The rise time of the stress wave generated by a large impact is typically a/v_i, where a is the projectile radius and v_i its impact velocity. The near-surface zone in this case is comparable in thickness to a fraction of the projectile radius. Since the cratering event itself displaces many thousands of times the projectile mass, the quantity of lightly-shocked, high speed ejecta is small, amounting to only a few percent of the projectile's mass (for ejecta speed>few km/sec). The fastest solid ejecta leave at about 1/2 the impact velocity.

Although the total quantity of high speed solid ejecta is thus small in comparison to the total crater ejecta, it is significant because no other process yields such high velocity fragments. Many meteorites appear to be near-surface samples of their parent bodies (many are regolith samples and one is a vesicular lava) and so may have been ejected by this process.     

Impact and penetration by L/D ≤ 1 projectiles

Calculations of steel target penetration by L/D ≤ 1 tungsten and tungsten alloy projectiles have been extended to L/D = 1/32 over the velocity range 1.5 to 5 km/s. The ratio of crater to projectile diameter tends to 1 as L/D decreases over this entire velocity range. For impact velocities of 1.5 and 3 km/s, penetration depth normalized by projectile length, P/L, increases with decreasing projectile L/D up to a maximum value and then decreases for still lower L/D. Experiments at impact velocities of 2 and 3 km/s confirm these results. For 5 km/s impact velocity, the calculations show P/L increasing with decreasing projectile L/D over the entire range 1/32 ≤ L/D ≤ 1. The projectile L/D for which the maximum P/L occurs appears to depend on the impact velocity. P/L generally scales with impact velocity as P/L v^f(L/D) where f(L/D) ranges from 0 for a long rod to, we believe, 2 in the limit as projectile L/D approaches zero. The calculations show for 1/8 ≤ L/D ≤ 1/2, P/L v^0.9; for L/D = 1/16, P/L v^1.5; and for L/D = 1/32, the new results give P/L v^1.9.     

Penetration of semi-infinite AD995 alumina targets by tungsten long rod penetrators from 1.5 to 3.5 km/s

The performance of confined AD995 Alumina against L/D 20 tungsten long rod penetrators was characterized through reverse ballistic testing. The semi-infinite ceramic target was cylindrical with a diameter approximately 30 times the rod diameter. The target configuration included a titanium confinement tube and a thick, aluminum coverplate. The impact conditions ranged from 1.5 to 3.5 km/s with three or four tests performed at each of six nominal impact velocities. Multiple radiographs obtained during the penetration process allowed measurement of the penetration velocity into the ceramic and the consumption velocity, or erosion rate, of the penetrator. The final depth of penetration was also measured.

Primary penetration approaches 75% of the hydrodynamic limit. Secondary penetration is very small, even at 3.5 km/s. The effective R_t value decreased from 90 kbar to 70 kbar with increasing impact velocity over the range of velocities tested.

In tests in which the ratio of target diameter to penetrator diameter was reduced to 15, R_t, dropped by 30% to 50%. When a steel coverplate was used, total interface defeat occurred at 1.5 km/s.     

The effect of projectile properties on target cratering

The effect of projectile properties on target cratering is evaluated for two basic target designs: a simple, half-space target and a half-space target protected by a shield. The comparison of unshielded and shielded target impacts is based on empirical evaluations and emphasizes the velocity range of 4–6 km/sec. A wider velocity range, 0–8 km/sec, is considered for evaluations of projectile property effects. This paper examines the effects of projectile strength, density, shape, size, velocity and particulation. It was observed that the presence of a shield amplifies the influence of projectile density, shape and size but mitigates the influence of projectile velocity. For shielded target impacts the properties of the projectile debris cloud behind the shield were used to predict the crater damage to the target.     

High-speed penetration into sand

The series of experiments aimed at the exploring high-speed impact of bullet on non-solid target were carried out at IPE RAS. The electro-discharge launcher (EDL) employed in these experiments can reach the projectile velocities of 4 km/s. The following topics were considered: the phenomena related to the high-speed penetration into non-solid targets, the parameters that influence the penetration depth and the projectile design suitable for the deepest penetration into sand. Experimental equipment allows the measurement of the penetration depth of bullet, its path inside the sand and the shock waves caused by the high-speed bullet impact. Experiments had shown the absence of significant deviation from a straight-line trajectory for the any tested bullet shapes at the impact velocity of 1.5–3.0 km/s. The most interesting result is the existence of a critical velocity for this type of interaction. The full bullet wear due to the friction with sand occurs at this velocity. The critical velocity value depends on bullet material and dimensions. Experiments show that exceeding the critical velocity leads to reduce in penetration depth. The influence of bullet material, shape and velocity on its penetration depth into sand was measured. These data allow a determination of the main characteristics of projectile for deep penetration into sand.