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.     

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.     

The effects of the failure diameter of an explosive on its response to shaped charge jet attack

In order to shed some light on the response of explosives to the attack of small-diameter projectiles such as shaped charge jets, we conducted a computational study using the 2DE code and the Forest Fire explosive initiation model. Simulations of copper-jet attack against Composition B were made in order to determine modes of initiation and critical velocity for initiation as a function of jet diameter. We modeled the jet as a nonstretching cylindrical projectile with a flat tip. Its diameter was varied between 0.3 mm and 12.0 mm and its velocity was varied between 0.8 km/s. and 15.0 km/s. We observed two modes of initiation: (1) prompt, impact-mode initiation for both subsonic and supersonic penetration and (2) delayed, penetration-mode initiation only for supersonic penetration by small-diameter jets. The velocity threshold for large subsonic jets agrees with the Jacob-Roslund formula. For jets with diameters smaller than the failure diameter of the explosive they attack, higher velocities than predicted by Jacobs-Roslund are required for initiation. A critical threshold between impact- and penetration-mode initiation was determined over the entire supersonic range. A similar threshold between penetration-mode initiation and initiation failure has not yet been determined due to limitations of the code.     

Penetration dynamics and interface defeat capability of silicon carbide against long Rod impact

To determine the behavior of silicon carbide (SiC) against long rod impact a detailed study with experiments in the velocity range from 0.8 to 3 km/s at normal impact conditions was performed in recent years. Interest ranged from penetration performance of intact and pre-damaged SiC to interface defeat capability of SiC. Together with impact data in the hypervelocity regime this paper provides a comprehensive overview of the penetration dynamics of SiC over a wide velocity range and during different phases of the penetration process.     

Degradation and destruction of optical surfaces by hypervelocity impact

This study investigates the damage caused by impacts of space debris and micrometeoroids (SD/MM) on mirrors of placed on spacecrafts in an orbit of 700 km and 1400 km altitude with an inclination of 48°. For the investigated orbits the maximum damage from impact degradation of the optical surface as well as the probability of total destruction by single particle hit has been calculated. Based on the NASA statistical standard model ORDEM 96, the calculation of SD particle fluxes shows that at 700 km altitude an average of 62000 impact damages per m² and per year are caused by particles with a diameter equal or larger than 1 μm. At 1400 km altitude the figure is reduced by 30%. The corresponding MM fluxes have been calculated with the Grün model and are 1.5 orders of magnitude smaller than the SD fluxes. For the generation of a damage law and for the determination of the total destruction limits, 50 impact damages were produced on coated and uncoated quartz glass samples, employing the impact facilities of the Ernst-Mach-Institute (EMI) and the Aerospace Department of the Technical University Munich (TUM/LRT). The particle sizes were varied between 3 μm and 1000 μm. The impact velocities were between 2.0 km/s and 16.1 km/s. Due to the irregular damages a clear correlation with the impact angle (0°, 30°, 60°) could not be proven. The diameter of the optically inactive surface after impact is proportional to E^0.458 (where E = kinetic energy of the impact). The experimental total destruction limit of 5 mm thick quartz glasses is reached with an impact energy of 13.5 J (Aluminum sphere, 0.9 mm diameter, 5 km/s impact velocity). The degradation analysis showed that 3.5 % of the optical surfaces of the mirrors in 700 km orbits (48 ° inclination) is destroyed within 10 years by space debris and micro-meteoroids. The probability of total destruction for the considered mirrors in 700 km altitude is in the percent range for an operational period of 10 years. Degradation damages and the probability of total destruction in an orbit in 1400 km is slightly below the values for the 700 km orbit.     

Experimental and numerical study of peculiarities at high-velocity interaction between a projectile and discrete bumpers

A high-velocity impact interaction of a polyethylene projectile (15 mm diameter) and aluminium projectile (6.35 mm diameter) with string and mesh bumpers (made of steel strings of 0.5–1.0 mm in diameter) was investigated experimentally and numerically. The study was aimed on detecting the projectile fragmentation peculiarities during projectile interaction with discrete bumpers. Since polyethylene has lower penetration resistance than aluminium, the effects inherent to discrete bumper penetration into the projectile must be more obvious for polyethylene. The string bumper is a set of parallel strings lying in a plane. The geometry of the string bumper which is simpler than the geometry of the mesh one also allowed one to get more understandable distribution of fragments on a thick aluminium witness-plate which was imposed behind the studied bumper to register the results of impact interaction for further analysis. The projectile velocity varied in the range of 1.7–3.8 km/s. The geometrical properties of such bumper-projectile system were characterized by two geometrical parameters: the parameter κ characterizing the bumper discreteness and equal to cell aperture-string diameter ratio, and the parameter ? defining the average number of cells falling within the projectile diameter.     

Projectile density, impact angle and energy effects on hypervelocity impact damage to carbon fibre/peek composites

This paper explores the effects of projectile density, impact angle and energy on the damage produced by hypervelocity impacts on carbon fibre/PEEK composites. Tests were performed using the light gas gun facilities at the University of Kent at Canterbury, UK, and the NASA Johnson Space Center two-stage light gas gun facilities at Rice University in Houston, Texas. Various density spherical projectiles impacted AS4/PEEK composite laminates at velocities ranging from 2.71 to 7.14 km/s. In addition, a series of tests with constant size aluminum projectiles (1.5 mm in diameter) impacting composite targets at velocities of 3, 4, 5 and 6 km/s was undertaken at incident angles of 0, 30 and 45 degrees. Similar tests were also performed with 2 mm aluminum projectiles impacting at a velocity of approximately 6 km/s. The damage to the composite was shown to be independent of projectile density; however, debris cloud damage patterns varied with particle density. It was also found that the entry crater diameters were more dependent upon the impact velocity and the projectile diameter than the impact angle. The extent of the primary damage on the witness plates for the normal incidence impacts was shown to increase with impact velocity, hence energy. A series of tests exploring the shielding effect on the witness plate showed that a stand-off layer of Nextel fabric was very effective at breaking up the impacting debris cloud, with the level of protection increasing with a non-zero stand-off distance.     

Failure and penetration response of borosilicate glass during short-rod impact

A series of reverse ballistic experiments reveal further properties of the failure front (FF) associated with the penetration of borosilicate glass by a gold rod. Importantly, the FF ceases to propagate a short time after the rod is fully eroded. The rods, 1 mm in diameter, were short (5–11 mm). The glass targets were 20-mm diameter cylinders, 60-mm or 100-mm long. Impact velocities varied between 1 and 2 km/s. The impact and penetration process was observed with five flash X-rays and a 16-frame high-speed optical camera. A FF propagates from the impact region. The velocity of FF propagation is an increasing function of the impact velocity. The termination of the FF can reasonably be predicted in most cases with a simple model that assumes a rarefaction wave, originating at the time of complete rod erosion, propagates from the bottom of the penetration channel to the FF at a speed equal to the bulk wave speed of undamaged glass.     

Penetration of tungsten alloy rods into shallow-cavity steel targets

This paper presents a combined numerical and experimental study on penetration of tungsten heavy alloy long rods (length-to-diameter ratio of 10) into thick RHA (rolled homogeneous armor) steel plates. The main objective of this study was to establish the effects of a shallow cavity at the front of the steel plate on the penetration process. Three experiments were performed at 1.5 km/s on target plates with a shallow-cavity of 19 mm diameter. These results were compared to existing penetration data obtained for flat plates over a range of 1.1–1.7 km/s. In the code simulations three target configurations were considered: a flat target surface without a cavity and two target plates with different cavity diameters (19 and 11.54 mm). The effect of the target’s free surface on the characteristic time that the penetrator takes to reach quasi-steady-state penetration into the target was investigated for three configurations. Based on the experimental results the effect of the shallow-cavity wall constraint on the penetration process was found to be insignificant. The code results matched the measured depths of penetration within the limits of the experimental accuracy for all configurations examined.     

铝双层板结构撞击损伤的板间距效应实验研究

为了研究空间碎片对航天器防护结构的超高速撞击损伤特性,采用二级轻气炮发射球形弹丸,对铝双层板结构进行了超高速撞击实验研究.弹丸直径为3.97 mm,撞击速度分别为(2.58±0.08)km/s、(3.54±0.25)km/s和(4.35±0.11)km/s,板间距为10~100 mm.实验得到了铝双层板结构在不同撞击速度区间的后板损伤模式.结果表明,弹丸撞击速度一定时,后板弹坑分布随前后板间距的不同而不同.前板背面返溅影响区和后板弹坑分布区随板间距的增大而增大,各弹坑分布区扩散角随板间距的增大而减小.     

Variation of crater geometry with projectile L/D for L/D ≤ 1

A series of hydrocode calculations and terminal ballistics experiments were performed to investigate the penetration mechanics of projectiles with L/D ≤ 1. Projectile L/D ranged from 1/32 to 1; impact velocity ranged from 1.5 to 5 km/s. Projectiles were tungsten or tungsten alloy, targets were RHA. The paper concentrates on the effect of projectile L/D on the size and geometry of the target crater. Normalized crater depth (or penetration) increases with decreasing projectile L/D and achieves a maximum at about L/D=1/8 for 1.5 km/s and 1/16 for 3 km/s, and then decreases with further decrease in L/D. For 5 km/s, P/L increases with decreasing L/D over the entire range studied. P/L scales with impact velocity as P/L V^f(L/D) where, we believe, f(L/D) approaches 2 as L/D 0. The ratio of crater to projectile diameter D_c/D decreases with decreasing L/D and approaches a value of 1 as L/D approaches zero for all velocities studied. The crater shape measured by P/D_c decreases with decreasing L/D; i.e., as L/D decreases, the crater changes from approximately hemispherical for L/D = 1 to a very shallow disk shape. The kinetic energy required per unit crater volume, KE/V_c, increases with decreasing L/D for L/D < 1/4. That is, cratering efficiency decreases with decreasing projectile L/D. For the impacts studied, KE/V_c increases from about 5 kJ/cm³ to 12 kJ/cm³ as projectile L/D is reduced from 1 to 1/32.     

Measuring hypervelocity impact velocity from micrometeoroid crater geometry

Guided by half-space computer simulations showing hypervelocity impact crater formation for an iron particle impacting an aluminum target and characteristic crater geometry changes with impact velocity over the range 8–40 km s⁻¹, we examined normal surface crater views and cross-sectional views through craters (>0.5 mm diameter) from samples retrieved from the NASA LDEF satellite and examined in the scanning electron microscope (SEM). While geometrical features suggested in the computer simulations were indeed observed for micrometeoroid craters in 6061-T6 aluminum targets and 303 stainless steel targets, there was no consistent estimate for impact velocities in any of the experimental samples, and velocity estimates based on measuring ratios of ejecta width/crater diameter and ejecta height/crater depth as well as ejecta height/crater diameter varied from 8 to 42 km s⁻¹; over the same range simulated. These results point to the need to create reference data from actual hypervelocity impact experiments in the laboratory, and systematic observation of residual crater geometries in the SEM. These experiments also demonstrate the uncertainty in assuming a fixed impact velocity for all impact craters in space materials as well as an apparent futility in attempting to correlate impacting particle velocity with post-mortem characteristics of a given crater.     

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.     

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.     

Experimental observations and computer simulations for metallic projectile fragmentation and impact crater development in thick metal targets

Stainless steel (3.18 mm diameter) spherical projectiles impacting 2.5 cm thick targets of nickel, copper, 304 stainless steel, and 70/30 brass at velocities ranging from 0.52 to 5.12 km/s were observed by SEM to form decreasing average fragment sizes with increasing impact velocity, beyond a fragmentation onset velocity of 0.7 km/s. Crater observations by optical microscopy and SEM were qualitatively simulated using an AUTODYN numerical analysis code, which also illustrated a decrease in fragmentation density within the target craters with increasing impact velocity. However, extrapolated simulations corresponding to impact velocities as high as 10 km/s showed residual fragmentation within these craters in contrast to extrapolations of the experimental fragment size versus impact velocity data indicative of zero fragment size at 6 km/s.     

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.     

Time-resolved penetration into pre-damaged hot-pressed silicon carbide

We have conducted a series of experiments to examine projectile penetration of cylindrical hot-pressed silicon carbide (SiC) ceramic targets that are pre-damaged to varying degrees under controlled laboratory conditions prior to ballistic testing. SiC was thermally shocked to introduce non-contiguous cracks. Another set of targets was thermally shocked and then additional damage was induced by load–unload cycling in an MTS machine while the ceramic specimen was confined in a 7075-T6 aluminum sleeve. Finally, targets were made by compacting SiC powder into a 7075-T6 aluminum sleeve. For each of these target types, long gold rod penetration was measured as a function of impact velocity v_p over the approximate range of 1–3 km/s, with most data between 1.5 and 3 km/s. Penetration as a function of time was measured using multiple independently timed flash X-rays. Results are compared with previous results for non-damaged (intact) SiC targets. Key results from these experiments include the following: (1) penetration is nominally steady state for v_p>1.5 km/s; (2) for all target types, the penetration velocity u is a linear function of v_p (except for the lowest impact velocities); and (3) it is found that u_intact<u_pre-damaged<u_{in-situ comminuted}<u_powder<u_hydrodynamic.     

铝球弹丸超高速正撞击薄铝板穿孔尺寸研究

利用2017-T4铝球弹丸高速正撞击不同厚度的2A12铝合金板,模拟空间碎片对航天器防护屏的高速撞击作用,分析铝合金板撞击穿孔尺寸特征。铝球弹丸直径为3.18mm~6.35mm,弹丸直径与铝板厚度之比dp/t为1.00~9.96,撞击速度为1.50km/s~6.98km/s,得到了铝球弹丸高速正撞击铝板的穿孔经验公式。实验结果表明:薄铝板高速撞击穿孔直径扩张率与弹丸直径、铝合金板厚度及撞击速度有关。当弹丸直径与铝合金板厚度之比dp/t一定时,薄铝板撞击穿孔直径扩张率随着撞击速度的增大而增大;当撞击速度一定时,薄铝板撞击穿孔直径扩张率与dp/t呈非线性关系,且随着dp/t的增加,对薄铝板撞击穿孔直径扩张率的影响减弱。     

Hypervelocity impact testing of micrometeorite capture cells in conjunction with a PVDF thin-film velocity/trajectory sensor and a simple plasma velocity detector

Five different small particle capture cell designs were evaluated for their ability to capture fragments and residue from 10–200 μm diameter glass projectiles and oblong olivine crystals impacting at 1–15 km/s in sufficient quantity for chemical and isotopic analyses. Aluminum multi-foils (0.1–100 μm thick with ≈10, 000 and 1800 μm spacing), foil covered germanium crystals, and 0.50 and 0.120 g/cm³ Aerogels, were positioned behind either multi-film (1.4–6.0 μm thick) polyvinylidene fluoride (PVDF) velocity/trajectory sensor devices of a simple wire-grid plasma velocity detector. All capture cells collected significant amounts of impactor debris behind the PVDF sensors from nominal 100 μm diameter glass projectiles and olivine crystals which struck the sensor at velocities up to 6.4 km/s. At velocities >8 km/s little or no debris penetrated the second PVDF film. Results were incolsive for velocities between 6.5 and 8 km/s. Plasma detector results showed identifiable impactor residue on Al foils for velocities up to 8.7 km/s and impact tracks with apparent debris imbedded in the Aerogels for velocities up to 12.7 km/s. Maximum foil penetration of glass spheres and olivine crystals were the same, but more particulate debris was associated with olivine crystal ipacts versus glass impacts. Foil spacing beyond one particle diameter had no effect on total penetration. Aerogels are identified as a capture cell media that warrants further investigation. The Al multi-foil capture cell with 100 μm net spacers is identified as the most effective of the other designs and offers the advantages of compact structure, low secondary ejecta from impacts, and easy recovery of impactor debris for analysis.