Debris cloud expansion studies

Properties of fragment clouds produced by hypervelocity perforation of metal plates have been experimentally investigated. Replica model techniques have been applied. Targets consisted of steel dual-plate systems. Projectiles were hard metal spheres of tungsten carbide (3 mm, 7 mm and 10 mm diameter, HRc 79) and steel spheres (6 mm and 12 mm diameter, HRc 63) at velocities ranging between 2.3 km/s and 4.5 km/s. Cloud expansion velocities have been measured by means of in-flight flash X-ray photograph series. Maximum and minimum fragment velocities at front and rear side of clouds have been determined. From impact crater patterns on witness plates, and X-ray photographs of debris clouds, projectile and shield fragments have been identified. It has been found that plate perforation holes and debris cloud parameters scale geometrically for 6 mm and 12 mm diameter steel and 7 mm and 10 mm diameter hard metal spheres. For the 3 mm diameter hard metal spheres only the maximum debris cloud velocity v_rmax scales; all other parameters show deviations, indicating non-uniformity of the plate perforation process at different plate thicknesses. The shape of the inner part of debris clouds of steel spheres is different from that of hard metal spheres, caused by the density difference. For steel spheres the debris cloud shape is a convex lense, the shape of the hard metal fragments becomes in the rear nearly hemispherical. Increasing of the impact velocity causes an increasing of the expansion velocity and a flattening of the debris clouds.     

An impact technique to accelerate flier plates to velocities over 12 km/s

Very high pressure and acceleration is necessary to launch flier plates to hypervelocities. In addition, the high pressure loading must be uniform, structured, and shockless, i.e., time-dependent to prevent the flier plate from either fracturing or melting. In this paper, a novel technique is described which allows the use of 100 GPa megabar loading pressures and 10⁹-g acceleration to launch intact flier plates to velocities of 12.2 km/s. The technique has been used to launch nominally 1-mm thick aluminum, magnesium, and titanium alloy plates to velocities over 10 km/s, and 0.5-mm thick aluminum and titanium alloy plates to velocities of 12.2 km/s.     

Advanced all-metal orbital debris shield performance at 7 to 17 km/s

Increasing demands on orbital debris shielding systems have spurred efforts to develop shields that are more efficient than the standard single-bumper system. For example, for a given total bumper mass, experiments at velocities near 7 km/s have shown that a multiple-bumper system is more efficient than a single bumper in preventing wall perforation. However, the performance of multiple bumper systems at velocities above 7 km/s is unknown. To address this problem, the cadmium surrogate-material technique described by Schmidt et al. [1] has been extended to two dual bumper systems. A complete dimensional analysis is developed to include similarity requirements for the intermediate layers. Results of experiments, for impact angles of 0° and 45°, are presented and compared to those for single bumpers, along with limited results for an equal-mass four-bumper shield. Surprisingly, for scaled velocities near 16 km/s at normal incidence, a single bumper defeats impactors approximately 30% larger in diameter than multiple bumpers of the same total areal density.     

Analysis of debris clouds produced by impact of aluminum spheres with aluminum sheets

Results of two-stage light gas gun testing of two diameters of aluminum spheres impacting 0.5 mm and 1.0 mm thickness aluminum plates were described in this paper. Impact velocities for these tests were between 3.16 km/s and 5.17 km/s. The components of debris cloud and damage patterns in the witness plate were described. The morphologic features of debris clouds such as shape, axial velocity, and diametral velocity were discussed. The size and number of fragments in the internal structure of debris cloud were not evaluated quantitatively, but described qualitatively. As a result, the shape of the leading face of the internal structure of debris cloud appeared to be sensitive to impact velocity, but not t/D ratio (bumper-thickness-to-projectile diameter ratio). The point at which the maximum diameter of the external bubble of debris cloud occurred had a same half spray angle of 30 degree and the last fragments ejected from bumper had a same half spray angle of 42 degree for each test. Fragments after the point mentioned above in the external bubble of debris cloud were ejected as several chains, the number of which is sensitive to impact velocity, but not t/D ratio. The changes in normalized velocity of the measurement points at debris cloud appeared the same trend as conclusions presented by Piekutowski except for the normalized internal structure expanding velocity. A certain value of t/D ratio, at two sides of which, the normalized internal structure expanding velocity appeared different variety trend existed.     

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.     

Propagation of hypervelocity impact fragment clouds in pressure gas

This study investigated the propagation of hypervelocity impact fragment clouds in pressure gas. Fragment clouds were generated through perforation of thin aluminium bumper plates by spherical aluminium projectiles. A thick aluminium backwall plate, placed inside a pressure container at a given distance from the bumper plate, caught the fragments to act as a witness plate for the residual damage potential of the fragments. Crater depth statistics are presented as a function of container pressure. The fragment cloud was photographed by means of an image converter camera. The images showed a strong deformation of the fragment cloud for increased container pressures and were used to extract residual velocities until up to 50 μs after impact. The deceleration of the velocity as a function of time after impact suggested an exponential decay function as the best fit to the curve. Thus, maximum fragment impact velocities on the backwall plate could be extrapolated from the axial cloud velocities. The extrapolated curves were compared with experimental time-of-flight measurements, and proved a good match. Fragment impact velocities and maximum crater depths were used to calculate maximum fragment particle sizes as a function of the container gas pressure.     

泡沫铝防护屏的Whipple防护结构弹道极限数值模拟研究

为研究泡沫铝板作为防护屏的Whipple防护结构抵御空间碎片超高速撞击的特性,模仿泡沫金属的生产原理建立了泡沫金属细观结构几何模型,结合自编的光滑质点流体动力学程序进行了超高速撞击数值仿真,通过与实验对比验证了模型的有效性.分别对相对密度为23.2%的理想均匀和非均匀开孔泡沫铝板作为防护屏的Whipple防护结构进行了数值仿真,得到了它们的弹道极限曲线,并与实心铝板作为防护屏的Whipple防护结构进行了对比分析.结果表明,相同面密度的泡沫铝板相对于实心铝板能够在更低的速度上将弹丸粉碎、液化及气化.泡沫铝板作为防护屏,在总体上拥有更好的防护性能;相同面密度的理想均匀泡沫铝板的防护性能总体上优于非均匀泡沫铝板.     

Simulation of hollow shaped charge jet impacts onto aluminium whipple bumpers at 11 km/s

The computational technique of Smoothed Particle Hydrodynamics (as implemented in the hydrocodes AUTODYN-2D and AUTODYN-3D) has been used to simulate the impact of hollow shaped charge jet projectiles onto stuffed Whipple bumper shielding. Due to limited availability of material models, the interim Nextel/Kevlar-Epoxy bumper was modelled as an equivalent thickness of aluminium. Stuffed Whipple bumper shields are used for meteoroid and debris impact protection of the European module of the International Space Station (the Columbus APM). A total of 56 simulations were carried out to investigate the impact processes occurring for shaped charge jet impact. Sensitivity studies were carried out on the influence of projectile shape, pitch, yaw and strength at 11 km/s to determine the range of debris cloud morphologies. The debris cloud structure was shown to be highly dispersed, and no projectile remnant was observed at the centre of the cloud. The mass of an aluminium sphere producing equivalent damage to a shaped charge jet projectile was in the range 1.5 to 1.75 times greater than the mass of the shaped charge jet projectile. Upon loading by the dispersed debris cloud, the interim bumper failed by spallation, producing fragments moving at 2 km/s or less. The fragments distorted the rear wall (pressure wall) of the shield but did not perforate it. The experimental data show rear wall deformation but to a lesser degree. Perforation of the rear wall, observed for one test, was not reproduced by the simulation. Nextel/Kevlar-epoxy material models are required to reproduce correctly the interim bumper failure under debris cloud loading.     

Response of woven ceramic bumpers to hypervelocity impacts

The multi-shock shield concept devised by Crews and Cour-Palais,¹ composed of multiple ceramic cloth bumper layers and an aluminum back sheet, was used to investigate the response of woven ceramic bumpers to a hypervelocity impact. Observations made on past hypervelocity impact test data show that areal density is the most important bumper characteristic for initially breaking up solid particles. Our research has shown that once the solid particle has been shocked into a cloud of liquid and vapor, the weave pattern of the cloth bumper can influence the ability of the shield to absorb and contain the energy of the debris cloud.

To design a weave that will absorb particle energy more efficiently, we need to understand the micromechanics of the interaction between the debris cloud and the cloth bumper. In this paper we discuss our observations on the response of a ceramic cloth bumper to a hypervelocity impact and the failure mode occurring at the individual strand level.     

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.     

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。     

Quantitative analysis of debris from SiC-fiber-reinforced aluminum-alloy targets impacted by spherical projectiles

Silicon-carbide-continuous-fiber-reinforced aluminum matrix composite targets were impacted with duralumin projectiles at velocities from 2.9 km/s to 4.3 km/s. The debris from the composite targets was monitored by flash, soft x-ray radiography. The spatial distribution of the leading half of the debris were quantified in terms of mass, velocity, and kinetic energy and compared with that of debris from monolithic aluminum-alloy targets. A material effect on the debris production was found through the experiment so that fragments from the composite targets were smaller in mass and size, but more in number than those from the monolithic bumper. An increase of the impact velocity brought the enhancement of fragmentation in the leading edge part of the debris produced from both the composite and the monolithic targets in comparison with lower velocity impacts. The 4.3 km/s impact for the composite gave the spatial densities of debris mass and kinetic energy biased toward the periphery of the debris cloud, while other lower velocity impacts gave the different densities biased toward a gun axis. Such peripheral distribution of debris was found at an impact velocity of 3.5 km/s for the monolithic target. In the present velocity range, the composite debris always exhibited its larger peripheral distribution than the monolithic one did.     

Impact experiments on low-temperature bumpers

This paper presents the results of hypervelocity impact experiments that were carried out at CISAS Impact Facility onto aluminum bumpers cooled down to −120 °C with liquid nitrogen and to −60 °C with solid carbon dioxide. The thickness of the targets was 0.8, 1, 2 and 3.17 mm, the diameter of the spherical projectiles was 1.5, 1.9, 2.3 and 2.9 mm and the impact velocity did span between 4 and 5 km/s. To establish if any temperature dependence exists in the bumpers’ impact response, two different features were analyzed: the hole size and the bumper protection capabilities. The latter property, that is related to the bumper capacity of producing debris cloud composed of fragments as fine and slow as possible, was assessed through observation of the damage patterns on witness plates and through measurements of the debris cloud tip velocity. Moreover, qualitative analyses of high-speed shadowgraphs representing the debris cloud evolution were performed. On one hand, it was found that low temperature has only minor influence on the hole diameter. On the other hand, the examination of shadowgraphs showed that the debris cloud structure varies with bumper temperature, even though it was not proved that such differences correspond to significant dissimilarities between damage patterns recorded onto witness plates.     

Advanced shield design for space station freedom

Due to the predicted increase in the severity of the orbital debris environment in low-Earth orbit, the baseline meteoroid/debris protection system for Space Station Freedom (S.S. Freedom) must be augmented on orbit. In response to this need, an advanced shield design effort is underway at NASA's Marshall Space Flight Center (MSFC). The results to date of this program are presented.

A series of 18 hypervelocity impact tests were conducted at MSFC's Space Debris Simulation Facility. These tests consisted of launching aluminum projectiles at velocities up to 7 km/s to evaluate various design solution. Parameters investigated include shield material and geometric configuration (thickness, spacing, orietation, and arrangement) in relation to the baseline aluminum “Whipple” bumper.

The results of the hypervelocity impact tests are presented. Comparison with protection offered by the baseline protection system is made. Evaluation of protection offered by candidate augmented systems and hydrocode simulations is performed. An assessment of the often-overlooked structural design onsiderations such as launch loads, on-orbit loads, extravehicular activity requirements, maintainability, etc., is presented. These analyses lead to identification of a candidate system to augmented the baseline meteoroid/debris protection system for the habitable modules of S.S. Freedom.     

Impact flash and debris cloud expansion of high-pure metal foils

Results of 2 mm aluminum spheres perforating Al, Cu, Mo, Au, Sn, and Zn metal foils of a purity > 99.9 % with thicknesses between 0.1 mm and 2.0 mm, densities of up to 20 g/cm³, melting temperatures of 500 – 3000 K and specific heats of fusion of 20 – 350 kJ/kg at impact velocities between v_p = 4.5 km/s and v_p = 9 km/s are presented. The influence of target thickness, target material properties and impact velocity on the perforation hole diameter, impact flash duration and expansion velocity, fragmentation and debris cloud formation at nearly constant areal density is demonstrated. The dependence of impact crater pattern at witness plates on target material density, thickness, impact velocity and areal density ratio between projectile and target material is discussed. For tin and lead evidence is given for the ability of digital scanning electron microscope analysis as an effective tool for indicating change of aggregation from solid into liquid and for the determination of relative projectile and target material quantities.     

Micrometeorite and space debris simulation for columbus hull components

An experimental impact simulation program is currently performed with respect to Columbus hull components. The main objectives are to establish a data base for an optimum design of meteoroid/debris protection shields (MDPS) as well as viewport components, and to obtain input data for numerical models which describe the penetration and perforation processes of meteoroid bumper and viewport systems.

As expected, it has been experimentally demonstrated that protection against particles in the order of 1 cm, at relatively low impact velocities (around 3 km/s), is extremely problematic.

Applying usual dual-plate Al bumper techniques would require unrealistically thick and heavy systems in order to safety stop such particles, which are expected to occur within the low earth orbit space debris complex.

Preliminary results obtained with multiplate Al targets as well as hybrid target systems (Al-ceramics, Al-Kevlar) indicate that the situation can be considerably improved with respect to the shielding efficiency at a given areal material density.

These investigations are still in progress. Results of the test series performed with Al dual-plate systems and with laminated glass targets as viewport components are reported and discussed.     

Fragmentation of a sphere initiated by hypervelocity impact with a thin sheet

Selected results of tests in which 9.53-mm-diameter, 2017-T4 aluminum spheres impacted 0.25-mm- to 4.80-mm-thick, 6061-T6 aluminum sheets are presented. Impact velocities for these tests ranged from 1.98 km/s to 7.38 km/s. Flash x-rays were used to view the debris clouds produced by the impacts. As impact velocity was increased, failure of the aluminum sphere progressed through the following stages of fracture and fragmentation: (1) formation of a spall failure at its rear surface, (2) development of a detached shell of spall fragments, and (3) complete disintegration of the sphere. The threshold impact velocity for development of the spall failure in the sphere was observed to be a function of the bumper-thickness-to-projectile-diameter ratio (t/D), and to increase as the t/D ratio decreased. When the debris cloud was fully developed, the disintegrated projectile formed its dominant feature--an internal structure, composed of a front, center, and rear element, located at the front of the debris cloud. The front element was small and consisted of finely-divided projectile and bumper material. The bulk of the fragmented projectile was contained in the center element, a disc-like structure made up of a large central fragment surrounded by numerous smaller fragments. A shell of fragments, spalled from the rear of the sphere, formed the rear element. Radiographs of the debris clouds were analyzed to determine the size and size distribution of certain fragments within the cloud. The size of the large fragment was shown to be dependent on impact velocity and t/D ratio. The smaller fragments in the center element were several times larger than the fragments in the shell of spall fragments forming the rear element. Detailed analyses of fragments in the shell of spall fragments were made. The analyses indicated their median Martin's statistical diameter exhibited an orderly dependence on impact velocity and t/D ratio.