Hypervelocity impact tests with bumper-walled structure against space debris

The experimental activities at Shock Wave Research Center of Tohoku University using a ballistic range are reviewed. First, the shock stand-off distance for a sphere and the shock shape over a sharp cone are measured in the hypersonic speed regime. These measurements are made for 30 mm diameter models, flight speeds between 2.5 and 4.0 km/sec and ambient pressure 4.2 and 76 mmHg. The flow field is visualized by the schlieren method using a short-pulse Nd-YAG laser as the light source. Shock stand-off distance and shock shape are shown to vary with the ambient pressure, demonstrating the effect of the chemical nonequilibrium. Secondly, hypervelocity impact tests are conducted for simulation of space debris impacts against a bumper shield. The bumpers are made of metal and nonmetal materials. The projectile made of high density polyethylene has a cylindrical shape of 14 mm diameter and 3.7 g in weight. The impact velocity is about 4 km/sec. The debris cloud is visualized by shadowgraph. The nonmetal bumper shields used in this study are more effective than the metal bumper in regard to both the bumper mass and defensive capacity. Introduction The ballistic range is one of the readily available impulse facilities for the fundamental investigation of the hypersonic flow phenomena. The so-called two stage light gas gun can accelerate a model to hypersonic speeds. The facility is used mainly for the study of hypersonic aerothermodynamics and for the hypervelocity impact tests. In Shock Wave Research Center of the Institute of Fluid Science of Tohoku University, experiments are in progress in a ballistic range with a 14 mmand 30 mm-bore two stage light gas gun. First, the shock stand-off distance for sphere and the shock shape over sharp cone are measured in the thermochemical nonequilibrium regime. In the past, a large number of experimental investigations on high temperature real-gas effects have been carried out in the shock tunnel. However, there exist uncertainties in the characteristics of the flow produced in a shock * Graduate student f Professor, Institute of Fluid Science, Tohoku University; Member AIAA. Copyright ©1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. tunnel in real-gas regime, and therefore it is necessary to validate the facility.Theoretically, the real-gas effects are being studied using computational fluid dynamics (CFD). However, the CFD calculation of nonequilibrium flow encounters many difficulties because of the complex processes of chemical reactions in the nonequilibrium state, particularly in the case of air. Therefore reliable experimental data are needed for validating shock tunnel results and CFD. One of the most appropriate reference quantity is the shock stand-off distance for a sphere and shock shapes for a sharp cone, because the heat absorption by the real-gas phenomena behind shock wave sensitively affects the shock stand-off distance and shock shapes.'' Ballistic ranges are the only impulse facility capable of producing a reliable data, because, in a ballistic range, a model flies in a quiescent atmosphere. Measurement of shock stand-off distance for sphere has been made by Lobb in the ballistic range (see Figure I). His experiment misses the range of the binary scaling parameter pR above 2X10 kg/m and the flight velocity below 4 km/sec. The accuracy of Lobb's experiment is unclear because of the relatively long pulse duration of the light source used for flow visualization and small size of the models. Therefore, we conduct an experiment using a Nd-YAG laser of very short pulse duration for the light source and use 30 mm-diameter models. The shock shapes have been also measured in real gas regime. However, these measurements are conducted in high enthalpy shock tunnels and expansion tubes.' As mentioned above, the data

With the continuous increase of centimeter-scale space debris, the exploration and design of new high-performance shields has become an urgent need. Based on the shield of active materials, the hypervelocity impact experiments with different projectile sizes and impact velocities were carried out by using a two-stage light gas gun. The image characteristics of debris clouds under different impact conditions were obtained and analyzed by laser shadowgraph photography. The damage characteristics of the rear wall of the active Whipple shield were studied. Through the statistical analysis of the number of craters, the influences of active materials on the fragmentation of projectiles under different impact velocities were obtained. Compared with the classical Christiansen ballistic limit equation, the protective performance of energetic active material shield was obtained, and the ballistic limit curve of the new shield was fitted. Analysis suggests that shock initiation characteristics of active materials under impact enhanced the shield performance. When impacted by the space debris, active material shield firstly uses its mechanical strength for primary crushing. During this process, the energetic material shield has an explosive reaction with an instantaneous temperature being as high as 3 800 K, which can promote fragmentation, melting and reduce the size of the space debris. At the same time, the explosion products with high temperature, pressure and high speed motion produce a negative acceleration to the projectile fragments, reducing the axial kinetic energy. The explosion products of the active materials are mostly gaseous, which greatly reduce the number of the fragments with penetration ability in the debris cloud. The penetration failure of the rear plate only comes from the fragments generated by the fragmentation of the projectile. Under the combined action of impact and explosion, the active materials shield can not only fully break and decelerate space debris, but also greatly reduce the number of solid debris in debris cloud, thereby produce a sharp rise in the spacecraft protection ability, and the maximum protection ability can be increased by 45% when the velocity is 2.31 km/s.

We have measured debris cloud generated by oblique impact. And in order to evaluate effect of oblique impact of aluminum spheres against a thin laminated target, hypervelocity impact test have been conducted. Impact velocity was approximately 2km/s. Impact angle was 0[deg] and 30[deg]. The experiments were performed to take images of the generated debris clouds behind target using three flash x-rays and to capture them softly using a stack of polystyrene sheets. And then, the images were analyzed to measure the velocity of each fragment. And the mass of recovered fragments were measured. As a result, it is found that at the impact obliquity of 30[deg], heavier and faster fragments were generated with a spray angle ranging from 20[deg] to 30[deg].

Hypervelocity impacts occur frequently in space due to dust that occurs naturally from comets or other space debris often called meteoroids; other debris is man-made and can have disastrous effects on spacecraft. Even though the particle may have a very small mass its momentum can be extremely high and destroy space craft. It is therefore vitally important to simulate the effects of hypervelocity impacts on vulnerable areas of satellites and space stations. A two stage light gas gun was previously developed for this purpose. In this paper we briefly describe two fiber optic based impact measurement systems that were tested at the light gas gun facility at the University of Kent to establish that they could provide data that could not be obtained by any other technique.

Hypervelocity impact testing of the pressurized mating adapters for the International Space Station

Orbital debris poses increasing threats to the space environment because of increasing space activities, therefore on-orbit hypervelocity impact should be simulated using the experiment by launch projectile into the target. Generally, ground-based experiments include three major sectors: projectile launch, impact monitoring including shock wave and debris cloud formation imaging, and finally result processing. For ground-based hypervelocity impact tests, various acceleration techniques such as light two and three-stage gas guns, plasma accelerators, electrostatic accelerators, and shaped charge accelerators have been used. This paper will primarily focus on those that are most relevant to current research on hypervelocity tests and would improve current research in the field of hypervelocity impact tests on composite material for primary satellite structures.

High-speed collisions of space debris with space structures produce debris clouds, the properties of which determine the collision resistance required of space structures. Debris clouds impact the pressurized walls of space structures; therefore, it is important to determine the contours of the debris clouds to support an efficient protective design of space structures. This paper proposes a new Bayesian cloud contour extraction method for accurately extracting the contours of debris clouds from images obtained in high-speed collision experiments. The method employs conditional entropy as an indicator of the extraction accuracy. In a departure from the conventional assumption of a Gaussian distribution, a realistic probability distribution is proposed to describe the histograms of image data. A new and more versatile method for cloud contour extraction is also proposed based on the trisection of the histograms. Using collision experiment images, it is demonstrated that the two proposed methods are superior to the conventional methods in terms of accurately extracting the debris cloud contours. The proposed methods can be used to measure the shape of a debris cloud and its rate of expansion, which will improve the interpretation of images of impact and explosion phenomena and contribute to the development of methods to protect space structures from space debris.

Impact responses and damage induced by a drop-weight instrument on GLARE 5 fiber-metal laminates (FMLs) with different thicknesses were studied. The effect of impactor mass was also considered. The damage characteristics were evaluated using both nondestructive ultrasonic and mechanical sectioning techniques. The ultrasonic C-scan technique could only assess the contour of entire damage area whereas more details of damage were obtained using the mechanical cross-sectioning technique. As expected, thicker GLARE 5 FMLs offered higher impact resistance. When subjected to the same impact energy, the entire damage contour enlarged as the specimen became thicker. Under the same impact condition, by reducing the impactor mass, the contact force escalated while the contact stiffness increased. Experimental results showed that the threshold cracking energy varied parabolically with respect to the impact velocity, metal volume fraction (MVF) and the specimen thickness. By increasing the metal volume fraction of the panels, the threshold cracking energy decreased parabolically. On the other hand, for the same MVF value, the cracking energy increased as the impactor mass increased. By increasing the panel thickness, the threshold cracking energy condition increased parabolically; whereas under the same impact velocity, the threshold cracking energy increased by increasing the impactor mass.

Pulsed supersonic liquid (water and diesel fuel) jets in the range of 1500 m/s to 1800 m/s have been produced and examined. A two stage light gas gun was used as a launcher to obtain the pulsed impact (velocity of 700m/s). In this paper, experimental results on the attenuation and the penetration distance of the liquid jets is presented. It was found that the attenuation is relatively high in the first 300 μs of the jet flight. The penetration distance is around 300–500 mm, this depending on the initial velocity, the nozzle geometry and the properties of liquid. The experimental results agree well with the estimation using conventional diesel spray formula. The shadowgraph image shows bow shock wave structures with multiple pulses which tend to enhance atomization and combustion. However, further examination of their atomization related to the jet attenuation and penetration distance is needed.

Micrometeoroid/Orbital Debris (MMOD) Impact Detection and Location Using Fiber Optic Bragg Grating Sensing Technology

Influence of fiber type on the impact response of titanium-based fiber-metal laminates

This study presents an experimental investigation into the high‐velocity impact resistance of three‐dimensional fiber metal laminates (3D FMLs) incorporating a nano‐reinforced syntactic foam core. Reinforced and unreinforced 3D FMLs were fabricated with varying nanoclay concentrations (0, 3, 5, and 7 wt.%) and subjected to high‐velocity impact testing. The impact experiments were conducted using a light gas gun and a 9 mm steel projectile, achieving an impact velocity of 235 m/s to determine the ballistic limits. The dynamic response and failure mechanisms of the laminates were characterized through field emission scanning electron microscopy (FESEM) to evaluate the influence of nanoparticle reinforcement on impact resistance. The results indicated that the incorporation of 5 wt.% nanoclay resulted in an 18.84% reduction in residual velocity and a 14.97% increase in energy absorption relative to the unreinforced 3D FMLs. Morphological analysis via FESEM and macroscopic inspection demonstrated enhanced interfacial adhesion between the resin and fiber, mitigated matrix microcracking, and reduced delamination, attributed to the nanoclay reinforcement. However, the presence of nanoclay diminished the adhesion strength at the aluminum‐composite interface, leading to exacerbated plastic deformation of the aluminum layers. Microstructural examination further revealed that nanoclay incorporation facilitated fiber fibrillation, thereby improving the energy dissipation capacity of the laminate under high‐velocity impact loading.Highlights Nanoclay‐reinforced 3D fiber metal laminates (FMLs) improve impact resistance, with 5 wt.% nanoclay yielding optimal ballistic performance and energy absorption under high‐velocity impact conditions. High‐velocity impact tests using a light gas gun and 9 mm steel projectile at 235 m/s determined the ballistic resistance of FMLs. FESEM analysis revealed enhanced interfacial adhesion, reduced matrix cracking, and improved delamination resistance, leading to superior energy dissipation in reinforced laminates. The 5 wt.% nanoclay FMLs showed an 18.84% reduction in residual velocity and a 14.97% increase in energy absorption compared to unreinforced samples. Excessive nanoclay (7 wt.%) led to nanoparticle agglomeration, increasing stress concentrations, crack density, and reducing overall mechanical performance.

Analytical modeling to predict the low velocity impact response of circular GLARE fiber–metal laminates

Over the past several years the interest in orbital debris has grown due to the hazard it poses to operating satellites. Models of the debris environment depend upon accurate assessments of the masses and sized of debris particles. Utilizing data from several hypervelocity impact tests and other sources, a mass-diameter relationship is determined for debris ranging in size from sub-millimeter particles to objects as large as derelict rocket bodies and inactive satellites. The accuracy of the mass-diameter relationship is examined and conclusions are reached.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work, the normal (0°) and oblique (30° and 45°) ballistic impact behavior of glass fiber-reinforced aluminum laminates (fiber metal laminate, FMLs) impacted by a rigid cylindrical projectile (with a flat nose) has been investigated from an experimental point of view. The ballistic impact tests were conducted on the FMLs using a one-stage gas gun at different impact angels, i.e. 0°, 30° and 45°. A high-speed camera was used to capture and record the experimental images and data during the impacting process. Different failure patterns were observed in the FMLs under oblique and normal impact, with the differences concentrated on the initial crack (in the back surface) and plugging damage (in both the front and back surface). The angular change in direction of the projectile during perforation was only observed during oblique impact tests while the maximum value of the angular change was observed when the impact velocity was close to its ballistic limit velocity. In addition, the angular change decreases with increasing impact velocity and is almost constant when the value of [Formula: see text] reaches a critical value. It can also be observed from the impact test results (both normal and oblique impacts) that FMLs exhibited the lowest ballistic limit velocity when the impact angle was close to 30°. In particular, normal impact shows a higher ballistic limit velocity than that of oblique impact while the ballistic limit velocity at impact angle 45° is slightly higher than that at 30°.