圆柱形长杆超高速正碰撞薄板结构破碎效应

超高速碰撞多层板结构破碎效应研究对空间碎片防护及动能武器毁伤效应研究有着重要意义。采用ANSYS/AUTODYN程序的SPH方法,对超高速碰撞碎片云的形成过程进行了数值模拟,某典型时刻一次及二次碎片云形貌的数值模拟结果与实验结果吻合较好,验证了计算方法和模型参数的正确性。在此基础上采用数值模拟方法,对钨合金、轧制均质装甲(Rolled Homogeneous Armor,RHA)及LY12铝三种材料的圆柱形弹体超高速碰撞薄板的破碎规律进行了研究,基于量纲分析方法得出了弹体破碎长度随弹靶材料特性、弹靶尺寸及初始撞击速度变化的关系式。并研究了钨合金及RHA两种材料的长杆弹对八层RHA板结构的超高速碰撞效应。     

Debris clouds generated by hypervelocity impact of cylindrical projectiles with thin aluminum plates

Orthogonal, flash x rays were used to observe the debris clouds produced by the hypervelocity impact of cylindrical aluminum projectiles with thin aluminum sheets or bumpers. Three major structural features were observed in the debris clouds--a front cone, a bulbous main debris cloud, and an inner cone. Inclination of the projectile at impact changed the orientation of these features and the severity of damage to the rear wall of a double-sheet structure; projectiles with the greatest inclination produced the most damage. Two experiments, using aluminum and copper as projectile and target or target and projectile, respectively, were performed to determine the source of material in each of the three structural features of the debris clouds. The front cone and main cloud were shown to consist of bumper debris while the inner cone was composed of projectile fragments.     

A comparison of hole size formation caused by a hypervelocity impact with a thin film using molecular dynamics and CTH

The relationship of the mass, velocity, and density of an impacting projectile to the hole formed as a consequence of a hypervelocity penetration is a subject of great importance in the study of Interplanetary Dust Particles and Orbital Debris. During the past twenty years extensive efforts have been made in developing computational procedures that model hypervelocity impacts. The vast majority of these projects have used hydrodynamic equations with either a Lagrangian or Eulerian grid or some hybrid of the two forms. Another numerical procedure that can be applied to the study of hypervelocity penetrations is molecular dynamics (MD). The appeal of MD to the problem of hypervelocity impacts lies in the fact that the thermodynamic variables of pressure, temperature, and density are found independently of each other without requiring an equation of state. The primary disadvantage of MD is the size of the system that can be effectively modeled. In this paper six different hypervelocity impacts are considered using MD and the hydrocode CTH developed at Sandia National Laboratories. The six impacts consist of a cube impacting a thin film at 7,9, and 11 km/s with an aspect ratio of one to one and two to one. The time evolution of the density, pressure, and temperature are compared for each of the methods. Finally the hole size created by the impacts are calculated for each method, and the results compared. Conclusions about the effectiveness of MD are offered with suggestions for future work.     

球形弹丸超高速碰撞破碎特性

讨论超高速碰撞数值模拟方法,用ANSYS/AUTODYN程序的SPH方法对球形弹丸超高速撞击时弹丸破碎、碎片云形成过程进行数值模拟并与实验结果比较,验证计算方法及模型参数的正确性。在此基础上研究钨合金、轧制均质装甲(Rolled Homogeneous Armor,RHA)两种材料球形弹丸破碎的临界速度随比值(ts/dp,ts为靶板厚,dp为弹丸直径)的变化规律,给出两种材料超高速碰撞时应变率及平均碎片尺寸随撞击速度的变化曲线以及碎片质量分布规律。     

Fragmentation of a valine molecule by electron impact

The formation of ion products of single and dissociative ionization of a valine molecule (C₅H₁₁NO₂) by high-energy (11.5 MeV) and low-energy (below 150 eV) electrons has been investigated by mass spectrometry. Mass spectra of this molecule and near-threshold functions of yield of its ion fragments, for which the magnitudes of occurrence energies are determined, have been obtained. The analysis of the changes in mass spectra of valine molecules irradiated with doses of 5 and 20 kGy in comparison with those for unirradiated molecules shows that high-energy irradiation changes irreversibly the structure of some of the initial molecules.     

Tumbling of hypervelocity rods induced by impact with oblique plate targets

We investigated the cause of tumbling by hypervelocity rods after impact with oblique plate targets. The projectiles were strong rods, length to diameter ratio of 6 to 10, prepared from aluminum (10 tests) or steel (5 tests), launched at velocities of 4.2 to 4.8 km/s, and impacted into like material targets. The rods had little or no initial yaw (the average yaw was 1.8°). The residual projectile properties of length, tumbling rate and radial velocity were measured and evaluated in a simple model for rod tumbling. The model is based on the observation that plastic shear continues at the nose of the rod for a finite time after target perforation. Based on the observed tumbling rate, duration of plastic flow and the inertia of the residual rod an implicit determination of the shear strength of the rod was obtained. The calculated shear strength was in fair agreement with static shear values.     

Experimental evidence of triboluminescence induced by hypervelocity impact

The emission of light due to crystal fracture, or triboluminescence (TL), is a phenomenon that has been known for centuries. One of the most common examples of TL is the flash created from chewing wintergreen Lifesavers^®. For the last couple of years, the authors have been measuring fluorescence properties of phosphors like zinc sulfide doped with manganese (ZnS:Mn). Preliminary results indicate that impact energies greater than 16 mJ produced measurable TL from ZnS:Mn. Light was generated from the interaction of a dropped mass and a small number of luminescence centers in the ZnS:Mn powder. To extend this research, a two-stage hypervelocity light gas gun located at NASA's Marshall Space Flight Center (MSFC) was used to evaluate equipment and settings that show promise for hypervelocity TL detection. In these experiments, a projectile was accelerated to approximately 5–6 km/s before striking a ZnS:Mn phosphor-coated aluminum plate. This paper will provide an overview into the first experimental evidence of TL emission from ZnS:Mn due to hypervelocity impact. It is hoped that these results will generate interest in future hypervelocity research.     

Scale modeling of hypervelocity impact

The significance of different Pi terms which result from a dimensional analysis of the parameters involved in hypervelocity impact is discussed. The consequences of distorting some physical phenomena in models are analyzed, and experimental verification is presented for the use of replica and dissimilar material models.     

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.     

Analogies and differences between quasi-static indentation and hypervelocity impact morphologies on thin solar cells

Morphologies produced by quasi-static indentation on thin Hubble Space Telescope (HST) solar cells show remarkable similarities to much of the hypervelocity damage sustained by the HST solar array whilst in orbit. Quasi-static indentation tests carried out with blunt and sharp indentors reveal analogies between static and dynamic (hypervelocity) indentation indicating similar fracture mechanics processes over the energy range evaluated. Understanding the static case assists to characterise better the dynamic process and bridge the intervening gap.     

Characteristics of hypervelocity impact debris clouds

This paper describes an experimental investigation of hypervelocity impact debris clouds produced by impacting metal rods with Kapton flyers in an electric gun facility. Soft copper witness plates placed in the path of the debris were cratered and coated with rod material. From the sizes of the craters on the witness plates we could obtain values for a cratering parameter containing the ,asses and velocities of the debris fragments that formed the craters. By combining the cratering parameter with rough estimates of the fragment masses, we then estimated the fragment velocities. By measuring the thickness and extent of the coating on the witness plates, we obtained a bound on the amount of material vaporized by the impact.     

Spectral measurements of hypervelocity impact flash

We have revisited the well-known phenomena of impact flash by examining the optical spectra generated by hypervelocity impacts at velocities up to several tens of kilometers per second. This particular effort, sponsored by an LDRD from our laboratories, has looked at the flash from impacts over a range of velocities from 6 to 25 km/s, using two different experimental environments. Both two- and three-stage light-gas guns and magnetically driven flyers on the Z accelerator were used. Here, we describe the latter set of experiments. Using standard tabulations of atomic spectral data, we were able to identify strong spectral lines from the principal materials used in the various shots. We demonstrated that the impact-flash spectra were qualitatively reproducible from shot to shot, and have confirmed the feasibility and credibility of using impact-flash spectroscopy for remote sensing applications such as meteoroid-impact or missile-defense engagement analyses.     

Review of modern hypervelocity impact facilities

The paper describes three hypervelocity impact facilities, their instrumentation, the laucher systems, the launch techniques for a large variety of projectile geometries, and the launcher performance. A very brief review is given of the research in the areas of military applications, meteorite impact simulation, basic impact research, and efforts to improve the performance of the light-gas guns and measurement techniques. An outline at future research programs is given.     

Debris clouds produced by the hypervelocity impact of nonspherical projectiles

The significant features of debris clouds produced by the normal impact of spheres are described and compared with the features of debris clouds produced by the normal impact of nonspherical projectiles. Projectile shape and orientation at impact are shown to have a significant effect on the ability of a single-sheet bumper shield to promote the breakup of the projectile and the dispersion of the projectile fragments. The debris clouds produced by the normal impact of spheres are “relatively benign” in terms of their potential for damage to the rear wall of a spacecraft. Debris clouds produced by nonspherical projectiles contain one or more very large fragments at their leading edge that significantly threaten rear wall integrity.     

Crater formation in a plastic target under hypervelocity impact

The analytical models of crater formation in a semi-infinite target under hypervelocity impact have been analyzed. It has been shown by numerical calculations that to approximately calculate the crater size for a narrow range of impact velocities, the model of an ideal plastic body can be used. A new analytical model of crater formation in a plastic target, which describes the experimental data in a wide range of impact conditions, is suggested. The crater formes are analyzed.     

Magnetic field produced by a thin sheet inductor of asuperconducting generator

A 3-D calculation of the magnetic field produced in the air by a thin sheet model of a superconducting generator's `horse saddle' type winding is presented. To be able to calculate the field everywhere in space, including on the winding, analytical expressions consisting of elliptic integrals are derived and numerical methods are used to solve them, permitting a new time-saving, efficient computation algorithm     

Experimental study on expansion characteristics of debris clouds produced by oblique hypervelocity impact of LY12 aluminum projectiles with thin LY12 aluminum plates

Tests of hypervelocity projectile impacts to a double-wall structure made of LY12 aluminum were performed using a two-stage light gas gun. In the bumper plate hole analysis, empirical equations that relate hole dimensions to impact parameters such as velocity, angle of obliquity and bumper plate thickness are obtained. The laser shadowgraphs in order to get the expansion of debris clouds were taken and the characteristic parameters obtained. The damage effects of the back wall varying with impact parameters were studied. The expansion of debris clouds was determined.     

Response of composite materials to hypervelocity impact

Investigation of composite materials response to hypervelocity impact by space debris has been carried out. In order to simulate hypervelocity impact, a unique laser driven flyer plate (LDFP) system was used, generating hypervelocity debris with velocities of up to 3 km/s. The materials studied in this research were Kevlar 29/epoxy and Spectra1000/epoxy thin film micro-composites (thickness of about 100 μm). Both Spectra and Kevlar fibers are used in long-duration spacecraft outer wall shielding to reduce the perforation threat. The micro-mechanical response of different composites was studied and correlated to the fiber, the matrix and the fiber/matrix interface properties. Visual and microscopic examinations of the damaged area identified fiber debonding as the prevailing failure mechanism. On the basis of a simple energy balance model it can be stated that for Spectra/epoxy composite the dominant mechanism is new surface creation, whereas for Spectra surface-treated fibers/epoxy the fiber pull out is the dominant mechanism. For Kevlar/epoxy fiber, pull out mechanism plays an important role.