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.     

An engineering model to predict perforation damage to plates impacted by high velocity debris clouds

This paper describes experiments and the development of a model to predict damage to metallic plates impacted by high velocity, multi-particle debris clouds. The experiments involved single steel spheres fired at a steel shatter plate at speeds near 1.5 and 2.0 km/sec to generate the debris clouds. In each series of tests, the impact velocity was controlled, and a witness plate was placed at increasing distances behind the shatter plate to observe the effects of debris particle dispersion on plate damage. This paper focuses on the variations, with plate spacing, in the size of the central region removed from the witness plates. The central hole size model compares the post impact kinetic energy distribution in a witness plate impacted by a debris cloud to the free impact residual kinetic energy in an equivalent plate impacted by an L/D=1 steel cylinder, at the ballistic limit velocity. This approach permits extension of the model to other plate materials through utilization of existing ballistic limit velocity data.     

Fracture behavior of silicon nitride ceramics subjected to hypervelocity impact

A new advanced ceramic thruster made of monolithic silicon nitride ceramics was developed for the planetary exploration spacecraft AKATSUKI (PLANET-C) at Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). To ensure its operation onboard the spacecraft, the reliability of the ceramic thruster against micrometeoroid hypervelocity impact has been investigated. Silicon nitride plates were impacted by spheres of stainless-steel and other materials with 0.2-0.8-mm diameters in the velocity range up to 8.0 km/s using a two-stage light-gas gun. Using crater depth data under various impact conditions, the penetration equation of silicon nitride was determined. The impacted samples showed fracture patterns of three types: cratering, cratering with spallation, and perforation. These fracture patterns were well categorized by the multiple forms of the penetration equation.     

Material Selection for Ceramic Gun Tube Liner

The U.S. Army Research Laboratory is investigating the application of ceramics as bore materials in advanced gun systems. The lower mass and improved high temperature performance of ceramics over traditional gun steels could produce new barrels with improved service life and lower weight while enabling the use of new propellants. Several different ceramics have been researched into which material would best survive the interior ballistic conditions for a variety of different caliber systems. The candidate materials are commercially available monolithic ceramics. Alumina, zirconia, three silicon carbide compositions, two silicon nitride compositions, and a SiAlON material were initially selected. A coupled approach of modeling and experimental verification led to the downselection of the silicon nitride and SiAlON materials as the most capable of surviving the interior ballistic conditions and functioning as a barrel liner. This paper describes the tests, presents the results, and discusses the reasons for these selections.     

Micrometeoroid impact on ceramic thin components for interplanetary probe

A new advanced ceramic thruster made of monolithic silicon nitride (Si₃N₄) is under development for the next interplanetary probe of PLANET-C Venus exploration mission in Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). In order for secure operation of a spacecraft with a ceramic component onboard a real mission, the reliability against micrometeoroid impacts on the ceramic component has to be investigated in addition to the quasi-static mechanical and thermal analyses and verifications. First, the risk probability of the micrometeoroid impacts was evaluated by using an interplanetary flux model, and the risk evaluation in terms of impact energy was proposed by combining the velocity distribution with the flux model. The probability of impacts on the ceramic thruster during the mission was estimated with this model. Second, hypervelocity impact tests were performed with a two-stage light-gas gun. Three types of failure were observed: one was only a crater formed on the impact surface. Another type was crater formation on the front-face and spall fracture on the back-face and in the last type a perforation was formed in addition to cratering and spalling. The samples did not either shatter or breakdown for the impact energies tested in this study. The impact failure morphology observed in this study showed dependency on the plate thicknesses and the projectile kinetic energy. The energy-based risk evaluation together with the series of the hypervelocity impact tests indicated that the silicon nitride ceramic thruster onboard the interplanetary probe would have only a local damage and survive during the mission term.     

A new analytical model to simulate impact onto ceramic/composite armors

A very simple one-dimensional and fully analytical model of ballistic impact against ceramic/composite armors is presented in this paper. The analytical model has been checked both with ballistic tests and numerical simulations giving predictions in good agreement with them. The model allows the calculation of residual velocity, residual mass, and the projectile velocity and the deflection or the strain histories of the backup material. These variables are important in describing the phenomenological process of penetration. Described are modifications to previous work of impact into ceramics combined with a new composites model. The development of this composite model is based on studies of the impact in yarns, fabrics and finally composites.     

Experiments and 2-D simulations of high velocity penetrations into ceramic tiles

This paper investigates the interaction of long-rod penetrators with thick ceramic tiles, sandwiched between steel plates, through several model experiments and 2-D simulations. Experimental data from low velocity penetrations have been used to calibrate the relevant properties of the ceramic specimens. The influence of increasing impact velocity on tile performance was then investigated through data and simulations of shaped charge jets penetrating the ceramic. We found that the ballistic efficiency of the ceramic tile is lower against high velocity (5 km/s) long-rods, in contrast with the common thesis that their improved performance against shaped charge jets is the result of their enhanced strength. On the other hand, our simulations clearly show that, for high strength ceramics, there is a radial motion of metal and ceramic debris towards the penetration axis. This effect is, probably, the main reason for the considerable improvement in the performance of ceramic tiles against shaped charge jets.     

An investigation of metal matrix composites as shields for hypervelocity orbital debris impacts

The improvement of space vehicle shield designs to resist penetration by hypervelocity impacts of meteoroids or man-made orbital debris can lengthen mission life and increase mission efficiency. One option to improve shields is to create new bumper materials which can be tailored to meet the requirements for effective shielding. Metal matrix composites are one such material. Fiber content, type, and orientation could be varied to tailor the material to the specific properties needed for weight efficient shielding. In this study, two varieties of aluminum matrix composites were investigated, one with continuous graphite fibers and one with silicon carbide particulates. The objectives of the study were: to compare the penetration resistance of the composite with the known resistance of aluminum; to study the penetration mechanics by comparing the condition of the composite after the impact test with the pre-test condition; to study the effects of fiber content and fiber orientation on penetration resistance; and to recommend a material “design” for metal matrix composites which would best protect a space vehicle from orbital debris. The composite bumpers did not perform significantly better than aluminum bumpers. The particulate composites are more effective bumpers than the continuous fiber composites for the conditions tested. The differences in the measured hole diameters resulting from the impact tests as compared to predicted hole diameters for the particulate composite bumpers, are within the expected differences for metallics. However, the continuous fiber composites had much larger holes than predicted.     

Fragmentation of targets during ballistic penetration events

An analytical target fragmentation model is developed to predict the number of armor debris fragments produced in a ballistic penetration event. The model employs an energy balance to estimate the energy available to propagate cracks in the target material and thus produce an estimate of the mean number of behind-armor debris fragments. The expected number of behind-armor debris fragments agrees well with the results of conventional ordnance velocity target penetration behind-armor debris tests. This analytical fragmentation model and test results were used as the basis for the development of a means of calibrating the parameters of a Weibull statistical distribution function to predict the probability distribution of the number of debris fragments produced in a ballistic impact. It was concluded that the armor fragmentation model was a good predictor of the number of fragments produced in a ballistic penetration event deserving further investigation.     

氮化硅陶瓷的液相连接研究

本文研究了用氧氮玻璃作为中间层材料连接氮化硅陶瓷．结果表明,在1600℃×30min、5MPa的外加压力条件下,氮化硅陶瓷的结合强度达到基体氮化硅陶瓷的57％．结合层内的结构与基体氨化硅十分相似,但是晶粒尺寸较细,两者结构上的一致性对于提高结合强度起着重要的作用．     

Selecting enhanced space debris shields for manned spacecraft

A research program was funded by the European space agency (ESA) to improve and optimize the shields used to protect the manned elements of the international space station (ISS) against impacts of micro-meteoroids and orbital debris. After a review of existing shielding systems and after a series of light gas gun (LGG) experiments to screen interesting new materials and configurations, the research focused on shields with a metallic outer bumper, an intermediate stuffing and an inner metallic wall (representing the pressure shell of a manned spacecraft). Additional LGG experiments were performed on several configurations, with bumpers containing aluminum foam or made from titanium and aluminum super-alloys and with several combinations of stuffing materials. The comparison of the test results showed that ceramic cloth (Nextel) plus aramid fabric (both 2D and 2.5D Kevlar weaving) used as intermediate bumper gave a good protection compared to the overall area density requested. Configurations with by-layered aluminum foam bumpers (sandwich panels with asymmetric Al face sheets and a core made from Al foam) and Kevlar stuffing showed excellent resistance to normal impacts at about 6.5 km/s. However, the influence of material properties varying from batch to batch and threshold phenomena made ranking among the tested options rather difficult. The test campaign showed that it was rather difficult to improve over the already good ballistic performances of the debris shields developed by Alenia Spazio for the ISS manned elements. The by-layered Al-foam bumper and Kevlar stuffing configuration was selected for additional tests, including low velocity and oblique impacts, to develop ballistic limit curves.     

Phase three penetration

Phase three penetration is defined as the target penetration that occurs after a high-velocity penetrator has fully eroded. Phase 3 penetration is due to one or the combination of after-flow and secondary penetration of the target by the eroded penetrator debris. Recent experimental data for long tungsten rods penetrating confined boron carbide, aluminum nitride, and silicon carbide targets are used to investigate phase 3 penetration. It is found for these three ceramic targets that the onset impact velocity for the occurrence of phase 3 penetration is very roughly 2 km/s. The phase 3 penetration increases with impact velocity approximately as v². For these experiments the phase 3 penetration appears to be due almost entirely to secondary penetration.     

Impact fragmentation of high-velocity compact projectiles on thin plates: a physical and statistical characterization of fragment debris

The high-velocity impact of a projectile onto a structure results in the creation and energetic expulsion of fragments of the interacting materials. The nature of this fragment debris is of concern in certain applications. Although more broadly applicable, the present study is motivated by a need to characterize the size and velocity distribution of fragments generated by orbital debris impacting external components of spacecraft structure, such as shielding and radiators. In this effort, statistical relations are developed to predict size, momentum and trajectory distributions of the debris. The underlying physics applied are those used in the fields of impact mechanics, thermodynamics of shocks, and statistical fragmentation. Equations from impact mechanics lead to predictions for mass, global momentum, and excess energy of the fragment debris. Relations from shock thermodynamics are developed to partition the initial kinetic energy into thermal and mechanical energies, and therefore to predict mass fractions of solid, liquid and vapor components and the subsequent dispersing motion of this fragment debris. Statistical methods of the energy-based Maxwell-Boltzmann type are pursued to characterize the inherently stochastic fragmentation event, emphasizing the extremes of fragment size and velocity. Computational simulations of impact events and data from impact fragmentation experiments are exploited in validating the underlying theoretical assumptions and the resulting impact fragmentation model.     

A model for deformation and fragmentation in crushable brittle solids

A unified framework of continuum elasticity, inelasticity, damage mechanics, and fragmentation in crushable solid materials is presented. A free energy function accounts for thermodynamics of elastic deformation and damage, and thermodynamically admissible kinetic relations are given for inelastic rates (i.e., irreversible strain and damage evolution). The model is further specialized to study concrete subjected to ballistic loading. Numerical implementation proceeds within a finite element context in which standard continuum elements represent the intact solid and particle methods capture eroded material. The impact of a metallic, spherical projectile upon a planar concrete target and the subsequent motion of the resulting cloud of concrete debris are simulated. Favorable quantitative comparisons are made between the results of simulations and experiments regarding residual velocity of the penetrator, mass of destroyed material, and crater and hole sizes in the target. The model qualitatively predicts aspects of the fragment cloud observed in high-speed photographs of the impact experiment, including features of the size and velocity distributions of the fragments. Additionally, two distinct methods are evaluated for quantitatively characterizing the mass and velocity distributions of the debris field, with one method based upon a local energy balance and the second based upon global entropy maximization. Finally, the model is used to predict distributions of fragment masses produced during impact crushing of a concrete sphere, with modest quantitative agreement observed between results of simulation and experiment.     

Comparative analysis of oblique impact on ceramic composite systems

An experimental programme is presented which investigated the performance of oblique, ceramic/metal, bilayer composite armours. The ceramics, alumina and silicon carbide, were backed by either Rolled Homogeneous Armour steel (RHA) or 7000 series aluminium. Using a model scale tungsten penetrator at two velocities (representing current and future ordnance threats) the effect of configuration on ballistic limit or depth of penetration (DOP) areal densities was determined. Areal densities of the DOP targets decreased with increasing ceramic thickness, achieving a minimum at zero residual penetration in the backing. The bilayer targets, loaded at the ballistic limit needed a larger areal density to defeat the penetrator. This areal density also decreased with ceramic thickness but showed a minimum with respect to ceramic thickness, as a result of reduced support by the thinner metallic backing. At 1450ms⁻¹ the most efficient system was found to be a SiC/Al, which demonstrated a 25% weight saving over the monolithic aluminium reference target. The Al-alloy backing performs better than RHA, and SiC better than Al₂O₃.     

动能弹侵彻多层陶瓷靶板数值模拟研究

结合试验对钨合金长杆弹垂直侵彻多层陶瓷靶板进行了三维数值模拟,得出了侵彻的物理图像及各种参量的变化规律。模拟结果中,后置钢靶剩余穿深和陶瓷破碎锥形状与试验基本一致。对于多层陶瓷靶板,每一层都会有漏斗形的破碎锥出现,且这些破碎锥的形状基本一致。随着陶瓷层数的增多,弹体的速度和动能下降速率逐渐变小。比较了相同厚度的多层和单层陶瓷靶板的抗弹性能,结果表明两者的陶瓷破坏形式不同,多层靶板的抗弹性能要优于相同厚度的单层陶瓷靶板,且仅在一定厚度范围内这种优势才较为明显。     

Layered Si3N4 composites with enhanced room temperature properties

Four silicon nitride multilayer composites were prepared by hot pressing. Internal stress distribution along the layer boundary dictates the anisotropy of mechanical properties of the composite. The room-temperature bending strength and fracture toughness of all layered composites was higher than the bending strength of related monoliths. Layered ceramic materials exhibited higher tolerance to flaws in comparison to the monolithic ceramic.     

Lateral confinement effects in long-rod penetration of ceramics at hypervelocity

Reverse ballistic experiments were conducted using gold long rods impacting cylinders of silicon carbide to study the effect of failure kinetics in ceramic penetration. Some of the early experiments impacted off-centered due to the dynamics of the barrel and sabot. Nevertheless, the data appeared to be in good agreement with centered impact, although conventional wisdom suggested that penetration resistance should decrease due to lateral confinement effects. Numerical simulations of the experiments were conducted to investigate and to quantify the influence of lateral confinement as a function of impact velocity for the ceramic targets. Above 3.0 km/s, close proximity to a lateral boundary results in less than a 2% increase in the penetration velocity.     

三种机械密封材料的摩擦磨损性能研究

研究了3种核主泵用机械密封陶瓷材料(氮化硅、氧化铝和碳化硅)在室温干摩擦条件下及水润滑条件下分别与氮化硅陶瓷球对磨的摩擦磨损性能。研究结果表明,在与氮化硅球干摩擦的3种材料中氧化铝陶瓷具有最大的摩擦系数和最小的磨损质量,氮化硅具有最小的摩擦系数。在氮化硅陶瓷自配对摩擦副摩擦磨损试验中,水润滑条件下氮化硅摩擦系数及摩擦质量损失都有很大程度的减小,且摩擦系数随转速增加而减小。综合考虑力学性能和摩擦磨损性能,选择氮化硅陶瓷作为核主泵机械密封材料更合适。     

Using a Single Transducer Ultrasonic Imaging Method to Eliminate the Effect of Thickness Variation in the Images of Ceramic and Composite Plates

This article describes a single transducer ultrasonic imaging method based on ultrasonic velocity measurement that eliminates the effect of thickness variation in the images of ceramic and composite plate samples. The method is based on using a reflector located behind the sample and acquiring echoes off the sample and reflector surfaces in two scans. As a result of being thickness-independent, the method isolates ultrasonic variations due to material microstructure. Its use can result in significant cost savings because the ultrasonic image can be interpreted correctly without the need for precision thickness machining during nondestructive evaluation stages of material development. Velocity images obtained using the thickness-independent methodology are compared with apparent velocity maps and c-scan echo peak amplitude images for monolithic ceramic (silicon nitride), metal matrix composite and polymer matrix composite materials having thickness and microstructural variations. It was found that the thickness-independent ultrasonic images reveal and quantify correctly areas of global microstructural (pore and fiber volume fraction) variation due to the elimination of thickness effects. A major goal achieved in this study was to move the thickness-independent imaging technology out of the lab prototype environment and into the commercial arena so that it would be available to users worldwide. The method has been implemented on commercially-available ultra-sonic can systems manufactured by Sonix, Inc. via a formal technology transfer agreement between NASA and Sonix.