Hypervelocity impact tests and simulations of single whipple bumper shield concepts at 10km/s

A series of experiments has been performed to evaluate the effectiveness of a Whipple bumper shield to orbital space debris at impact velocities of 10 km/s. Upon impact by a 19 mm (0.87 mm thick, L/D 0.5) flier plate, the thin aluminum bumper shield disintegrates into a debris cloud. The debris cloud front propagates axially at velocities of 14 km/s and expands radially at a velocity of 7 km/s. Subsequent loading by the debris on a 3.2 mm thick aluminum substructure placed 114 mm from the bumper penetrates the substructure completely. However, when the diameter of the flier plate is reduced to 12.7 mm, the substructure, although damaged is not perforated. Numerical simulations performed using the multi-dimensional hydrodynamics code CTH also predict complete perforation of the substructure by the subsequent debris cloud for the larger flier plate. The numerical simulation for a 12.7 mm flier plate, however, shows a strong dependence on assumed impact geometry, i. e., a spherical projectile impact geometry does not result in perforation of the substructure by the debris cloud, while the flat plate impact geometry results in perforation.     

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。     

聚能装药垂直侵彻靶后破片的散布规律

靶后破片是造成装甲内部环境二次毁伤的主要媒介,准确掌握其在靶后一定距离和面积上的散布规律具有重要意义。通过X光试验和有限元数值模拟对靶后破片云形态特征进行了研究,建立了破片速度散布的数学模型,并通过后效铝板获得了破片的散布情况,得到了不同厚度靶板下破片速度、破片数量等特征参数随飞散角的变化规律,为聚能装药毁伤效应评估提供参考。     

EFP垂直侵彻靶后破片云描述模型

针对靶后破片是影响装甲保护能力和聚能装药毁伤的主要问题,基于EFP垂直侵彻的靶后破片,建立其初始靶后破片云的数学描述模型,并在此基础上采用有限元仿真软件AUTODYN-3D对EFP垂直侵彻钢靶形成靶后破片的过程进行数值模拟。数值模拟结果与靶场实验结果进行对比,结果表明:仿真的EFP成型参数、靶后破片空间分布状态和靶板开孔特征均与实验较为吻合。因此,证明该仿真模型和所得靶后破片云初始描述模型具有较高的可信度,可以为EFP对装甲目标的毁伤评估方面提供一定的参考。     

EFP垂直侵彻靶后破片云描述模型

针对靶后破片是影响装甲保护能力和聚能装药毁伤的主要问题,基于EFP垂直侵彻的靶后破片,建立其初始靶后破片云的数学描述模型,并在此基础上采用有限元仿真软件AUTODYN-3D对EFP垂直侵彻钢靶形成靶后破片的过程进行数值模拟。数值模拟结果与靶场实验结果进行对比,结果表明:仿真的EFP成型参数、靶后破片空间分布状态和靶板开孔特征均与实验较为吻合。因此,证明该仿真模型和所得靶后破片云初始描述模型具有较高的可信度,可以为EFP对装甲目标的毁伤评估方面提供一定的参考。     

A Stacked-Shell Finite Element Approach for Modelling a Dynamically Loaded Composite Bolted Joint Under in-Plane Bearing Loads

This paper presents the results of a study into a novel application of the “stacked-shell” laminate modelling approach to dynamically loaded bolted composite joints using the explicit finite element code PAM-CRASH. The stacked-shell approach provides medium-high fidelity resolution of the key joint failure modes, but is computationally much more efficient than full 3D modelling. For this work, a countersunk bolt in a composite laminate under in-plane bearing loading was considered. The models were able to predict the onset of damage, failure modes and the ultimate load of the joint. It was determined that improved debris models are required in order to accurately capture the progressive bearing damage after the onset of joint failure.     

Experimental and numerical simulation of high velocity impact on steel targets

The perforaton process of steel plates at normal impact by cylindrical steel fragments together with the debris cloud expansion have been studied in the velocity range 2 - 3 km/s. The fragments have a length-to-diameter ratio of 1.035 and a mass of 51g. Fragment and target materiass are 9SMn28 and C45, respectively. Two plate thicknesses of 20 and 30 mm have been tested. These thicknesses are in the order of the penetration depth in the semi-infinite target. In addition the cratering in the semi-infinite target has been investigated. The crater dimensions on the target front side are comparable for both, the plate targets and the semi-infinite targets. The degree of fragmentation in the debris cloud increases with velocity and is smaller in case of the 30 mm target. The ratio of longitudinal to lateral dimensions of the debris clouds is independent of the target thickness, but dependent on the distance from the plate rear side. This ratio increases with distance and converges at larger distances versus nearly hemispherical expansion. A further goal of this paper is the application of a Lagrangian code to the numerical simulation of the impact process in the semi-infinite target. For this purpose the LS-DYNA2D code with a new erosion option has been used. Material input data are the static material properties as well as shock wave data determined from planar impact tests for the steels used here. LS-DYNA2D with its new erosion option can predict in a good agreement the particle velocity history of the planar impact tests and the crater shapes in the semi-infinite target.     

Failure probability of laminated architectural glazing due to combined loading of wind and debris impact

Building façades are vulnerable to wind and wind-borne debris during extreme weather conditions like hurricanes. Laminated glazing is widely used as window glazing material to ensure the integrity of the building interiors. Wind-borne debris has been classified as small-hard and large soft missiles representing small gravel to large wooden bars that constitute the debris impacting the glazing during severe storms. Failure of laminated window glazing due to combined effect of wind and debris is studied. Stress analysis is done using finite element code ABAQUS. This is used in conjunction with a mechanics based statistical model to predict the cumulative probability of inner glass ply breakage in laminated glazing. A parametric study involving failure probability of inner glass ply for different geometry of laminated glazing is also performed.     

碎片云撞击声发射信号能量特征小波包分析

利用小波包分析技术对碎片云撞击载荷作用下铝合金板声发射信号的能量分布特征进行了研究。首先,介绍了碎片云撞击信号的获取方案及撞击引起的损伤情况;其次,对获取的声发射信号进行小波包分析,得到了信号在频率带上能量分布特征图。最后,讨论了碎片云撞击损伤特征与声发射信号能量分布的关系。分析结果发现,对于相同质量的弹丸,随着其破碎程度的提高,形成的碎片云对后板的损伤程度减少;弹丸具有的初始速度越大,弹丸破碎越完全,碎片云撞击声发射信号中的能量越小;当弹丸破碎程度低时,碎片云撞击引起的声发射信号能量集中在约488kHz以下;弹丸破碎程度越高,信号中488kHz以上的能量所占总能量的比例越大。     

椭球弹丸超高速撞击防护屏碎片云数值模拟

低地球轨道的各类航天器易受到微流星体及空间碎片的超高速撞击.本文采用AUTODYN软件进行了椭球弹丸超高速正撞击及斜撞击防护屏碎片云的数值模拟.给出了三维模拟的结果.研究了在相同质量的条件下,不同长径比椭球弹丸以不同速度和入射角撞击防护屏所产生碎片云的特性,并与球形弹丸撞击所应产生的碎片云特性进行了比较.结果表明:在相同的速度下,不同长径比椭球弹丸撞击的碎片云形状、质量分布和破碎程度是不同的,随撞击入射角的增加弹丸的破碎程度增大,滑弹碎片云的数量增加;随撞击速度的增加,弹丸的破碎程度也增加.     

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.     

A comparison of fragmentation models

The key to conducting an accurate lethality assessment is the use of a robust assessment methodology. One of the critical components of a lethality assessment is the characterization of the debris cloud created by the initial high speed impact. Without a proper characterization, it is impossible to obtain an accurate prediction of the response of an interior target component to subsequent debris cloud impact loadings. The fast-running codes FATEPEN2, KAPP-II, and PEN4 contain fragmentation models that characterize the debris cloud fragment population resulting from a high speed impact. The objective of the work described in this paper as to compare the predictions of the fragmentation models within these three codes over the 1–16 km/s impact velocity regime. This objective was achieved through a parametric study of debris cloud material characterization using the fragmentation schemes in the FATEPEN2, KAPP-II, and PEN4 semi-empirical lethality assessment schemes for a variety of projectile and target materials and configurations.     

球形爆炸容器动力响应的强度分析

运用ＤＹＴＲＡＮ程序中的欧拉计算方法,模拟了作用于球形爆炸容器内壁的反射超压波形。运用解析法和三维有限元程序ＬＳ－ＤＹＮＡ,对容器壳体在反射超压作用下的动力响应进行了强度分析,给出了容器的几个特征点的等效应力历史和重要区域的等效应力云图。分析结果对类似爆炸容器的强度设计和安全使用具有参考意义。     

Integral model for the description of the debris cloud structure and impact

The purpose of the present paper is to introduce a new integral model capable to describe the evolution of the debris clouds originated after normal-impacts of orbital debris over a Whipple shield. This work had been developed at Alenia Spazio in the context of a degree thesis. Several numerical SPH simulations of debris impacts on a Whipple shield configuration were performed to determine the ballistic limit and to compare it with semi-empirical damage equations. In the present paper, the numerical simulations were used to investigate the typical behaviour of experimental debris clouds ([6] and [9]) and to support the development of the integral model.

With respect to previous papers ([1], [2], [3], [10]) in which a spherical shell-wise debris cloud was considered, here we try to introduce more realistic assumptions. We approximate the cloud's shape also introducing ejecta veil effects, which produce a multiplication of the deposited momentum upon the underneath wall. In the present model, the most peculiar hypothesis is a cinematic self-similar behaviour that is, whatever the shape is, the debris cloud evolves keeping unchanged its shape. Then, the material is opportunely distributed inside a volume and the choice of that distribution is described taking into account the results of the numerical simulations. Knowing the spatial material distribution and treating the cloud as a fluid, we can estimate the load time history and the drag-unitary force induced by the cloud impacting upon the rear wall. Of course, such a method uncouples the dynamic response of the rear wall from the evolution of the debris cloud. The balances of mass, momentum and energy allow three global and unknown parameters to be determined. The one-dimensional theory of impact ([10]) is used to take into account the conversion of part of the initial kinetic energy into internal thermal energy. No integration of differential equations is performed since complex propagation phenomena are taken into account through the effects they globally produce. The model still presents some free parameters related to the integral formulation. These parameters cannot be calculated through any balance condition, but they must be imposed to get a good, global reproduction of the debris cloud. The choice of these parameters is still the weak aspect of the method, and it depends on the consideration of the results obtained with more sophisticated tools, as, for instance, SPH simulations. The spatially defined load time history obtained with the debris cloud integral model can be used for further analysis on the back up plate.     

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.     

A single energy-based parameter to assess protection capability of debris shields

Protecting spacecraft structures against hypervelocity impacts (HVIs) of space debris, which may cause fatal damage to the spacecraft structures, has received wide attention. In this paper, the numerical simulation of hypervelocity solid–solid impacts is conducted and an energy-based parameter to assess protection capability of debris shields is proposed. To numerically simulate the hypervelocity impact phenomena, a two-dimensional improved smoothed particle hydrodynamics (SPH) method with new particle generation and particle merger techniques is used. The spatial and temporal distributions of the kinetic energy flux density of a debris cloud at the position of the upper surface of a pressure wall are calculated, and the correlation between the kinetic energy of the debris cloud and the deformation and fracture behavior of the pressure wall is discussed. Finally, based on the maximum value of the total kinetic energy of debris cloud per unit area at the position of the upper surface of a pressure wall, an energy-based parameter to assess protection capability of debris shields is proposed.     

一种改进的特征匹配算法在碎片云测量建模中的应用

为满足超高速撞击典型Whipple防护构型的损伤评估需求,利用图像处理技术对碎片云序列阴影图像进行深入研究.使用超高速序列激光阴影成像仪得到三组不同实验条件下碎片云发展过程的高清阴影图像,分别对每组最具代表性的2帧进行图像处理分析;根据碎片云图像特点以及碎片运动特性,提出了一种改进的碎片二次特征匹配算法,该方法包含碎片...     

Effects of scale on debris cloud properties

Results of tests using various thicknesses of 6061-T6 aluminum sheet and 6.35-, 9.53-, 12.70-, and 15.88-mm-diameter, 2017-T4 aluminum spheres are described. Impact velocities for these tests ranged from 3.77 to 7.38 km/s. Multiple-exposure, orthogonal-pair, flash radiographs of the debris clouds produced by the impacts were analyzed to provide quantitative data which described the size and velocity of a number of characteristic morphologic features in the debris clouds and the sizes and size distributions of fragments in the structural elements of the debris cloud.The axial and diametral velocities of these morphologic features were shown to be the same, regardless of sphere diameter, when debris clouds produced by impacts with similar bumper-thickness-to-projectile-diameter ratios and impact velocities were compared. As a result, the dimensions of these debris clouds differed only by the differences in the diameters of the spheres that produced them.An analyses of fragment sizes showed that the equivalent diameter of the large projectile fragment along the center line of the debris cloud scaled with projectile diameter; the dimensions of fragments forming the shell of spall fragments at the rear of the debris cloud did not scale with projectile diameter. The large central fragment appeared to originate from near the center of the sphere and was a part of the sphere which remained intact after all processes that worked to reduce the size of the sphere were complete. Formation of spall-shell fragments was a shock-related process which was sensitive to rate effects and other material properties that did not scale.     

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 simple model for debris clouds produced by hypervelocity particle impact

A simple debris cloud model is developed by considering the one dimensional shock wave motion in the material together with the catastrophic fragmentation theory by Grady. The model provides a simple method for calculating the velocities at the outer perimeter of the cloud and the average particle size in the cloud.