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.     

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.     

超高速碰撞产生等离子体及其对逻辑芯片的干扰效应

为理解和评估超高速碰撞产生等离子体及其对航天器逻辑芯片的电磁干扰效应,进行二级轻气炮强冲击加载实验模拟超高速撞击;利用郎缪尔三探针诊断系统对弹丸撞击2A12铝板产生等离子体的电子温度和电子密度在给定位置处进行诊断测量,建立逻辑芯片信号采集系统对给定位置处逻辑芯片遭受干扰进行监测分析。结果表明,撞击速度在2.5~3.5km/s范围时均能产生等离子体,等离子体电子温度和电子密度均随撞击速度而增加,其中电子密度与撞击速度呈指数关系。超高速碰撞产生等离子体对逻辑芯片运行状态的干扰主要表现为三种形式,分别是传输信号瞬态中断而后恢复、输出逻辑关系短暂失真和逻辑门失效。     

高速粒子撞击作用下LF6合金多层靶结构防护能力研究

针对总厚度为４ｍｍ的ＬＦ６合金双层靶和总厚度为２ｍｍ的三层靶进行了直径为２ｍｍ,速度分别为５．８和７．２ｋｍ／ｓ的ＧＣｒ１５粒子 撞击试验,并对双层靶进行了不同前靶厚度和靶间距的撞击试验,试验结果表明：与同样碰撞条件下半无限体靶上产生的破坏情况相比,多层靶被击穿的总厚度远淖于半无限体靶上形成的弹坑深度,采用多层靶结构可显著提高材料的抗高速粒子撞击能力,并大大降低航天器抗高速粒子撞击的防护结构的重量     

铝球弹丸高速正撞击金属网防护屏实验研究

利用二级轻气炮发射2017-T4铝球弹丸高速撞击金属网,通过金属网后面观察板弹坑分布研究金属网对高速撞击铝球的破碎作用及次生碎片粒子群分布特性,分析观察板弹坑分布与铝球直径、金属网面密度关系。获得铝球弹丸高速正撞击具有不同编织参数金属网时观察板弹坑分布模式。结果表明,铝球弹丸高速正撞击金属网后在观察板上产生多条呈放射状分布近似对称的触须状弹坑簇;触须状弹坑簇数量、长度随弹丸直径、撞击位置、金属网面密度不同而不同;相同撞击条件下铝球弹丸高速正撞击网格孔中心时,观察板触须状弹坑簇数量相对较多。     

基于小波分析技术的高速撞击声发射源定位

针对在轨航天器遭受空间碎片撞击损伤的定位问题,利用二级轻气炮发射铝弹丸撞击铝板来模拟空间碎片对航天器结构的损伤;通过声发射传感器实时记录结构中的时域波形信号,结合板波的频散特性,分析了高速撞击穿孔损伤时波动在铝板中的传播模式.基于小波时频分析技术研究了高速撞击损伤的定位问题,分析了波速对定位精度的影响.结果表明,基于小波分析技术的高速撞击声发射源定位能够满足撞击损伤的定位要求,为解决航天器在轨遭受空间碎片撞击的损伤定位提供了一种新的方法.     

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。     

多层隔热材料对填充式结构高速撞击损伤影响的实验研究

在填充式结构中加入多层隔热材料(MLI),利用二级轻气炮发射铝球弹丸在真空环境下对其进行高速撞击实验,获得了MLI位于不同位置时的防护结构损伤模式,研究MLI对填充式结构高速撞击损伤与防护特性的影响。结果表明:当MLI位于首层薄铝板前侧时,薄铝板穿孔尺寸增大,首层薄铝板耗散弹丸撞击动能的能力增强,有助于填充式结构高速撞击防护性能提高;当MLI位于首层薄铝板后侧时,弹丸击穿薄铝板后次生碎片云团的膨胀扩散受到抑制,不利于填充式结构高速撞击防护性能提高;在相同撞击条件下,当MLI位于填充层前侧时,填充层中心穿孔尺寸增大,当MLI位于舱壁前侧时,舱壁弹坑分布范围减小。     

板间距对铝板多冲击结构高速撞击防护性能影响的试验研究

为了研究板间距变化对铝板多冲击结构高速撞击损伤与防护特性的影响,采用二级轻气炮发射铝球弹丸对具有不同板间距的双层、三层、四层和五层铝板结构进行了高速撞击试验,弹丸直径分别为3.97 mm、5 mm和6.35 mm,撞击速度为1.72~4.88 km/s,撞击角度为0°。结果表明:在铝球弹丸的弹道段撞击速度区间,板间距变化对铝板多冲击结构的高速撞击防护性能无显著影响;在铝球弹丸的破碎段撞击速度区间,对于相同的总防护间距,具有不同板间距的铝板多冲击结构的高速撞击防护性能存在明显差异;基于该试验数据定义的三层、四层和五层铝板结构的板间距因子,可为具有高效抗高速撞击能力的铝板多冲击结构的板间距设计提供依据。     

多孔火山岩超高速撞击蜂窝夹层板试验研究

为研究航天器蜂窝夹层结构的超高速撞击防护性能,采用轻质多孔火山岩弹丸模拟微流星体,进行超高速撞击试验,研究蜂窝夹层板的损伤特性。结果表明:采用硅橡胶垫片,结合弹托使用,可实现轻质、脆性火山岩弹丸的超高速完整发射;在火山岩弹丸超高速撞击条件下,蜂窝夹层板主要发生正面蒙皮穿孔、蜂窝芯层坍塌、背面蒙皮花瓣开裂、脱胶等损伤模式;正面蒙皮穿孔直径随弹丸直径的增大而增大;蜂窝芯层坍塌面积和背面蒙皮损伤面积不仅与冲击能量、弹丸直径相关,还与冲击位置相关。     

Crater distribution on the rear wall of AL-Whipple shield by hypervelocity impacts of AL-spheres

All spacecraft in low orbit are subject to hypervelocity impact by meteoroids and space debris, which can in turn lead to significant damage and catastrophic failure. In order to simulate and study the hypervelocity impact of space debris on spacecraft through hypervelocity impact on AL-Whipple shield, a two-stage light gas gun was used to launch 2017-T4 aluminum alloy sphere projectiles. The projectile diameters ranged from 2.51 mm to 5.97 mm and impact velocities ranged from 0.69 km/s to 6.98 km/s. The modes of crater distribution on the rear wall of AL-Whipple shield by hypervelocity impact of AL-spheres in different impact velocity ranges were obtained. The characteristics of the crater distribution on the rear wall were analyzed. The forecast equations for crater distribution on the rear wall of AL-Whipple shield by normal hypervelocity impact were derived. The results show that the crater distribution on the rear wall is a circular area. As projectile diameter, impact velocity and shielding spacing increased, the area of crater distribution increased. The critical fragmentation velocity of impact projectile is an important factor affecting the characteristics of the crater distributions on the rear wall.     

Measuring hypervelocity impact velocity from micrometeoroid crater geometry

Guided by half-space computer simulations showing hypervelocity impact crater formation for an iron particle impacting an aluminum target and characteristic crater geometry changes with impact velocity over the range 8–40 km s⁻¹, we examined normal surface crater views and cross-sectional views through craters (>0.5 mm diameter) from samples retrieved from the NASA LDEF satellite and examined in the scanning electron microscope (SEM). While geometrical features suggested in the computer simulations were indeed observed for micrometeoroid craters in 6061-T6 aluminum targets and 303 stainless steel targets, there was no consistent estimate for impact velocities in any of the experimental samples, and velocity estimates based on measuring ratios of ejecta width/crater diameter and ejecta height/crater depth as well as ejecta height/crater diameter varied from 8 to 42 km s⁻¹; over the same range simulated. These results point to the need to create reference data from actual hypervelocity impact experiments in the laboratory, and systematic observation of residual crater geometries in the SEM. These experiments also demonstrate the uncertainty in assuming a fixed impact velocity for all impact craters in space materials as well as an apparent futility in attempting to correlate impacting particle velocity with post-mortem characteristics of a given crater.     

Experimental study of morphology scaling of a projectile obliquely impacting into loose granular media

The morphology scaling of a spherical projectile obliquely impacting into loose granular media is experimentally investigated. The influences of projectile’s releasing distance, diameter and oblique impact angle are mainly considered. Based on the experimental results, four scaling laws are eventually proposed to describe the variations of the length, width, depth of impact crater and the penetration depth of projectile after impacting. We find that when the impact angle is larger than a critical value, these quantities all exhibit power law dependences on the releasing distance, diameter and impact angle of projectile, which are analogous to that obtained in other similar vertical impacting experiments. It is also observed that once the oblique impact angle exceeds this critical value, the tadpole-shaped impact crater may commonly evolve into an elliptical one. At small impact angles, we find that the scaling laws on both the width and the depth of impact crater are still valid, although the corresponding fitting exponents have slightly deviated from those values at larger impact angles. However, the length of crater and the penetration depth of projectile seem to no longer yield such proposed scaling laws, possibly due to the different physical mechanism induced by the rebounding movements of projectile at small impact angles.     

An analytical model of hole size in finite plates for both normal and oblique hypervelocity impact for all target thicknesses up to the ballistic limit

This paper presents, for the first time, a single comprehensive analytical model for the hole size produced by hypervelocity impact into finite plates. This model is based on experimental data for 2017 aluminum spheres impacting 2014, 2024 and 6061 aluminum plates.

The significance of this model is that it spans the entire range of target thickness from very thin to very thick, which makes it possible to determine when the impact conditions are those of thin target behavior (where the hole size increases with increasing target thickness and debris formation and damage is important) and when the impact conditions are those of thick target behavior (where the hole size decreased with increasing target thickness and the debris formation is significantly decreased). The model makes it clear that the target thickness that divides the thin target regime from the thick target regime is a function of velocity. This means that an impact configuration which exhibits thick target behavior at common experimental velocities could actually exhibit thin target behavior at velocities in the tens of kilometers per second such as that of meteroid impacts. This hole size model also includes the effects of oblique impact and computes both the major and the minor diameters of the hole.

This paper also raises, for the first time, the possibility that the commonly accepted models for crater diameter (and by implication those for penetration depth as well), which are taken to be a power function of velocity, might be wrong. Only a linear dependence on velocity for the crater diameter is consistent with the linear velocity dependence of this and all other accepted models of hole diameter in finite plates. If this is correct, it would raise questions about the validity of using any target damage computer models, that are based on the old crater modeling equations, to extrapolate to higher velocities.     

Hypervelocity impact on isotropic composites with metal or ceramic inclusions

Experimental results of studying the hypervelocity impact on isotropic heterogeneous composites consisting of an epoxy or aluminum matrix containing fine-grained metal (Al, Pb) or ceramic (SiO₂) inclusions are given. The aim of the study is to develop composite materials offering higher penetration resistance to a high-velocity projectile than the component material. This resistance is characterized by the magnitude of the ratio of the crater depth in a thick target to the diameter of spherical projectile. In the case of two particulate composites studied it is shown that the crater depth from impact of steel projectiles is lower about by one projectile diameter than for homogeneous lead or aluminum over the impact velocity ranged from 3 up to 11 km/s.     

Cavity and crater depth in hypervelocity impact

We discuss the depth of cavities and craters caused by hypervelocity impacts as a function of impact parameters such as impact velocity, projectile and target densities, and projectile diameter, in two extreme cases: the penetration of intact projectiles at low impact pressure and the hemispherical excavation at very high impact pressure. The relations between the depth and the impact parameters are obtained. Then, previous experimental results are compiled; crater depth normalized by projectile diameter and the ratio of projectile and target densities is plotted for glass, plastic, and metal projectiles and metal, rock, ice, foam, sheet-stack, and aerogel targets. The trends of the data are consistent with the relations in the extreme cases.     

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.