【作者】 丁莉；

【导师】 庞宝君； 张伟；

【作者基本信息】 哈尔滨工业大学 ， 固体力学， 2008， 博士

【摘要】 随着航天事业的发展,空间碎片环境日益恶化,空间碎片对在轨航天器的威胁越来越严重。对航天器进行空间碎片防护设计成为时代的必需和今后发展的必然趋势,我国航天事业特别是载人航天及空间交会对接等一系列航天活动的发展对航天器进行有效的空间碎片防护设计提出了迫切的要求。空间碎片与航天器的相对撞击速度大约在1km/s到16km/s范围内,空间碎片防护的重点是与航天器的碰撞概率极高的直径小于1厘米的微小碎片,其平均质量密度约为2.8g/cm3,与铝或铝合金接近。双层板防护结构,也被称为Whipple防护结构,包含前、后两层板,前板代表防护屏,后板代表航天器的舱壁,其常用材料为铝或铝合金,是最基本的防护措施,也是国际空间站广泛采用的防护方案。撞击极限用于描述防护结构在空间碎片撞击下处于临界失效的状态,撞击极限的研究是防护方案设计中进行空间碎片撞击风险评估时不可缺少的一个环节,而国内目前还缺乏相关的撞击特性数据,尚未开发出工程可用的完整的撞击极限方程。本文以空间碎片防护结构设计为工程背景,以抵御毫米级空间碎片的双层板防护结构为研究对象,根据双层板防护结构在不同撞击参数条件下呈现撞击极限分段特征,在对各段撞击效应进行分析的基础上,按防护结构前板和后板在各段的损伤破坏过程与机理,分别建立力学模型获得了空间碎片撞击双层板防护结构为防止后板失效所需要的后板极限厚度函数关系式,建立了三个速度段的撞击极限方程。进行的主要工作如下:研究了不同速度下的撞击现象,根据双层板防护结构在不同撞击速度下呈现撞击极限分段特征,在对各段撞击效应进行分析的基础上,提出了不同速度段撞击极限方程的建立方法。根据弹道段弹丸撞击前板后一般在前板形成单个剪切孔且质量不发生改变的特点,基于能量守恒定律,研究了弹丸穿透前板后的剩余速度,得到了弹丸撞击半无限体后板成坑的坑深,采用半无限体靶板坑深与有限厚靶板极限厚度之间的关系建立了弹道段撞击极限方程。根据破碎段弹丸撞击前板后形成含固体颗粒的碎片云的特点,认为碎片云颗粒撞击半无限体后板成坑深度由最大碎片成坑深度及其它小碎片成坑深度组合而成,基于对碎片云成坑的研究,建立了半无限体后板成坑深度的无量纲表达式,进而建立了破碎段撞击极限方程。分析的同时还建立了最大碎片直径的无量纲表达式。根据液化/气化段弹丸撞击前板后形成的碎片云由气化或液化的粒子构成的特点,假设后板所受载荷为均匀分布,基于板的弯曲理论,采用瑞次法获得简支圆板承受部分均布载荷作用下位移的近似解,通过对板的极限分析,建立了液化/气化段撞击极限方程。探讨了双层板结构撞击极限研究时的分段问题。采用量纲分析法建立了适用于不同材料的弹丸初始破碎速度的无量纲经验表达式。本文通过分段建立力学模型以反映双层板防护结构在不同速度范围内具有不同撞击效应的物理力学过程,利用已有关于成坑、穿孔等基础性研究成果,分别建立了三个速度段的撞击极限方程,其预测结果与实验结果吻合较好。所取得的研究成果,为风险评估和防护设计工程应用提供了技术基础,揭示了撞击效应的物理力学过程和机理,也为开发研制新型多层防护结构提供了超高速撞击特性研究的理论基础,具有一定的工程应用价值和理论指导意义。更多还原

【Abstract】 With the development of human’s space technology and activities, the space debris environment is getting more and more deteriorated, which results in a great threaten to the safety of on-orbit space vehicles. The severe situation of space debris environment makes it necessary and inevitable to design shielding for spacecraft. Furthermore, the development and activities of the nation’s space technoloty, espetially those on manned spacecraft and spacecraft rendezvous, propose an urgent demand to design effective shielding for spacecraft against space debris.The relative impact velocity between space debris and spacecraft is about 1km/s to 16km/s. Due to their numerousness and the resulting high probability of collision, the emphasis of shielding design is small space debris with diameter less than 1cm, whose mass density is about 2.8g/cm3, which is close to that of aluminium or aluminium alloy.The most basic shielding structure is dual-wall shielding structure, which is also widely adopted in the International Space Station. Dual-wall shielding structure, also called Whipple shielding structure, consists of a front wall and a rear wall, which represent the bumper and the module of spacecraft respectively. Generally, the materials of dual-wall shielding structure are aluminium or aluminium alloy.Ballistic limit is used for decribing shielding structure’s critical status between failure and not failure when subjected to the impact of space debris. To access the space debris impact risk in designing shielding structure, it’s necessary and inevitable to obtain the shielding structure’s ballistic limit. Nevertheless, there exists no complete ballistic limit equations domistically that can be applied in engineering, due to the lack of relative data of impact characteristic.This paper takes space debris shielding design as the engineering application background, takes dual-wall shielding structure against space debris of millimeters as research object. Due to the characteristic that the ballistic limit of dual-wall shielding structure can be divided into different sections under different parameters, based on analysis on the impact effects of different ranges, by considering the damage process and mechanism of the front and rear wall under different ballistic limit ranges, this paper establishes a mechanical model for the different ballistic limit ranges of dual-wall shielding structure under impacts by space debris. As a result of the models, this paper obtains the functional relation of critical thickness to prevent the failure of the rear wall when impacted by space debris, establishes the ballistic limit equations for the three velocity ranges. The main contents of the paper are as follows:The paper studies the impact phenomenon under different velocities and observes the characteristic of dual-wall shielding structure that the ballistic limit can be divided into different sections under different impact velocity ranges. Based on the individual analysis of impact effects under different ballistic limit ranges, the paper proposes the modelling method to establish the ballistic limit equations for different velocity ranges.In the ballistic range, semi-infinite plate subjected to impact by projectile is investigated. Base on conservation of energy and the feature that after impacting the front wall, the projectile will not change its mass and a hole is generated in the front wall, the remnant velocity of the projectile after perforating the front wall is investigated, as a result of which the paper obtains the crater depth of the rear semi-infinite plate. Making use of the relation between crater depth of semi-infinite plate and critical thickness of rear wall, the paper establishes the ballistic limit equation in the ballistic range.In the shatter range, the debris cloud is analyzed. Due to the feature that the debris cloud consists of solid particles, the crater depth of the semi-infinite rear wall is decomposed into two parts, one caused by the largest particle and one caused by the rest cloud particles. Base on the analysis of debris cloud cratering, the paper gives a non-dimensional expression for crater depth of semi-infinite rear wall. As sequence, the paper establishes the ballistic limit equation for shatter range. At the same time, the paper also gives the non-dimensional expression of the diameter of the largest debris particle.In the melt/vaporize range, debris cloud after impact consists of gas or liquid particles. For simplification, the paper assumes that the rear wall is subjected to uniform load when impacted by the debris cloud. Base on bending theory of plates and by Rize method, the paper obtains the approximate displacement of simple-supported circle plate subjected to partial uniform load. Afterward, the paper establishes the ballistic limit equation for melt/vaporize range through the analysis of the plate.The paper also studies the division of velocity ranges for the ballistic limit analysis of dual-wall structures. Using dimensional analysis, the paper establishes a non-dimensional empirical expression for fragmentation-initiation velocity of the projectile, which is valid for different projectile materials.By dividing into different sections, the paper establishes mechanical models for different ballistic limit ranges to reveal the physical process that dual-wall shielding structure responses differently under impacts of different velocity ranges. Existing basic research results on cratering and perforation are adopted. As a result, the paper establishes the ballistic limit equations for the three velocity ranges, the predictions of which agree well with experimental data. The research findings of the paper has some significant meanings and is valuable in engineering applications and providing theoretical guidelines. It provides technical foundation for risk assessment and shielding design applications. It reveals the physical process and mechanism of impact effects. And for developing new multilayer shielding structure, it also provides theoretical foundations for studying the hypervelocity impact characteristics.更多还原