【作者】 朱凼凼；

【导师】 庞宝君；

【作者基本信息】 哈尔滨工业大学 ， 固体力学， 2012， 博士

【摘要】 空间环境随着人类太空活动的增多而日益恶化，在轨运行的航天器受到空间碎片和微流星体高速撞击的威胁也不断增大，迫切需要开展航天器防护结构抵御空间碎片和微流星体撞击特性研究。目前，人们往往采用铝合金球形弹丸来模拟空间碎片开展地面高速撞击实验。对于微流星体，由于其物性复杂，撞击特性难以掌握，一般借用模拟空间碎片的铝合金弹丸撞击防护结构损伤特性数据开展微流星体撞击风险评估并进行防护结构设计，这将可能导致“过设计”或“欠设计”。随着载人航天尤其是深空探测事业的发展，微流星体已成为航天活动不可忽略的重要风险因素，迫切需要研究典型微流星体高速撞击航天器防护结构的损伤破坏效应。基于以上背景，针对微流星体高速撞击航天器防护结构的损伤破坏效应问题开展了探索性研究工作。系统地研究了微流星体模拟材料选择原则、弹丸制作技术、弹丸高速撞击实验技术、仿真验证等问题，分别选取高脆性高熔点、高脆性低熔点、多孔脆性等典型材料制作模拟弹丸，开展微流星体高速撞击航天器防护结构损伤破坏效应的地面模拟实验与数值仿真研究，获得了一些基础数据，可以为航天器防护结构设计和风险评估提供技术支撑。主要研究内容如下：首先，在微流星体物性特性分析基础上，提出了模拟微流星体弹丸材料的选择原则及其弹丸制备方法。根据微流星体化学组成成份及其物理力学特性已有研究成果，针对高脆性高熔点、高脆性低熔点、多孔脆性等三种典型物性微流星体进行研究，提出了用金刚石材料弹丸模拟高脆性高熔点微流星体，用火山岩或硅酸盐质材料模拟多孔脆性微流星体，用冰质材料模拟低熔点高脆性微流星体的研究方案，并研究弹丸制备方法。针对微流星体具有形状不规则、易破碎、易融化等特点，从弹托设计、垫片选择、制冷装置配备等方面研究不同特点弹丸的高速撞击实验弹丸发射技术。高脆性高熔点微流星体弹丸硬度高，打磨难度大，制作成的弹丸往往具有不规则形状，提出设计内喇叭状的弹托以确保不规则的高脆性高熔点微流星体弹丸高速撞击靶板，并取得成功；多孔脆性微流星体弹丸承受发射过程产生的冲击波时极易发生破碎，在弹丸和弹托之间加入一种EVA橡胶阻抗材料垫片，可确保弹丸在发射过程中不会提前发生破碎，保障其着靶前的完整性；高脆性低熔点微流星体弹丸采用模具注水的方式制作，由于具有在常温下易融化的特点，采用加装专用制冷设备的方式来确保低熔点冰弹丸发射成功。地面实验表明，三种高速撞击实验技术是可行、有效的。研究了高脆性高熔点微流星体对航天器Whipple防护结构的撞击特性，并与空间碎片高速撞击损伤效应进行对比分析。选取金刚石颗粒制作的微流星体弹丸，开展了9次地面模拟实验，分析了4组典型数据，获得了高脆性高熔点微流星体高速撞击Whipple防护结构的损伤效应，根据弹丸在一定速度下会产生石墨化现象，提出了中低速、高速下防护此类微流星体撞击的设计重点。结果表明，随着撞击速度的不断增大，后靶板的高温高压效应也越大，导致金刚石弹丸从完全的金刚石成份过渡到金刚石石墨混合成份再过渡到完全的石墨成份，并得出了碳质微流星体石墨化现象是区别高熔点高脆性微流星体与空间碎片损伤效应的主要原因；通过损伤效应分析得出，如果采用等质量和等尺寸的铝合金弹丸对高脆性高熔点的微流星体进行风险评估，可推测出防护结构是欠设计的。针对微流星体存在不同矿物质成份的特点，通过地面实验和数值仿真研究了多孔脆性微流星体高速撞击航天器Whipple防护结构的损伤破坏问题。采用天然的火山岩和人工制备的硅酸盐质弹丸，分别开展了7次和11次高速撞击实验，选取5组和6组典型实验结果进行分析，获得了在不同撞击速度下多孔脆性微流星体对防护结构的撞击损伤效应，并通过仿真分析了损伤规律，得到了此类微流星体的撞击损伤效应比同速同质的空间碎片模拟弹丸铝合金要小的结论。结果表明，由于火山岩和硅酸盐质弹丸具有多孔脆性特性，在撞击前靶板后，弹丸破碎程度高，形成的碎片云也很均匀分散，从而削弱了对后靶板的撞击损伤效应，相比同质量铝弹丸而言，其撞击损伤效应要弱；分析表明如果采用等直径的铝合金弹丸对多孔脆性微流星体进行风险评估，可以认为防护结构是过设计的。最后，针对微流星体的主要来源彗星中存在大量固态冰的现象，对高脆性低熔点微流星体弹丸高速撞击航天器Whipple防护结构的损伤特性进行了研究。采用低温环境中制备的冰弹丸模拟高脆性低熔点微流星体，开展了12次高速撞击实验，选取5个典型结果进行分析，得到了在高脆性低熔点微流星体撞击下前靶板发生变形、穿孔、裂纹和撕裂的损伤特性。通过数值仿真计算了高脆性低熔点冰弹丸高速撞击防护结构的损伤特性，拟合得到了防护结构的撞击极限曲线，并与铝合金弹丸撞击极限曲线进行对比分析。结果表明，冰弹丸撞击前靶板的损伤模式以花瓣型撕裂为主，前靶板的损伤范围远大于弹丸几何尺寸，随弹丸速度的增加，碎片云撞击速度也不断增加，导致对后靶板的损伤程度增加；通过比对仿真获得的撞击极限曲线可知，如果采用等尺寸的铝合金弹丸对高脆性低熔点微流星体进行风险评估，可以认为防护结构是过设计的。综上，研究所获得的地面实验和仿真数据以及高速撞击损伤规律对优化航天器防护微流星体结构设计和风险评估具有一定的参考价值，这些成果对保障在轨航天器长期、可靠、安全运行具有重要的指导意义。特别是关于微流星体弹丸材料选择和实验方法，以及高脆性高熔点、高脆性低熔点、多孔脆性模拟微流星体弹丸高速撞击典型航天器防护结构损伤效应分析成果对于建立微流星体防护设计系统具有工程应用参考价值。更多还原

【Abstract】 With the increase of human space activities, the space environment isdeteriorating, and the high-speed impaction of space debris and micrometeoroidthreaten orbiting spacecrafts at any time. Therefore, it is very urgent to carry outthe impact characteristics study on spacecraft shield structure against space debrisand micrometeoroid. People tend to use aluminum spherical projectile to simulatespace debris ground high-speed impact experiments. Due to the complexity ofmicrometeoroid physical properties, its impact properties are difficult to grasp.Generally damage characteristic data of aluminum alloy projectile simulating spacedebris impacting on shield structure are used to carry out micrometeoroid impactrisk assessment and shield structure design, which may lead to design too much orbe lack of design. With the development of manned space flight, and especiallydeep space exploration, micrometeoroid has become an important risk factor forspace activities, which can not be ignored. So it is urgent to study damage effectsof typical micrometeoroid high-speed impaction on spacecraft shield structures.Based on the above background, some exploratory research has done in thispaper about the damage effects of micrometeoroid high-speed impaction onspacecraft shield. The principle of micrometeoroid simulation materials selection,production technology of the projectile, projectile high-speed impact experimenttechniques, simulation and others have mainly been studies systematically. Sometypical materials with high brittleness and high melting point, high brittleness andlow melting point, and porous brittle were selected and producted to do someresearch on micrometeoroid high-speed impact characteristic on shield structure.Some basic data were obtained, which could provide technical support for thestructure design and risk assessment of spacecraft shield. The main contents wereas follows:Firstly，based on the analysis of micrometeoroid physical characteristics,material selection principle and production methods of projectile which were usedto simulate micrometeoroid were proposed. According to existing research resultsof the micrometeoroid chemical composition and physical mechanical properties,three typical physical properties of micrometeoroid have been studied includingthe micrometeoroid with high brittleness and high melting point, high brittlenessand low melting point, and porous brittle. And diamond material projectile wasused to simulate micrometeoroid with high brittleness and high melting point, volcanic rocks or silicate material were used to simulate porous brittlemicrometeoroid, and icy material was used to simulate micrometeoroid with lowmelting point and high brittleness. The projectile production method has also beenstudies.Due to micrometeoroid characteristics such as irregular in shape, brokeneasily, melting easily and so on, projectile launch technology of high-speed impactexperiments of the different characteristics projectile have been studied includingthe sabot design, gasket selection, refrigeration equipment and others. Themicrometeoroid projectile with high brittleness and high melting point was hardand was difficult to be polished. Its shape was often irregular. To ensure thesuccess of micrometeoroid projectile with high brittleness and high melting pointimpact experiments, the sabot was been designed to be inner horn-like sabot.Porous brittle micrometeoroid projectile was easily to be broken when it withstandthe shock waves generated by the emission process. The study found that it couldensure that projectiles would not be fractured in advance during launch and alsoensure their integrity before landing on the plate through adding EVA rubberimpedance gasket between projectile and sabot.Th micrometeoroid projectile with high brittleness and low melting point wasproduced by mold injection. Because of its melting characteristics at roomtemperature, special refrigeration equipments were installed to ensure the successof low melting point icy projectiles launch. The ground high-speed impactexperiments showed that three technologies of high-speed impact experimentswere feasible and effective.The damage effects of micrometeoroid with high brittleness and highmelting point impact on spacecraft shield structure have been studies and analyzed,which were compared with space debris high-speed impact damage effects. Themicrometeoroid projectiles produced by diamond particles were selected to carryout9times ground simulation experiments.4series of typical data were analyzed.And the damage effects of micrometeoroid with high brittleness and high meltingpoint impact on the Whipple shield structure were abtained. The design focus ofshield structure impacted by such micrometeoroid was revealed at low speed andhigh speed because the projectile speed would produce the phenomenon ofgraphitization. The results showed that high temperature and high pressure effectsof the rear plate was greater, which led to diamond projectile transform from a fulldiamond to the mixed composition of diamond and graphite, and then the fullgraphite composition with increasing of impact velocity. And the main reason thatdistinguished damage effects of micrometeoroids with high brittleness and high melting point from that of space debris was micrometeoroid’s graphitizationphenomenon. If the same quality and size of the aluminum projectile was used todo risk assessment on micrometeoroid with high brittleness and high melting point,the shield structure was thought to be lack of design according to obtained damageeffects.The damage effects of porous brittle micrometeoroid high-speed impact onspacecraft Whipple shield structure were studied through ground experiments andsimulation studies according to the micrometeoroid characteristics with differentminerals composition. The natural volcanic rocks and artificial silicate projectilewere adopted, and7times and11times high-speed impact experiments werecarried out respectively. The5and6set of typical experiment results were selectedand analyzed, and the damage effects of porous brittle micrometeoroid impact onshield structures were obtained at defferent speed. The paper come to a conclusionby simulation analysis that impact damage effects by porous brittle micrometeoroidis smaller than that of space debris with the same speed and quality. The resultsalso showed that the projectile was broken much and the debris cloud wasdispersed after impacting on the front plate, which weakened the damage effect onthe rear plate because of the porous brittle characteristics, and then cause lessimpact damage than the same quality aluminum projectile. And analysis showedthat the shield structure is designed too much if the same diameter aluminumprojectile was adopted to conduct risk assessment on the porous brittlemicrometeoroid.Last，there has lots of ice in comets which produced micrometeoroids, so thepaper studies the impact damage characteristics on spacecraft shield structure by iceprojectile with high brittleness and low melting point. The experiments adopted theice projectiles produced in low-temperature environment to simulate micrometeoroidwith high brittleness and low melting point, and twelve high-speed impactexperiments were carried out. Five typical results were selected and analyzed, whichabtained much impact damage characteristics such as big deformation, perforationcrack, tear damage and so on. The paper also simulates impaction damagecharacteristics by ice projectile, and obtained the ballistic limit curve which has beencompared with limit curve got by aluminum projectile. The results show that thedamage mode of ice projectile impaction on the front plate is petal-type tear, and withthe increasing of the ice projectile’s velocity, the debris cloud’s velocity also increasedwhich lead to more serious damage to the rear plate. By compared the impact limitcurve which is got from the simulation of ice projectile with that of aluminum’s, theresult can be obtained that shield structure is thought to be over designed if it conduct risk assessment by the same size aluminum projectile.In summary, the disciplines and data from the ground impact experiments andsimulation can be useful to the design and risk assessment of spacecraft’s shieldstructure. The results also have important value for long-term, reliable, safe operationof in-orbit spacecraft. Especially the choice of projectile’s material and experimentmethods, as well as the impact damage characteristics obtained by three typicalmicrometeoroids which have properties as high brittleness and high melting point,high brittleness and low melting point, and porous brittle, are of great significancefor the establishment of micrometeoroid protection design system.更多还原