温度对平流层飞艇蒙皮渗透的影响研究

氦气填充的平流层飞艇在临近空间环境中运行,受到太阳辐照,蒙皮温度变化较大。蒙皮的氦气渗透关系着平流层飞艇运行的时间等问题。从理论分析与实验角度得到温度与蒙皮渗透性的关系,通过数值计算平均渗透率,结合飞艇外形及内部压力范围,估算飞艇的寿命。     

刚度构型对飞艇定常流固耦合特性的影响研究

飞艇作为临近空间高分辨率观测的重要平台,力学性能研究非常重要。飞艇的主体材料一般由柔性蒙皮构成,容易在气动作用下产生较大的变形,存在较强的流固耦合效应,是其力学性能研究的关键。该文采用松耦合方法形成了定常流固耦合计算方法,并且针对流场与结构的模型展开了详细的计算,和实验结果进行了验证。针对不同刚度构型飞艇模型的计算结果显示:硬式飞艇不需考虑流场和结构的耦合效应,半硬式和软式飞艇的耦合效应较明显。其中半硬式飞艇,耦合效应主要影响区域为柔性最大的橡胶部分,考虑耦合效应后,飞艇位移变形量增加约5%。软式飞艇,变形最为明显的是飞艇的尾部和头部,在来流作用下会出现明显的抬头位移,最大位移增量为225%。此外还采用量纲分析方法,得到了艇体变形与膜材料弹性模量、内压、来流的变化规律。当模型与实物满足几何相似、材料相似和动力学相似的条件下,变形将满足几何相似律。     

基于双轴拉伸试验的飞艇蒙皮材料非线性分析

飞艇蒙皮为多功能层压织物材料,力学行为呈现复杂的非线性,合理表征其非线性的力学模型对飞艇结构设计与分析至关重要。本文对飞艇蒙皮材料试件进行了7个应力比双轴拉伸试验,基于正交异性材料模型,采用应变残差平方和最小方法计算弹性常数,建立线性力学模型;根据试验数据建立应力弹性常数响应面,建立以应力为变量的完整三次式非线性力学模型。并根据此力学模型建立飞艇蒙皮材料有限元分析模型,通过数值模拟七种应力比下的双轴拉伸试验,分析结果的应力分布和分缝位移与试验现象一致。将分析得到的应力-应变曲线与试验结果进行对比,两者能很好的吻合,表明非线性力学模型及分析方法适用于飞艇结构分析。     

大尺度刚柔组合飞艇结构的静动态力学性能分析

刚柔组合体的大变形行为和复杂连接接触给飞艇大尺度结构的力学分析、设计和制造带来了挑战。该文选择德国先进的Zeppelin NT飞艇作为研究对象,飞艇结构由内部骨架与外部蒙皮连接而成,是典型的刚柔组合体结构。飞艇骨架的主要结构单元为桁架梁,若采用精细化模型,建模工作量大,因此通过对代表性桁架梁进行精细化分析,得出梁的截面力学参数,建立了等效简化梁模型,使得计算成本大为降低。为了验证有限元方法对柔性结构模态分析的适用性,推导了无限长圆柱形膜结构的二维振动模态频率理论解,并与有限元模拟得到的数值结果进行比较,两者误差较小。将蒙皮振动引起周围空气运动的附加质量引入有限元分析模型,得到蒙皮与骨架结构合理的模态振动频率。该文建立了大尺度刚柔组合飞艇结构的力学分析方法,并验证了方法的可行性。     

蒙皮波动对飞艇阻力的影响

通过求解雷诺平均Navier-Stokes方程,采用SST两方程湍流模型,研究了蒙皮以不同波长、频率以及波幅作波动时对飞艇流场特性产生的影响。研究结果表明:沿流向蒙皮的波动会引起绕飞艇流场的显著改变。当蒙皮上下表面的波动同相位时,在固定波动幅度和频率条件下,波动的波长减小,流动分离会加剧,时间平均的阻力系数增加;在固定波动波长和频率条件下,波动的波幅增加,流动分离加剧,时间平均的阻力系数增加,而当波幅减小到一定程度时,蒙皮波动对阻力系数基本没有影响;在固定波动波长和幅度条件下,波动频率增加,非定常效应增强,阻力系数减小,甚至出现负值,即可以为飞艇提供推力;此外,适当的波幅和波长组合也可以减小阻力系数。当蒙皮上下表面的波动相位相反时,波长与波幅变化带来的影响与同相位的情况相似;固定波动波长、幅度,波动频率增加,非定常效应增加,由于上下表面的非定常效应是相互抵消的,虽然阻力系数会出现瞬时负值,但是时间平均的阻力系数不会出现负值。     

织物类蒙皮材料中心切缝撕裂破坏强度分析

将复合材料弹性参数偏轴转换理论引入Hedgepeth细化模型,使模型应用范围拓展到倾斜切缝。进而应用Griffith能量理论,并结合试验现象,针对倾斜切缝模型推导了蒙皮材料抗撕裂强度公式。由理论结果可知,蒙皮材料的抗撕裂强度与材料的内因(弹性参数、纱线编织密度等)及外因(切缝倾角、切缝长度等)有关,是由膜材材料性质及损伤参数共同决定的。通过与其他撕裂强度理论及试验结果进行对比分析,验证了所推导理论及所得结论的正确性。所得结论可为蒙皮材料的强度设计及飞艇结构的安全性评估提供理论参考。      

国外飞艇最新发展概述与分析

本文重点介绍了世界各国飞艇的最新发展现状,并对未来飞艇发展趋势进行了分析,最后对我国飞艇发展提出了建议。     

含初始裂纹的平流层飞艇用蒙皮薄膜撕裂行为

为了研究含初始裂纹蒙皮薄膜的抗撕裂行为,选用Kevlar纤维增强的具有预制初始裂纹切口(PIC)的平流层飞艇用蒙皮薄膜,采用弹塑性断裂力学平面应力分析方法,考虑经纬向纱束之间的滑移摩擦效应,分析了薄膜裂纹尖端的撕裂强度与变形形式,建立了裂纹尖端撕裂物理模型和基于摩擦效应修正的等差法拉伸变形计算模型,获得了裂纹尖端应力集中区的应力分布。为验证计算模型的合理性,分别对PIC长度为10、20、30及40mm的试样进行了撕裂强度试验。结果表明:当PIC宽度比率不超过0.50时,模型计算值与试验值的误差小于4.12%;与改进的应力强度因子法相比,所建计算模型具有更高的计算精度,为平流层飞艇蒙皮撕裂强度的设计提供了一种有效的方法。     

SiO2热控涂层的制备

用离子束溅射工艺在石英、LY12和卫星蒙皮材料上制备了不同厚度和发射率的SiO2薄膜,研究了厚度对薄膜光学、热学性能的影响规律。用直流磁控溅射工艺制备了氧化铟锡(ITO)薄膜,研究了厚度对薄膜光学、电学性能的影响规律。利用前两部分研究成果在LY12和卫星蒙皮材料上制备成功了发射率可达0.45、光谱反射率大于0.7、同时电性能满足空间抗静电要求的复合热控薄膜。     

单侧涂层浮空器蒙皮材料的近场动力学模型

基于近场动力学方法,构建了浮空器蒙皮材料的近场模型。首先阐述了近场动力学的基本理论,表明了蒙皮材料的材料性质及结构。然后将蒙皮材料离散为空间上的质点,基于复合材料的近场模型,分析了编织条件下,质点本构力和应变能密度的组成,推导了质点间的本构力方程及近场参数。最后利用动力松弛法编程模拟了材料的力学性能。结果表明,在该近场模型下,蒙皮材料受力下的拉伸-应变曲线能与其他模拟结果相对应,并且材料的拉伸模量符合实验结果。     

Mechanical property characterization of film-fabric laminate for stratospheric airship envelope

A stratospheric airship can offer a cost effective alternative to earth orbit satellites for telecommunication and science observation. To float in the stratosphere with very thin air density, the airship needs to be designed with envelope materials that are extremely light, flexible and of high strength. Film-fabric laminates, which consist of single plain woven fabric layer impregnated in polymer matrix and are laminated with thin films for environmental and leakage protection, have unique material characteristics compared to conventional composite structures that can be exploited in the design of the high altitude airship envelope materials. In this study, the material characterization of a film-fabric laminate developed for stratospheric airship envelop was conducted. First, uni-axial tests were performed for fabricated specimens to obtain tensile properties. The tests were done in the thermal chamber at low, room, and high temperatures to investigate the temperature dependency. Next, the effective tensile properties were predicted by geometrically nonlinear finite element analyses. The analyses were done for unit cells where the detailed fiber tow architecture was modeled discretely. The analysis results were compared to the test results and investigated focusing on the geometrical nonlinearity and the micro-structural behavior of the laminates.     

飞艇囊体薄膜材料的双向拉伸试验及结构仿真

飞艇囊体膜材的弹性常数是飞艇外形设计、结构分析、动力学分析的基础。本文根据正交异性平面应力模型假设,应用双向拉伸试验方法获得了飞艇囊体膜材HV130在不同载荷比条件下的经纬向弹性模量和泊松比。对飞艇囊体进行应力分析,得到囊体应力的理论解及环向应力和轴向应力的载荷比。根据飞艇囊体受力情况,选取对应的弹性常数,对飞艇进行不同压差条件下的静力学仿真分析。利用非接触应变测量系统测试不同压差条件下飞艇囊体的变形情况,验证了双向拉伸试验所得的弹性常数的准确性和仿真分析的可靠性。本文能为飞艇的外形设计和结构分析提供参考。      

有机光折变聚合物的设计制备研究进展

有机/聚合物光折变材料是一类在信息传输、存储及信息处理等方面有着很大发展潜力的非线性光学材料,文中介绍了有机光折变材料的几种典型应用,综述了目前研究较为深入的几类有机光折变聚合物材料的组成特征和性能特点,并对其近年来材料的设计思想和制备研究进展进行分类表述,分析了材料体系中存在的亟待解决的瓶颈问题。最后对有机光折变聚合物材料的实用性及发展方向进行了展望。     

Tearing Behaviors of Flexible Fiber-Reinforced Composites for the Stratospheric Airship Envelope

Tearing behaviors of the envelope material is important for the stratospheric airship because it directly decides the service life of the airship. Uniaxial tensile tests of the specimens with different initial damage were performed to study the tear propagation properties of a new kind of envelope material for the stratospheric airship. A Matlab program was developed to simulate the mechanical properties in the tensile process. The interaction forces between warp and weft yarns were considered, and the yarns in the transition region between deformed region and non- deformed region were assumed as hinges in the simulation. It is discovered that the interaction factor, which represents interaction force between different components of the material, and the frictional coefficient between warp and weft yarns are the crucial factors for the tensile curves of the material. The tear strength and the damage mode of the envelope material are determined by the number of the cutoff yarns and the declination of the initial cracks, respectively.     

Green composites: A review of adequate materials for automotive applications

This study provides a bibliographic review in the broad field of green composites seeking-out for materials with a potential to be applied in the near future on automotive body panels. Hereupon, materials deriving from renewable resources will be preferred as opposed to the exhaustible fossil products. With the technical information of bio-polymers and natural reinforcements a database was created with the mechanical performance of several possible components for the prospect green composite. Following the review, an assessment is performed where aspects of suitability for the candidate elements in terms of mechanical properties are analyzed. In that section, renewable materials for matrix and reinforcement are screened accordingly in order to identify which hold both adequate strength and stiffness performance along with affordable cost so as to be a promising proposal for a green composite.     

A review of advanced high performance, insensitive and thermally stable energetic materials emerging for military and space applications

Energetic materials used extensively both for civil and military applications. There are continuous research programmes worldwide to develop new materials with higher performance and enhanced insensitivity to thermal or shock insults than the existing ones in order to meet the requirements of future military and space applications. This review concentrates on recent advances in syntheses, potential formulations and space applications of potential compounds with respect to safety, performance and stability.     

NBR／PVC发泡与阻燃材料的研究进展

综述了最近十几年的丁腈橡胶（NBR）、聚氯乙烯（PVC）的发泡材料和阻燃材料的研究进展。分别对NBR／PVC发泡材料、NBR／PVC阻燃材料和NBR／PVC泡沫阻燃材料的研究进展进行了总结,并指出NBR／PVC泡沫弹性体的阻燃技术发展缓慢,未来发展空间很大,将会成为NBR／PVC的一个新的发展趋势,应该受到重视。