SiC/CVD SiC复合涂层的抗氧化及抗热震性能研究

为了提高C/SiC复合材料耐高温性能,采用泥浆浸渍裂解与真空化学气相沉积(CVD)在材料表面制备了SiC/CVD SiC复合涂层,通过XRD、SEM分析了涂层组成与结构;研究了复合涂层的高温抗氧化(700～1 500℃)和抗热震性能。结果表明,泥浆浸渍法制备的SiC涂层具有一定的封孔效果,可使材料开孔率下降,但高温抗氧化效果并不佳,1 200℃氧化10 min后材料弯曲强度保留率下降明显仅有86%。CVD SiC涂层结构致密,与SiC封孔涂层结合较好,在700～1 500℃具有较好的抗氧化效果,随着氧化温度的升高,氧化后涂层完好,表面O元素逐渐增加,材料失重率缓慢增加但不大于0.5%,且材料性能并未下降。涂层材料在1 200℃-10 min短时热震5次后材料弯曲强度保留率仍有95%以上,且未出现开裂、剥落等热震损伤。在1 200℃-30 min长时热震10次后,涂层材料基本被完全氧化,材料失去保护作用,弯曲强度下降至90%左右。     

基于连续损伤模型的复合材料波纹梁压溃分析

复合材料的耐撞性受到了广泛重视,而波纹梁因其优异的抗屈曲构型被广泛应用于飞机翼梁和直升机底板等经常发生碰撞的结构中。进行了复合材料波纹梁的屈曲分析,研究了高度对波纹梁破坏模式的影响。建立复合材料波纹梁的连续损伤单波模型,层内基于Hashin判据建立含损伤因子的损伤刚度矩阵,层间根据二次名义应力准则和B-K准则模拟损伤演化,并通过典型复合材料波纹梁压溃试验验证了所建立模型的正确性。基于单波分析模型,通过施加周期性边界条件和反对称边界条件,研究了多波结构的吸能特性。     

基于双环滑模控制的直/气复合控制系统设计

直/气复合控制导弹具有强干扰、强非线性以及强耦合等特点，传统的姿态控制器难以适用于该种复杂干扰并存的情况，文章提出了基于双环滑模控制的直/气复合控制器。首先采用有限时间收敛趋近律分别构造内外环滑模控制器，并将角速度回路的滑模变量量化为直接力指令，以解决空气舵与姿控发动机之间的耦合问题。接着使用非线性扩张状态观测器估计综合干扰，从而设计控制器补偿侧向喷流干扰及模型不确定性等综合干扰的影响。然后基于李雅普诺夫方法证明了控制系统闭环稳定，分析了干扰补偿对控制器收敛域的影响。最后仿真结果表明，该方法跟踪速度快，动态过程平稳，具有较强的干扰抑制能力，具有很强的鲁棒性。     

绕月微卫星精确撞月轨道设计

为实现约束条件下的精准可控撞月,提出了基于Lambert问题的精确撞月轨道设计方法。通过求解Lambert问题,可得到撞月轨道轨控时刻的速度脉冲初值解,然后通过打靶法迭代得到撞月轨道的精确解。以"龙江二号"微卫星轨道为例,对撞月点经纬度的覆盖性,以及燃料约束下同一撞月点可行的轨控弧段进行全面分析。最后,通过月球南极水冰探测的撞月轨道设计案例,以验证本文提出的轨道设计方法的有效性。     

How do interplanetary shock impact angles control the size of the geoeffective magnetosphere?

In this paper, we investigate temporal and spatial magnetosphere response to the impact of interplanetary (IP) shocks with different inclinations and speeds on the Earth’s magnetosphere. A data set with more than 500 IP shocks is used to identify positive sudden impulse (SI⁺) events as expressed by the SuperMAG partial ring current index. The SI⁺ rise time (RT), defined as the time interval between compression onset and maximum SI⁺ signature, is obtained for each event. We use RT and a model suggested by Takeuchi et al. (2002) to calculate the geoeffective magnetospheric distance (GMD) in the shock propagation direction as a function of shock impact angle and speed for each event. GMD is a generalization of the geoeffective magnetosphere length (GML) suggested by Takeuchi et al. (2002), defined from the subsolar point along the X line toward the tail. We estimate statistical GMD and GML values which are then reported for the first time. We also show that, similarly to well-known results for RT, the highest correlation coefficient for the GMD and impact angle is found for shocks with high speeds and small impact angles, and the faster and more frontal the shock, the smaller the GMD. This result indicates that the magnetospheric response depends heavily on shock impact angle. With these results, we argue that the prediction and forecasting of space weather events, such as those caused by coronal mass ejections, will not be accurately accomplished if the disturbances’ angles of impact are not considered as an important parameter within model and observation scheme capabilities.     

Influence of pre-tension on ballistic impact performance of multi-layer Kevlar 49 woven fabrics for gas turbine engine containment systems

In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences of the number of Kevlar layers and pre-tension were discussed particularly. Test results were used to analyze failure modes and energy absorption characteristics of multi-ply Kevlar fabrics. Results show that there are two kinds of impact damage for fabrics: global deformation mainly involving stretching of yarns in the impact region and fabric wrinkle from both sides to the impact zone, and local damage characterized by yarn fracture, yarn pull-out, and yarn unraveling. The energy absorption capability of Kevlar 49 woven fabrics improves with the number of fabric layers. The energy absorbed by multi-layer fabrics increases slightly at the beginning and then decreases substantially with pre-tension. The work in this paper can provide guidance for designing light-weight multi-layer fabrics containment systems.     

单/双轴预拉载荷对碳纤维复合材料高速冲击性能的影响研究

针对发动机工作时受预载荷的叶片受到外物冲击的情况,设计一种面内单轴及双轴预加载装置,开展单轴与双轴不同大小预拉载荷下碳纤维/环氧树脂复合材料（T700/TDE-86）的高速冲击试验,探究预拉载荷对复合材料抗冲击性能的影响,并结合超声C扫描分析预拉载荷对损伤面积的影响。结果表明：面内初始载荷对复合材料层合板抗冲击性能和分层损伤面积有显著影响;预拉载荷会提高靶板的抗弯刚度,减少靶板吸收的能量,减小弹道极限,且在双轴预拉情况下更明显;弹体击穿靶板后分层损伤面积几乎不变,而预拉载荷会减小分层损伤面积,且在双轴预拉情况下更明显。     

钛及钛合金表面耐磨热处理

综述了近年来为提高钛及钛合金表面耐磨性而采用的热处理表面改性技术,如渗氮、渗硼、离子注入、激光合金化等。讨论了每种工艺方法所获表面改性层的结构和性能特征及其适应范围。其中着重介绍了离子氮化和激光合金化工艺,比较了各自的优缺点,并提出了应进一步研究的方向。     

弹性梁碰撞阻尼识别的新方法

首先将连续碰撞系统离散成包括任意个模态的状态方程,然后基于Hertz定理和能量平衡原理,证明弹性碰撞阻尼取决于碰撞冲量和最大碰撞力,提出了确定弹性梁碰撞阻尼的新方法,解决了碰撞阻尼识别中的关键问题。最后由两个弹性梁的碰撞实验检验了其正确和有效性。     

胸腹部不同部位撞击伤特点及损伤机理

用摆锤式冲击台对１１３只家兔胸、腹不同部位进行了钝性撞击实验。撞击速度６．７～１０．５ｍ／ｓ,相对压缩量０．１８～０．５０。观测到侧胸撞击伤重于正胸撞击,侧胸撞击易引起升主动脉损伤和肋骨骨折,还易引起肝脏损伤。上腹撞击损伤重于侧腹撞击,上腹撞击易引起肝脏损伤。提出胸部撞击要着重于侧胸部防护,腹部撞击要着重于上腹部防护。提出用冲量ＭＩ和冲击功ＷＩ分别估计胸部和上腹部撞击损伤程度及其ＤＥ,５０值。