基于数字图像相关方法微裂纹萌生试验研究

为了进一步研究疲劳裂纹在萌生阶段的特点,本文结合数字图像相关方法 (Digital Image Correlation Method,DIC)设计并组建了配合液压疲劳试验机加载的原位观测系统。同时针对DIC测量方法中的关键技术进行研究,分别提出了一种可应用于视场宽度2mm下DIC计算的微小散斑制备方法,以及空间调节方法以提高试验可靠性。最后应用该系统开展针对航空发动机火焰筒材料GH536的微裂纹自然萌生试验。通过采取两种不同的DIC分析策略,分别获得疲劳过程中的总应变幅以及最大累积塑性应变的演化规律。结果表明总应变幅演化可确定自然萌生裂纹位置,最小可识别50μm裂纹;最大累积塑性应变分析可得萌生寿命占比约85%,并在裂纹出现后塑性应变急剧增加。     

用CT图像分析C／C复合材料的内部缺陷

总结了不同类型三向增强Ｃ／Ｃ复合材料ＣＴ检测图像及其对应的内部缺陷,结果表明：ＣＴ技术主要缺陷区与正常区存在的密度差异,对Ｃ／Ｃ复合材料内部进行质量检测,但在某些特定条件下,相同种类的缺陷可能表现出不同的ＣＴ图像,不同种类缺陷可能产生类似的ＣＴ图像,缺陷类型的判定必须与其它检测手段相结合才可确定,ＣＴ检测也有可能漏检部分缺陷。     

C/C复合材料密度的CT定量无损检测技术

讨论了利用水模试样和石墨试样标定CT检测过程中影响CT值的因素(系统噪声、产品尺寸、检测参数、摆放位置等)对CT值的影响,然后利用C/C复合材料试样建立CT值和材料密度的拟合曲线和拟合公式.结果表明系统噪声、产品尺寸、检测参数、摆放位置等对CT值的影响很小,C/C复合材料织物和复合物CT值和材料密度的拟合公式分别为P=(T+793)/659和P=(T+100)/860,说明利用CT值可以对C/C复合材料的密度进行定量定义.     

一种抗野值自适应滤波算法及在MEMS-SINS/GPS中应用

针对噪声统计特性不准确以及量测信号中出现的野值对滤波的不利影响,提出一种基于Kalman滤波的抗野值自适应滤波算法。该算法通过对估计误差的实时监测来调整渐消因子或进行抗野值计算,使滤波器在统计特性不准确或存在野值干扰的情况下仍为最优估计。将其应用到MEMS-SINS/GPS组合导航系统中,仿真结果表明该算法能有效降低统计特性不准确及野值给系统造成的不利影响。     

Trailing-edge scalloping effect on flat-plate membrane wing performance

This investigation studies the effect of trailing-edge scalloping on the lift and drag force coefficients of flat, membrane wings that vibrate at low Reynolds numbers (<61,000). A series of rigid, flat plate frames with moderate aspect ratio and repeating membrane cell structure were studied and compared to a rigid plate and a rigid scalloped plate. Lift and drag measurements were acquired using an external force-balance; flow fluctuation measurements were captured with a hot-wire. Results showed that the size and aspect ratio of the latex cell had a greater impact on lift than scalloping and that scalloping had a greater effect on drag than the cell aspect ratio. Compared to the solid wings, the membrane wings exhibited higher lift and drag coefficients, likely due to both effective cambering and dynamic interaction with the free shear layer. While trailing-edge scalloping decreased both the lift and drag coefficients relative to no scalloping, the greater effect was on drag, thus, increasing aerodynamic efficiency. The maximum lift-to-drag ratio was attained for a 25% scallop with a repeating cell aspect ratio of one. A unique nondimensional scaling of the membrane vibration peak frequency is also presented.     

用于压电料位计的微弱信号检测电路设计

设计了一种用于压电料位计的微弱信号检测电路,从防积分饱和电荷放大、带通滤波、精密检波、两级比较和逻辑控制五个方面介绍了其工程实现。能够实现单极性电源供电处理交流信号,实时监测料位计输出电荷大小,并转换为开关信号输出;具备灵敏度调节功能,可以根据不同物料的阻尼特性,有针对性地设置动作阈值;能够根据用户需要设置输出电平极性,提高了料位计的灵活性和适应性。结合理论计算、仿真分析和试验测试,验证了设计的合理性和正确性。     

隔振平台对姿态控制系统影响分析及参数选择

为实现卫星的高精度高稳定度姿态控制,在控制力矩陀螺群(CMGs)和星体之间加装了隔振平台。首先依据整星动力学简化模型推得了隔振系统传递函数矩阵;然后分析了隔振平台的使用给姿态控制系统带来的影响,并提出了一种既能使CMGs隔振平台满足隔振要求,又能保证姿态控制系统充分稳定性的参数选择方案;最后通过数值仿真的方式验证了所提出的参数选择方案的合理性。     

不完全角度CT图像重建的模型与算法

为了提升不完全角度计算机断层成像(CT)图像的重建精度和重建效率,研究了有限角度和稀疏角度下的CT图像重建问题,提出新的全变差最小化目标函数,通过将上一步迭代重建的图像作为反馈加入到新的迭代之中,不断更新目标函数的已知项。在算法求解时,采用增广Lagrangian罚函数方法,将约束问题非约束化,并将之转化为等价的3个子问题,通过在交替方向上求解子问题来获得优化问题的最优解。实验结果表明,该算法重建出的图像信息完整,细节清晰,重建精度高,与Split Bregman算法相比,本文算法结果的相对均方误差可下降42.1%~98.5%,条纹指标可下降42.8%~98.5%。     

面向Micro-PNT系统的微陀螺敏感结构参数化有限元仿真研究

针对Micro-PNT系统中多环和微半球陀螺敏感结构在设计阶段三维实体仿真分析存在的模型复杂、网格特征较难匹配结构特征、模型复用性较低等问题,提出一种基于低维单元简化建模,并通过实常数和截面定义等方式对特征结构进行全参数化表征的分析方法。通过对比,在相当的分析精度下,参数化分析中所需的节点数量仅为三维实体仿真的2%和43%,仿真效率提高显著,可加快陀螺设计收敛进程,支撑Micro-PNT技术发展。     

Effective metal mold method for the production of bionic adhesives based on electrochemical modifications

Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads. Their mainstream manufacturing method is molding. Due to most molds are made of silicon or silicon-based soft templates, and have poor wear resistant or vulnerability to high temperature, limiting their use in large-scale manufacturing. Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties. However, the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging. In this study, using electrodeposition techniques, the shape of the micropores is modified to obtain end-controlled pores. The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated. Furthermore, the mechanism of non-uniformity evolution of the microporous morphology is revealed. The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process. As a result, typical bionic adhesives with tip-expansion are obtained. Moreover, corresponding adhesion mechanics are analyzed. The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures, providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.