Study on an automatic multi-pin insertion system for preparing Z-pin composite laminates

As a three-dimensional layer enhancement technology, the Z-pin technology is suitable for manufacturing composite prepreg laminates and can also effectively improve their interlaminar properties. In order to manufacture Z-pin composite parts efficiently, this paper proposes a transi- tional insertion system, and according to the technical requirements of the transitional insertion process and the functional requirements of the transitional insertion platform, proposes a transition insertion plan which can insert multiple Z-pins into a carrier. A prototype machine has been designed and made, and a series of function debugging and verification experiments have been car- ried out on the machine. Some problems show up during the experiments, but based on the analysis of the reasons, this paper provides lots of solutions, and finally demonstrates the feasibility and practical value of the system. The results show that the system meets all technical requirements of the Z-pin insertion process. It is capable to insert multiple Z-pins into a foam carrier; as a result, the system is as much as 5 times more efficient than existing equipment, and the deviation for the insertion distance can be controlled within 0.3 mm. This Z-pin transitional insertion platform pro- motes the use of Z-pins in national defense and lays the foundation for commercializing the Z-pin technology.     

Damage characteristics and constitutive modeling of the 2D C/SiC composite: Part Ⅱ–Material model and numerical implementation

In this work, a macroscopic non-linear constitutive model accounting for damage, inelastic strain and unilateral behavior is proposed for the 2D plain-woven C/Si C composite. A set of scalar damage variables and a new thermodynamic potential expression are introduced in the framework of continuum damage mechanics. In the deduced constitutive equations, the material's progressive damage deactivation behavior during the compression loading is described by a continuous function, and different deactivation rates under uniaxial and biaxial compression loadings are also considered. In damage evolution laws, the coupling effect among the damage modes and impediment effect of compression stress on the development of shear damage in different plane stress states are taken into account. Besides, the general plasticity theory is applied to describing the evolution of inelastic strain in tension and/or shear stress state. The Tsai–Wu failure criterion is adopted for strength analysis. Additionally, the material model is implemented as a user-defined material subroutine(UMAT) and linked to the ABAQUS finite element software, and its performance is demonstrated through several numerical examples.     

有机-无机Nano-SiO2/DCPDCE杂化材料的性能

为解决传统商用nano-SiO2粒子在双环戊二烯型氰酸酯(DCPDCE)树脂基体中容易团聚的问题,利用Sol-Gel法制备的有机-无机nano-SiO2为填料对DCPDCED进行改性。研究了有机-无机nano-SiO2含量对nano-SiO2/DCPDCE杂化材料力学性能、介电常数、介电损耗因子的影响。结果表明:有机-无机nano-SiO2较商用nano-SiO2在DCPDCE中分散更优;当有机-无机纳米SiO2含量为3.0wt%时,杂化材料的综合性能最优。     

多频谱兼容隐身材料研究进展

多频谱兼容隐身材料具有明确的研究和应用背景。综述了国内外在红外及雷达兼容隐身材料、红外及可见光兼容隐身材料、红外与激光兼容隐身材料等多频谱兼容隐身材料技术的发展以及多频谱兼容隐身材料在热点领域如光子晶体、掺杂氧化物半导体等所取得的研究成果和进展,指出今后的多频谱隐身材料发展的方向和重点。     

开孔曲面自动铺放轨迹规划算法研究

为解决开孔曲面自动铺放轨迹规划问题,提出在前处理中将孔边界内外的曲面接合成完整曲面的方法,采用STL文件提取网格化曲面信息并重构开孔曲面拓扑,按照设定算法获得“连续”的铺放轨迹后,再按孔边对轨迹点进行信息整理得到后置处理所需的最终铺放轨迹点信息.研究了迭代法和投影法在轨迹线与孔边界交点的求取方法,综合比较2种算法的效率和精度后,发现投影法更适于开孔曲面的轨迹规划.根据上述算法,编写了基于VC++ 6.0平台的轨迹规划程序,以整体复合材料前机身为例进行算法验证,证明了提出的开孔曲面自动铺放轨迹规划算法的合理性和正确性.     

基于结构设计的自调节铺放轨迹规划算法

通过分析预浸带/纱在曲面上的铺放工艺性,提出以轨迹测地曲率作为铺放工艺性测度,构建一种基于结构设计的自调节轨迹规划算法,兼顾自动铺放中的铺放工艺性和结构设计要求.该算法是在满足结构设计的前提下,将预浸带/纱轨迹从结构设计所确定的方向按特定方式向测地线方向偏转,从而减小预浸带/纱的变形.本文以固定角度法作为结构设计准则、以最大容许偏转角法定义修正函数,以此为例阐述具体算法及实施过程.基于Visual C++平台,进行C++和SQL混合编程,以某型进气道为模型进行了算法仿真,并进行了进气道和锥壳的铺放试验.结果表明:容许偏转角的增大有助于缓解预浸带/纱的变形.     

天线罩用宽频透波材料的发展现状

综述了天线罩用宽频透波材料的发展现状,分析了影响透波材料性能的因素,系统讨论了宽频透波天线罩的制备方法.研究指出介电性能是评价材料透波性能的一个重要标准,选用低介电材料和提高材料孔隙率可实现材料宽频透波,新的介质材料的开发和研究将是今后天线罩制造技术发展的一个主要发展方向.     

挖补修理对复合材料层合板拉伸性能的影响

挖补修理是一种先进的复合材料层合板损伤修理技术,分为斜接法和阶梯法两种类型。本文研究不同修补结构对斜接法挖补修理试验件力学性能的影响。对斜接法楔形砂磨斜坡比率为1:10、1:20、1:30和1:40的复合材料层合板修理试验件的拉伸性能进行了研究,同时总结了斜接法修理后试件的断裂位置特征。结果表明:斜接法斜坡比率为1:30的挖补修理试件的抗拉强度最好,外加补片会提高试件的抗拉强度,外加补片层数2层为宜。断裂类型主要有脱胶断裂和补片断裂。     

深空探测用热防护材料的现状及发展方向

综述了热防护材料的发展历史,重点介绍了深空探测用烧蚀防热材料体系,并通过Pioneer Venus、

Galileo、Stardust 等探测任务的热防护系统(TPS)选材方案分析,对未来深空探测TPS 材料进行技术需求分析。

     

战斗机8~14μm波段红外特征及低发射率材料隐身效果

对某典型战斗机在8~14μm波段范围内的红外积分辐射强度空间分布进行了数值计算,考虑了大气透过率的影响,计算了使用红外搜索跟踪系统对战斗机进行探测时的探测距离,并分析了该战斗机采用低发射率材料后的红外隐身效果.战斗机的流场采用商用Fluent软件进行计算,红外辐射特征及探测距离采用自开发的NUAA-IRSE软件进行计算.计算结果表明:在8~14μm波段,周向角一定时,俯仰角越大红外积分辐射强度越大;俯仰角一定时,周向角越大红外积分辐射强度越大.采用低发射率材料后,战斗机在整个空间方向范围内,其红外积分辐射强度降低,战斗机红外隐身效果提高.