【作者】 郑锡涛；

【导师】 叶天麒；

【作者基本信息】 西北工业大学 ， 固体力学， 2003， 博士

【摘要】 三维编织结构复合材料作为一种新型高级的复合材料，在国外得到迅速的发展，而国内对于这种结构复合材料的研究相对较少。本文采用控制体积单元法与试验观察相结合的方法研究了三维编织复合材料的细观结构，并采用数值计算方法分析了三维编织复合材料的弹性性能，具有一定的理论价值和实际工程意义。 三维编织结构复合材料是完全整体、连续、多向的纺线(纤维束)的网络，充填以延性材料，这类新材料已失去通常复合材料的层合板概念，由此，层合板复合材料层间脆弱的致命弱点在编织结构复合材料中得到克服，所以编织结构复合材料具有高的强度和刚度(包括在厚度方向)，接近实际形状的制造，高的冲击韧性、高的损伤阻抗，和按实际设计要求的特定的航空航天方面的使用功能，因而广泛地受到工业界和学术界的关注。文中从三维编织物的编织工艺入手，得到编织复合材料的几何结构，建立了织物纱线构造模型(FAM-Fabric Architecture Model)，进而分析其力学性能；另外，通过试验研究了这种复合材料的力学性能。主要的研究内容包括以下几个方面： 系统地研究了采用四步法1×1方型编织工艺编织的预成形件及其增强的复合材料的细观结构。提出了纱线椭圆形横截面假设，考虑了编织纱线的细度和编织纱线填充因子的影响。根据编织过程中携纱器的运动轨迹特点，将预成形件划分为三个不同的区域，分别定义了不同的控制体积单元，识别了预成形件的两种局部单胞模型，分析了预成形件的纱线构造，并导出了编织结构参数之间的关系，同时给出三维编织复合材料的设计方法。主要的编织结构参数包括试件的外形尺寸、主体纱行数和列数，三个区域各自所占的体积百分比、编织纱线的细度、纱线填充因子、纤维体积含量、编织角以及编织花节长度。 以精确的复合材料单胞模型为基础，从最小的可重复的单胞入手，对单胞的结构进行简化分析，认为纤维是平直的，将单胞中的四个不同方向的纤维束看成是空间四个不同方向的单向复合材料，纤维束的性能可以等价于单向复合材料的宏观性能。采用复合材料中的细观力学分析方法，计算单向复合材料的弹性常数。认为每一纤维束的纤维体积含量与整个单胞的纤维体积含量相等。采用三维应力—应变分析，在单胞的长度方向积分和平均，在给定的应变边界条件下，采用刚度体积平均的方法，预测三维编织结构复合材料的有效弹性模量；在空间多向应力的基础上，通过对三维编织结构复合材料破坏机理的探讨，摘要提出了适用于三维编织复合材料细观强度失效准则，预测三维编织结构复合材料的强度性能。在有限元分析中，提出了处理材料不均匀性问题的“等效有限申，元”方法，解决了像三维编织复合材料这类具有复杂细观结构的复合材料的有限单.元离散化问题。同时探讨了编织工艺参数，如内部编织角、表面编织角、纱线填充因一子、纤维体积含量等对力学性能的影响。结果发现编织角、纤维体积含量明显地影响其拉压模量和强度，随着编织角的增大、轴向纤维体积含量的减小，拉伸模量和强度降低，而在编织角相同时，随着纤维体积含量的增大，拉伸弹性模一录、拉仲强度、弯曲弹性模量、弯曲强度均增大，而泊松比随着纤约体积含量的增大而减小。与试验结果进行了对比，表明该力学模型能较理想地须报拭维编织结构复合材料的刚度和强度性能。 二维编织结构复合材料的发展历史不是很长，还有不少理论和试验工作要去做，本文为这种结构复合材料的进一步研究提供了基础。更多还原

【Abstract】 In recent years, structural textile composites have established themselves as the advanced material system of choice in many load-bearing applications including aerospace components, automobile components, and biomedical implants. The yarn architecture of three-dimensional (3-D) braided composites produced by the four-step 1×1 braiding technique and their effective elastic properties were studied in this dissertation with experimental investigation and a numerical method, respectively.Three-dimensionally braided structural composites have distinct structure that is fully integrated, continuously spatial fiber-network impregnated with ductile material. The new innovative materials have not plies as conventional composites have, and put an end once and all to low interlaminar strength showing in laminate materials. Because of their enhanced stiffness and strength in the thickness direction, near-net-shape design and manufacturing, superior damage tolerance and specified aerospace function, the braided composites are gaining more and more attention of industry and academia. The research in this dissertation began with braiding process of three-dimensional textile perform. A new fabric architecture model (FAM) was set up. The geometric structure of braided composites was recognized and the mechanical properties of the composites were analyzed. The primary research can be listed as follows.In this thesis, a control volume method was employed to model the microstructure of 3-D braided performs produced by the four-step 1×1 square braiding process and their reinforced composite materials. According to the movement traces of yarn carriers on the braiding machine bed, a perform was divided into three regions, i.e. interior, surface and corner, and distinct control volumes were defined for each region. Analyzing the control volume of each region, the yarn architecture of perform was described and three kinds of local unit cell were identified. Then the relations between the braiding parameters of the perform were derived. Based on the analysis of the perform, two local unit cells for the 3-D braided composite material were obtained and the relations between the braiding parameters were modified. Finally, the method of designing a 3-D braided composite was given. The braiding parameters include the dimensions of sample, the braiding yarn of main part, the volume proportion of each region to whole structure, the size of the braiding yam, the yarn packing factor, the fiber volume fraction, the braiding angle and the braiding pitch length.Furthermore, a methodology based upon the concept of fabric unit cell structure was developed for studying the elastic properties of three-dimensional braided composites. In order to facilitate the analysis of the minimum repeated unit cell, the following geometrical characteristics were assumed: (a) All the yarn segments parallel to a diagonal direction or braiding axis in all unit cells lying in the samelayer of the perform are treated as forming inclined lamina or horizontal lamina after matrix impregnation, (b) Fibers were considered to be straight and unidirectional. Fiber interlocking and bending due to the interaction at the centers of the unit cell were not taken into account, (c) A unit cell can be further considered as an assemblage of four inclined unidirectional lamina and one horizontal unidirectional lamina. Each inclined unidirectional lamina was characterized with a unique fiber orientation and had the same thickness. Furthermore, the fiber volume fraction of each inclined and horizontal unidirectional "lamina was assumed to be the same as that of the composites. Three-dimensional stress-strain analysis was applied to each unidirectional lamina that was assumed to be transversely isotropical under on-axis coordinate system. Carrying out the integration and averaging of stiffness yielded the effective elastic moduli of 3-D braided structural composites. Based upon failure mechanisms of 3-D braided composites, a kind of micro-structural strength criterion was s更多还原