【作者】 宋广兴；

【导师】 齐乐华；

【作者基本信息】 西北工业大学 ， 机械设计及理论， 2007， 硕士

【摘要】 C／C复合材料作为理想的高温结构材料，其优异的高温性能和力学性能越来越受到重视，并在航空航天领域得到了广泛的应用。C／C复合材料的性能与纤维的类型、增强方向、编织方式以及基体碳的微观结构等因素密切相关。由于碳／碳复合材料制造周期长、成本高、工艺复杂，因而通过实验，分别测定它们的力学性能去进行方案的选优是不现实的。最合理的方法是对各种不同织物结构的C／C复合材料先进行理论预报，在理论上定性选定织物结构后，再投资进行材料的工艺优化研究，以节省投资和缩短研制周期，实现复合材料—设计—工艺—评价一体化。本文运用近年来倍受关注的均匀化理论，结合有限元法，对非编织C／C复合材料的宏观等效性能进行了数值预报，对细观结构应力进行了数值模拟与分析，得到了一些对该材料优化设计具有一定指导意义的结果。 首先，本文以渐进展开均匀化理论为基础，将均匀化理论与有限元相结合，建立了用来预测非编织C／C复合材料等效弹性参数的均匀化有限元方程，实现了宏细观的有效结合。 其次，针对CVI工艺制备的单向增强及非编织C／C复合材料，运用均匀化方法和有限元相结合的方法对其等效弹性参数进行了预报与分析。论文首先分别建立了单向增强及非编织C／C复合材料的细观结构模型，针对单胞的周期性边界条件，在前人的基础上通过等效处理使其在胞元一级得到了满足，建立了等效周期性边界条件，即所谓的固定边界条件。然后，分别对上述两类材料的等效弹性参数进行了预测，并与文献及实验结果进行了比较，验证了均匀化有限元法的有效性。接着考察了两种细观结构模型下相材料参数的选取对1D C／C复合材料等效性能参数的影响，发现随着碳纤维体积分数的增加，该材料的等效弹性模量单调增加，而泊松比则有所下降。在此基础上，进行了二次均匀化计算，分析了纤维体积分数、纤维取向角及基体性能等参数对平纹及斜纹碳布叠层细编穿刺C／C复合材料等效性能参数的影响，探讨了它们之间的相互制约和耦合作用的影响，提出了应合理选取各细观结构参数，一定程度上为实现该材料的优化设计奠定基础。此外，分析了单胞模型存在缺陷时对该材料性能的影响。 最后，对单向增强及非编织C／C复合材料的细观应力场分布进行了数值模拟，分析了细观参数及结构变化对应力场的影响，此外，对单胞存在缺陷时的细观应力场进行了模拟，得到了一些有意义的结果。更多还原

【Abstract】 Carbon/carbon(C/C) composites offer unique mechanical properties for high temperature applications where high strength, wear resistance, and lightweight components are desirable. For these reasons C/C composites have been extensively investigated and applied. Some factors, such as carbon fiber types, carbon fiber directions, knitting styles and carbon matrix microstructure, will influence the mechanical properties of C/C composites. However, it is too difficult to determine the mechanical properties of C/C composites by testing them with various knitting styles, because of the complicated manufacture processing, long times and high product cost, to optimize knitting structures. It is a good way to choose good knitting structures by theory predicting, then to research the optimization of material manufacturing process. The research in this paper intends to combine homogenization method with finite element method (FEM), and to predict effective parameters and micromechanics of nonwoven C/C composites in microcosms. Some useful results acquired will afford instructions for optimal design of these composites.First, the brief theory of homogenization method has been given. Then, the finite element method is combined with homogenization theory (HFEM) to predict the effective properties of nonwoven C/C composites and realize the effective combination of macro and microcosmic. Then, this method (HFEM) is applied to predict and analysis the effective properties of 1D, 2D and 2.5D C/C composites. For these, the base cell of 1D and 2D C/C composites are constructed. By equivalent treatment, the periodical boundary condition of unit-cell can be satisfied in element, which is called fixed displacement conditions. Based on these, HFEM is used to predict the effective properties 1D, 2D and 2.5D C/C composites. By comparing the results of present method with those of other methods and experimental, it is considered that more accurate results of effective elastic modulus can be obtained by means of HFEM. Further, the influence of material parameter to the effective properties of 1D C/C composites is analyzed with two cell models. It is found that the effective elastic modulus will increase and poiss ratio will decrease with the increasing of carbon fiber contains. Moreover, the effective properties of 2D and 2.5D C/C composites based on 1D results are calculatet and the influence and coupling of parameter, such as carbon fiber contains, carbon fiber direction angle and carbon matrix performance, to the effective properties of 2D plain woven cloth and twill woven cloth C/C composites are analyzed and some useful results are obtained. It is proposed that the microscopic structure parameters should be selected reasonably to acquire expected C/C composites. The influence of defects in the base-cell models to the effective properties is studied. The research is the foundation of C/C composites optimal design.Finally, the micro structure stress of 1D and 2D C/C composites in the base-cell models are simulated and dicussed, the influence of varying micro structure parameters and structure changing to microstructure stress field are analyzed and the influence of defects in the base-cell models to microstructure stress field are studied. The results showed that the different stations and shapes of defects will affect the microstructure stress field.更多还原