【作者】 孙颖；

【导师】 李嘉禄； 陈利；

【作者基本信息】 天津工业大学 ， 纺织工程， 2003， 博士

【摘要】 本文全面系统地研究了二步法方型三维编织复合材料的细观结构，并采用细观力学分析方法对其有效弹性性能进行了分析预测。 二步法三维编织复合材料的组分材料和增强体的细观结构对其宏观力学性能起着重要的作用。本文对其细观结构作了准确的单胞划分，定义了三种细观结构的单胞模型。即大单胞模型，亚单胞模型和子单胞模型。基于子单胞模型，通过计算轴纱内纱线填充因子，考虑了轴纱受编织纱挤压产生的变形，进而，建立了复合材料编织结构参数之间的关系，准确地计算了复合材料的纤维体积含量。同时，给出了二步法三维编织工艺的设计步骤，并由纱线挤紧状态确定出编织工艺的设计范围。 本文基于内部子单胞模型，提出了类似层合板结构的单胞力学模型，应用经典层合板理论实现由纤维和基体的性能、单胞力学模型的几何参数以及单层板的纤维体积含量分析并计算了二步法方型三维编织复合材料的有效弹性性能。 本文基于大单胞模型，提出了对二步法方型三维编织复合材料进行细观结构离散的思想，并建立有限元分析模型。其中，轴纱、编织纱和基体均被视为两端铰接的空间杆单元，复合材料用离散的杆单元组成的桁架结构代替。利用有限元分析软件包MARC实现单轴拉伸静载实验的模拟，分析了二步法三维编织复合材料的弹性性能，同时，预测了轴向拉伸模量随轴纱与编织纱线密度之比和节距长度变化的趋势。 本文设计并完成了单轴拉伸性能实验，在获得二步法三维编织复合材料宏观拉伸模量和泊松比的同时，对两种理论分析模型的预测结果进行了验证。预测结果与实验结果的比较显示了细观力学的两种分析模型都可以较为有效地分析二步法三维编织复合材料的力学性能。更多还原

【Abstract】 In this thesis, the yarn architecture of the two-step rectangular three-dimensional braided composites was studied comprehensively and the effective elastic properties have been analyzed by means of two kinds of micro mechanical method.The properties of components and the microstructure play an important role in the mechanical properties of two-step three-dimensional braided composites. Analyzing the microstructure of composites truly, three kinds of unit cell structures have been identified, i.e. large unit cells, sub unit cells and micro unit cells. The deformations of axial yarns packed by braider yarns have been calculated through the changes of fiber packing fractions of axial yarns. The relations between the braiding parameters of the composites were derived and the fiber volume fraction of the composites was computed exactly. The process of designing a two-step 3-D braided composite was given. The window of braiding process was given with the yarn jamming condition.The model of the analogous laminar unit cell has been proposed based on the micro unit cells. The classical laminated plate theory was utilized to analyze the mechanical properties of two-step 3-D composite materials. In this methodology, the effective elastic properties were predicted through the properties of fiber and resin, the geometry of the laminated plate model and the fiber volume fraction.Furthermore, the finite element model has been established on the basis of the large unit cells of the composites. The composite material was considered as an assemblage of a finite number of unit cells. In this model, axial yarns, braider yarns and resin were treated as spatial beam elements. Each unit cell is then treaded as space truss. Three-dimensional finite element method can be employed for the mechanic analysis. Utilizing the finite element software MARC, the monotonic tension tests of the beam samples were simulated. Parametric study showed the range of variability in the elastic modulus of the composites.The parameters include the linear density ratio of axial yarn to braider yarn and the braiding pitch length.The two model predictions were found to be in good agreement with the results of monotonic tensional tests performed in this study. The resolution method and the numerical method can be used to analyze the mechanical properties of two-step three-dimensional braided composites effectively.更多还原