【作者】 王新峰；

【导师】 王鑫伟；

【作者基本信息】 南京航空航天大学 ， 工程力学， 2007， 博士

【摘要】 机织复合材料是由两组纱线在织机上沿各自的方向交织而成。纤维束的相互交织使得机织复合材料具有许多优异的性能,如增强了面内和层间的强度、提高了损伤容限和抗冲击性能以及具有良好的仿形能力等。因此,机织复合材料作为一种结构材料受到日益广泛的关注,并已在航空航天、生物医学工程以及汽车工业等领域得到了广泛的应用。为了更加有效的设计和使用机织复合材料,需对它们的力学性能进行深入的研究。本文在细观纤维尺度和宏观单胞尺度两个尺度上分别建立了纤维束力学模型和机织复合材料力学模型。并采用三维实体有限元方法,研究了平面机织复合材料和三维机织复合材料的刚度、强度性能以及在各种载荷作用下的损伤演化过程。首先基于纤维的六角形堆积假设,在细观尺度建立了纤维束单胞模型。根据纤维和基体的性能分别对基体单元和纤维单元采用相应的强度准则,研究了不同组分材料、不同纤维体积含量纤维束的各项力学性能。通过有限元计算结果与已有理论公式预测结果的对比分析,修正了部分现有的刚度和强度预测公式。建立了宏观尺度的平面机织复合材料三维卷曲几何模型,可更为准确地反映其内部几何结构。并将细观纤维束的研究结果引入该模型,研究了平纹机织复合材料在拉伸、压缩和面内剪切载荷作用下的力学响应,分析了其破坏机理。还进行了三维机织正交浅联复合材料的细观几何结构研究。在细观观测的基础上,采用Hermit样条函数建立一种新的三维机织复合材料几何模型。利用该模型研究了三维机织复合材料在经向拉伸、纬向拉伸和面内剪切载荷作用下的损伤演化过程。在宏-细观两个尺度上的有限元分析中,均采用了周期性边界条件以保证单胞边界面的应力连续和位移连续。并且当单元出现损伤后,对细观纤维束单胞和宏观机织复合材料单胞中的损伤单元均按特定方向进行刚度折减,抛弃了以往损伤分析中常用的“单元消失”方法。本文还进行了树脂传递模塑(Resin Transfer Molding,RTM)成型工艺的研究,并自行设计和制作了一套螺旋加载式多通道RTM成型装置,制备了三维机织复合材料试验件。进行了拉伸、压缩和剪切试验,获得了部分平面机织复合材料和三维机织复合材料的基本力学性能数据。试验结果与有限元分析结果吻合较好,验证了本文多尺度模型和分析方法的正确性。更多还原

【Abstract】 Woven fabric composites are constructed by weaving two fiber tows into each other. The interlacing of fiber bundles makes the composite materials possess several advantages, for example, increase of the intra- and inter-laminar strength, damage tolerance, and impact resistance, and ability of making near net shape structural components. Consequently, woven composites, as a structural material, have received more and more attention recently. The materials have been widely used in the areas of aeronautical and aerospace engineering, bio-medical engineering, and automotive industry. For more effective use and design of woven composites, it is desirable to investigate deeply their mechanical properties.In this dissertation, two-scale models, the microscopic repeated unit cell (RUC) model for yarn and the macroscopic repeated unit cell model for woven composite, are presented, and 3D finite element analyses are performed to predict the effective stiffness, the effective strength, and the damage evolution process of plain woven composites and the 3D woven composites. The micro-RUC model for the yarn is built based on a hexagonal array of fibers. The properties, such as elastic constants and strengths, of different fiber/matrix systems with various fiber volume functions are obtained based on FE analysis together with appropriate failure criteria of the two basic constituents of the composite (fiber and matrix). Modifications to the existing theoretical formulas for calculations of stiffness and strength of yarns have been made based on the comparisons between the predicted results and data given in the literature.A macro-geometry model, named three-dimensional curve model, is established to characterize more accurately the inter-structure of plain woven composites. The numerical results of yarn obtained on the microscopic repeated unit cell (RUC) model are adopted as the properties of impregnated tows in the macroscopic analysis. The responses of the composites under tensile, compress and shear loadings are obtained by using 3D FE method. Then, the microstructure of 3D woven orthogonal interlock composite is studied in detail experimentally. Based on the observations, a novel model is built by using the Hermit spline functions. The 3D FE analysis are performed on the new model for studying the damage evolution of 3D woven composites under tensile loadings in both warp and weft directions and under shear loadings.The periodic boundary conditions are applied to the two-scale models during the 3D FE analysis in order to ensure that both the displacement and stress are continuous on the boundary surfaces. Once damages occur, the stiffness reduction is considered in particular orientations in both the micro- and macro-scale RUCs, thus, the“element disappear”technique, commonly used in previous researches, is abandoned. The process of Resin Transfer Molding(RTM)is also studied in the thesis. A RTM equipment is designed and manufactured in the laboratory. Specimens of 3D woven composites are manufactured with house-made RTM equipment. Tensile, compressive and shearing tests are performed. The fundamental mechanical properties of plain woven composites and 3D woven composites are obtained. The experimental data agree well with the predicted results, thus, the correctness of the established two-scale models and analysis method have been verified.更多还原