【作者】 李向华；

【导师】 袁慎芳；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2005， 博士

【摘要】 三维多向编织复合材料由于其本身所具有的优异性能,被称之为第三代纤维增强复合材料,广泛应用于航空航天等各领域,将光纤传感器编入三维编织复合材料结构中,可以实现编织结构内部性能参数的检测,有助于推进材料结构的健康状况、制作工艺和强度刚度性能预计的研究工作。本文从材料结构的设计思想出发,对光纤传感器编入三维编织复合材料结构内部的细观胞元模型、组分性能关系以及光纤传感技术用于编织材料性能的测试作了初步的理论和实验研究。 首先,建立了两种不同的光纤传感器编入三维编织复合材料结构方法下的内胞模型,研究了其内胞模型中光纤与纱线接触线形状以及体积关系,给出了胞元模型中不同组分的纤维体积含量的表达式,得出一些相应的结论。 从先前的几何分析出发,基于修正倾斜层板理论模型,推导了不同光纤传感器编入编织结构方式的刚度性能预计公式,计算了材料结构模型的弹性模量和泊松比,建立了 Michelson 干涉型传感测试实验系统进行实验。实验结果验证了修正倾斜层板模型理论的合理性。 荷载在胞元模型中的分配和传递是研究分析光纤传感器在编织结构内部进行结构性能参数测试的重要环节之一,本文对编入光纤的单胞进行了理论分析,研究了编入光纤的三维编织复合材料内胞和面胞的布尔生成过程,结合设定的边界条件和连续条件,在变分原理的基础上,对于空间组合的多相介质系统,建立各项的格林函数和基体、纱线和光纤部分及相互界面上的平衡解析方程。同时对单胞模型运用有限元结构分析软件进行几何建模,分析了单胞模型等价于实验形式的相似等效连续条件和边界条件。 光纤 Bragg 光栅传感器灵敏度高, 可实现点测量和准分布测量。采用光纤Bragg 光栅编入编织复合材料结构内部,建立了拉伸测试的光纤 Bragg 光栅传感系统并对结构内部应变进行了检测,并将实验结果与等效边界条件下模拟分析的计算结果作了比较。 最后,针对编入光纤光栅的三维编织复合材料试件拉伸失效模式进行了分析研究,探讨光纤光栅对结构试件由弹性形变区域到塑性形变区域过渡过程的预计作用,从细观角度上分析了结构的破坏机理和机制。更多还原

【Abstract】 The 3-dimensional multi-directional braided composites have been considered as the third-generation strengthen composites for their outstanding performance and are now being widely used in many fields, such as aeronautics & astronautics. Optical fiber sensors co-braided into the 3-D braided composite structures can be used to detect internal structural parameters of the structure, and are helpful to promote correlated researches on braided composites’ health monitoring, manufacturing process and stiffness or strength prediction. The relationship among micro unit cell, composing properties, meso-braided structures and optical fiber sensing technology used in the testing of the braided composites are studied in this thesis are firstly established for the optical fiber co-braided in the structure using two different methods. The unit cell models for the optical fiber sensors co-braided into the structures by two ways are firstly constructed, the contacting track between optical fiber and yarns and the geometric relationship in the unit cell are discussed subsequently, fiber volume fraction formula of each constituent is given, so does some corresponding conclusions. Based on the above geometric analysis, stiffness properties of the two unit cell models are developed by the means of correct inclined laminate theory, Young’s modulus and Poisson ratio are calculated, A Michelson polarized sensing experiment system is established to validate the efficacy of above analysis. The experimental results are corresponding to the prediction value. Loading transferring and assignment analyses in the unit cell model are always important to the structural performance parameters testing. In this paper, theoretical research is conducted on the Boolean operation of the internal cell model and the constructions of 3-D Green’s functions of heterogeneous medium; The constituent condition and boundary condition are also presented; Heterogeneous components equilibrium equations based on variation principle are proposed. Geometrical modeling is constructed by using FEM structural analysis software; Effective constituent condition and boundary condition of unit cell model equivalent to experimental condition are also discussed. Fiber Bragg grating sensors have the virtue of good sensitivity and are applied to point detecting and quasi-distributed testing. In this paper fiber Bragg grating sensing system for tension test to determine the internal strain are implemented, comparison are given between the theoretical and stimulation results under the effective boundary conditions. Tensile strength experiments and failure analysis are carried out for 3-D braided composites by co-braided optical Bragg gratings. Mechanical properties are investigated from the macroscopic view, so does the failure mechanism of braided structures from the microscopic view. SEM analyses of the specimens fracture on the basis of tensile experiments are conducted. All these results provide an experimental basis for further studies on the strength prediction and failure criterion’s setup by the means of co-braided optical fiber sensors.更多还原