【作者】 焦志文；

【导师】 周储伟；

【作者基本信息】 南京航空航天大学 ， 工程力学， 2009， 硕士

【摘要】 本论文的研究分为两部分。第一部分采用多尺度的有限元方法研究了圆管状三维机织复合材料的力学性能,第二部分对一种三维机织复合材料的疲劳刚度下降进行了试验研究和细观有限元模拟。第一部分:1.建立了圆管状三维机织复合材料的微、细观多尺度单胞模型,用微观单胞描述了纱线束中纤维和基体两相材料的非均匀性;用细观扇形单胞代表圆管中纤维束的细观几何。分别讨论了微、细观单胞满足的周期性边界条件,给出了单胞上平均应力、应变的计算方法。用商用软件多点约束法的方法实现了上述微,细观单胞多轴荷载下的周期性边界条件。2.用上述多尺度的单胞模型对一种圆管状三维机织复合材料结构进行了多尺度耦合分析。首先由微观单胞计算出纤维束的平均弹性常数;再通过细观单胞分析,得到材料的宏观弹性常数。实现了由组分材料性能及编织参数预测圆管的宏观弹性性能。随后研究了复杂荷载下从大到小各尺度耦合的应力分析。对于圆管环向应力非周期分布的情况,建立了嵌入细观单胞的环状模型。第二部分:1.对一种三维机织复合材料分别进行了静态拉伸及拉-拉疲劳性能试验,得到了试验件的初始刚度,静强度和疲劳载荷下剩余刚度退化曲线,对试验件疲劳损伤演化进行拍摄了,并对疲劳断裂后的试验件的微、细观断裂面进行了观察,总结出材料的疲劳损伤机理。2.建立了上述三维机织复合材料疲劳损伤的有限元模型,对疲劳加载进行了模拟,研究了疲劳累积损伤下材料力学性能的退化模式,给出了材料的疲劳失效判断准则和疲劳剩余刚度退化模型。利用商用软件ABAQUS的UMAT用户子程序功能实现了疲劳累积损伤的有限元模拟。更多还原

【Abstract】 This paper is divided into two parts. In the first part ,A multi-scale coupled numerical model was developed to investigate the mechanical behaviors of 3D woven composite pipe first. In the second part, researching fatigue damage on 3D woven composite with the finite element simulation and experimental methods.In the first part:1. Micro- and meso-scale unit cells were built to represent the inhomogeneity of fiber tow and weave structure of 3D woven composite pipe, respectively. The periodic boundary condition of the camber shape meso-scale unit cell was specified. Then, the micro, meso unit cell of the periodic boundary conditions were implemented on the commercial software by Multi-point constraint method(MPC), and multi-axial loads either in terms of average stresses or average strains can be easily applied through master-slave node technology.2. Multi-scale coupled numerical approaches for 3D woven composite pipe structure were pursued. The macro-scale stiffness of 3D woven pipe was obtained by averaging stiffness of unit cells from micro-scale to meso-scale. Using the multi-scale unit cells, the converse stress analysis process under multi-axial loads was carried out, i.e. to transfer stresses from macro-scale to meso-scale and finally micro-scale. A model of embedding meso-unit cell into a homogenous ring was suggested for meso stress analysis in case of meso-scale stress without periodicity in annular direction.In the second part:1. static tensile and tensile - tensile fatigue tests on 3D woven composite were performed to work out the material’s initial stiffness, staticstrength and residual strength degradation. The fracture surfaces were observed using a scanning electron microscope(SEM), and the material fatigue damage mechanism was summed up.2. a finite element model was estalished to research fatigue damage on 3D woven composite. A degraded mode of the material properties on fatigue damage was developed by stress analysis under fatigue loading. The fatigue failure criteria and the sudden material property degradation rules of unidirectional fiber-reinforced composite laminates have been developed. The fatigue damage accumulation was simulated with the user-defined material (UMAT) subroutine of ABAQUS.更多还原