基于Micro-CT的三维编织复合材料精细化建模与力学性能分析

发布时间：2018-09-05 08:49

【摘要】：三维编织复合材料既是一种材料又是一种结构,通过特殊的编织工艺可以直接编织成各种复杂形状,避免二次加工,使其在具有高比强度和比高刚度的同时不存在易分层等一系列问题,在航空航天和民用领域具有很大的应用潜力。因此,能够快速和准确地对三维编织复合材料的力学性能进行分析与评估显得愈发重要。三维编织复合材料的细观结构特征决定了它的宏观力学性能,建立一个能够精确反映其细观结构的模型至关重要。本文从细观角度出发,结合图像处理和断层扫描技术(Micro-CT),构造三维编织复合材料的细观几何模型,进而对材料的力学性能进行分析。首先,介绍了一种基于Micro-CT的三维编织复合材料精细化几何模型重建方法。利用Micro-CT对三维四向编织复合材料进行逐层断层扫描,采用滤波、膨胀和收缩等方法处理扫描切片图像,编写了程序自动识别切片图像内所有纤维束的截面轮廓,通过对纤维束截面图进行轮廓提取、离散、插值、截面重建等操作,把纤维束截面图转化为拓扑数据,建立了与材料真实细观结构相一致的精细化模型。该精细化建模方法具有通用性,可用于其他三维编织复合材料的几何建模。其次,在三维编织复合材料精细化几何拓扑结构基础之上,采用一种非均匀Voxel网格对材料的模型进行有限元离散,并对材料的宏观有效性能进行计算分析。纤维束内部Voxel网格单元尺寸呈梯度变化,在精细刻画材料内部相界面处的几何特征的同时降低了模型的计算规模。从精细化模型中提取一个代表性单胞模型和一个小尺寸模型,采用体积平均化方法计算材料工程常数,并且与理想椭圆截面的代表性单胞模型结果进行对比分析。针对纤维束打捻现象,研究了纤维束扭曲对材料宏观力学性能的影响。最后,采用刚度折减模型对三维编织复合材料在单轴拉伸载荷作用下的累积损伤过程进行模拟分析。采用应力平均化技术去除Voxel网格在不同相界面引入的应力集中,再利用平均化的应力判断组分材料是否发生损伤,然后考察三种计算模型(从精细化模型中提取的代表性单胞模型、从精细化模型中随机提取的小尺寸模型和椭圆截面的理想代表性单胞模型)、纤维束不同扭曲程度以及Voxel网格尺寸对计算结果的影响。
[Abstract]:Three-dimensional braided composites are both a kind of material and a kind of structure. Through special braiding technology, they can be woven into various complex shapes directly, avoiding secondary processing. Because of its high specific strength and high stiffness, it does not have a series of problems such as easy stratification and so on, so it has great application potential in aerospace and civil fields. Therefore, it is more important to analyze and evaluate the mechanical properties of 3D braided composites quickly and accurately. The macroscopic mechanical properties of 3D braided composites are determined by their microstructural characteristics. It is very important to establish a model that can accurately reflect the microstructure of braided composites. In this paper, a mesoscopic geometric model of 3D braided composites is constructed by combining image processing and Micro-CT, and the mechanical properties of the composites are analyzed. Firstly, a method of 3D braided composite fine geometric model reconstruction based on Micro-CT is introduced. Three-dimensional four-direction braided composite material was scanned layer by Micro-CT. The scanning slice image was processed by filtering, expanding and shrinking methods, and the program was written to automatically recognize the cross-section contour of all fiber bundles in the slice image. By means of contour extraction, discrete, interpolation, section reconstruction and so on, the fiber bundle section is transformed into topological data, and a fine model consistent with the real meso-structure of the material is established. The refined modeling method is universal and can be used in geometric modeling of other 3D braided composites. Secondly, based on the refined geometric topology of 3D braided composite, a non-uniform Voxel mesh is used to discretize the material model by finite element method, and the macroscopic effective performance of the material is calculated and analyzed. The size of the Voxel mesh cells in the fiber bundle varies in gradient, which reduces the computational scale of the model while accurately characterizing the geometric characteristics of the interface of the internal phase of the material. A representative cell model and a small size model were extracted from the refined model, and the material engineering constants were calculated by volume averaging method, and the results were compared with the results of the representative cell model with ideal elliptical section. According to the twisting phenomenon of fiber bundle, the effect of fiber bundle twist on the macroscopic mechanical properties of the material was studied. Finally, the cumulative damage process of three dimensional braided composites under uniaxial tensile loading is simulated by using stiffness reduction model. Stress averaging technique is used to remove the stress concentration introduced by Voxel mesh at different phase interfaces, and then the average stress is used to judge whether the component material is damaged or not. Then three kinds of computational models (the representative unit cell model extracted from the refined model) were investigated. Small size model and ideal representative cell model of elliptical section are extracted from the refined model. The effects of different twisting degree of fiber bundle and Voxel mesh size on the calculation results are discussed.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB332

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