混凝土开裂在细观层次上的数值模拟研究

发布时间：2018-07-05 16:01

本文选题：混凝土 + 细观层次　；参考：《昆明理工大学》2013年硕士论文

【摘要】：混凝土是一种典型的多相非均质复合材料,它的力学性能主要依赖于其内部各相材料的力学性能。在一定的试验基础上,采用数值模拟方法不仅可以直观地反映混凝土细观断裂破坏的全过程,还可以反映骨料的形状、含量及界面过渡区(ITZ)等对混凝土宏观力学性能的影响。在确保计算模型可靠和有效的前提下,可以替代部分试验,避开试验条件的限制及人为操作误差等对结果的影响。本文依据细观力学理论,将混凝土看作由骨料、砂浆及两者之间的粘结界面组成的三相复合材料,用MATLAB自编程序生成随机分布的骨料颗粒几何模型,从中选取代表性体积单元作为混凝土试样,并运用有限元分析软件ABAQUS对其在单轴拉伸、压缩荷载作用下的破坏全过程进行了数值模拟研究,并对试件的细观损伤与宏观破坏之间的联系进行了分析探讨。采用ABAQUS有限元分析软件对混凝土试样中的骨料、砂浆和界面分别赋予各自的材料属性并分别进行网格划分。对混凝土试样施加随时间变化的位移荷载来进行数值模拟研究。计算结果表明：界面过渡区是混凝土的薄弱环节,首先在界面单元上出现微裂纹,而后向相邻的砂浆单元扩展,微裂纹不断扩展,延伸,合并,最终导致试样破坏。这说明,混凝土的宏观力学性能受细观结构的制约。混凝土细观结构的损伤和破坏是引起宏观破坏的内因和基础。数值模拟结果和试验结果一致,证明了所建模型的有效性和可行性。通过本文研究可知,界面过渡区是混凝土的薄弱环节,混凝土的损伤断裂最先发生在界面区,随着界面微裂缝的不断扩展,延伸,合并,最终导致试件破坏。即混凝土的细观损伤是宏观破坏的内因和基础,而试件的宏观破坏是细观损伤不断积累和发展的结果。本文具体工作如下： 1、对混凝土材料在细观层次上损伤断裂的理论进行了研究,对混凝土材料的破坏机理和断裂损伤的物理机制进行了研究。 2、利用MATLAB程序化设计语言首先生成满足给定区间上随机分布的骨料颗粒的圆心坐标,再根据圆心坐标合格的判别条件进行判定,最终生成圆形及椭圆形骨料颗粒的混凝土试件的几何模型。 3、介绍了有限单元法的基本原理,等参单元的力学分析及等参单元在本文中的应用。 4、对几何数值模型选取代表性体积元作为混凝土试样,对其在单轴受拉、受压荷载作用下进行数值模拟研究,找出混凝土内部裂纹的扩展规律。对所得到的曲线进行分析得出相关结论。 5、对界面的厚度取值进行研究,从而找出界面厚度不同对混凝土力学性能的影响规律,为混凝土数值模拟时界面厚度的选取提供依据。
[Abstract]:Concrete is a typical heterogeneous composite material. Its mechanical properties mainly depend on the mechanical properties of each phase material. On the basis of certain tests, the numerical simulation method can not only directly reflect the whole process of microfracture failure of concrete, but also reflect the influence of aggregate shape, content and interface transition zone (ITZ) on the macroscopic mechanical properties of concrete. On the premise of ensuring the reliability and effectiveness of the calculation model, the partial test can be replaced, and the influence of the limit of test conditions and the error of artificial operation on the results can be avoided. In this paper, according to the theory of mesomechanics, the concrete is regarded as a three-phase composite composed of aggregate, mortar and the bond interface between them, and the random distribution of aggregate particle geometry model is generated by MATLAB program. The representative volume element is selected as the concrete specimen and the finite element analysis software Abaqus is used to simulate the whole failure process of the concrete under uniaxial tensile and compression loads. The relationship between meso-damage and macro-damage is analyzed and discussed. Abaqus finite element analysis software is used to divide the aggregate, mortar and interface of concrete samples into their own properties and mesh. A numerical simulation study was carried out on concrete specimens subjected to displacement loads varying with time. The results show that the interfacial transition zone is the weak link of concrete. At first, there are microcracks on the interface elements, but then on the adjacent mortar elements. The microcracks continue to expand, extend and merge, resulting in the failure of the specimens. This shows that the macro-mechanical properties of concrete are restricted by the mesoscopic structure. The damage and failure of concrete meso-structure is the internal cause and foundation of macro-damage. The numerical simulation results are in agreement with the experimental results, which proves the validity and feasibility of the proposed model. Through the study of this paper, it can be seen that the interface transition zone is the weak link of concrete, and the damage and fracture of concrete first occur in the interface area. With the continuous expansion, extension and merging of the micro-cracks in the interface, the ultimate failure of the specimen is caused. That is, the meso-damage of concrete is the internal cause and foundation of macroscopic damage, while the macroscopic damage of specimen is the result of the accumulation and development of meso-damage. The specific work of this paper is as follows: 1. The theory of damage and fracture of concrete material at meso level is studied. The failure mechanism of concrete material and the physical mechanism of fracture damage are studied. 2. Firstly, the center coordinates of aggregate particles which meet the random distribution in a given interval are generated by MATLAB programming language. Then the geometric model of concrete specimen with circular and elliptical aggregate particles is formed according to the criterion conditions of the center coordinates. 3. The basic principle of the finite element method is introduced. The mechanical analysis of isoparametric element and the application of isoparametric element in this paper. To find out the law of crack propagation in concrete. By analyzing the obtained curves, the relevant conclusions are drawn. 5. The thickness of the interface is studied to find out the influence of the thickness of the interface on the mechanical properties of concrete. It provides a basis for the selection of interface thickness in numerical simulation of concrete.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528

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