基于格构模型的混凝土开裂过程多尺度数值研究

发布时间：2018-03-29 05:22

本文选题：混凝土　切入点：开裂过程　出处：《哈尔滨工业大学》2014年硕士论文

【摘要】：混凝土是一种多相复合的非匀质材料，其开裂过程与内部结构密不可分。许多年来，国内外大量的研究者致力于水泥基材料开裂过程的研究，提出过大量的裂缝模型，但基本停留于宏观层次研究，没有深入到材料微观结构，也很难给出裂缝动态开裂过程。针对上述问题，本文将多尺度方法与格构断裂模型相结合，首先开发了一种实时跟踪裂缝宽度动态变化过程的Python程序算法完成了微观尺度下水泥浆体格构断裂分析，然后针对细观尺度随机骨料投放，，提出了采用HYMOSTRUC3D模型快速生成三维随机球形骨料模型研究了细观尺度砂浆与混凝土的开裂过程。本文主要研究内容如下：采用随机度的概念定量描述了水泥基材料不规则、非匀质性质，并分析了随机度对格构断裂模拟的影响。结果表明：随机度能够反映了材料内部物相不均匀程度。随着随机度增大，格构模型整体弹性模量，抗拉强度以及峰值应变均减小。基于格构断裂模型的计算理论，推导了格构模型裂缝宽度理论计算公式，编写了MATLAB以及Python程序，将其植入商用有限元计算软件ABAQUS中，能够跟踪格构模型不同应力水平下裂缝宽度数值变化。该程序算法的基本思想为：每次格构断裂计算中，不从格构系统中直接剔除σ/ft比值最大单元，而是设置为裂缝单元，裂缝单元是指单元的弹性模量数值设置为相对于其他格构单元可以忽略不计，即二者弹性模量的比值趋于0。通过计算裂缝单元节点位移增量得到变形量的精确值，如果每次重新计算数据库中所有裂缝单元的变形量，那么，就实现了对不同应力水平下裂缝宽度变化跟踪计算。本文数值结果表明，本算法能够有效追踪裂缝宽度动态变化过程。在随机骨料模型方面，本文利用MATLAB编程进行数字图像处理，借鉴F. Bernard采用NIST's CEMHYD3D程序代码生成了砂浆结构模型的方法，提出采用HYMOSTRUC模型快速生成三维随机球形骨料模型。这解决了当前混凝土数值模拟中随机骨料投放效率低下的问题。基于递阶的多尺度建模方法，采用HYMOSTRUC3D模型生成了水泥浆体微观结构晶格图像，并离散化为二维晶格图像建立格构网络模型。对微观尺度下水泥浆体进行格构系统线弹性有限元计算。将微观尺度下得到的水泥浆体本构关系作为细观尺度下砂浆格构分析的输入参数，对细观尺度砂浆进行非线性有限元计算，这种非线性是通过多步迭代降低单元的弹性模量与抗拉强度的方法实现的。按照这样的多尺度格构断裂分析方法得到了混凝土的应力应变曲线、裂缝位置分布图、不同应力水平下的裂缝宽度分布等。特别地，从裂缝位置分布图来看，裂缝最先在初始孔隙周围产生，然后逐渐向内部扩展形成主裂缝，裂缝宽度分布总是表现出两个正态分布的叠加，第一个正态分布均值代表微裂缝宽度，且微裂缝数目大多占50%左右；第二个正态分布均值代表大裂缝宽度，且裂缝数目与应力水平相关。裂缝分布图表明：砂浆与混凝土中裂缝首先在界面过渡区产生然后逐渐向水泥浆或砂浆基体中发展。
[Abstract]:Concrete is a multiphase inhomogeneous material, the cracking process and internal structure are inseparable. For many years, a lot of researchers at home and abroad dedicated to the process of cracking of cement based materials, put forward a lot of crack model, but the basic stay at the macro level, not deep into the microstructure of the material, but also it is difficult to give a dynamic crack cracking process. Aiming at the above problems, the multiscale method of lattice fracture model combining Python program algorithm firstly developed a real-time tracking of the dynamic process of the crack width of the micro scale cement physical structure fracture analysis, then the meso scale random aggregate supply, put forward the rapid generation of HYMOSTRUC3D models of three-dimensional random aggregate model of spherical cracking process of meso scale mortar and concrete. The main research contents of this paper are as follows:
By using the concept of quantitative description of the randomness of cement-based materials is irregular, heterogeneous nature, and analyzes the randomness of lattice fracture simulation. The results show that the random degree can reflect the material internal phase inhomogeneity. With random degree increases, the lattice model overall elastic modulus, tensile strength and the peak strain decrease.
Theoretical calculation of lattice fracture model based on lattice model, deduced the theoretical calculation formula of crack width, write MATLAB and Python procedures, into the commercial finite element software ABAQUS, can track the change of lattice model of crack width values under different stress levels. The basic idea of the program is: each lattice algorithm fault calculation, do not constitute the system directly removed o /ft the ratio of the maximum unit from the grid, but is set to crack element, crack element is to set the elastic modulus value unit as compared to other lattice elements can be ignored, i.e. the ratio of the two elastic modulus tends to 0. through the exact value calculation of crack element node displacement increment deformation if the amount of deformation, each re calculate all crack element in the database so as to achieve the different change of crack width under the stress of the tracking calculation. The numerical results show that the algorithm can effectively track the dynamic change process of crack width.
In the random aggregate model, this paper uses the MATLAB programming of the digital image processing, using F. Bernard using NIST's CEMHYD3D code generation method of mortar structure model, the rapid generation of three-dimensional random aggregate model of spherical HYMOSTRUC model. It solves the problem that when the numerical concrete random aggregate on the problem of low efficiency.
Multiscale modeling method based on hierarchical, using HYMOSTRUC3D model to produce cement paste microstructure and lattice image, discrete two-dimensional lattice image establish lattice network model. On the micro scale cement paste for lattice system of linear elastic finite element calculation. The cement paste microstructure scale under the constitutive relation as the input parameters of the meso scale lattice analysis of mortar, mortar of meso scale nonlinear finite element calculation, the nonlinear is implementation method to reduce the elastic modulus and tensile strength of the unit through the iteration. According to multiple scales the fracture analysis of the concrete stress-strain curve, crack distribution map, under different stress level of the crack width distribution. Especially, judging from the position of the crack distribution, the crack was first produced in the initial void around, and then gradually inward Part of the formation of the main crack propagation, crack width distribution always showed two normal distribution overlay, micro crack width first normal distribution mean, and the number of micro cracks are mostly accounted for about 50%; second normal distribution mean crack width, and the number of cracks and the stress level. The crack distribution map shows that: cement mortar and concrete cracks in the first generation of interface transition zone and then gradually to the development of cement paste or mortar matrix.

【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】：2014
【分类号】：TU528

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