受载条件下混凝土超声传播特性的数值模拟研究

发布时间：2018-09-05 13:36

【摘要】：水工建筑物多以混凝土为主要材料,并且多数均服役多年,诊断其健康状态是一项重要的工作。其中,水工建筑物健康与否又可以混凝土结构实际工作应力予以反映。而在检测应力方法中,超声波检测是其中较为准确、便捷的方式之一。目前,针对混凝土应力与声学参数之间的研究多是借助试验方法进行,但在试验过程中,难免出现一些不可避免的因素对超声波传播产生一定影响,致使其中一些声学参数规律与其原本具备的规律有所差异。鉴于此,本文开展受载条件下混凝土超声波传播特性的数值模拟研究,主要研究内容及成果如下:(1)针对实验室混凝土的制备要求,参照《水工混凝土试验规程》中有关二级配混凝土的规定,基于随机骨料模型理论,借助MATLAB生成实验室混凝土二维细观模型中骨料各顶点的坐标点,并写入TXT文件,由它导入AUTO-CAD软件,实现二维细观模型的部件分类,由此可在ABAQUS软件中建立sj(砂浆)、jm(界面)、gl(骨料)三大部件予以后续计算。(2)基于混凝土破坏损伤机理,且从其受力特性(主要为受压)分析,采用基于规范推导的塑性损伤模型作为混凝土二维细观模型中各组分的本构关系,其中以隐式有限元法求解,实现混凝土细观模型的单轴受压损伤分析,而以显式有限元法求解,实现超声波在混凝土细观模型中的传播。(3)基于ABAQUS软件,提出一种建立应力场与声场耦合的分析方法。其具体过程为:提取受力变形后的各单元坐标,重构几何模型;以塑性损伤模型中损伤因子与弹性模量之间的关系与过镇海所给的泊松比的建议取值公式,重定义模型的基本属性,通过上述方式保存混凝土细观模型在应力场中的某种状态,而后模拟超声波在“已处理”的混凝土二维细观模型中传播。(4)以本文提出的耦合应力场与声场的方法实现受载条件下的混凝土超声波传播的模拟,在获得相应时域波形图之后,以快速傅里叶变换与小波分析对其进行时频分析,获取一些基本声学参数:波速、首波振幅、最大振幅、主频、主频幅值、谱面积、加权谱面积,通过分析发现加权谱面积、首波振幅、波速对应力变化相对敏感,然后使用ORIGIN软件分别将它们与应力进行拟合,获得应力与声学敏感参数之间的关系式。
[Abstract]:Most hydraulic structures use concrete as the main material, and most of them are in service for many years. It is an important job to diagnose their health status. Whether the hydraulic structure is healthy or not can be reflected by the actual working stress of concrete structure. In stress detection, ultrasonic detection is one of the more accurate and convenient methods. At present, the research on the relationship between concrete stress and acoustic parameters is mostly carried out by means of test method, but in the process of test, some inevitable factors will inevitably affect the ultrasonic propagation. As a result, some of the rules of acoustic parameters are different from their original ones. In view of this, numerical simulation of ultrasonic propagation characteristics of concrete under loading conditions is carried out in this paper. The main research contents and results are as follows: (1) according to the requirements of the preparation of laboratory concrete, According to the regulations of hydraulic concrete Test Code, based on the theory of random aggregate model, the coordinate points of each vertex of aggregate in the two-dimensional mesoscopic model of laboratory concrete are generated by MATLAB and written into the TXT file. It is introduced into AUTO-CAD software to realize the component classification of two-dimensional mesoscopic model. Three parts of sj (mortar) / jm (interface) / gl (aggregate) can be established in ABAQUS software for subsequent calculation. (2) based on the damage mechanism of concrete, three parts of sj (mortar) / jm (interface) / gl (aggregate) can be established in ABAQUS software. Based on the analysis of its mechanical properties (mainly under pressure), the plastic damage model derived from the code is used as the constitutive relation of each component in the two-dimensional meso-model of concrete, in which the implicit finite element method is used to solve the problem. In this paper, uniaxial compression damage analysis of concrete mesoscopic model is realized, and the propagation of ultrasonic wave in concrete mesoscopic model is realized by explicit finite element method. (3) based on ABAQUS software, an analytical method to establish coupling of stress field and sound field is proposed. The concrete process is as follows: extracting the coordinates of each element after deformation, reconstructing the geometric model, taking the relationship between the damage factor and the elastic modulus in the plastic damage model and the recommended Poisson's value formula for the Poisson's ratio given by the cross Zhenhai as the formula, the relationship between the damage factor and the elastic modulus in the plastic damage model is used. The basic properties of the model are redefined to preserve some state of the concrete mesoscopic model in the stress field. Then the ultrasonic wave propagation is simulated in the "treated" two-dimensional mesoscopic concrete model. (4) the method of coupling stress field and sound field proposed in this paper is used to simulate the ultrasonic propagation of concrete under loading conditions. Based on the time-frequency analysis of fast Fourier transform and wavelet analysis, some basic acoustic parameters are obtained: wave velocity, first wave amplitude, maximum amplitude, main frequency amplitude, spectral area, weighted spectral area. The amplitude and velocity of the first wave are relatively sensitive to the stress changes, and then the relationship between the stress and the acoustic sensitive parameters is obtained by fitting them with the stress by using ORIGIN software.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV33

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