【摘要】：水工建筑物多以混凝土為主要材料,并且多數(shù)均服役多年,診斷其健康狀態(tài)是一項重要的工作。其中,水工建筑物健康與否又可以混凝土結(jié)構(gòu)實際工作應(yīng)力予以反映。而在檢測應(yīng)力方法中,超聲波檢測是其中較為準確、便捷的方式之一。目前,針對混凝土應(yīng)力與聲學(xué)參數(shù)之間的研究多是借助試驗方法進行,但在試驗過程中,難免出現(xiàn)一些不可避免的因素對超聲波傳播產(chǎn)生一定影響,致使其中一些聲學(xué)參數(shù)規(guī)律與其原本具備的規(guī)律有所差異。鑒于此,本文開展受載條件下混凝土超聲波傳播特性的數(shù)值模擬研究,主要研究內(nèi)容及成果如下:(1)針對實驗室混凝土的制備要求,參照《水工混凝土試驗規(guī)程》中有關(guān)二級配混凝土的規(guī)定,基于隨機骨料模型理論,借助MATLAB生成實驗室混凝土二維細觀模型中骨料各頂點的坐標點,并寫入TXT文件,由它導(dǎo)入AUTO-CAD軟件,實現(xiàn)二維細觀模型的部件分類,由此可在ABAQUS軟件中建立sj(砂漿)、jm(界面)、gl(骨料)三大部件予以后續(xù)計算。(2)基于混凝土破壞損傷機理,且從其受力特性(主要為受壓)分析,采用基于規(guī)范推導(dǎo)的塑性損傷模型作為混凝土二維細觀模型中各組分的本構(gòu)關(guān)系,其中以隱式有限元法求解,實現(xiàn)混凝土細觀模型的單軸受壓損傷分析,而以顯式有限元法求解,實現(xiàn)超聲波在混凝土細觀模型中的傳播。(3)基于ABAQUS軟件,提出一種建立應(yīng)力場與聲場耦合的分析方法。其具體過程為:提取受力變形后的各單元坐標,重構(gòu)幾何模型;以塑性損傷模型中損傷因子與彈性模量之間的關(guān)系與過鎮(zhèn)海所給的泊松比的建議取值公式,重定義模型的基本屬性,通過上述方式保存混凝土細觀模型在應(yīng)力場中的某種狀態(tài),而后模擬超聲波在“已處理”的混凝土二維細觀模型中傳播。(4)以本文提出的耦合應(yīng)力場與聲場的方法實現(xiàn)受載條件下的混凝土超聲波傳播的模擬,在獲得相應(yīng)時域波形圖之后,以快速傅里葉變換與小波分析對其進行時頻分析,獲取一些基本聲學(xué)參數(shù):波速、首波振幅、最大振幅、主頻、主頻幅值、譜面積、加權(quán)譜面積,通過分析發(fā)現(xiàn)加權(quán)譜面積、首波振幅、波速對應(yīng)力變化相對敏感,然后使用ORIGIN軟件分別將它們與應(yīng)力進行擬合,獲得應(yīng)力與聲學(xué)敏感參數(shù)之間的關(guān)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.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TV33

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