【摘要】：混凝土在使用過(guò)程中，由于長(zhǎng)期荷載、環(huán)境腐蝕、材料老化、構(gòu)件破損等因素作用，混凝土內(nèi)部逐漸產(chǎn)生損傷積累，使結(jié)構(gòu)的承載能力和耐久性能下降，減少了結(jié)構(gòu)的使用壽命。如何有效地預(yù)測(cè)在役混凝土的損傷演變情況是當(dāng)前混凝土工程亟待解決的關(guān)鍵性問(wèn)題之一。而現(xiàn)有混凝土損傷作用的研究多采用線性超聲波理論進(jìn)行試驗(yàn)和理論分析，具有很大的局限性，對(duì)混凝土損傷后表現(xiàn)的非線性特性研究較少。因此，本文在非線性波動(dòng)理論和統(tǒng)計(jì)損傷力學(xué)的基礎(chǔ)上，采用考慮不同影響因素作用下的單軸受載混凝土的超聲波測(cè)試試驗(yàn)，得到了與應(yīng)力相關(guān)性較好的超聲參數(shù)和敏感性影響因素，并從理論上對(duì)混凝土損傷與超聲參數(shù)的本構(gòu)關(guān)系進(jìn)行了分析。本文的研究工作及主要研究成果如下： （1）為了研究骨料比、發(fā)射主頻、干燥程度對(duì)混凝土超聲參數(shù)與應(yīng)力相關(guān)性的影響，，論文開(kāi)展了不同骨料比、發(fā)射頻率和干燥程度下的單軸受載混凝土的超聲波測(cè)試試驗(yàn)。并對(duì)試驗(yàn)方案的布置、儀器的使用和試驗(yàn)參數(shù)的確定做了詳細(xì)的介紹。 （2）采用快速傅立葉變換和頻譜分析的方法實(shí)現(xiàn)了對(duì)聲波信號(hào)的處理，提取了與應(yīng)力相關(guān)性較好的超聲參數(shù)，并對(duì)超聲參數(shù)隨應(yīng)力變化的規(guī)律進(jìn)行了分析，得到了能正確反映這一規(guī)律的聲學(xué)敏感性參數(shù)。 （3）考慮不同骨料比、發(fā)射頻率和干燥程度對(duì)混凝土超聲參數(shù)與應(yīng)力相關(guān)性的影響，分析了不同因素對(duì)混凝土聲學(xué)參數(shù)隨應(yīng)力變化的影響規(guī)律，得到了對(duì)聲學(xué)參數(shù)與應(yīng)力相關(guān)性較為敏感的各影響因素的大小。 （4）從細(xì)觀損傷力學(xué)的角度出發(fā)，分析了現(xiàn)有考慮單個(gè)微裂紋擴(kuò)展作用的混凝土損傷模型，確定了單個(gè)微裂紋在擴(kuò)展的不同階段對(duì)應(yīng)變的貢獻(xiàn)，并由此確定了微裂紋的擴(kuò)展作用機(jī)制。并在微裂紋擴(kuò)展機(jī)制和Weibull統(tǒng)計(jì)損傷理論的基礎(chǔ)上，確定了混凝土統(tǒng)計(jì)損傷本構(gòu)模型，建立了混凝土損傷與波速和非線性超聲參數(shù)的本構(gòu)關(guān)系，并分析了該本構(gòu)關(guān)系的合理性。
[Abstract]:During the use of concrete, due to the effects of long-term load, environmental corrosion, aging of materials, damage and accumulation of concrete, the bearing capacity and durability of the structure are decreased. The service life of the structure is reduced. How to effectively predict the damage evolution of in-service concrete is one of the key problems to be solved. However, most of the existing researches on concrete damage are based on linear ultrasonic theory, which has a great limitation, and there is little research on the nonlinear characteristics of concrete after damage. Therefore, on the basis of nonlinear wave theory and statistical damage mechanics, the ultrasonic testing test of uniaxial loaded concrete considering different influence factors is adopted in this paper. The influence factors of ultrasonic parameters and sensitivity are obtained, and the constitutive relationship between damage and ultrasonic parameters of concrete is analyzed theoretically. The main research results are as follows: (1) in order to study the effects of aggregate ratio, emission frequency and drying degree on the relationship between ultrasonic parameters and stress of concrete, different aggregate ratios are carried out in this paper. Ultrasonic testing test of uniaxial loaded concrete at emission frequency and dry degree. The layout of the test scheme, the use of the instrument and the determination of the test parameters are introduced in detail. (2) the fast Fourier transform (FFT) and spectrum analysis are used to process the acoustic signal. The ultrasonic parameters with good correlation with stress are extracted, and the variation of ultrasonic parameters with stress is analyzed, and the acoustic sensitivity parameters are obtained. (3) different aggregate ratios are considered. The effects of emission frequency and drying degree on the relationship between ultrasonic parameters and stress of concrete are analyzed. The influence of different factors on the variation of acoustic parameters with stress is analyzed. The influence factors which are sensitive to the correlation between acoustic parameters and stress are obtained. (4) from the point of view of mesoscopic damage mechanics, the existing concrete damage models considering the effect of single microcrack propagation are analyzed. The contribution of a single microcrack to strain in different stages of growth is determined, and the mechanism of microcrack propagation is determined. On the basis of microcrack propagation mechanism and Weibull's statistical damage theory, the constitutive model of concrete's statistical damage is established, and the constitutive relation of concrete's damage with wave velocity and nonlinear ultrasonic parameters is established, and the rationality of the constitutive relation is analyzed.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TU528

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