基于非线性超声特性的混凝土损伤试验研究

发布时间：2018-08-23 20:35

【摘要】：混凝土在使用过程中，由于长期荷载、环境腐蚀、材料老化、构件破损等因素作用，混凝土内部逐渐产生损伤积累，使结构的承载能力和耐久性能下降，减少了结构的使用寿命。如何有效地预测在役混凝土的损伤演变情况是当前混凝土工程亟待解决的关键性问题之一。而现有混凝土损伤作用的研究多采用线性超声波理论进行试验和理论分析，具有很大的局限性，对混凝土损伤后表现的非线性特性研究较少。因此，本文在非线性波动理论和统计损伤力学的基础上，采用考虑不同影响因素作用下的单轴受载混凝土的超声波测试试验，得到了与应力相关性较好的超声参数和敏感性影响因素，并从理论上对混凝土损伤与超声参数的本构关系进行了分析。本文的研究工作及主要研究成果如下：（1）为了研究骨料比、发射主频、干燥程度对混凝土超声参数与应力相关性的影响，，论文开展了不同骨料比、发射频率和干燥程度下的单轴受载混凝土的超声波测试试验。并对试验方案的布置、仪器的使用和试验参数的确定做了详细的介绍。（2）采用快速傅立叶变换和频谱分析的方法实现了对声波信号的处理，提取了与应力相关性较好的超声参数，并对超声参数随应力变化的规律进行了分析，得到了能正确反映这一规律的声学敏感性参数。（3）考虑不同骨料比、发射频率和干燥程度对混凝土超声参数与应力相关性的影响，分析了不同因素对混凝土声学参数随应力变化的影响规律，得到了对声学参数与应力相关性较为敏感的各影响因素的大小。（4）从细观损伤力学的角度出发，分析了现有考虑单个微裂纹扩展作用的混凝土损伤模型，确定了单个微裂纹在扩展的不同阶段对应变的贡献，并由此确定了微裂纹的扩展作用机制。并在微裂纹扩展机制和Weibull统计损伤理论的基础上，确定了混凝土统计损伤本构模型，建立了混凝土损伤与波速和非线性超声参数的本构关系，并分析了该本构关系的合理性。
[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.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

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