三轴压力作用下混凝土脆-韧转换条件与测试技术研究

发布时间：2018-06-24 15:17

本文选题：围压混凝土 + 韧性　；参考：《宁波大学》2013年硕士论文

【摘要】：混凝土在压缩载荷作用下，能够表现出两种截然不同的破坏形式，一是脆性破坏，二是韧性变形。在单轴压缩载荷下表现为脆性破坏，破坏机制为微裂纹的扩展，最终导致宏观裂纹。而在三轴压力作用下表现为韧性变形，机制为混凝土内孔隙压溃。本文主要研究了三轴压力作用下混凝土发生脆-韧转换所需的围压条件以及碳纤维导电混凝土损伤-电阻率关联关系。前者以围压混凝土为研究对象，首先通过理论研究了无限大基体中单个孔被压溃的条件，该条件即是混凝土由脆性材料转换为韧性材料的条件，从理论上推导了出现该种转换的条件：混凝土的（环向压力）/（轴向压力）的比值需满足cr（当混凝土材料的泊松比0.15~0.2时， cr0.22~0.25）。然后，设计实验通过实验进行实际验证混凝土出现脆-韧转换所需要的围压条件，实验研究表明：混凝土的（环向压力）/（轴向压力）的比值小于cr时也有可能出现脆-韧转换，因此理论上得出的混凝土发生脆-韧转换时的临界比值cr是混凝土发生脆-韧转换的一个充分条件。后者以碳纤维填充混凝土复合材料为研究对象，研究了不同碳纤维含量下混凝土的导电性能与损伤演化的关联关系。采用轴向静态压载和准静态循环压载，并且同时对试件进行超声波检测和电阻实时测量的方法，得到在荷载连续变化条件下试件的电阻和超声波波速变化规律。根据损伤定义和应力波理论，得到混凝土损伤演化与超声波波速变化之间的关系，最终得到混凝土损伤与其电阻率之间的关联关系。研究结果表明：混凝土的损伤与其电阻率之间具有较好的相关性。研究还发现，该复合材料在进行电阻测量时具有明显的电极化效应。实验表明：1）存在着临界的碳纤维体积分数fcr（fcr=0.7%），当碳纤维含量达到或超过fcr时，碳纤维的电阻率存在急剧下降现象。2）当碳纤维的体积分数小于等于1.3%时，，对此类混凝土进行电阻测量时存在极化效应。3）混凝土的电阻率不是关于损伤的一个单值函数，而是损伤的一个多值函数。本部分的研究得到了该种混凝土的损伤演化规律，可以用来预测此类混凝土的服役寿命。
[Abstract]:Under compression load, concrete can show two distinct failure forms, one is brittle failure, the other is ductile deformation. Under uniaxial compression load, brittle failure occurs, and the failure mechanism is microcrack propagation, which leads to macroscopic crack. Under the action of triaxial pressure, the ductile deformation is observed, and the mechanism is the collapse of pore in concrete. In this paper, the confining pressure conditions for brittle ductile transition of concrete under triaxial pressure and the relationship between damage and resistivity of carbon fiber conductive concrete are studied. The former takes confining pressure concrete as the research object. Firstly, the condition of crushing single hole in infinite matrix is studied theoretically, which is the condition for the conversion of concrete from brittle material to ductile material. The conditions for this conversion are derived theoretically: the ratio of concrete (circumferential pressure) to axial pressure (cr) (when the Poisson's ratio of concrete material is 0.15 ~ 0.2, cr0.22~0.25) is obtained. Then, the experiment is designed to verify the confining pressure condition of concrete for brittle-ductile transition. The experimental results show that the ratio of concrete (annular pressure) / (axial pressure) is less than cr, and the brittleness to ductility transition is also possible when the ratio of concrete to axial pressure is less than cr. Therefore, the critical ratio cr for brittle-ductile transition is a sufficient condition for brittle-ductile transition of concrete. The relationship between electrical conductivity and damage evolution of concrete with different carbon fiber content was studied. The axial static ballast and quasi-static cyclic ballast are adopted, and the ultrasonic wave velocity of the specimen are obtained under the condition of continuous load variation. According to the damage definition and stress wave theory, the relationship between the damage evolution and the ultrasonic wave velocity is obtained, and the relation between the concrete damage and its resistivity is obtained. The results show that there is a good correlation between the damage of concrete and its resistivity. It is also found that the composite has obvious polarization effect in resistance measurement. The experimental results show that there exists a critical carbon fiber volume fraction (fcr) (fcr0. 7%). When the carbon fiber content reaches or exceeds fcr, the resistivity of carbon fiber decreases sharply. 2) when the volume fraction of carbon fiber is less than or equal to 1. 3%, The resistivity of concrete is not a single function of damage, but a multivalued function of damage. In this part, the damage evolution law of this kind of concrete is obtained, which can be used to predict the service life of this kind of concrete.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528

【共引文献】