受弯CFL加固钢板中表面裂纹扩展行为研究

发布时间：2018-08-20 15:04

【摘要】：钢结构在工程界的广泛应用使得钢结构的修复加固成为一项经常性的工作，由于FRP加固技术的高强高效、良好的耐疲劳性能以及适应性强等特点使得FRP加固钢结构技术应用越来越普遍。另一方面，由于表面裂纹是钢结构中重要缺陷之一，而且表面裂纹的扩展对钢结构的运营存在安全隐患，因此，对FRP加固钢结构中表面裂纹的疲劳扩展行为进行研究具有重大的科学意义和工程应用价值。 本文以采用本课题组发明的碳纤维薄板（Carbon Fiber Laminate，简称CFL）加固含表面裂纹的钢板为研究对象，探讨了CFL加固钢板中表面裂纹的应力强度因子计算方法及其疲劳扩展规律。本文的主要研究内容及结论如下： 1）对疲劳裂纹扩展理论及应力强度因子的有限元算法进行分析，提出了将J积分与特殊单元相结合的有限元计算方法，以解决裂纹尖端的奇异性问题。 2）利用有限元软件ABAQUS，建立了三点弯曲载荷下含表面裂纹钢板的三维计算模型。通过将表面裂纹应力强度因子的有限元计算结果与Newman-Raju公式计算值的比较，探讨了裂纹前缘第一层单元的边长L与裂纹深度a之比L/a、围绕裂纹前缘的单元层数D、每层单元划分份数E以及沿裂纹前缘方向划分份数S等对有限元计算结果的影响，给出了最优有限元参数值，从而确立了表面裂纹前缘应力强度因子的计算方法。 3）探讨了裂纹形状比a/c、相对长度c/W和CFL厚度tC对加固效果（应力强度因子KI下降率，ROD）的影响。研究结果表明，θ=0°处ROD随a/c或c/W增长而增加；θ=90°处ROD随着a/c增长先迅速减小后趋于稳定，但随着c/W增长先减小后迅速增长；CFL加固效果随着CFL厚度增加而增加，但是这种增长趋势在tC≤0.4mm前较明显，超过该厚度后ROD增长逐渐趋于平缓。 4）成功地将“Beach-mark”法应用于三维表面疲劳裂纹的扩展实验，并对具有不同裂纹参数a/c、a/t的受三点弯曲荷载作用下含三维表面裂纹的钢板试件实施了疲劳裂纹扩展实验研究，得到了CFL加固和未加固试件在弯曲疲劳荷载作用下的a~N和c~N实验曲线。 5）对受弯钢板中三维表面裂纹的疲劳扩展规律进行了探讨。研究结果表明：①CFL加固受弯试件中表面裂纹在长度和深度方向的扩展规律都能用Paris模型进行描述；未加固试件裂纹长度方向的扩展规律也可用该模型很好地描述，但裂纹深度方向的扩展却不满足Paris模型；②通过数据拟合得到了未加固试件裂纹长度方向、加固试件裂纹长度和深度方向的三维表面裂纹疲劳扩展速率的半经验公式；③CFL加固能抑制表面裂纹的扩展，降低其疲劳扩展速率。
[Abstract]:The widespread application of steel structure in engineering field makes the repair and strengthening of steel structure become a regular work, because of the high strength and high efficiency of FRP reinforcement technology, Due to its good fatigue resistance and strong adaptability, steel structure strengthened by FRP is more and more widely used. On the other hand, because the surface crack is one of the important defects in steel structure, and the propagation of surface crack has hidden danger to the operation of steel structure, therefore, It is of great scientific significance and engineering application value to study the fatigue propagation behavior of surface cracks in steel structures strengthened by FRP. In this paper, the method of calculating the stress intensity factor of the surface crack in the steel plate strengthened by CFL and its fatigue propagation rule are discussed. The carbon fiber sheet (Carbon Fiber Laminate, (abbreviated as CFL) is used to strengthen the steel plate with surface cracks as the research object. The main contents and conclusions of this paper are as follows: 1) the theory of fatigue crack growth and the finite element method of stress intensity factor are analyzed, and a finite element method combining J integral with special element is proposed. In order to solve the singularity problem of crack tip. 2) using finite element software Abaqus, a three-dimensional model of steel plate with surface crack under three-point bending load is established. By comparing the finite element results of the stress intensity factor of surface cracks with the calculated values of Newman-Raju formula, The influence of the ratio of the edge length L of the first layer element of the crack front to the crack depth a, the number of the element layers around the front edge of the crack, the partition number E of each layer and the fraction S along the front edge of the crack on the finite element calculation results are discussed. The optimal finite element parameter value is given. The calculation method of the stress intensity factor at the front edge of the surface crack is established. 3) the effects of the crack shape ratio a / c, the relative length C / W and the thickness of CFL t C on the reinforcement effect (the stress intensity factor Ki drop rate and the ROD) are discussed. The results show that the ROD increases with the increase of a / c or c / W at 0 掳, and the ROD decreases rapidly and then stabilizes with the increase of a / c at 胃 / 90 掳, but decreases first and then increases rapidly with the increase of c / W, and the reinforcement effect increases with the increase of CFL thickness. However, the growth trend is obvious before TC 鈮，

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