钢结构疲劳裂纹应力强度因子计算及裂纹扩展路径分析-结构工程专业论文.docxVIP

ABSTRACT Based on linear elastic fracture mechanics and Haihe Bridge, this paper studies the propagation mechanism of the existed cracks under cycled vehicle loads. The formula presented by Paris has become the most popular one to determine the propagation rate of fatigue cracks. This formula introduce a parameter- stress intensity factor (SIF). There are many methods to determine the SIF of crack tip, such as analytical methods and finite element method based on simulation. In part one, three types of cracks have been studied. Using software ABAQUS, J-integral method, extrapolation method and node displacement method are applied to determine the SIF. After calculating, we compare the results of the three methods with results from analytical function to confirm the accuracy of each finite element method. Besides we compare the results from different element types and mesh sizes to testify the applicability of these methods under various circumstance. Through the analysis, the most accurate and effective method is selected to be applied in the research of L-crack in square steel tube. We obtain the SIF of web and flange when the tube bears the tensile pressure or moment. Then we combine the results of cracks with different length. We perform the regression analysis with the results and obtain a fitting equation which can be seen as the analytical formula of square steel tube with L-crack. Later, we add the tensile formula to moment formula and apply the combined one to rectangular steel tube under both tensile pressure and moment. The results of the combined formula fit perfectly to the calculation results. In the last part of this paper, we take advantage of extended finite element method (XFEM) to simulate the propagation path of crack. The analysis based on local model of Haihe Bridge which has microsmall crack. The simulated vehicle loads are applied to the U-rib to forecast the propagation tendency of the existed cracks. We also use the finite element method to