【作者】 祝时召；

【导师】 李国清；

【作者基本信息】 华中科技大学 ， 工程力学， 2006， 硕士

【摘要】 “疲劳”是引起工程结构和构件失效的最主要原因。钢结构桥梁在使用过程中会产生疲劳裂纹,这是无法避免的。根据统计数据,桥梁焊接结构中90%的失效为疲劳失效。因此,研究焊接结构的疲劳裂纹扩展至关重要。本文的目的是研究天兴洲大桥用钢14MnNbq钢和焊接件的疲劳裂纹扩展规律。首先本文介绍了研究所采用的试验条件和试验方法:试验按相关国家标准进行,试样采用中心裂纹试样,焊接件的焊接工艺按天兴洲大桥的焊接工艺制作。然后,本文给出了由试验获得的三种不同应力比条件下14MnNbq钢和焊接件的疲劳裂纹扩展数据及Paris公式拟合结果。结果表明:在双对数坐标下,疲劳裂纹扩展速率与应力强度因子幅度之间呈现良好的线性关系;14MnNbq焊接件热影响区是疲劳裂纹扩展的薄弱区域,对比14MnNbq钢母材和焊肉,在疲劳裂纹开裂和稳定扩展的初期阶段,焊接热影响区的疲劳裂纹扩展速率较高。同时,本文还给出了试验测得的14MnNbq钢的断裂韧性结果。最后,本文介绍了对14MnNbq钢母材和焊接件的全范围疲劳裂纹扩展性能的研究,采用四参数Forman公式拟合全范围试验数据,给出了14MnNbq钢母材和焊接件的全范围疲劳裂纹扩展表达式。研究中发现:在不同应力比以及疲劳裂纹扩展的各个阶段,疲劳试验数据与理论公式预测之间都吻合得很好,可以用四参数的Forman公式有效地表征14MnNbq钢母材和焊接件的全范围疲劳裂纹扩展性能,所有的试验结论和理论预测符合疲劳裂纹扩展的一般规律。更多还原

【Abstract】 Fatigue is the main reason to failures of engineering structures and components. It is unavoidable that fatigue cracks initialize when steel bridges are constructed and fatigue cracks grow when the bridge is working. According to the statistic data, 90 percent of failures occurred in steel welded bridges result from fatigue. Therefore, it is very important for welded structures to study the mechanical properties concerned with fatigue crack growth in the steels and welds.The purpose of this thesis is to study the fatigue crack growth of 14MnNbq steel and welds, which are used in Tian Xing Zhou Bridge. Firstly, we introduced the experiments conditions and methods in our research: the experiments proceeded according to related national standards; specimen use center crack tension specimen, The welds welding procedure refer to Tian Xing Zhou bridge design technology.Afterwards, this thesis displayed 14MnNbq steel and welds fatigue crack growth data, which were obtained by experiments that under 3 different stress ratio conditions, the results of Paris formula fitting were also given. The results indicate that fatigue crack growth rate data and stress intensity factor range present high linear relationship under log-log plot. It is found that14MnNbq welds HAZ(heat affected zone) is the weak area. Comparing with base metal, welded seam and HAZ, the fatigue crack growth rate in HAZ is higher during crack initiation and stabilizes growth stage. Meanwhile, 14MnNbq fracture toughness result was also given by experiments.Finally, we introduced the research on full-range fatigue crack performance of 14MnNbq steel and welds. A four-parameter Forman formula fitted full-rang experiment data is used, and full-range fatigue crack growth expression of 14MnNbq steel and welds is presented. It is found that fatigue test data and theoretical predictions agree well with each other under different stress ratio and in three stages of fatigue crack growth. Therefore, the four-parameter Forman formula can be used to represent full-range fatigue crack performance of 14MnNbq steel and welds effectively. All the experiment results and theory forecast meet fatigue crack growth general rule.更多还原