钢桥面板切割热影响区疲劳裂纹扩展规律与失效机理研究

To investigate the serious fatigue diseases around incisions in orthotropic steel bridge decks and the new damage introduced by structural reinforcement using thermal cutting on original structures, the crack growth behavior and failure mechanism of orthotropic steel decks in heat affected zone (HAZ) are taken as the research object in this project. The residual stress of thermal cutting, micro characteristics of fatigue fracture, spatial propagation of surface initial cracks and crack growth of heterogeneous materials are focused on. Scientific experiment and theoretical research are used to complete this study: (1)Temperature field and cooling process of HAZ are analyzed, and the distribution of thermal residual stress is explored, calculation methods for residual stress in HAZ are finally set up considering the influence of structure details and hole shapes in orthotropic steel decks. (2) Microscopic characteristics of fatigue fracture under true force field are firstly analyzed, spatial propagation laws of surface cracks are revealed under typical initial cracks and stress modes, an equivalent initial crack length model for two-dimensional fracture is then established. (3) Relationships of stress intensity factor and crack growth rate in the crack tip are explored, the influence of material properties degradation to crack growth rate is revealed, and finally the fatigue life prediction model considering residual stress and heterogeneous material properties degradation of HAZ is put forward. In all, theoretical foundations will be provided by this research for study of fatigue cracking mechanism of incision, fatigue life prediction, structural optimization and fatigue reinforcement of orthotropic steel bridge decks.

针对既有正交异性钢桥面板存在严重的切口疲劳病害，以及疲劳加固难免在原结构上进行热切割造成新的损伤等问题，本课题以揭示钢桥面板切割热影响区的疲劳裂纹扩展规律和失效机理为目标，关注钢桥面板的切割残余应力、疲劳断口微观特征、表面裂纹空间扩展特性和非均质材料裂纹扩展速率。联合试验和理论开展研究，内容包括：①掌握切割温度场分布规律及冷却时间历程，探究切割残余应力分布规律，建立钢桥面板考虑构造细节及孔型影响的切割残余应力计算方法；②解析真实受力环境下疲劳断口的微观特征，揭示典型初始裂纹形态及受力模式下表面裂纹空间扩展规律，建立适用于二维断裂问题的等效初始裂纹长度模型；③探究切割热影响区应力强度因子与裂纹扩展速率的内在关系，揭示材料性能劣化对裂纹扩展速率的影响，建立切割热影响区考虑残余应力和材性非均质劣化的疲劳寿命预测模型。研究成果可为钢桥面板切口疲劳开裂机理、寿命预测、细节优化和疲劳加固提供理论基础。

针对既有正交异性钢桥面板存在严重的切口疲劳病害，以及疲劳加固难免在原结构上进行热切割造成新的损伤等问题，本课题以揭示钢桥面板切割热影响区的疲劳裂纹扩展规律和失效机理为目标，关注钢桥面板的切割残余应力、疲劳断口微观特征、表面裂纹空间扩展特性。采用现场轮载试验、盲孔法和X射线衍射仪等残余应力测试设备、SEM设备、有限元分析等进行试验和理论分析。研究表明：初始缺陷、残余应力、不合理构造细节和超载，为钢桥面板弧形切口疲劳开裂的主因，选择合理的横隔板切割与焊接速度，有利于减小弧形切口处的残余应力和高应力区，优化疲劳性能。掌握了切割温度场分布规律及冷却时间历程，探究切割残余应力分布规律；研究了真实受力环境下疲劳断口的特征；建立了切割热影响区考虑残余应力和材性非均质劣化的疲劳寿命预测模型。提出了弧形切口疲劳裂纹采用切割修复方法，应力峰值降低比例超过50%；探索并尝试采用CFRP粘贴加固钢桥面板弧形切口疲劳裂纹，切口疲劳寿命提高接近8倍。本项目共申请发明专利4项，发表论文16篇，编写专著1部。研发了钢桥面板切割热影响区的疲劳防治技术，研究成果应用于两个工程项目，创造近500万元的疲劳修复经济效益。