预应力碳纤维复合材料加固损伤钢构件抗疲劳机理及设计理论

Fatigue failure of damaged steel members are usually emanated from initial defects with following crack propagation. In this proposal, prestressed Carbon Fiber Reinforced Polymer (CFRP) materials will be adopted to strengthen steel members with mode I and mixed mode I/II cracks. Firstly, damaged steel plates will be patched with prestressed CFRP and subjected to tension fatigue loading. Meanwhile, damaged steel beams will also be repaired and subjected to four-point bending fatigue test. Several parameters, which are stress of prestressed CFRP, inclined angle, initial damage degree, CFRP stiffness, material type, temperature and humidity, are to be considered. Fatigue crack propagation and failure modes will be examined during fatigue tests. Thereafter, numerical analysis will be conducted with the exploitation of both finite element method and boundary element method. The efforts is aimed to study the evolution principles of fatigue behavior of CFRP strengthened steel members with initial damage considering complex stress fields, temperature and humidity. Theoretical models will be established with knowledge of fracture mechanics. And the correction factors will be introduced to consider the effects of repairing. Subsequently, the criterion of crack propagation direction and fatigue life model will be proposed. Finally, the mechanism of fatigue improvement will be revealed for damaged steel members strengthened with CFRP. The fatigue design method for damaged steel members repaired with prestressed CFRP will be suggested on the basis of test, numerical and theoretical achievements.

以含I型和I/II混合型疲劳裂纹的损伤钢构件为研究对象，对采用预应力碳纤维复合材料（CFRP）加固损伤构件的疲劳性能进行研究。首先进行预应力CFRP加固受拉损伤钢板试件以及受弯损伤钢梁疲劳试验，考察不同预应力大小、裂纹角度、损伤程度、CFRP材料刚度、材料类型以及温湿度等参数作用下疲劳裂纹的扩展规律和失效模式。随后采用有限元和边界元数值方法进行模拟分析，研究复杂应力状态和温湿度环境下的疲劳性能演化规律。根据断裂力学理论导出引入修正项的应力强度因子计算公式，建立疲劳裂纹萌生方向的相关准则和疲劳裂纹扩展路径的寿命预测模型。基于试验、数值和理论研究成果，揭示预应力CFRP提高损伤钢构件疲劳性能作用机理，提出预应力CFRP加固损伤钢构件抗疲劳设计方法。

由于实际工程中初始裂纹的随机性以及荷载的复杂性，裂纹会处于混合型裂纹状态。裂纹在循环荷载作用下会进一步扩展直至发生疲劳破坏。为保证钢结构安全，采用碳纤维增强复合材料（CFRP）对加固损伤构件的疲劳性能进行研究。首先进行预应力CFRP加固受拉损伤钢板试件以及受弯损伤钢梁疲劳试验，考察不同预应力大小、裂纹角度、损伤程度、CFRP材料刚度、材料类型等参数作用下疲劳裂纹的扩展规律和失效模式。为系统考察混合型疲劳裂纹的扩展，先后对含斜裂纹试件、紧凑型试件以及四点弯曲试件等进行疲劳试验，测试不同的KII/KI 值下的疲劳性能和CFRP 加固效果。..在试验的基础上，利用边界元方法或采用Python语言编写ABAQUS自动建模脚本，进行含裂钢板的疲劳裂纹扩展有限元模拟，计算裂纹尖端应力强度因子，估算含裂纹钢板的剩余疲劳寿命。数值模拟结果与试验结果对比表明，有限元模拟能够较为准确地模拟疲劳裂纹扩展路径以及计算含裂纹钢板的剩余疲劳寿命。在此基础上进行参数分析，研究复杂应力状态的疲劳性能演化规律。此外，还采用非接触全场变形测量数字图像相关（DIC）技术，测量钢板表面初始裂纹尖端的应力强度因子，初步探索了DIC技术对钢板在疲劳作用下裂纹扩展轨迹的监测效果。..根据断裂力学理论导出引入修正项的应力强度因子计算公式，建立疲劳裂纹萌生方向的相关准则和疲劳裂纹扩展路径的寿命预测模型。提出的SIF实用计算公式经过验证，可用于预测试件的疲劳寿命，供设计参考。本课题基于试验、数值和理论研究成果，揭示了预应力CFRP提高损伤钢构件疲劳性能作用机理。