变幅重复荷载作用下粘贴CFRP补强含损伤钢梁疲劳性能

This study will be focused on the fatigue behaviour of damaged steel beams strengthened by carbon fibre reinforced polymer (CFRP) materials subjected to variable amplitude repeated loading. Typical variable amplitude repeated loading is to be selected. Fatigue performance of CFRP-steel double-lap joints will be first investigated to explore the interfacial behaviour, based on which a bond-slip model under variable amplitude repeated loading will be proposed. Afterwards, fatigue experiments will be performed to quantify the effect of variable amplitude repeated loading on the interfacial debonding and crack propagation of damaged steel beams flexurally retrofitted by CFRP. Three-dimensional finite element/boundary element models will be developed incorporating the proposed bond-slip model. After the numerical simulation is validated by the experimental results, a parametric study will be conducted to supplement the test data. The results will be used to put forward a simplified approach for assessment of the relationship between crack propagation versus debonding extension. The far-field load shared by the CFRP and the crack mouth opening restraint effect offered by the CFRP will be evaluated. Subsequently, an approach based on fracture mechanics for estimating the stress intensity factor at the crack tip of the strengthened steel beams subjected to variable amplitude repeated loading will be derived. The approach will be verified by the experimental and numerical results of the crack propagation and fatigue life. It will then be adopted in a reliability analysis of the strengthening system. Eventually, the fatigue behaviour assessment and strengthening design method of damaged steel beams repaired by CFRP subjected to variable amplitude repeated loading will be obtained.

以变幅重复荷载作用下粘贴碳纤维增强复合材料（CFRP）补强含损伤钢梁的疲劳性能为研究对象，进行试验研究、数值模拟和理论分析。选取典型变幅重复荷载，通过CFRP-钢双面搭接节点试验研究，探索CFRP-钢界面粘结性能演化机理，提出变幅重复荷载作用下CFRP-钢界面粘结滑移模型。开展变幅重复荷载作用下粘贴CFRP补强含损伤钢梁试验研究，揭示变幅重复荷载对粘结失效和裂纹扩展的影响作用。继而建立精细化三维钢梁数值模型，引入粘结滑移关系，预测相应裂纹扩展和疲劳寿命，和试验数据对比验证。展开参数分析，提出裂纹扩展和界面粘结失效相关关系简化分析方法，进而计算补强体系中CFRP承担的外荷载和提供的裂纹张开约束作用，提出裂纹尖端应力强度因子计算方法，通过试验数据和数值结果验证。同时考虑输入变量的不确定性，展开补强体系可靠度分析。最终提出变幅重复荷载作用下粘贴CFRP补强含损伤钢梁疲劳性能分析及加固设计方法。

粘贴碳纤维增强复合材料(CFRP)补强含损伤钢结构，能够有效降低损伤钢结构的局部应力，抑制疲劳裂纹扩展，延长疲劳寿命。目前对变幅重复荷载作用下的CFRP补强钢结构体系性能认识不足。本项目以变幅重复荷载作用下CFRP粘贴补强钢构件为研究对象，分别从材料层次的CFRP-钢界面粘结性能和构件层次的CFRP粘贴加固钢梁疲劳性能展开。推导了CFRP-钢界面粘结-滑移性能一般表达式，采用CFRP-钢界面粘结性能数据库标定，统一了界面粘结-滑移本构，适用于不同的破坏模式和加固材料，探明了结构粘胶抗拉强度、剪切模量和厚度对界面粘结-滑移性能的影响机制。CFRP-钢粘结界面常幅疲劳试验表明，CFRP-钢界面的疲劳寿命与荷载比成负相关，构建了其S-N曲线。提出了界面粘结疲劳失效破坏准则，当荷载比低于0.6时，界面粘结-滑移曲线的包络曲线为三角形；当荷载比大于0.6时，其包络曲线为梯形。提出适用于Araldite 2015试件损伤参数随归一化循环次数变化的表达式。分析了不同疲劳荷载加载历史对CFRP-钢界面残余粘结性能的影响。考虑了疲劳循环加载造成的残余滑移，将粘结界面分为粘结失效区、损伤区、未粘结失效区，建立了疲劳荷载作用后界面残余粘结-滑移关系模型。揭示了变幅疲劳荷载对CFRP-钢界面粘结性能的作用机理，厘清了荷载变化对界面粘结性能损伤速率的影响规律，建立了变幅疲劳荷载作用下损伤速率计算表达式。开展了变幅疲劳荷载作用下CFRP加固含损伤钢梁疲劳性能研究，认识了过载迟滞作用对裂纹扩展的影响规律，揭示了高低重复荷载和低高重复荷载作用下CFRP加固钢梁疲劳失效机理。发明了Fe-SMA无损机械连接装置，3分钟即可施加400MPa以上的预应力。提出了Fe-SMA恢复应力最优激发策略，探明了Fe-SMA在复杂服役条件下的恢复应力演化特征。揭示了疲劳和温度荷载共同作用对加固效率的影响机制，明确了加固体系在服役环境条件下的有效性。建立了考虑Fe-SMA恢复应力演化的Fe-SMA加固损伤钢结构疲劳性能三维精细化数值模型和简化分析方法。研究成果有助于完善CFRP材料补强钢构件理论体系，进一步推广CFRP材料在钢结构疲劳性能提升领域的应用。