环境腐蚀及复杂应力场耦合下钢桥焊接节点疲劳损伤机理及演化规律

The lifecycle of welded joints of steel bridge can be divided into three stages: formation, growing and degradation. Considering the effects of corrosion environments on fatigue damage evolution in different stage, the mechanism of fatigue damage evolution on welded joints under multiple stress fields and environment corrosion is investigated based on the different stress fields in different stages. In the formation stage of welded joints, residual stress fields are simulated finely by 3D coupled thermal-mechanical nonlinear finite element analysis. In the growing stage of welded joints, multi-dimensional stress histories and the changes of stress concentration on welded details after corrosion are obtained by multi-scale finite element analysis and sub-structure modeling method. Using fatigue tests on many groups of specimens of welded joints, the relationship between environment corrosion factors and fatigue damage evolution rule is founded. According to hot-spot stress approach and damage mechanics theory combined with fatigue test result, fatigue damage evolution formulation on welded joints of steel bridge under multiple stress fields and environment corrosion is established. Assessment on durability of welded joints of steel bridge will be carried out based on reliability theory, when some internal and external random parameters involving corrosion and fatigue are taken into account. Research achievements will be used widely for practical structure in indirect or direct ways and benefit to scientific and technological progress and technological innovation in bridge engineering.

基于钢桥焊接节点生命历程中孕育期、成长期及退化期不同的应力场状态，考虑不同阶段环境腐蚀对疲劳损伤演变的影响，对环境腐蚀及复杂应力场耦合下钢桥焊接节点疲劳损伤演化机理进行研究。在焊接节点孕育期，考虑焊缝细节构造及焊接过程热-应力耦合,对焊接节点残余应力场进行3维非线性有限元精细数值模拟。在成长期,以多尺度数值仿真分析及子结构技术为研究手段，对钢桥焊接细节的多维应力历程进行多尺度分析,并研究腐蚀后焊接节点应力集中程度的变化；通过多组模型试验，建立环境腐蚀因素与焊接节点复杂应力场下疲劳损伤间的变化关系。基于热点应力分析和损伤力学理论，结合疲劳损伤试验实测结果，确立环境腐蚀及复杂应力场耦合下焊接节点疲劳损伤机理及演化方程。基于可靠度理论，考虑焊接节点内在及外在随机性因素，探讨腐蚀及疲劳共同作用下钢桥焊接节点耐久性评估方法。研究成果具有较广泛的直接或间接应用前景，有力促进桥梁科技进步及技术创新。

受应力集中及原生初始缺陷影响，焊接节点是钢桥疲劳设计的关键部位，环境腐蚀会加速疲劳损伤累积及裂纹扩展，钢桥疲劳设计时还缺乏对环境影响下焊接节点疲劳行为进行系统深入的研究。本项目基于焊接节点生命历程中孕育期、成长期及退化期不同的应力场状态，考虑不同阶段环境腐蚀对疲劳损伤演变的影响，对环境腐蚀及复杂应力场耦合下十字形焊接节点疲劳损伤演化机理进行研究。在孕育期考虑焊缝细节构造及焊接过程热-应力耦合,对焊接节点残余应力场进行3维非线性有限元精细数值模拟。在成长期以多尺度数值仿真分析为研究手段，构造不同倾角全熔透承载十字形焊接接头，模拟正应力和剪应力共同作用下的复杂应力场，分析得到热点正应力集中系数和热点剪应力集中系数随倾角的变化情况。对3种不同腐蚀损伤下的45°倾角全熔透承载十字形焊接节点进行疲劳试验，得到不同腐蚀状态下S-N曲线。研究腐蚀损伤对焊接接头热点应力集中系数和疲劳缺口系数的影响，提出了不同腐蚀深度和应力幅下的腐蚀疲劳寿命影响系数的表达式。基于断裂力学理论，分析不同蚀坑尺寸、裂纹形状比和裂纹深度对焊接节点应力强度因子的影响规律。根据不同腐蚀下十字形焊接节点的S-N曲线得到疲劳裂纹扩展速率公式参数，采用数值方法模拟十字形焊接接头的疲劳裂纹扩展，采用最大周向应力准则对裂纹扩展速率公式进行修正。基于损伤力学方法，定义裂纹尺寸为损伤变量，结合疲劳试验结果确定了不同腐蚀程度下十字形焊接接头Chaboche损伤演化方程的材料参数，得到了十字形焊接接头的损伤曲线和疲劳寿命预测方程。基于可靠度理论，考虑焊接节点内在及外在随机性因素，探讨了腐蚀及疲劳共同作用下钢桥焊接节点耐久性评估方法。研究成果具有较广泛的应用前景，为钢桥焊接节点的腐蚀疲劳损伤评估提供科技支撑，为在役钢桥的损伤诊断及延寿补强提供理论依据。对完善钢桥焊接节点疲劳分析理论及疲劳设计方法有直接的技术推动作用。