钢桥典型焊接接头残余应力松弛及其对复合型裂纹扩展速率的影响研究

Welding is the main method to connect the steel bridge, but the residual stress induced by welding in welded joint has a complex spatial distribution and with a large value. It will seriously affect the fatigue life and crack growth rate of bridge structure. If it is assumed that the welding residual stress is uniformly distributed along the plate thickness and the residual stress relaxation under the working stress is neglected, it will inevitably lead to a large design error for the steel bridge. Residual stress is one of the main factors affecting the fatigue cracking of welded steel bridges. A combination method of experiment and numerical simulation is proposed to study the remaining life of steel bridges under cracked working conditions. For the U rib-to-deck joint and T joint of steel bridges, the spatial distribution of residual stress will be studied; the relaxation law of the residual stress under the loading mode similar to the actual working state will be investigated under cyclic loading; the failure criterion and related fracture mechanics parameters for mixed-mode crack will be determined for Q345qD steel; further study of mixed-mode crack growth rate of welded joints will be conducted with considering the residual stress relaxation. For practical application, the prediction models which can reflect the residual stress spatial distribution characteristics and relaxation law will be summarized; the evaluation method of crack growth rate (life) will be established; then these research results can provide scientific basis for steel bridge design and remaining life assessment.

焊接是钢桥的主要连接方式，焊接接头中的残余应力不仅数值较大，且空间分布复杂，会对结构的疲劳寿命和裂纹扩展速率产生不利影响。若假定焊接残余应力沿板厚均匀分布，同时忽略残余应力在工作应力下的松弛效应，势必会带来较大的设计误差。残余应力是影响焊接钢桥疲劳开裂的主要因素之一，为研究钢桥在含裂纹状态下的剩余寿命，拟采用试验和数值模拟相结合的方法，以U肋加劲板和T型焊接接头为研究对象，来研究其残余应力空间分布特征；采用与实际工作状态相似的加载模式来研究空间分布的残余应力在循环荷载作用下的松弛规律；确定桥钢Q345qD复合型裂纹开裂的失效准则及相关断裂力学参数，进一步研究考虑残余应力松弛效应情况下焊接接头复合型裂纹的扩展速率。从应用层面，总结推导可反映钢桥典型焊接接头残余应力空间分布特征和松弛规律的预测模型；建立可有效评估复合型裂纹扩展速率（寿命）的方法体系；为钢桥设计和剩余寿命评估提供科学依据。

钢结构桥梁的应用和推广，促进了我国交通运输网络的不断完善。焊接作为钢桥的主要连接方式，会导致桥梁焊接接头在焊后残留数值较大的残余应力，这会对钢桥的服役耐久性产生非常不利的影响。目前，对于钢桥典型焊接接头残余应力空间分布及稳定性研究相对匮乏；焊接和循环加载模拟仿真过程中材料高温拉伸力学性能和常温循环力学性能的表征参数缺乏；残余应力对复合型裂纹扩展速率的影响机理研究尚不完善。针对以上不足，本项目开展了桥梁典型对接焊接头的高温拉伸力学性能测试试验，考虑了焊接接头的材料不均匀性（母材及焊缝金属），提出了对应位置金属的屈服强度、弹性模量、极限强度及应力-应变曲线的高温本构预测模型；开展了针对对接焊接头（母材及焊缝金属）常温循环荷载试验，标定了对应位置金属的Chaboche循环塑性本构模型参数，为后续的仿真模拟提供了真实的材料参数支撑。开展了针对U肋加劲钢桥面板和T型焊接接头残余应力的测试试验与仿真模拟，研究分析了残余应力表面分布规律及空间分布特征；模拟分析了U肋加劲钢桥面板在循环荷载作用下残余应力松弛效应，提出了综合考虑循环周次、应力幅值和应力比影响因素的残余应力松弛预测模型；模拟分析了T型焊接接头在循环荷载作用下残余应力松弛效应及演化规律，并基于循环加载试验验证了残余应力松弛模拟结果的合理性。推导了U肋加劲板焊趾处表面裂纹的权函数，考虑焊接残余应力的空间分布特征，分析了残余应力对U肋加劲钢桥面板表面裂纹应力强度因子的影响规律。以实际桥梁工程为背景，建立了钢箱梁节段多尺度三维有限元模型，考虑焊接残余应力和车辆荷载的耦合效应，基于试验标定的断裂力学材料参数C和m，研究了不同裂纹形态下U肋加劲钢桥面板的疲劳裂纹扩展寿命。相关研究成果可为钢结构桥梁的疲劳细节设计和服役耐久性评估提供理论基础及技术支撑。