基于微观机制的H型钢梁柱刚接节点延性断裂机理与设计对策研究

Micromechanics-based fracture models of structural steels can capture the combined effects of the stress triaxiality and plastic strain on crack initiation. They can accurately predict ductile fracture initiation with large scale yielding region and no initial flaw thus can be used to predict earthquake-induced fractures. Firstly, the parameters in the micromechanical models for Q235, Q345 and Q460 steel are calibrated through tests and finite element analyses, and the main factors affecting the parameter values are obtained. Then, the micromechanical fracture criteria for each steel can be established. Secondly, quasi-static cyclic loading tests of four H steel beam-column rigid connection models are conducted to get the whole process of crack initiation, crack development until complete failure of the connections under extremely low cycle fatigue loading. Thirdly, the element that is suitable for the post-fracture path analyses of the H steel beam-column rigid connections under extremely low cycle fatigue loading and the corresponding ABAQUS subroutine are edited. The reliability is verified through the comparison with test results. The influential effect of connection fracture on the bearing capacity and hysteretic behavior is obtained. Finally, through finite element parametric analyses, the main factors affecting the ductile fracture of the H steel beam-column rigid connections are studied and the measures to control ductile fracture of the connections are proposed, which contributes to prevent accidents of steel structures under earthquakes and has theoretical and social significance.

钢材的微观机制模型能抓住应力三轴度和塑性应变对裂纹开展的影响，能准确预测大范围屈服和无初始裂纹情况下的延性裂纹开展，可用于预测地震作用引起的断裂。本项目首先通过试验和有限元分析，校准Q235钢、Q345钢和Q460钢的微观机制断裂预测模型参数，得到影响参数的主要因素，建立各种钢材的微观机制断裂判据；然后进行4个H型钢梁柱刚接节点模型的拟静力往复加载试验，得到节点在超低周往复荷载作用下由节点开裂、裂缝发展直至完全丧失承载力的破坏全过程；随后编写适用于超低周往复荷载作用下的H型钢梁柱刚接节点裂后路径分析的单元及相应的ABAQUS子程序，通过与试验结果的比较验证其可靠性，揭示节点断裂对承载力和滞回性能的影响效应；最后通过有限元参数分析，研究影响H型钢梁柱刚接节点延性断裂的主要因素，提出控制节点延性断裂的设计对策，这必将有助于防范地震作用下的钢结构事故，具有重要的理论意义和社会意义。

近年来发生的钢结构的断裂事故表明，对于地震作用下钢框架梁柱节点断裂行为机理的研究，具有很大的社会意义。钢结构在地震作用下的断裂属于超低周疲劳，其破坏性质属于典型的延性断裂。基于微观机制的断裂模型可用来预测钢结构节点的延性断裂。本项目进行了Q235钢、Q345钢及ER-50型焊材制成的光滑圆棒单向拉伸试验，圆周平滑槽口试件的单向拉伸试验和超低周疲劳试验及对应的有限元分析，并进行了圆周平滑槽口试件单向拉伸试验拉断的试件的断口扫描电镜试验，校准了Q235钢、Q345钢及ER-50型焊材在单调荷载作用下和超低周往复荷载作用下的微观机制模型参数。将本项目校准的Q345钢的断裂韧性参数、损伤退化参数和特征长度参数，与已校准的另一批Q345钢的对应参数进行了对比，结果表明不同批次的Q345钢断裂韧性参数离散性较小，而损伤退化参数离散性较大，特征长度参数离散性较小。进行了Q460钢和ER55-G型焊材制成的光滑圆棒试件单向拉伸试验和圆周平滑槽口试件的单向拉伸试验及对应的有限元分析，并进行了圆周平滑槽口试件单向拉伸试验拉断试件的断口扫描电镜试验，校准了Q460钢和ER55-G型焊材的微观机制模型参数。分别对剪切型及拉剪型平板切口试件、平板槽口试件进行了断裂试验。随后，利用扫描式电子显微镜对各试件断口处的微观断裂机制进行了观察分析,考察了应力状态对结构钢材断裂性能的影响，并利用试验结果对Rice-Tracey延性断裂准则进行了校准。试验研究结果表明应力状态对 Q460钢的延性与微观断裂机制有显著的影响。Rice-Tracey延性断裂准则可以准确地捕捉材料在不同Lode角下的延性下降趋势。本项目的研究成果为地震作用下钢框架梁柱节点断裂行为机理的研究提供了基础。