地震作用下高强结构钢延性断裂机理与断裂评估方法研究

Ductile fracture performance of high strength structural steel is an important factor affecting the safety of its structure system in earthquake. Thus, development of a scientific method for assessing the ductile fracture of high strength structural steel is of great importance for engineering practice. This research project aims to investigate the ductile fracture mechanism of Chinese Q550 and Q690 high strength steels under seismic loading by using the cyclic loading test, micro-defects synchronized analysis and numerical simulation conducted on the notched specimens. Subsequently, the relationships between stress state, loading history and micro-fracture mechanism of materials are established using the representative volume element method. A novel micro-mechanism based ductile fracture model, considering the effects of the multiaixial stress states and complex loading history, is proposed for the high strength steel. A finite element analysis user subroutine is developed to capture material’s fracture initiation and crack propagation. Finally, the multi-scale fracture mechanism of the ductile crack evolved on the typical welded beam-to-column connection is revealed by conducting the ultra-low cycle fatigue test on the connection. Based on the research results, a multi-scale ductile fracture assessment method for high strength steel beam-to-column connection subjected to seismic loading is established. The research results of this project will provide new ideas for the fracture prediction and post-disaster damage assessment of high strength steel structure.

高强度结构钢材的延性断裂性能是影响地震灾害中高强钢结构体系安全性的重要因素，提出科学评价高强钢延性断裂性能的方法具有重要的工程意义。本项目以国产Q550与Q690高强度结构钢材为研究对象，拟采用切口试件循环加载试验、微观缺陷同步观测分析与精细化数值模拟方法，探究两类高强钢地震作用下的延性断裂机理；随后，基于代表性体积单元法，明确应力状态、加载历史与材料微观断裂机制间的量化关系，提出考虑多轴应力状态与加载历史效应的高强钢延性断裂模型，开发可正确模拟钢材延性裂纹扩展的有限元算法程序；最后，基于典型框架梁柱焊接节点的超低周疲劳加载试验，探究材料延性裂纹在梁柱节点中的跨尺度演化机理，并以材料微观断裂机理指标为判据建立高强钢焊接节点的多尺度延性断裂评估方法。本项目研究成果将为高强钢结构的断裂预测与灾后损伤评估提供新的方法与依据。

高强度结构钢材的延性断裂性能是影响地震灾害中高强钢结构体系安全性的重要因素，提出科学评价高强钢延性断裂性能的方法具有重要的工程意义。基于以上背景，本项目开展了如下研究内容：首先，对Q690高强钢多轴应力状态下的延性断裂机理开展了研究。基于多种切口试件加载试验与微观观测方法，揭示了Q690高强钢多轴应力状态下的断裂机理，获取了材料断裂机制与应力状态间的同步演化关系；其次，开展了高强钢弹塑性力学模型与数值模拟算法程序研究。基于塑性力学与计算力学方法，建立了一种考虑多轴应力状态效应的弹塑性本构模型，开发了该模型的数值算法程序，并利用Q690高强钢试件的试验数据校准了模型参数。所提出的本构模型能准确预测高强钢多轴复杂应力状态下的弹塑性力学响应；最后，对高强钢延性断裂模型进行了研究。基于Lee-Mear椭球形孔洞缺陷膨胀理论与Bai-Wierzbicki破坏准则，建立了高强钢材料硬化性能、微观缺陷与应力状态间的定量关系，提出了一种考虑应力三轴度与Lode角效应的延性断裂模型，并利用高强钢断裂试验数据对模型的正确性与精度进行了验证。所提出的延性断裂模型可准确预测高强钢多轴应力状态下的断裂萌生时刻与延性极限。本项目研究成果为地震作用下高强钢结构的断裂预测与灾后损伤评估提供了实用性的方法。