结构钢材及其焊缝与构造低温疲劳性能的力学机理及设计方法研究

Recently, fatigue damage and brittle fracture accidents occurs frequently in steel structures, especially at low temperature. The most majority of land area in China are cold in winter, and steel structures in cold regions are more prone to fatigue damage. However, the researches about the effect of low temperature on fatigue property of steel strcuture are insufficient. In this project, a series of tests, combined with theoretical analysis and numerical simulations will be carried out to investigate the fatigue properties of commonly used structural steels and their welds at low temperature. The fatigue strength and the fatigue crack propagation rate model of the structural steels and their welds at low temperature will be obtained, the material parameter prediction formulas used in the model will be proposed as well. Furthermore, the fatigue life model considering the low temperature effect will be established, which include notch strain model and fracture mechanics model. The typical welded joints test will be conducted to confirm the effective of the model and the parametric analysis will be carried out by the model. Based on the results of the study, fatigue design curves and simplified calculation formulas at low temperature will be obtained; the cryogenic fatigue resistant design theory will be basically formed and the fatigue life assessment method will be put forward. The research for this project has significant effects on the improvement of design codes for steel structure and the guarantee for the structural safety and reliability, the economic significance is remarkable as well.

近年来钢结构发生疲劳破坏和低温下脆性断裂的重大事故屡见不鲜，我国存在大范围的寒冷地区，低温将增加结构发生疲劳破坏的概率，而目前国内外有关钢结构低温疲劳性能方面的研究尚相对薄弱。针对钢结构实际工程中所面临的低温疲劳破坏问题，以及目前相关研究的不足，本申请项目采用理论分析、试验研究和数值模拟相结合的方法，从结构钢材、焊缝和构造、疲劳细节和节点等三个层面开展逐步深入的研究。积累结构钢材及其焊缝在低温下的疲劳强度等材性数据，得到低温疲劳裂纹扩展速率模型；提出低温下疲劳裂纹扩展的材料参数预测公式；建立考虑低温效应的疲劳全寿命模型，包括缺口应变模型和断裂力学模型；进行典型焊接接头的验证性试验，进而进行参数化分析，得到适用性较强的低温疲劳设计曲线和简化计算公式，提出较为完整的低温抗疲劳设计理论和疲劳寿命评估方法。本项目的研究对于完善钢结构设计规范，提高钢结构的安全性、经济性具有重要意义。

在往复交通荷载作用下，钢结构桥梁的关键细节极易发生疲劳破坏，而在冬季严寒地区服役的钢结构桥梁还面临着低温冷脆破坏的威胁。因此，为了进一步明确钢桥在低温环境下的疲劳性能，本课题采用试验研究和数值模拟相结合的方法，从结构钢材、焊缝及其焊接细节的层面，在室温和低温环境下，系统进行了结构钢材采用应力和应变控制的疲劳性能试验研究；结构钢材的疲劳裂纹扩展速率和门槛值应力强度因子测试；钢桥典型焊接细节的正应力疲劳性能试验研究；横向角焊缝和侧向角焊缝连接细节的剪应力疲劳性能试验研究；采用经过试验验证的三维疲劳裂纹扩展方法，进一步研究了焊接工字型受弯梁细节在低温环境下的疲劳性能。从而揭示了低温对钢桥结构钢材、焊缝及其焊接细节、构件的影响规律，结果表明低温环境不会恶化结构钢材及其焊接细节的疲劳性能。.本项目积累了丰富的低温疲劳数据，为低温寒冷地区钢结构桥梁的疲劳设计和寿命评估提供了有力的数据支撑和技术保障，对促进钢结构桥梁在低温寒冷地区的推广、应用和运营维护，具有重大的工程实践意义和学术参考价值。