大跨桥梁缆索疲劳-腐蚀耦合所致性能劣化的多尺度描述和可靠度分析

At present, performance degradation caused by the coupling action of corrosion and fatigue load is not considered in the durability assessment of the bridge. This project is aiming at the “cable controlling life” system. Based on the modern technology and methods such as the structural health monitoring, laboratory artificial corrosion-fatigue acceleration test, multi-scale theory and so on, performance evaluation methods of the cable under the action of corrosion-fatigue coupling are researched. The research focuses on the birthplace of the performance degradation-damage, and the whole life process from the beginning of micro damage-pitting corrosion at material level, to micro-crack nucleation and extension at component level, until to the macro damage accumulation at structure level. The reasonable characterization and quantification of damage and performance degradation under the different level and scales is revealed. The multi-scale degradation model is established which not only could predict the fatigue damage under the macro-scale, but also describe the pitting damage evolution, and the nucleation and propagation of micro crack under the micro-scale. The mechanism of damage evolution and degradation is researched due to the coupling action of fatigue which could accelerate corrosion rate and corrosion which could intensify fatigue crack propagation. Based on the multi-scale modeling strategy and multi-scale damage mechanics theory, the framework of computational mechanics is improved. The time-variant reliability theory of stochastic process of degradation process induced by the corrosion-fatigue coupling is established. These could provide the criterion and theoretical basis for the durability evaluation of the long-span bridge.

目前大跨桥梁耐久性评估尚未考虑由于腐蚀介质和疲劳荷载耦合作用所引起的性能劣化。本项目拟针对桥梁“生命索”体系，结合结构健康监测、人工腐蚀-疲劳加速试验、多尺度理论等现代技术与方法，基于多尺度力学开展缆索在腐蚀-疲劳耦合作用下性能评价方法的研究。从性能劣化的发源地——损伤入手，围绕材料层次的微损伤——点蚀伊始，至构件层次的微裂纹成核、扩展，至结构层次的宏观损伤累积直至失效的全生命过程，揭示不同层次、尺度上损伤度和劣化度的合理表征和量化，建立既能合理描述宏观尺度损伤演化、又能综合反映微细观尺度的点蚀损伤演化、微裂纹成核与扩展群体行为的多尺度劣化模型，研究疲劳加速腐蚀速率、腐蚀加剧疲劳裂纹扩展这一耦合作用诱致的损伤演化和劣化机理，基于多尺度建模策略和多尺度损伤力学理论完善现有计算力学框架，创建缆索体系腐蚀-疲劳耦合所致劣化随机过程的时变可靠度理论，为大跨桥梁结构耐久性评估提供判据和理论基础。

缆索支承型桥梁是现代桥梁的主要结构形式之一，包括悬索桥、斜拉桥和系杆拱桥等。服役期间，缆索体系的安全性是桥梁安全的重要条件之一。Watson和Stafford经过长期调查发现，缆索是桥梁最易损坏的构件，其容易引发“逐个击破”的多米诺骨牌效应的结构破坏。由于长期承受交变载荷并暴露于污染严重的自然环境中，腐蚀介质和疲劳载荷的耦合作用所导致的缆索体系的性能劣化和腐蚀疲劳失效是其典型的失效模式之一。. 本项目在总结国内外有关金属腐蚀疲劳破坏及缆索性能劣化规律的基础上，从腐蚀疲劳损伤演化理论出发，基于对腐蚀缺陷本质特征的合理描述，利用元胞自动机技术建立了含初始缺陷的缆索的数值模型，编写了用户材料子程序对其损伤演化过程进行数值模拟，评估了考虑腐蚀因素的缆索的损伤及寿命，并对其失效机理进行分析。设计了一种新型试验装置，实现对多根缆索钢丝的同步脉动疲劳加载。开展了含预制缺陷的桥梁索用钢丝的通过含预制缺陷钢丝的疲劳试验、腐蚀疲劳试验和疲劳裂纹扩展试验，获得其疲劳S-N 曲线、腐蚀疲劳S-N 曲线和疲劳裂纹尺寸-循环次数曲线，分析不同腐蚀因素、表面缺陷的形貌特征对钢丝疲劳性能的影响规律。基于扫描电镜对断口形貌进行分析，并通过理论分析和数值模拟实现了缆索用钢丝的疲劳损伤演化过程、腐蚀疲劳损伤演化过程和疲劳裂纹扩展过程的可视化。. 本项目的研究成果可较好预测含初始缺陷的缆索的剩余寿命，揭示缆索的腐蚀疲劳失效机理以及不同类型、尺度的初始腐蚀缺陷对疲劳性能的影响，在一定程度上能替代腐蚀疲劳试验，大大节省了试验时间和费用。设计的新型试验装置以传统疲劳试验机为基础，可实现对多试样的多级同步脉动疲劳加载，可妥善考虑腐蚀介质与疲劳荷载的耦合作用，能弥补传统疲劳试验耗时久、难以耦合腐蚀环境的不足，大大缩短腐蚀疲劳试验的时长。同时，提出的基于连续损伤力学、断裂力学和扩展有限元结合的方法可实现缆索疲劳损伤演化、腐蚀疲劳损伤演化和疲劳裂纹扩展过程的可视化。