核电安全端异种金属焊接接头的环境致裂机理与寿命模型

The aim of this project is to address the environmentally induced cracking mechanism and crack propagation prediction model of safe-end dissimilar material welded joints in advanced nuclear power plant due to the corrosion-fatigue loading in high-temperature water. This research can be used to ensure the longlife and reliable service of some key components used in nuclear power. The following issues will be focused in the present project: (1) Developing the surface coupling chemo-mechanical model of stress assisted diffusion and environmentally assisted fatigue on the basis of the analysis of the surface chemical reaction near crack-tip under fatigue loading. This research can be used to describe the effect of high-temperature water environment on the fatigue resistance and crack propagation of local zones of weld. (2) Describing the time- and environment-dependent relaxation of welding residual stress and its effect on the crack propagation rate on the basis of fatigue experiments using small specimens. The effect of competition behavior among residual stress, environment, and microstructure on crack propagation mechanism neat fusion line can be clarified. (3) Developing the prediction model of fatigue crack propagation rate through the combination of crack-tip strain rate model and strain-rate gradient theory.The effect of welding residual stress and environment on the fatigue life can be reflected in this model. In this interdisciplinary program, the mechancial, chemical and material analyses were included. Through the accomplishment of this project, the basic rule of environmental fatigue of the materials used in advanced nuclear power plant through the view point of chemo-mechanical analysis can be found and the life prediction model which can be used for engineering application can be developed. Also, this project could provide some important insights on the improvement of the long-life design and manufacturing of the key components in advanced nuclear power.

面向先进核电关键部件长寿命可靠运行的需求，针对高温水环境腐蚀与疲劳交互作用下安全端异种金属焊接接头的环境致裂机理及裂纹扩展预测模型开展研究。主要包括：（1）通过疲劳载荷下裂纹尖端化学反应的适时测量与分析，建立应力协助扩散及环境促进疲劳相耦合的化学－力学模型，实现高温水环境促进疲劳进程的科学解释；（2）通过焊接接头各微区试样的疲劳实验，揭示焊接残余应力疲劳进程中的释放机制，澄清残余应力、环境效应及材料微观结构相互竞争效应对接头熔合线附近的疲劳裂纹扩展路径的影响规律并建立映射关联；（3）基于新近发展起来的裂尖应变率模型和应变率梯度理论，建立包含环境效应及残余应力参量、物理意义明确的疲劳裂纹扩展预测模型。本项目体现了力学、化学和材料等多学科领域的交叉，可望从化学-力学角度阐明核电高温水环境下疲劳失效的基本规律并建立预测方法，为核电安全端异种金属焊接接头的寿命设计方法和制造水平提升提供科学支持。

本项目重点研究高温腐蚀条件下的多尺度裂纹扩展行为及寿命设计方法。项目组经过四年的努力，在复杂载荷条件下多尺度裂纹扩展试验和理论、化学—力学交互作用下的寿命预测模型、基于表面改性的抗疲劳制造理论与技术等方面取得了一些有影响的研究成果。项目负责人以第一作者及通讯作者发表SCI检索论文16篇，授权国家专利授权11项、软件著作权3项。项目完成期间，项目负责人荣获教育部科学研究优秀成果奖—青年科学奖（2016、全国共9人）、中国机械工业科技进步一等奖（2016、排名4）、上海市科技进步一等奖1项（2015、排名1）、中国机械工程学会青年科技成就奖（2015）；项目负责人入选上海市十大青年科技英才（基础研究类）（2014）、教育部霍英东青年教师基金（2014）、教育部首批青年长江学者（2015）、国家杰出青年基金（2017）等人才计划支持。参与项目的研究生三人获得国家奖学金，连续两届荣获中国腐蚀与防护学会“优秀论文奖”（2014、2015）。培养博士研究生4名，硕士研究生8名。