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多尺度下裂纹断裂过程区力学特性分析【中文摘要】以应力腐蚀破裂(SCC)为代表的环境致裂(EAC)问题是影响核电设备长期 安全运行的关键问题，而裂纹尖端微观区域的力学状态是影响环境致裂裂纹扩展速率的重要 因素之一。借助多尺度方法，本文对裂纹断裂过程区力学特性进行了分析和研究。主要完成 研究内容和取得成果如下：(1)利用有限元软件计算出紧凑拉伸试样的裂纹尖端应力强度因子 KI值,其结果与理论值一致，从而验证了利用ABAQUS计算裂纹尖端相关断裂参量的可行 性;(2)在研究内聚应力等相关理论的基础上,推导出了研究尺度与材料弹性模量的近似关系， 并确定了介观尺度上的弹性模量；(3)在宏观尺度上建立了全局有限元计算模型和子模型，得 到了裂纹尖端应力应变场分布，结果表明利用子模型技术获得比较准确的裂纹尖端应力应变 场分布是可行的；(4)在介观尺度上利用平均晶粒尺度的方式建立了裂纹沿晶扩展模型，得到 了裂纹尖端断裂过程区的微观应力应变场;(5)当应力强度因子为30MPa.m1/2时，分析了介观 尺度上在裂纹沿晶扩展过程中裂纹长度对Mises应力、最大主应力和应变的影响，结果表明, 裂纹扩展长度对试样整体应力应变分布影响不大，而对裂纹尖端区域有较大影响;(6 )介更多 观尺度上对比分析了弹性模量为210GPa和420GPa时在裂纹扩张过程中的裂纹尖端应力应 变场，结果表明弹性模量对应力的影响较大而对应变的影响不明显。本文研究成果为进一步 分析研究裂纹尖端断裂过程区的应力应变状况，以及EAC裂纹扩展定量预测研究奠定了一定 的理论基础。【英文摘要】 Environmentally assisted cracking (EAC)，especially stress corrosion cracking (SCC)，is a core issue in the long-term safety operation of the nuclear power equipments，and the mechanical state in crack tip is one of the important factors affecting the EAC growth rate. With multi-scale method，the mechanical properties in the fracture process zone were analyzed and researched in this study.The main research tasks and results are as follows:(1) Through comparing the stress intensity factor (KI) of compact tension specimen calculated by finite element software with the theoretical value，the feasibility of calculating fracture parameters of crack tip in ABAQUS software was verified.(2) The relationship between the elastic modulus (E) of the material and research scale was studied based on deriving the cohesive stress theory and other relevant theories. And the elastic modulus of the material on meso-scale was determined.(3) Global model and sub-model of the finite element were built in th.e macro-scale，and stress-strain field nearby the crack tip was analyzed， and the results show that the detailed stress-strain in the crack tip could be obtained by using the sub-model technique.(4) In meso-scale，the crack growth model was also established by assuming the crack propagating along the grain boundary， and the detailed stress-strain field in the crack tip was obtained.(5) The effect of crack length on Von Mises stress，and maximum principal stress and strain was analyzed in meso-scale when equivalent KI equals 30MPa.m1/2. And the results show that except for crack tip area，the stress-strain distribution in whole specimen is not affected.(6) The stress-strain in the crack tip was analyzed when the elastic modulus is 210GPa and 420GPa in meso-scale， respectively， and the results show that the elastic modulus has great influence on stress but little on strain.The conclusions provide a theoretical foundation for further analyzing the stress-strain in the fracture process zone and researching the stress corrosion cracking along the grain boundary.【中文关键词】环境致裂；多尺度；有限元法；断裂过程区；应力应变【英文关键词】 Environmentally assisted cracking (EAC); Multi-scale ; Finite element method; Fracture process zone; Stress-strain
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