核电安全端异种金属焊接接头应力腐蚀开裂裂尖力学特征

发布时间：2018-04-04 03:24

本文选题：应力腐蚀开裂　切入点：异种金属焊接接头　出处：《西安科技大学》2015年博士论文

【摘要】：核电压力容器安全端异种金属焊接接头应力腐蚀开裂(SCC)裂尖力学状态是分析SCC机理及定量预测裂纹扩展速率的关键因素之一。本文采用理论研究和弹塑性有限元分析相结合的方法,通过建立焊接接头三点弯曲试样模型,研究了界面裂纹与亚界面裂纹裂尖局部力学特征的影响因素,并对核反应堆压力容器安全端异种金属焊接接头不同位置处界面裂纹及亚界面SCC裂纹扩展驱动力进行了分析。完成的主要工作如下:(1)对高温高压水环境中核电结构材料SCC机理进行了研究,阐明了核电结构材料裂尖局部微区域的应力应变是促使SCC裂尖氧化膜破裂的主要驱动力,并在很大程度上决定了SCC裂纹扩展速率,提出了断裂力学和弹塑性有限元相结合的SCC裂纹扩展驱动力研究方法。(2)通过建立安全端焊接接头材料的匀质试样模型,分析了不同材料SCC裂尖局部微区域力学特征,得到了匀质材料裂纹扩展对裂尖微区域局部力学场的影响,为研究异种金属焊接接头中的SCC裂纹扩展驱动力提供参照基准。(3)针对安全端焊接接头材料的力学性能不均匀性,通过建立双金属材料界面裂纹扩展弹塑性有限元模型,得到了材料屈服强度失配、应变硬化指数失配以及裂纹扩展对界面裂纹裂尖微区域应力及应变分布的影响规律,并得到了核电安全端焊接接头SCC界面裂纹扩展驱动力。(4)建立了异种金属焊接接头裂纹扩展的扩展有限元(XFEM)模型,通过采用XFEM中的粘性片段和虚拟节点法,分析了具有力学性能不均匀特征的界面裂纹扩展行为,讨论了焊接接头裂纹扩展趋势特征。(5)通过建立双金属材料亚界面裂纹的计算模型,讨论了裂纹处于界面两侧,裂纹与界面之间距离以及屈服强度失配对亚界面裂纹裂尖局部力学特征的影响规律,得到了裂纹扩展对亚界面裂纹裂尖局部微区域应力及应变场的影响规律。(6)建立了核电安全端异种金属焊接接头有限元模型,分析了低合金钢、镍基合金焊材及奥氏体不锈钢焊接区界面及亚界面裂纹裂尖局部微区域应力和应变的分布规律,得到了焊接接头力学性能不均匀场中SCC裂纹扩展驱动力的分析方法。
[Abstract]:The mechanical state of stress corrosion cracking (SCC) crack tip of safety end dissimilar metal welded joint of nuclear power pressure vessel is one of the key factors to analyze the mechanism of SCC and to predict the crack growth rate quantitatively.In this paper, by using the method of theoretical study and elastic-plastic finite element analysis, the influence factors of the local mechanical characteristics of the crack tip of the interface crack and the sub-interface crack are studied by establishing the three-point bending specimen model of the welded joint.The driving forces of interface crack and sub-interface SCC crack propagation at different positions of safety end dissimilar metal welded joint of nuclear reactor pressure vessel are analyzed.The main work of this paper is as follows: (1) the SCC mechanism of nuclear power structure materials in high temperature and high pressure water environment is studied. It is shown that the stress and strain in the local micro-region of the crack tip of nuclear power structure material is the main driving force to promote the rupture of the oxide film at the crack tip of SCC.The crack growth rate of SCC is determined to a great extent. A new method for studying the driving force of crack growth in SCC is proposed, which combines fracture mechanics with elastic-plastic finite element method. The homogeneous specimen model of welded joint material with safe end is established.The local micromechanical characteristics of SCC crack tip of different materials are analyzed, and the effect of crack propagation on the local mechanical field of crack tip is obtained.In order to study the driving force of SCC crack growth in dissimilar metal welded joints, the reference datum is provided. Aiming at the inhomogeneity of mechanical properties of welded joints at the safety end, an elastic-plastic finite element model for interfacial crack propagation of bimetallic materials is established.The effects of yield strength mismatch, strain hardening exponent mismatch and crack propagation on the stress and strain distribution in the micro-region of the interfacial crack tip are obtained.A finite element finite element model for crack growth of dissimilar metal welded joints is established by using the viscous segment in XFEM and virtual node method, and the driving force of crack growth at SCC interface of safety end welded joint of nuclear power plant is obtained.The crack propagation behavior of interface with inhomogeneous mechanical properties is analyzed. The crack propagation trend characteristics of welded joints are discussed. The calculation model of sub-interface crack in bimetallic material is established and the crack is located on both sides of the interface.The effect of the distance between crack and interface and the failure of yield strength on the local mechanical characteristics of crack tip of sub-interface crack is studied.The effect of crack growth on the stress and strain field in the local micro-region of the crack tip of sub-interface crack is obtained. The finite element model of dissimilar metal welded joints at the safety end of nuclear power plant is established, and the low alloy steel is analyzed.The distribution of stress and strain at the interface and crack tip of Ni-base alloy and austenitic stainless steel is studied. The analysis method of the driving force of SCC crack propagation in the inhomogeneous field of mechanical properties of welded joints is obtained.
【学位授予单位】：西安科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TL351.6;TG407

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