【作者】 赵凌燕；

【导师】 薛河；

【作者基本信息】 西安科技大学 ， 安全技术及工程， 2014， 博士

【摘要】 以安全端异种金属焊接接头为代表的核电关键焊接结构环境致裂已成为影响压水堆电站长期安全运行的关键问题。这种焊接接头通常是在低合金钢管嘴堆焊镍基合金形成隔离层后，再用镍基合金焊材（如82/182合金）将隔离层与不锈钢安全端焊接在一起。异种金属焊接接头组织和力学性能的不均匀性、几何结构的不连续性、焊接缺陷以及残余应力的影响，给直接利用实验室数据定量预测核电异种金属焊接接头的在役寿命带来困难。为解决核电关键焊接构件在役寿命定量预测和定期检修的问题，本文对异种金属焊接接头标准断裂力学试样和不同承载情况下的安全端异种金属焊接接头环境致裂裂纹尖端局部力学特征及其对裂纹扩展速率的影响进行了研究，完成的主要工作如下：(1)比较分析了核电关键材料环境致裂裂纹扩展速率的定量预测方法，提出了一个适用于全尺寸构件、复杂载荷以及残余应力的高温水环境中异种金属焊接接头环境致裂速率的预测模型。(2)根据182合金-A533B低合金钢异种金属焊接接头熔合区的硬度梯度分布，结合弹塑性有限元方法，建立了焊缝熔合区附近的非匀质材料模型，消除了应力应变的间断性，减少了材料性能突变对计算结果造成的影响，为研究焊接力学性能不均匀性对异种金属焊接接头环境致裂行为的影响提供了一种新方法。(3)对不同位置异种金属焊接接头试样裂纹尖端的应力应变场和扩展驱动力进行了数值模拟计算，研究了萌生于182合金焊缝的裂纹在熔合线附近的扩展行为，得出了裂尖塑性应变率对裂纹扩展路径的影响。(4)基于建立的非匀质材料模型，模拟了正常工况下安全端异种金属焊接接头轴向内表面裂纹前缘的应力应变场，对裂纹扩展驱动力进行了讨论，发现在塑性应变和应力三轴度的共同作用下，裂纹扩展方向受到材料屈服强度的影响而发生偏转。(5)模拟了一次超载情况下，安全端异种金属焊接接头纹前缘的应力应变场，得到了裂纹位置和深度不同时，一次超载系数对异种金属焊接接头裂纹扩展驱动力的影响规律。(6)对工作应力和残余应力交互作用下，含轴向内表面裂纹的安全端异种金属焊接接头的局部应力、应变、塑性应变率和J积分进行了分析，定量预测了环境致裂裂纹的扩展速率，研究了残余应力对裂纹扩展形态的影响。更多还原

【Abstract】 Environmentally assisted cracking (EAC) in safe-end dissimilar metal welds (DMW),which represent welded components in nuclear power plants, has become a critical issueaffecting the long-term operation and safety of pressurized water reactors (PWR).Nickel-based alloys are generally pre-deposited on the low alloy steel nozzle face to form thebuttering. Then welding is carried out between the buttering and the stainless steel safe-endpipe with nickel-based alloys such as Alloy82/182. It is very difficult to directly predict theEAC growth rate of actual welded components by laboratory data because of the effects ofDMW microstructure and mechanical heterogeneity, discontinuous geometry, welding defectsand residual stress. To develop the technique of quantitative prediction on service life andpreventive maintenance of key welded components in nuclear power plants, the localmechanical characteristics at EAC crack tips of standard fracture mechanics specimens andsafe-end DMW under different loading conditions were analyzed in this dissertation. Mainworks performed are as follows:(1) The approaches to quantitatively predict EAC growth rate of key materials in nuclearpower plants were analyzed and discussed. A prediction model of EAC growth rate infull-size DMW structures with complex operating loads and residual stress inhigh-temperature water environment was proposed.(2) According to the gradient distribution of hardness in the fusion boundary (FB) regionof an Alloy182-A533B low alloy steel DMW, a heterogeneous material model adjacent to FBregion in weld metal was established by using elastic-plastic finite element method. Thediscontinuity of stress and strain is eliminated, the effect of material properties mutation oncalculation results is reduced, and more realistic welded mechanical heterogeneity is obtainedby using this model. A new method is provided to research the influence of welded mechanical heterogeneity on EAC behavior in DMW.(3) The stress-strain field and crack driving force at crack tip on different location ofDMW specimens were simulated and discussed in details. Growing behavior of crack initiatedin Alloy182weld metal near FB line was investigated. The effect of plastic strain rate oncrack growing path was concluded.(4) Based on the established heterogeneous material model, the stress-strain fieldsaround crack fronts of DMW under operating loads were simulated. The DMW crack drivingforce was also discussed. As a result of the combined effect of local plastic strain and stresstriaxiality, the crack growth direction deviates due to the influence of material yield strength.(5) The local stress-strain fields around crack fronts of safe-end DMW were simulatedand discussed under the one single overload. And the effect of one single overload ratio onDMW crack driving force was also discussed with different crack location and depth,.(6) The local stress, strain, plastic strain rate and J-integral around the inner surface axialcrack fronts of safe-end DMW were investigated under the combined effect of operating loadsand residual stress. The EAC growth rates of DMW with residual stress were quantitativelypredicted. The effect of weld residual stress on crack growing state was also analyzed.更多还原