本文選題：釬焊接頭 + 多軸應力�。� 參考：《華東理工大學》2016年博士論文

【摘要】：近年來,釬焊技術在航空航天、燃氣輪機及燃料電池等高溫服役條件下得到了廣泛的應用。在高溫下,蠕變及蠕變損傷引起的裂紋擴展是導致釬焊接頭失效的主要原因之一。釬焊接頭中存在的釬焊殘余應力、熱應力與外加載荷疊加使釬焊接頭處于復雜的多軸應力狀態(tài),對釬焊接頭的蠕變失效產生較大的影響。本文以Inconel625/BNi-2釬焊接頭為研究對象,對其多軸應力狀態(tài)下的蠕變損傷及裂紋擴展性能進行研究,探討釬焊接頭的失效規(guī)律,為釬焊接頭在高溫條件下的壽命預測提供參考。論文的主要研究工作和相關結論如下：(1)對釬焊接頭中的基體材料Inconel625合金和釬料BNi-2的蠕變性能進行了試驗研究�？紤]尺寸效應,特別針對釬料提出了一種與釬焊接頭中釬料厚度相類比的小試樣。通過高溫單軸拉伸(常規(guī)試樣、小試樣)試驗分別獲得了Inconel625合金和釬料BNi-2兩種材料的蠕變應變曲線,并基于Norton方程擬合獲得相應的蠕變本構參數(shù),為蠕變損傷本構模型參數(shù)的擬合和有限元分析提供了基礎數(shù)據(jù)。(2)結合Kachanov-Rabotnov蠕變損傷模型的優(yōu)點,通過修正Liu-Murakami模型,建立了描述多軸應力狀態(tài)下蠕變三階段的本構模型�；谠撃Ｐ�,利用ABAQUS的CREEP模塊嵌入Fortran子程序,對Inconel625合金蠕變裂紋擴展行為進行有限元分析,并通過試驗進行了驗證。結果表明,修正的蠕變損傷模型可準確描述Inconel625合金蠕變裂紋的擴展情況,解決了Kachanov-Rabotnov模型有限元計算收斂困難的難題,同時避免了Liu-Murakami模型因分析過程中σ1/σeq比值過大或比值小于0而出現(xiàn)與實際情況不符的問題。(3)對釬焊接頭Inconel625/BNi-2的裂紋擴展行為進行了研究。根據(jù)微觀金相組織,將釬焊接頭分成母材、擴散區(qū)和釬料三個區(qū)域。考慮殘余應力和熱應力的影響,基于上述修正的模型,通過賦予各區(qū)域不同屬性,對釬焊接頭的蠕變損傷及裂紋擴展行為進行了有限元分析。進而采用緊湊拉伸(CT)試樣對釬焊接頭進行試驗研究,獲得了釬焊接頭的失效區(qū)域及蠕變裂紋擴展速率,證明了該修正模型可準確描述釬焊接頭蠕變裂紋擴展行為。研究發(fā)現(xiàn)擴散區(qū)的性能對釬焊接頭的蠕變裂紋擴展行為具有較大的影響,提高擴散區(qū)的蠕變應變率有利于延長釬焊接頭的使用壽命。(4)對釬焊接頭蠕變裂紋擴展行為的影響因素進行了參數(shù)化分析。對不同釬料厚度、試樣尺寸、殘余應力和熱應力下的釬焊接頭蠕變裂紋擴展行為進行了有限元分析,結果表明,適當增大釬料厚度和試樣尺寸均有利于提高裂紋擴展的孕育期；消除殘余應力不但能夠極大地提高釬焊接頭的裂紋擴展孕育期,同時還大大降低了裂紋擴展速率,有利于提高釬焊接頭的使用壽命；而釬焊接頭中熱應力的存在改變了接頭中的應力分布,對于延長其使用壽命是有利的。(5)基于上述本構模型及研究方法,本文以一航空發(fā)動機回熱器的設計為例,對回熱器整體結構在設計工況條件下(650℃、3MPa)的蠕變損傷和使用壽命進行了模擬分析。結果顯示,回熱器結構失效位置位于釬縫區(qū)域,連續(xù)運行34,900小時后,裂紋貫穿整個釬料區(qū)域,不能達到連續(xù)工作40,000小時的設計要求。當換熱主管的壁厚增加50%,連續(xù)工作40,000小時后釬料區(qū)域的裂紋長度為1.1mm,約占管壁壁厚的1/3左右。此時,回熱器能夠繼續(xù)正常工作,滿足航空發(fā)動機安全運行的要求。然而壽命的延長是以重量的增加為代價的,整個回熱器的重量增加約10%。所以進一步提高釬料的抗蠕變性能是提高航空發(fā)動機回熱器強度、降低重量的重要發(fā)展方向。
[Abstract]:In recent years, brazing technology has been widely used in high temperature service conditions such as aeronautics and Astronautics, gas turbine and fuel cell. At high temperature, the crack propagation caused by creep and creep damage is one of the main causes of brazing joint failure. The brazing residual stress, thermal stress and external loading charge are superimposed on the brazing joint to make the brazing filler metal. The welding head is in a complex multi axis stress state, which has a great influence on the creep failure of brazed joint. This paper takes the Inconel625/BNi-2 brazing welding head as the research object, studies the creep damage and crack propagation performance under multi axis stress state, and discusses the failure law of brazing joint, which is the life of brazed joint under high temperature. The main research work and the relevant conclusions of the thesis are as follows: (1) the creep properties of the base material Inconel625 alloy and the solder BNi-2 in the brazed joint are studied. Considering the size effect, a small sample of the brazing joint is presented in particular to the brazing joint in the brazing joint. The creep strain curves of two kinds of Inconel625 alloy and BNi-2 are obtained by the tensile test (conventional and small sample), and the corresponding creep constitutive parameters are obtained based on the Norton equation. It provides the basic data for the fitting of the creep damage constitutive model parameters and the finite element analysis. (2) combined with the creep damage model of the creep damage model. By modifying the Liu-Murakami model, a constitutive model describing the three stage of creep in a multiaxial stress state is established. Based on this model, the finite element analysis of the creep crack propagation behavior of the Inconel625 alloy is carried out by using the CREEP module of the ABAQUS to be embedded in the Fortran subprogram. The results show that the modified creep has been carried out. The variable damage model can accurately describe the creep crack growth of Inconel625 alloy and solve the difficult problem of the convergence difficulty of the finite element calculation of the Kachanov-Rabotnov model. At the same time, it avoids the problem that the Liu-Murakami model is too large or the ratio is less than 0 in the analysis process. (3) Inconel625/ for the brazing joint. The crack propagation behavior of BNi-2 was studied. According to micrometallographic microstructure, the brazed joints were divided into three regions: the base material, the diffusion zone and the solder. Considering the influence of the residual stress and thermal stress, the creep damage and the crack propagation behavior of the brazed joint were finite-element based on the modified model. Then the brazed joint was tested by the compact tension (CT) specimen, and the failure region and the creep crack propagation rate of the brazed joint were obtained. It was proved that the modified model can accurately describe the creep crack propagation behavior of the brazed joint. The effect of increasing the creep strain rate of the diffusion zone is beneficial to prolonging the service life of the brazed joint. (4) the factors affecting the creep crack propagation behavior of the brazed joint are parameterized. The finite element analysis of the creep crack propagation behavior of the brazed joints under the thickness of the solder, the size of the sample, the residual stress and the thermal stress is analyzed. The results show that the proper increase of the thickness of the solder and the size of the sample can improve the incubation period of the crack growth, and the elimination of residual stress can not only greatly improve the incubation period of the crack propagation of the brazing joint, but also greatly reduce the rate of crack propagation and improve the service life of the brazing joint. In changing the stress distribution in the joint, it is beneficial to prolong its service life. (5) based on the above constitutive model and research method, this paper takes an aeroengine regenerator design as an example to simulate the creep damage and service life of the regenerator overall structure under the design condition (650 degrees, 3MPa). The results show that The structure failure position of the regenerator is located in the brazing seam area. After 34900 hours of continuous operation, the crack runs through the whole solder area and can not meet the design requirements for continuous work for 40000 hours. When the wall thickness of the heat exchanger is increased by 50%, the length of the crack in the solder area is about 1.1mm after 40000 hours of continuous work, and it is about 1/3 of the wall thickness of the tube. The device can continue to work properly to meet the requirements of the safe operation of the aero engine. However, the prolongation of the life span is at the expense of the increase of the weight. The weight of the whole regenerator increases about 10%., so the further improvement of the creep resistance of the solder is an important direction for improving the strength of the regenerator and reducing the weight of the aero engine.
【學位授予單位】：華東理工大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG454

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