【作者】 杨治国；

【导师】 高德平；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2007， 博士

【摘要】 涡轮盘是燃气涡轮发动机关键件之一。涡轮盘材料是制约其技术性能、可靠性及安全性的关键因素。随着高性能航空发动机的发展,对涡轮盘材料的性能要求越来越高,也越来越严格,即要求更高的综合性能及长期工作的稳定性。本论文在目前国内外研究工作的基础上,对粉末冶金合金的力学性能进行了较为系统的研究,并结合工程实际,对粉末冶金盘件的疲劳寿命和破裂转速进行了较深入的研究,为粉末冶金合金在工程中的应用进行了有益的探索。论文的主要工作和贡献如下:1、开展了粉末高温合金材料FGH95力学特性试验,掌握了FGH95的基本力学性能。试验表明,镍基粉末高温合金是一种机械硬化材料,在温度420℃到650℃、应变率介于0.0001 s?1和0.01 s?1的情况下,对杨氏模量、屈服极限和塑性模量的影响并不明显。FGH95粉末合金的LCF试验表明,R=-1时,420℃~650℃范围内,温度对LCF寿命的影响可以忽略,但当R=0时,温度对LCF寿命有着较大的影响。与拉伸性能相比,镍基粉末冶金的压缩强度和压缩疲劳性能更加优异,材料的抗压缩疲劳能力远胜于抗拉疲劳能力。不同温度和不同应力水平的蠕变试验表明,温度和应力水平对FGH95的蠕变性能有明显影响,随着温度和应力水平的增加,材料抵抗蠕变变形的能力迅速下降。由材料的疲劳裂纹扩展试验可以看出,在不同温度下(430℃和600℃)测得的疲劳裂纹扩展速率基本在同一个数量级内,说明在测试的两种温度下,疲劳裂纹的扩展速率对温度不敏感。2、采用Gurson塑性理论研究了含夹杂粉末高温合金材料的细观力学行为。研究结果表明,空穴洞中心位置和空穴洞形状对空穴体积增长率和空穴体积成核率有着显著影响,夹杂位置和夹杂形状对空穴体积增长率和空穴体积成核率有着显著影响,因此,空穴洞和夹杂对粉末合金材料构件的寿命有明显的影响。夹杂物离基体表面的距离对材料损伤影响比较大,夹杂物离基体表面越近越容易引起基体的破坏,夹杂物引起的表面裂纹是材料损伤的主要原因。3、采用Gurson塑性理论研究了含夹杂粉末冶金材料的疲劳特性。研究结果表明,夹杂物的形状对疲劳寿命的影响比较大。同时,随着疲劳循环次数的增加,基体的最大空穴体积成核率不断增大,当积累到一定程度时,基体将发生断裂破坏。4、采用K-R蠕变损伤模型分析了粉末冶金材料在复杂应力下的蠕变损伤。研究结果表明,切口形状对切口试样的最大损伤位置分布有很大的影响。不同切口半径的试样蠕变寿命有很大区别。对于C型和U型切口试样,切口半径越大,寿命越短;V型切口试样,切口张开角度越大,寿命越短。采用光滑圆棒试样和带孔平板试样对处于不同温度复杂应力状态下的FGH95高温合金的低周疲劳(LCF)性能进行了研究,建立了疲劳寿命与循环应力范围的函数关系,并采用涡轮盘模拟件进行了验证。5、通过粉末冶金涡轮盘在试验状态下的有限元分析,确定了涡轮盘的危险位置,并根据建立的疲劳寿命与应力范围的关系,对涡轮盘的疲劳寿命进行了预测。计算与试验结果的误差值在工程允许范围之内,表明本文计算方法可以应用于工程设计。采用三种方法对粉末盘的破裂转速进行了计算,并与试验结果进行了对比。结果表明,三种方法的计算结果相差较小,该轮盘具有大于试验破裂转速(122%n设计)的储备能力。6、研究了粉末高温合金盘件的裂纹萌生和扩展寿命。采用两种不同模型对粉末冶金导流盘的应力和应变进行了分析,分别考虑了导流盘上通气孔和槽道对结果的影响。计算结果表明,由于在导流盘止口槽道根部没有采用圆角过渡,产生了很大的应力集中,出现明显的塑性应变,导致裂纹萌生与扩展,最终使导流盘断裂破坏。分析结果与试验结果吻合较好。采用数值模拟和断口观测技术对疲劳裂纹的扩展寿命进行了分析,建立了相关的疲劳裂纹扩展公式,得到了导流盘的疲劳裂纹萌生寿命和扩展寿命,二者所得结果具有较好的一致性。更多还原

【Abstract】 Turbine disk is a key part of the gas turbine–engine, the material used by turbine disk is pivotal for the techno- performance,reliability and security. Following the development of high performance aero-engine, the material which is used in turbine disk is more and more stringent, namely, good integrative capability and long-term stability are demanded. In this dissertation the systemic study of powder metallurgy is performed. Based on the present study, the mechanics performances of Powder Metallurgy(PM) Ni-base Superalloy are systemic studied by experiment. And then, integrating with engineering, the fatigue life and burst speed of the real turbine disk are studied, and some useful exploring works of the applying of the PM is carried out. The main works and contributions of this dissertation are listed as follow.1、The experiment study of high temperature alloy material FGH95 is carried out,and the basic mechanical performances are griped. From the experiment study, it can be seen that nickel-base powder metallurgy (PM) FGH95 superalloy is strain hardening material. The experimental results of tensile testing show that the effect of strain rate on the Young’s modulus, tensile yield strength, and plastic modulus can be neglected at temperature from 420℃to 650℃. On mode R=-1, the influence of temperature on low cycle fatigue life can be ignored. But on mode R=0, the influence of temperature on low cycle fatigue life is serious. Compared with the tensile test results, the compressive strength limit and the compression fatigue life of PM is very high, and exceed a half of the tensile strength limit of PM. From the experiment results of creep, it show that the influence of temperature and stress level on FGH95 is evident. Along with the increasing of the temperature and stress level, the resistance of creep deformation of PM decreases quickly. Form the fatigue crack expand test it concludes that the fatigue crack expand speed is closed between the test temperature 420℃and 650℃.2、Based on Gurson’s model, analysis of finite deform plastically damage for tension specimen has been analyzed in PM alloys including inclusions. Special attentions have been paid on the influence of the location and shape as well as size of the inclusions on the void enlargement, nucleation and stress redistributing. It has been found that the influence is much high. Therefore the life of the PM alloys is also influenced by the above inclusion information. The simulation results shows that the distance between inclusion and surface have much influence on the damage of matrix. The inclusion nearest surface is the main factor that causes the fracture of the powder metallurgy materials.3、The fatigue study is carried out on the powder metallurgy materials with inclusion using Gurson model. The research shows that the shape of inclusion has strong influence on the fatigue strength of matrix. The max VVFG of matrix decreases with the increasing of the cycle loading. The result shows that the accumulation of VVFN is the main reason which causes damage of material.4、Numerical calculation with K-R damage law has been performed to study the creep damage of power metallurgy material under multiaxial stress states. The calculation results show that the notch shape has much influence on the maximum creep damage distribution. Notch radius has a great influence on creep life. For C-type and U-type notched specimen, the creep life decreases with notch radius increasing. For the V-type notched specimens, the rupture life decreases with increasing the notch angle. The low-cycle fatigue (LCF) behavior of smooth round specimen and a plate containing holes specimens made of powder metallurgy superalloys (FGH95) is studied by experiment and finite element method at different temperatures. A low-cycle fatigue life model has been proposed for the powder metallurgy superalloys under multiaxial stress states. The LCF life is a power function of true stress range corresponding to the maximum and minimum loadings. Further, a simulating specimen of turbine disk has been studied to validate the LCF life model. Good agreement has been obtained between finite element analysis and experimental results.5、In order to assure the security of PM turbine disk, the stress distributing of turbine disk is calculated by FEM. The danger point of turbine disk is found. Based on the formulation of stress range and fatigue life, the cycle number of turbine disk is estimated, which is accordant with the test result. The burst speed of turbine disk is calculated by the use of three different methods, those are the equality stress method, the small deformation analytic method and the large deformation analytic method, and the results are compared with the test. The calculation results show that the values of numeration are closed to the experiment value, and the value of large deformation analytic method is more secure.6、The distributing of stress and strain of turbine disk is computed using of two different FEM models, which are calculated the effection of ventilating hole and the cut of the disk. The results of calculation show that the stress concentration is serious because of the lack of circle angle in the root of the cut. This is the main factor for the sprout of crack, and finally induces the breakage of the disk. This conclusion is consistent with the experiment result. At the same time, the fatigue life of the disk is analyzed by numerical simulation and the photo of SEM. From the interval of fatigue strip, the formulation of the extend velocity of fatigue crack can be established, which can be used to estimate the sprout life and the extend life of the fatigue.更多还原