【作者】 卿华；

【导师】 温卫东； 江和甫；

【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】 涡轮冷却叶片作为航空发动机的核心部件之一,工作环境十分恶劣,承受着高温、高压、高转速的工作负荷。涡轮冷却叶片在某种程度上不仅决定着航空发动机设计性能的优劣,而且也是结构性故障发生最多的部件之一,所以对涡轮冷却叶片开展试验和理论研究具有十分重要的工程应用价值。本文在目前国内研究现状的基础上,采用试验和有限元模拟对镍基单晶冷却叶片进行较系统的研究,为镍基单晶冷却叶片的工程实际应用进行有益的探索。论文的主要工作和结论表现在以下方面:1、探讨了描述晶体塑性各向异性性质的晶体滑移本构模型。采用切线系数法,对晶体塑性滑移理论编制了率相关晶体塑性滑移本构模型的有限元子程序,并将其植入有限元软件Abaqus中。根据晶体塑性理论的特点,给出了局部坐标系和整体坐标系下更新应力应变的方法。2、开发了温度梯度试验系统,在温度梯度下对不含气膜孔和含气膜孔的试样进行拉伸和疲劳试验。试验结果表明:温度梯度对材料的拉伸和疲劳性能有一定的影响;通气状态下比非通气的试样屈服强度高;由于受气膜孔附近应力集中影响,带气膜孔试样的屈服强度急剧下降,同时通气状态下的低周疲劳寿命高于同等应力水平下的非通气的寿命。3、采用含与不含气膜孔平板试样,研究了[001]、[011]和[111]晶体取向980℃不同保载时间和应力条件下的镍基单晶合金DD6的循环蠕变性能。研究发现,DD6单晶合金的高温蠕变疲劳性能存在明显的方向性,试样形状及表面状态是影响单晶合金寿命的重要因素,特别是气膜孔的存在显著地降低了材料的循环蠕变寿命,不含气膜孔平板试样蠕变损伤起主要作用,含气膜孔平板试样疲劳损伤起主要作用。同时在高温条件下,不同保载时间的蠕变和疲劳损伤对试件的破坏起重要作用,蠕变与疲劳的交互作用会大大缩短材料的使用寿命。4、对带孔和不带孔的某第二代镍基单晶合金平板试样进行了蠕变性能试验研究与有限元对比计算。高温蠕变试验表明,平板试样的晶体取向和是否开孔对蠕变寿命有明显的影响。气膜孔导致蠕变寿命降低,对[001]取向的影响大于[111]取向。在高温低应力条件下,[001]取向的蠕变性能优于[111]取向。有限元分析结果表明,气膜孔改变了模型中的应力分布,在孔附近产生了高应力,导致模型蠕变寿命降低。有限元计算蠕变持久寿命与试验结果吻合,说明采用基于分切应力的蠕变持久寿命计算模型是合理的。5、针对镍基单晶冷却叶片气膜孔,建立一个含气膜孔的CELL模型,对此进行流固耦合及传热分析,并作为弹塑性以及蠕变持久分析的前提。建立有限元模型,根据不同取向的单向试验结果,根据不同温度和不同滑移系的模型参数,详细分析了温度梯度对气膜孔模型弹塑性以及蠕变持久寿命的影响。分析结果表明,温度梯度对材料性能的影响比较大,考虑材料的性能时不能忽视温度梯度的影响。本文的初步研究表明,温度梯度对材料蠕变损伤、蠕变寿命的影响比较大,气膜冷却时存在的温度梯度提高了叶片的蠕变持久寿命。6、选取单晶冷却叶片模型为研究对象,在气动和传热分析的基础上对存在温度梯度的冷却单晶叶片进行弹塑性分析。计算结果表明,冷却空气下叶片的最大应力比最高温度下叶片的最大应力小7.8MPa,说明冷却空气提高了叶片的强度,同时冷却空气也可以提高叶片的工作温度。冷却空气下叶片的最大分切应力比最高温度和最低温度下的最大分切应力都小。冷却空气大大提高了叶片的工作寿命。冷却空气下叶片的最大位移介于最高温度和最低温度的最大位移之间,顶端的最大轴向位移介于最高温度和最低温度之间,并且轴向位移的分布比较类似,相比局部失效模型而言,温度梯度对位移分布的影响不大。7、采用双参数蠕变损伤模型,对某发动机各向异性单晶涡轮叶片进行蠕变变形分析。应用多学科优化设计理论对单晶叶片晶体取向进行优化设计。分析结果表明:叶型积叠线方向的晶体取向偏角和随机取向的晶向角,对单晶叶片的叶尖蠕变变形具有较大的影响,对单晶叶片的晶向进行优化设计,具有重要的工程应用价值。更多还原

【Abstract】 Turbine blade is an important part of the aero-engines. To improve the thermal efficiency and the power output, advanced gas turbine engines work at a very high temperature (1500-1900K). The temperature is far above the melting point of the turbine blade material. Cooling techniques are used to decrease the thermal stress and ensure that turbine blades operate without failure. Based on the actuality of present research, the Ni-based single crystal cooling blade is studied by experiment and finite element method (FEM) in this thesis. The main work and conclusion is obtained as following:Based on finite deformation crystallographic constitutive model, Tangent stiffness type methods for rate dependent was employed, a rate-dependent constitutive model for single crystals was implemented into ABAQUS。The correlation was established between resolved Shear Stress, strain and macroscopic stress, strain by orientation tensor.An experimentation system at high temperature gradient was developed, and the specimen with cooling hole and without cooling hole were designed to carry out tension and fatigue test at temperature gradient. The experiment result shows that the temperature gradient has influence on the tension and fatigue behavior of specimen. The yield stress with cooling air is higher than that without cooling air, and the yield stress with cooling hole is lower than that without cooling hole as the effect of stress concentration. The low fatigue life with cooling air is higher than that without cooling air.The fatigue-creep properties of DD6 single crystal supperalloy with [001], [011], [111] crystallographic orientations has been investigated at 980℃. One half of specimens are plates with film cooling holes. The experimental results show the fatigue-creep properties of DD6 are obviously anisotropic. The film cooling hole will reduce the fatigue-creep life of material; The creep damage play a major effect on the plate specimen without film cooling holes; but the fatigue damage plays a major effect on the plate specimen with film cooling holes. Under high temperature, the fatigue and creep damage at different dwell time with 5 min and 30 min play a main role in facture of test specimens. Interaction between fatigue and creep will greatly shorten using life of material.Plate specimens were used to model turbine blades with cooling holes. Experimental and numerical study on the creep behavior of a second generation nickel-based single crystal has been performed with these modeling specimens. The results of creep test at high temperature show that crystallographic orientations and cooling holes have noticeable influence on the creep life. Compared with that of the specimen without cooling holes, the creep life of the specimen with cooling holes is lower for both [001] and [111] orientations. The cooling holes have larger influence on the creep life in [001] orientation than that in [111] orientation. The creep behavior under high temperature and low stress conditions in [001] orientation is better than that in [111] orientation. The finite element analysis (FEA) results reveal that the cooling holes change the stress distribution in the specimen and cause stress concentration near the holes, which result in the decrease of creep life. As the creep life obtained from FEA is accordant to that from experiment, it is reasonable to calculate the creep life with the model based on the resolved slip stress.A cell model with film cooling hole was taken out from nickel-based single crystal cooling blade. Distributions of pressure and temperature of the model were given based on the fluid and heat transfer. An FEM model of crystal was built, the crystallographic stress characterization was analyzed based on the rate dependent constitutive, and the creep life of cell model was analyzed based on the creep parameters of the different slip systems. The result shows that there is an obvious temperature gradient around film cool. And the distribution of displacement and Von Mises stress has remarkable gradient due to the temperature gradient. The creep life of cell model is influenced greatly by the film cool. And the influence of [111] orientation is much more than [001] orientation.The nickel-based single crystal cooling blade with temperature gradient was analyzed based on the rate dependent constitutive. The result shows that the cooling air improves the strength of the cooling blade. And the cooling air improves the maximum resolved shear stress of the blade. Compared with the cell model, the distribution of the stress and strain at temperature gradient is not obvious.A two-damage-variable creep constitutive model has been used to analyze the creep deformation of nickel-based single crystal turbine blades. The crystallographic orientation optimization is performed by multidisciplinary design optimization theory. The analysis results show that controlled orientation and uncontrolled orientation have profound influence on creep deformation of single crystal turbine blades. The blade crystallographic orientations should be optimized for a better creep property.更多还原