【作者】 张鹏；

【导师】 刘凯； 宋丹龙；

【作者基本信息】 西安理工大学 ， 机械工程， 2023， 硕士

【摘要】 指尖密封作为一种新型柔性密封技术,在航空发动机、燃气涡轮机等重大机械装备的流体密封部位具有较好的应用前景。磨损寿命和迟滞泄漏是评价指尖密封性能的主要标准,然而,两者的改善措施存在相互制约的难题。C/C 复合材料具有独特的自润滑和耐磨损等优良特性,因此将其应用于指尖密封技术对提升指尖密封的综合性能具有十分重要的意义。目前,围绕C/C复合材料指尖密封展开的研究大多是将其均质化处理,并没有深入考究其内部编织纤维的分布状态对指尖密封结构工作性能的影响,然而,指尖密封碳纤维预制体结构的差异会引起其力学性能的改变。基于上述情况,本文建立了平纹编织C/C复合材料指尖密封多尺度模型,研究了其纤维编织结构对指尖密封静动态刚度特性的影响,为对C/C 复合材料指尖密封的优化与应用提供了参考。首先,在细观尺度上,模拟了约束条件下纤维编织单元的“编织”过程,拟合出了纤维束型线方程,在此基础上,建立了平纹编织C/C复合材料细观结构几何模型,并计算了细观编织复合材料中纤维束的各向异性力学常数。利用ABAQUS有限元软件建立了平纹编织C/C复合材料指尖密封的多尺度模型。其次,构建了平纹编织C/C 复合材料指尖密封片上周向分布的各指尖梁模型,并按指尖梁周向分布位置每90°为一组分为四组,利用有限元方法分析了平纹编织C/C复合材料指尖密封片上每根指尖梁的径向静刚度,并总结其径向静刚度沿指尖片周向的分布规律。此外,建立了指尖梁刚度计算理论并设计了指尖梁刚度试验,将计算结果和试验结果与仿真结果进行对比,结果显示:每一组所在的90°跨度范围内,在指尖片上周向分布的指尖梁的径向静刚度随着所处位置的角度增大呈现先减小后增大的变化规律。最后,为指尖密封靴底添加正弦变化动态位移激励,分别研究了平纹编织C/C 复合材料指尖梁刚度随指尖靴位移幅值和转子转速的变化关系。结果表明:当转子转速取一定值,改变指尖靴位移幅值,指尖梁的径向动刚度随着位移幅值的增加而增大;当位移激励的幅值取一定值时,改变转子转速大小,指尖梁的径向动刚度随着转子转速的增大而增大;研究了动态位移激励下指尖梁径向动刚度沿周向分布特性,并将其和静态激励下的结果作对比,结果表明:在0°～90°跨度范围内,指尖片上周向分布指尖梁的径向动刚度和静刚度随着指尖梁所在位置角度的增大都呈现出先减小后增大的规律,但动刚度的量值大于静刚度,且动刚度随所在位置角度变化的波动程度更大。更多还原

【Abstract】 As a new type of flexible sealing technology,fingertip sealing has a good application prospect in the fluid sealing parts of major mechanical equipment such as aircraft engines and gas turbines.Wear life and hysteresis leakage are the main criteria for evaluating fingertip sealing performance,however,there are difficulties in improving the two measures.C/C composite materials have unique self-lubrication and wear resistance,so its application to fingertip sealing technology is of great significance to improve the comprehensive performance of fingertip sealing.At present,most of the research on the fingertip sealing of C/C composite materials is homogenized,the influence of the distribution state of the internal woven fiber on the working performance of the fingertip sealing structure is not deeply studied,however,differences in the structure of fingertip sealed carbon fiber preforms can cause changes in their mechanical properties.Based on the above situation,in this paper,a multi-scale model of fingertip sealing of plain woven C/C composites is established,the influence of fiber braid structure on the static and dynamic stiffness characteristics of fingertip seals was studied,which provided a reference for the optimization and application of C/C composite fingertip seals.Firstly,at the mesoscale,the "weaving" process of the fiber braiding unit under the constraint is simulated,and the fiber bundle line equation is fitted,on this basis,a mesotropic structure geometric model of plain woven C/C composites is established,and the anisotropic mechanical constants of fiber bundles in meso-woven composites are calculated.ABAQUS finite element software was used to establish a multi-scale model of fingertip sealing of plain woven C/C composites.Secondly,A model of each fingertip beam distributed in the circumferential direction of the plain woven C/C composite fingertip seals was constructed,and it was divided into four groups every 90° according to the circumferential distribution position of the fingertip beam.The radial static stiffness of each fingertip beam on the plain woven C/C composite fingertip seal sheet was analyzed by finite element method,and the distribution law of radial static stiffness along the circumference of the fingertip sheet was summarized.In addition,the calculation theory of fingertip beam stiffness is established and the fingertip beam stiffness test is designed,and the calculation results and experimental results are compared with the simulation results,The results show that:within the 90°span of each group,the radial static stiffness of the fingertip beams distributed around the fingertip sheet shows a change law of first decreasing and then increasing with the increase of the angle of the position.Finally,the dynamic displacement excitation of sinusoidal change is added to the fingertip sealing sole,the relationship between the stiffness of the fingertip beam of the plain weave C/C composite with the amplitude of the fingertip shoe displacement and the rotor speed were studied.The results show that:when the rotor speed takes a certain value and the fingertip shoe displacement amplitude is changed,the radial dynamic stiffness of the fingertip beam increases with the increase of the displacement amplitude;when the amplitude of the displacement excitation takes a certain value,the rotor speed is changed,and the radial dynamic stiffness of the fingertip beam increases with the increase of the rotor speed;the circumferential distribution characteristics of the radial dynamic stiffness of the fingertip beam under dynamic displacement excitation were studied,and the results under static excitation were compared.The results show that:in the span range of 0°～90°,the radial dynamic stiffness and static stiffness of the fingertip beam distributed in the circumferential direction of the fingertip sheet showed the law of first decreasing and then increasing with the increase of the position angle of the fingertip beam,but the magnitude of dynamic stiffness is greater than the static stiffness,and the dynamic stiffness fluctuates more with the angle of the position.更多还原