Multi-scale Modeling And Stiffness Characteristics Studies Of Fingertip Seals Of Plain Weave C/C Composites

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.