| Large bypass aero engine is one of the important components of aircraft.As a high-tech product in the field of modern aerospace technology,aero engine shows the military capability of a country.The traditional fan blade is prone to different forms of failure due to the action of pneumatic,centrifugal and other loads,and its mass and life determine the power and efficiency of the aero engine.With the gradual development of the aerospace field,the traditional metal fan blades of aeroengines with high density and low strength have been difficult to meet the needs of aviation development,and carbon fiber composite fan blades with lightweight and high-strength characteristics have gradually entered our field of vision.However,how to design scientific composite fan blades with excellent mechanical properties and vibration characteristics has become the most important.Tracing back to the source and learning from nature,a variety of organisms in nature have gradually evolved a variety of specific structures with excellent performance,which provides us with scientific inspiration to help us solve the problem of product design.In this thesis,the idea of bionics is integrated,and mantis shrimp,lobster,coelacanth with high-strength structure and sea eagle with excellent flight ability are used for reference.Combined with mechanical performance testing and simulation analysis,the biomimetic layup angle and the lamination structure scheme are optimized.At the same time,different overlay design methods are proposed.Through the comparison of design level,process and finite element,the higher precision overlay design method is selected.The forming conditions of composite fan blades are also studied,and the forming process with good forming precision and high theoretical curing rate is optimized.Finally,based on the paving design method,biomimetic ply angle and laminated structure explored above,the composite fan blade is designed and the vibration characteristics are analyzed,and the lamination scheme with excellent performance is dedicated to proposing the composite fan blade ply scheme.The main research contents of this thesis are as follows:（1）According to the characteristics of the composite fan blade flow surface members,two covering modes from suction surface to pressure surface and from center surface to suction surface and pressure surface are proposed.Firstly,the ply sequence diagrams obtained by the two methods are compared and analyzed.The ply sequence diagrams from the suction surface to the pressure surface produce a phenomenon of curling at the root tenon,while the ply sequence diagrams from the center surface to the suction surface and the pressure surface have a regular shape,which indicates that the ply quality generated by this ply method is higher.Then,the overlay areas of the suction and pressure surfaces obtained by the two covering modes are compared with the traditional mode,and the results show that the error of the covering results from the center to the suction and pressure surfaces is smaller and the precision is higher.Finally,the simulation analysis model obtained by the two covering modes is compared by the finite element mapping.The mapping results from the center surface to the suction surface and the pressure surface are more realistic.Therefore,according to the results of the comparative analysis of the two covering modes,it can be concluded that the covering modes from the center plane to the suction surface and the pressure surface are more suitable for the covering design of composite fan blades.（2）The idea of bionics is integrated into the design of the composite fan blade ply angle.Mantis shrimp claws,lobster claws and coelacanths with excellent mechanical properties are selected,and six ply angle schemes are designed on the premise of meeting the design criteria of composite fan blade ply.It includes the biomimetic small-angle single helical and the biomimetic big-angle single helical imitating mantis shrimp crayfish sticks;biomimetic multistage nonlinear helical and biomimetic decreased nonlinear helical imitating lobster clamp;biomimetic grouped double helical and biomimetic synchronous double helical imitating coelacanth scales.Then,the tensile,compression,bending and impact mechanical properties of the laminates with different ply angles are tested and simulated.The performance indexes of different biomimetic ply schemes are explored,and the inherent damage mechanism of biomimetic ply schemes with excellent mechanical properties is analyzed,providing a new design scheme for the ply angle design of composite fan blades.（3）The two-dimensional and three-dimensional scanning of the composite fan blade reduction components prepared under different forming processes are carried out,and the two-dimensional and three-dimensional forming accuracy of their blade tip,blade middle and blade root are compared and analyzed.The results show that the theoretical curing rate of each part of the fan blade reduction component reached 100%when the temperature is above 120℃,and the residual stress caused the smallest warping deformation at 120℃,in which the suction surface deviation is 1.04 mm and the pressure surface deviation is 0.98 mm.Therefore,the forming temperature of 120℃is more in line with the forming process of carbon fiber composite fan blades.（4）Based on the staggered structure of the sea eagle wing feathers,the biomimetic design of the laminated mode of the composite fan blade scale components is carried out,and three biomimetic laminated structures of single arrow type,double arrow type and diamond type are designed respectively.The bending properties of the blade tip and blade root of the composite fan blades prepared by three biomimetic laminated structures and the traditional step laminated structures are investigated,and the bending test force peak and damage morphology under different laminated structures are compared.The results show that the biomimetic diamond laminated structures have the best deformation resistance and are suitable for the preparation of composite fan blades.（5）Three kinds of structural biomimetic composite fan blades are designed according to the optimal design methods of center plane to suction surface and pressure surface in the previous chapters,the diamond laminated structure,the biomimetic small angle single helical,the biomimetic decreasing nonlinear helical and the biomimetic grouped double helical ply angles.The speed of 230 rad s-1 is applied to the fan blade and the static strength analysis is carried out.The results show that the maximum displacement at the tip of the biomimetic decreasing nonlinear helical fan blade and biomimetic group double helical fan blade are within the allowable deformation range,and the safety factor reaches 2.57 and 3.11,respectively.At the same time,the modal simulation analysis of the two fan blades in this state is carried out.The biomimetic double helical composite fan blades have only one resonance point at the rated speed,and the frequency margin and speed margin of the first two modes are both greater than15%,indicating that the mechanical properties and vibration characteristics of the biomimetic double helical composite fan blades are the best.It provides a feasible scheme for the design of composite fan blades. |
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