Research On Vibration Characteristic Analysis Of The 2.5D Braided Composite Blades

The 2.5D braided composite is a new kind of structural material, which had been popularly researched recently. Besides the common properties of most composites, like the light weight, high specific strength and modulus, this new material also shows better delamination resistance, excellent damage tolerance and good designability, which can be prospectively used in the high-tech industrial domains, such as the aviation and aerospace fields.In this thesis, theory and test researches were carried out on the stiffness and vibration modals of the 2.5D braided composite blades. The main works and conclusions include:(1) The RTM process was adopted for the manufacture of the 2.5D braided composite plates.The specimens for the static tensile and the vibration modal tests were designed and prepared.(2) The static tensile tests were carried out for the elastic modulus and strengths in both warp and weft directions on three different kinds of 2.5D braided composites. Non-contact measurement technique was adopted in the vibration modal experiments in both directions on the composite flat blades. Effective test data were obtained.(3) A new meso-model of the 2.5D braided composite was developed by adopting the hypothesis of rectangle section shape for warps, and biconvex section shape for wefts. Combined with the CHAMIS composite material mechanics, the prediction model of the elastic modulus can be established by two means which were based on the overall-RVE and double-RVEs(inner-RVE and outer-RVE). The results show that the elastic modulus predicted by both methods are coincident, and the predicted elastic moduluses have a good agreement with the test values.(4) The vibration modals of the 2.5D braided composite flat blades were analyzed by two equivalent methods. One is based on the overall-RVE, the other based on the double-RVEs. The bending stiffness, tensile stiffness and the differential equation of vibration motion can be obtained. The finite element method were adopted to calculate the modal of the blades,the results showed that equivalent method based on the overall-RVE for the composite blades was worse efficient than the method based on the double-RVEs,whose predicted modes has a better agreement with the vibration modal experiments.