The Vibration Characteristic Analysis Of A Rotating Composite Thin-walled Beam Under Hygrothermal Environment

The composite thin-walled beam with it’s light quality, high strength and some other excellent mechanical properties is widely used in engineering applications, several important examples are advanced helicopter rotors, wine turbine blades, mechanical arms and so on. The existence of deformation coupling caused by the anisotropy of composite materials make dynamics behavior quite complex, the rotating speed as well as hygrothermal environment adds to this tendency. Correspondingly, the vibration characteristics investigation of this structure is of significance in theory and practice. The influence of the external factors like temperature, humidity, rotation and inclined angle on the coupling vibration is the main work in this thesis as follows:(1) The background and significance of this research is illustrated in Chapter 1. The research status of composite thin-walled structures, rotating composite structures and composite structures under hygrothermal environment in academia is introduced. Moreover, a brief statement of the main research is also offered in this section.(2) In Chapter 2, the model of composite thin-walled beam is built and the governing equations of coupling equations is derived on the basis of classical shell theory, the constitutive relationship of single composite layer in hygrothermal environment and the Hamilton’s energy principle. The coupling vibration characteristics of two kinds of laminated composite configuration thin-walled beam, circumferentially uniform stiffness and circumferentially asymmetric stiffness, is discussed. Besides, numerical simulations are employed to study the impacts of temperature, humidity and fiber orientation angles on the vibration frequencies of beams.(3) In Chapter 3, the rotation is taken into consideration for the composite thin-walled beam and the relationship between the rotation speed and natural frequencies of this structure is investigated. Firstly, the kinetic and potential energy density of a unit length of composite beam is given and the Hamilton’s energy principle is applied to deduce the coupling vibration governing equations and boundary conditions, which are then compared with what are expressed in Chapter 2 to certify the stiffness and boundary changes brought about by the rotation parameter. The Galerkin method is utilized to obtain the eigenvalue determinant. Lastly, the influence of the rotation as well as the combined effects of rotation speed with other factors is analyzed.(4) The coupling vibration characteristics of the rotating composite thin-walled beam with an inclined angle in hygrothermal environment are researched in Chapter 4. The modeling method and coupling governing equations are obtained at first, and then just like in Chapter 3, made comparisons with those derived before for the purpose of stating the effect of inclined angle. The regulation of vibration characteristics of the rotating composite thin-walled beam is investigated when the external factors such as inclined angle, rotation speed and fiber orientation angles acting on the beam change.