Study Of The Predicted Modal Damping Of Composite Thin-Walled Closed-Section Beams

With the development of society, people's demand for energy is increasing. Coal, oil and other energy sources have dropped sharply. The development new renewable energy is imminent. The wind energy as an inexhaustible, clean new energy is recognized. Many counties have already started to use wind turbine power generation. Typical large wind turbine blades mostly use structure of thin-walled composite closed beams. This structure is also widely used in modern helicopter rotor blades and aerospace design. Therefore, it has great value for study thin-walled composite closed beams structure. This has very important significance for promoting the effective use of green energy.First, the deformation of the thin-walled closed composite beams with coupled 1D free vibration is investigated. The structural modeling is split into two parts:a two-dimensional analysis over the cross section and a linear analysis of a beam along the beam span. The two-dimensional cross-sectional analysis is based on the force-deformation relationship equations. Hamilton's principle is employed to derive the equations. The Galerkin's method is employed in order to solve the coupled differential equations. Numerical results of the first bending-dominated and first twisting-dominated modal frequencies are obtained for the cantilevered composite box beam. Second, the micromechanics stiffness and damping theory are used to calculate off-axis stiffness and damping characteristics of single-layer composite material. The thin-walled composite beam energy dissipation in any deformation model is calculated. Third, analytical formulas of the modal damping ratio are derived on the basis of maximum strain energy theory. Numerical results are obtained for composite thin-walled beam. The effects of fiber orientations, box-section aspect ration and length aspect ration on modal damping are investigated. It must be considered the impact of box-section aspect ration when predicate modal damping. But the length aspect ration had no effect on the modal damping.Finally, the composite sample experimental steps of wind turbine blade are described. The principles of DMA is introduced. The dissipation factor and storage modulus expression of composite materials are given.