Study Of The Dynamic Characteristics Of The Constrained Damping Sandwich Plates

With the wide use of viscoelastic material in engineering to control the vibration and the appearance of new viscoelastic material in recent years, the dynamic problem of viscoelastic complex structures becomes more and more important. Theoretical analysis and numerical computation for dynamic characteristic of the sandwich plate with constrained damp layer are presented in this paper.The dynamic characteristic of monolayer plate is analyzed by the finite element method, and relevant finite element computation program is compiled. The plate element is the eight-node arbitrary quadrilateral element based on the Mindlin hypothesis, the reduced integral is introduced to avoid the shear-locking problem of the Mindlin plate element. Numerical examples show that the program is valid and reliable. The sandwich plate element in next chapter is based on this program.A numerical computation method of the natural frequency and the loss factor of the sandwich plate with constrained damping layer is given in this paper. On the basis of minor distortion and linear elasticity hypothesis, the dynamic equation of sandwich plate with constrained damping layer is presented, and a sandwich plate element is developed. The natural frequency and the loss factor of the sandwich plate are extracted by the complex eigenvalue method, and the effect of the thickness and the stiffness of the viscoelastic material and the boundary condition to the natural frequency and loss factor of the structure are discussed respectively, some suggestion is given for the optimal damp treatment. Numerical examples show that the increase of thickness of the damping layer is beneficial to improve the loss factor of the structure, and the module of viscoelastic material has a optimal value to acquire the best damping effect.The modal experiment of monolayer plate, unconstrained damped plate and constrained damped sandwich plate and the response experiment under the harmonic excitation are done. The modal parameters got are compared with the result of theoretical computation. The former theory is validated. Data preparation is provided for the computation of the response of sandwich plate in next chapter.A simplified finite element numerical method to compute the dynamic response of the sandwich plate with constrained damp layer under harmonic excitation is presented, the direct integration method is used. The viscoelastic material is regarded as elastic material and its damp is regarded as viscous damp, The modal damp got from the experiment is used to calculate the damp coefficient. Theresponse under harmonic excitation is computed and compared with the test result. Results indicate that this simplified method is valid. A simple method is given for the approximate computation in engineering. Because the constitutive relations of viscoelastic materials vary with the frequency and temperature, much work is still needed to be studied further.