Analyses of sandwich beams and plates with viscoelastic cores

A hybrid damping scheme using passive constrained damping layers (PCLD), and surface bonded piezoceramic actuators was proposed for interior cabin noise and vibration control in helicopters. In order to evaluate the performance of these treatments, we need to understand the dynamic behavior of sandwich structures. The analyses of sandwich structures are complicated by the frequency dependent stiffness and damping properties of viscoelastic materials. The methods developed in this thesis specifically deal with finite element methods and assumed modes methods to this problem.; A spectral finite element method (SFEM) was developed in the frequency domain for sandwich beam analysis. The results of natural frequencies and frequency responses for two cantilevered beams with different span of PCLD treatments were presented and validated by experimental results and other analyses; including the assumed modes method (AM), and conventional finite element method (CFEM). The SFEM method implicitly accounts for frequency dependent stiffness and damping of viscoelastic materials. However, CFEM and AM method have to use additional internal dissipation coordinates to account for these properties. The Golla-Hughes-McTavish (GHM) damping method was used in both analyses. Also SFEM improves accuracy of frequency predictions compared to the results of CFEM and AM method because of its higher order interpolation functions.; We expected to extend SFEM method to two-dimensional sandwich plate structures. But it is extremely difficult to solve the governing equations for a sandwich plate. An alternative method was developed to update the traditional AM method by using plate mode shapes. The plate mode shape functions were solved directly based on the Kantorovich variational method for both transverse bending and in-plane vibration of isotropic rectangular plates. These plate mode shapes were employed to calculate sandwich plates in AM method. The results of natural frequencies; loss factors and frequency response functions were calculated and validated by experimental data and the results by using beam and rod mode shapes. The comparable results were achieved for both analyses with less modes in the case of using plate mode shapes.