Finite element analyses for sandwich structures with a viscoelastic-constrained layer

Reduction of vibration and acoustic noise in machinery and aircraft structures has been an important issue to designers for many years. Reduction in resonant response of vibrating panels has been successfully achieved by adding surface damping treatments to the panels. There are two types of surface damping treatments: unconstrained-layer treatments and constrained-layer treatments. For unconstrained-layer treatments, a layer of viscoelastic material is applied to the structure. This viscoelastic material then dissipates energy through cyclic tensile-compressive strains when the structure is in bending vibration. For constrained-layer treatments, a stiff layer is added to the top of a soft viscoelastic layer to act as a constraining layer. This constraining layer causes the middle viscoelastic layer undergo significant shear deformation and dissipates energy during bending vibration. Resonant frequencies, loss factors, and steady-state response are important parameters to monitor in constrained-layer structures.; This paper studies vibration control of plate/shell structures through use of a passive constrained layer (PCL) damping treatment. To analyze the dynamic behavior and vibration damping treatments of the general plate/shell structures, a finite element code (VDPCL) was developed using modified degenerated shell finite element theory based on the two 9-node Lagrange shell elements. The developed shell finite elements have 18 physical nodes for the upper and bottom layers and 9 pseudo nodes for the viscoelastic-constrained layer. The proposed modeling for the damped sandwich structures can simulate effectively damping mechanism through the relative displacements between the upper and lower layer.; Numerical results are presented to demonstrate resonant frequencies and loss factors of a damped sandwich plate. The obtained results based on Complex Eigen-value Method are compared with existing analytical and other numerical results using Modal Strain Energy Method. For the structural optimization study, the variation of the resonant frequencies and loss factors due to the various thicknesses of the Viscoelastic Material (VEM) and the constraining layer has been studied.