Comparison of Active Constrained Layer Damping by Using Extension and Shear Mode Piezoceramic Actuators

We analyze, numerically by the finite element method, three-dimensional electromechanical deformations of a thick laminated plate with layers made of aluminum, a viscoelastic material and a piezoceramic (PZT). Two arrangements of layers are considered. In one case a central PZT layer is surrounded on both sides by viscoelastic layers and aluminum layers are on the outside surfaces. The PZT is poled in the longitudinal direction and an electric field is applied to it in the transverse direction. Thus shearing deformations of the PZT layer dominate over its extensional deformations. In the second arrangement, the aluminum layer is in the middle and the PZT layers are on the outside. The poling direction and the electric field are along the thickness of the PZT layer. Extensional deformations of the PZT layer are significantly more than its shearing deformations. The problem formulation incorporates geometric nonlinearities and the constitutive relation for the PZT includes quadratic terms in the electric field. For each set up of the layers, the system is excited at its first natural frequency. The enhancement in damping induced by the actuation of the PZT layers is ascertained, and the optimum thicknesses of the viscoelastic layers and the PZT layers for maximum damping are determined. The effect of nonlinear terms in the constitutive relation for the PZT is ascertained. The problem of exciting the laminated plate simultaneously at the first and the second frequenci~s and annulling these has been scrutinized. It is found that the energy of electric deformations of the PZT material is more for the shear mode actuators than that for the extension mode actuators.