In this work, the dissipation mechanism of the viscoelastic damping layer on the sound transmission through composite sandwich plates is numerically investigated for active constrained layer damping structures. Based on the constitutive model theory of the viscoelastic material, acoustic finite element models of the composite sandwich plates are established. Numerical simulations are conducted on two different kinds of composite plates, whose sandwich layer is viscoelastic damping or linear elastic, for comparative investigation on the incident sound transmission loss, vibration displacement amplitude, and phase of the structure layers. Results show that vibration of composite plates with linear elastic sandwich layer is controlled by vibration modes of each layer at different phases, but that of composite plates with viscoelastic damping sandwich layer is controlled by the vibration mode of the whole plate at the same phase. It is shown that the shear deformation of the viscoelastic damping layer produces vibration energy dissipation when closely adhering to elastic constrained layers, and the sound transmission performance of the constrained layer damping structure distinctly does not follow the conventional mass law.

constrained layer damping,sound transmission,viscoelastic damping,finite element model