In the present analysis, dynamic responses of sandwich plates with uniformly or nonuniformly damaged adhesive layers are compared with those of the perfectly bonded plates. In this regard, a direction-dependent (orthotropic) Kelvin–Voigt viscoelastic representative element whose coefficients vary in the radial direction is employed to model the irregular/damaged adhesive layer. It is the first time that the effects of the nonuniform stiffness/viscoelasticity distribution of the adhesive layer on the dynamic behaviors are evaluated, especially for circular plates. The core or face sheets may be made from homogenous or heterogeneous materials. To extract accurate results, a C1-continuous zigzag plate theory with interlaminar transverse stress continuity is employed. The resulting governing equations are extracted based on the principle of minimum total potential energy and solved by a Kantorovich-type power series solution in conjunction with the fourth-order Runge-Kutta numerical time integration scheme. Results reveal that the influence of the uniformly and unevenly damaged layer on the dynamic responses of the damaged sandwich plates is especially remarkable when rigid layers are utilized. Moreover, online health monitoring based on the deviation of the dynamic amplitude with respect to a predefined target is more efficient than using the indirect changes in the natural frequencies and phase shifts.
