A new surface-damping concept with an active-passive hybrid constraining layer (HCL) is proposed to improve the damping performance of traditional active constrained layer (ACL) systems. Instead of using a piezoelectric constraining layer, passive and active materials are used together to constrain the viscoelastic material layer. A generic model of the HCL treatment is presented. Non-dimensional equations of motion and boundary and connecting conditions are derived. The closed-form solutions to the equations are developed and analyzed. It is shown that by properly selecting a passive constraining material and assigning appropriate lengths for the active and passive constraining parts, HCL can outperform a system with pure active PZT coversheet, both in terms of its fail-safe ability and closed-loop damping performance.

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