Constrained layer damping treatments with actively enhanced actions

This thesis studies self-contained constrained layer treatments with active-passive hybrid damping. In particular, two shortcomings of traditional active constrained layer (ACL) configurations, the low active control authority and weak constraining action of the active cover sheet, are addressed. The objective is to design a treatment with the best combination of open-loop (for fail-safe property) and closed-loop (for performance) damping.; A comprehensive study of enhanced active constrained layer (EACL) treatments is first performed to understand the effects of using edge elements to increase the control authority for different host structure strain distributions. It is found that to select the best stiffness distribution of the edge elements for damping performance, various system parameters including the host structure strain field need to be considered. When multiple strain fields exist at the same time, the EACL is still possible to provide higher open-loop and closed-loop damping by selecting proper edge element stiffness compared to ACL.; A new configuration, active-passive hybrid constrained layer (HCL), is proposed to improve the constraining action of the ACL cover sheet while maintaining its active action. Instead of using a purely active constraining layer, active and passive materials are connected together to form a hybrid cover sheet. It is shown analytically and experimentally that by selecting a stiffer passive constraining material and assigning appropriate active material coverage ratio, the HCL can outperform the ACL, both in terms of its open-loop and closed-loop damping performance. The effects of the active and passive materials distribution in the constraining layer and the strain distribution in the host structure are also investigated.; A better open-loop and closed-loop damping combination can be obtained by integrating the EACL and HCL. The hybrid constraining layer will create significant shear deformation in the viscoelastic layer even when stiff edge elements are used for a uniform strain field. This configuration offers considerable open-loop damping while maintaining strong closed-loop damping. Compared to the individual EACL or HCL design, the integrated EACL-HCL system provides more flexibility to meet different open-loop and closed-loop damping requirements.