| Passive stand-off layer (PSOL) and slotted stand-off layer damping treatments are presently being implemented in many commercial and defense designs. In a PSOL damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer (PCL) damping treatment. In an SSOL damping treatment, slots are included in the stand-off layer. In this research analytical and finite element models were developed and experimental studies conducted in order to analyze the contribution of the stand-off layer to the overall system damping in PSOL and SSOL damping treatments applied to one dimensional beam structures. The mathematical model for the PSOL, or non-slotted stand-off layer case, characterized the treated beam as a boundary value problem which was then solved using the method of distributed transfer functions by Yang and Tan. The SSOL, or slotted stand-off layer case was solved mathematically with transfer matrices using a periodic structure approach. These two mathematical models were then verified with finite element analysis using ANSYS.; The experiments, mathematical and numerical models were all specifically designed so that specific geometric and material properties of the stand-off layer could be varied in order to determine the contribution of these stand-off layer characteristics to the overall system damping. Some significant findings from this study indicated that although the inclusion of slots in the stand-off layer may provide advantages such as reduced total treatment mass and increased conformability when applying these treatments to curved surfaces, the addition of these slots did not improve the damping performance. In addition, the bonding layers used to fabricate these treatments were found to be non-negligible in many configurations and these layers had a noticeable and significant effect on the frequency response of the structure. Changing the tensile moduli of the stand-off layer had a significant and noticeable effect on the frequency response functions measured in the experiments and predicted by the mathematical and finite element models. The experimental results from the study described in Chapter 8 further indicated that for beam structures, solid stand-off layer damping treatments made from lighter density rigid foams outperformed slotted stand-off layer damping treatments made from higher density rigid foams of greater total treatment mass. |
