Optimization of standoff constrained layer damping for sandwich composite panels

Stand-off constrained layer damping treatments have been found to be effective for vibration and noise reduction in high specific stiffness structures, such as carbon fiber honeycomb sandwich composites. The sandwich composites studied are representative of construction in pressurized aircraft. Techniques to design treatments for such composites are explored. First, the effect of changing the standoff height and coversheet thickness for four combinations of visco elastic layer thickness and standoff width on the damping loss factor is studied using finite element analysis and the modal strain energy method. Combinations of parameters resulting in maximum loss factor are identified, the greatest value being 0.39. An alternative design process was developed based on formal optimization to meet a noise reduction goal. A random mechanical load was used to excite a sandwich composite beam for a specified standoff width, visco elastic material thickness and coversheet thickness. The standoff height was minimized to meet an average RMS vibration response prediction. Finally an experimental study was conducted to determine if the analysis technique is valid. Two sandwich beams were constructed and excited as in the analysis. The RMS velocity reduction between 3000 Hz and 3600 Hz for a 1.27 cm standoff height was found to be 31% more than a 0.635 cm standoff height in the experiment while in the analysis it was found be 16%.