Some fundamental issues of constrained layer damping treatments
Constrained layer damping (CLD) treatment is a widely used surface damping treatment for controlling vibration and noise. The most commonly used mathematical formulation for a beam with the CLD treatment was developed by Mead and Markus. In their formulation, the longitudinal displacements of the base beam and the constraining layer are assumed to be dependent. As a result, the Mead-Markus formulation only applies for some boundary conditions. In the first issue, the error of the Mead-Markus formulation was investigated as a function of the thickness of viscoelastic layer and was shown to be large for certain common boundary conditions. A modified Mead-Markus formulation that allows the longitudinal motion of the base beam and constraining layer to be independent is suggested as a remedy.The second issue in the dissertation is a study of thickness deformation of the viscoelastic material in CLD treatments. The first goal is to confirm experimentally that thickness deformation exists. The experimental results showed that our experimental method is able to measure thickness deformation as low as 0.5%. We found that thickness deformation increases as thickness of the viscoelastic layer increases. In addition, partial treatments tend to have larger thickness deformation than full treatments. The second goal is to evaluate the accuracy of a mathematical model developed by Miles and Reinhall that accounts for thickness deformation. Comparisons of the numerical results with the experimental measurements indicated that consideration of thickness deformation can improve the accuracy of existing constrained layer damping models when the thickness deformation is noticeable.In the third issue, with a goal of reducing the weight penalty of CLD treatments, two feasibility studies were conducted to investigate the use of microcelullar foam as damping and standoff layer material. Modified polyethylene teraphthalate (PETG) microcellular foam was used in our studies. Our results show that the loss factor of PETG foam with densities from 42 kg/m 3 to 240 kg/m3 is in the range of 2% to 8%. In addition, use of microcellular foam as standoff layer can reduce vibration amplitude up to 80% with only a 2% to 3% weight penalty.
- Mechanical engineering