Type of Document Dissertation Author Austin, Eric Michael Author's Email Address ema@clemson.edu URN etd-101898-162311 Title Influences of Higher Order Modeling Techniques on the Analysis of Layered Viscoelastic Damping Treatments Degree PhD Department Engineering Mechanics Advisory Committee

Advisor Name Title Inman, Daniel J. Committee Chair Batra, Romesh C. Committee Member Dillard, David A. Committee Member Hendricks, Scott L. Committee Member Saunders, William R. Committee Member Keywords

- Damping
- Viscoelasticity
- Sandwich Beams
Date of Defense 1998-11-13 Availability unrestricted AbstractMuch of the work done on active and passive constrained layer beams is done withmathematical models proposed by Kerwin and extended by

DiTaranto, Mead and Markus, and others. The mathematics proposed by these early

researchers was tailored to fit the damping treatments in use at that time: thin foil

damping tapes applied to panels for noise reduction. A key assumption was that all layers had identical transverse displacements. While these assumptions are

reasonable when the core layer, normally a soft viscoelastic material(VEM), is thin and

the constraining layer is weak in bending, there are many situations in

industry and in the literature where the ``Mead and Markus'' (MM) assumptions should be

questioned. An important consequence of the MM modeling assumptions is that the strain

energy in the VEM core is dominated by shear strain, and this in turn means that only the shear modulus is of primary importance. This is fortunate since only the shear modulus is

available to engineers for viscoelastic materials used for layered damping treatments. It

is a common practice in industry and academia to simply make an educated guess of the

value of Poisson's ratio. It is shown in the dissertation that this can result in

erroneous predictions of damping, particularly in partial-coverage configurations. Finite

element analysis is used to model both the MM assumptions and a less-restrictive approach

commonly used in industry. Predictions of damping from these models are compared against

models with elements from C0 elements and a C1-capable element that

matches tractions at material interfaces. It is shown that the time-honored modal strain

energy method is a good indicator of modeling accuracy. To assess the effects of the MM

assumptions on an active PZT used as a constraining layer, closed-loop damping versus gain

is determined using both the MM and higher order elements. For these analyses, the

time-dependent properties of the viscoelastic material are represented by a Maxwell model

using internal variables. Finally, the basic MM premise that all

layers share the same transverse displacement is disproved by experiment.

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