Doctoral Dissertations

Date of Award

12-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Grzegorz Kawiecki

Abstract

The primary objective of this study is to develop a more accurate research and design tool than those in the currently available literature for active constrained layer treatments applied in bending. A finite element model is presented that extends current finite element model for Euler-Bernoulli beams with segmented active constrained layer damping treatments towards a more physically motivated model. Active Constrained layer damping utilizes modern piezoelectric materials as the constraining layer for these types of damping treatments. Preliminary studies have confirmed that strains in the bonding layers can have a significant effect on damping ratios at modal frequencies, especially when relatively thin compliant piezo materials are used for constraining layers. Previous researchers that have developed three layer finite element models assumed perfect no-slip adhesion between adjacent surfaces of the beam,viscoelastic layer, and constraining layer or have merged the bonding layers(using materials of similar stiffness) with the base beam and constraining layer. Incertain instances this can contribute to reduced accuracy when predicting damping. In This study, a five layer beam element has been developed that models bonding layer strain energy in the two bonding layers for a structure treated with constrained layer damping.The new finite element presented here more precisely models the physical nature of a beam with a constrained layer damping treatment regardless of the relative stiffness of the chosen materials. The capability to model partial or full coverage and to also do mesh convergence studies are incorporated.The effectiveness of the finite element model is validated experimentally for both active and passive constraining layers. The damping is represented using an elastic displacement fields(ADF)to model the frequency dependent stiffness and damping properties in viscoelastic materials as presented by Lesieutre and Bianchini[1995]. Frequency dependence is useful when comparing various damping treatments that alter modal frequencies to some degree. The finite element model is then used to demonstrate damping performance sensitivity on various parameters for low frequency fundamental mode vibration of a cantilever beam.The parameters investigated were upper bonding layer stiffness, active constraining layer stiffness, segment length, and viscoelastic layer thickness. In addition, damping performance trends were also predicted for variations in the derivative and proportional control feedback gains. Thisstudy showed all of these parameters can affect active constrained layer damping performance significantly and that bonding layer stiffness is significant when using relatively compliant active constraining layer materials like piezo film. In addition,for a given beam design with specified active constrained layer and viscoelastic layer thicknesses, an optimum number of segments and an optimum segment length exist that results in best damping performance.

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