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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A theoretical and experimental study of modal interactions in metallic and laminated composite plates

Oh, Kyoyul 14 August 2006 (has links)
This dissertation focuses on nonlinear modal interactions in plates. Our first investigation involved the activation of a two-to-one internal resonance in the response of a metallic cantilever plate. Although the plate was excited around the frequency of its second bending mode, its response contained a contribution from its first torsional mode. The frequency ratio between the bending and torsional modes was nearly two-to-one. Next, we investigated the energy transfer from high-frequency to low-frequency modes in a cantilever graphite-epoxy composite plate (90/30/ — 30/ — 30/30/90)<sub>s</sub>. The plate was excited around the natural frequency of its seventh (third torsional) mode. For some excitation amplitudes and frequencies, we observed the activation of a low-frequency (first bending) mode accompanied by an amplitude and phase modulation of the seventh mode. We studied combination resonances in the responses of cantilever composite plates with the layups (90/30/ — 30/ — 30/30/90)<sub>s</sub> and (—75/75/75/ — 75/75/ — 75)<sub>s</sub> to harmonic base excitations. We activated the combination resonance f<sub>e</sub>≈ ω₂ + ω₇ in the (90/30/ — 30/ — 30/30/90)<sub>s</sub> plate, where the w; are the natural frequencies of the plate and f<sub>e<sub> is the excitation frequency. In the (—75/75/75/ — 75/75/ — 75)<sub>s</sub> plate, we activated the external combination resonance f<sub>e<sub>≈ 1/2(ω₂+ω₅) and the combination internal resonance f<sub>e</sub>≈1/2(ω₂+ω₁₃) ≈ ω₈. We carried out an experimental-modal analysis (EMA) of a nonclassically supported plate with and without a constrained-layer damping (CLD) patch attached on its upper left-hand side surface. The natural frequencies and mode shapes were used to ascertain the effect of the CLD patch. / Ph. D.

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