Optimization and uncertainty quantification of multi-dimensional functionally graded plates

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Date
2018
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University of Alabama Libraries
Abstract

Functionally graded structures (FGS) are structures that have varying properties in one or more directions that yield better performance over homogenous structures. The grading is usually considered through the thickness of beams, plates, or shells with different grading profiles. In this work, the design and analysis of multi-dimensional functionally graded nanocomposite structures are of interest with a focus on the material grading in the in-plane directions of plates, and the effect of the uncertainties in the elastic properties on the mechanical performance. The dissertation consists of six chapters; chapter one provides a literature review of the recent developments in the area of functionally graded structures, a brief overview of the properties and modeling of nanocomposites, and the uncertainty quantification of nanocomposites. The second chapter proposes a method for the design of multi-dimensional functionally graded structures based on the polynomial expansion of the volume fraction of the reinforcement. The third chapter extends the proposed method to design complex non-rectangular domains via coordinates transformations, and study the effects of the boundary conditions, loading type, and grading direction. The fourth chapter studies the reliability of in-plane FG plates by considering multiple sources of uncertainties (e.g. reinforcement size, volume fraction, and distribution). The fifth chapter studies the nonlinear dynamic and static responses of the FG plates by considering the post-flutter and the post-buckling behaviors. The sixth and last chapter provides a summary of the work done and the proposed future work. Throughout the dissertation work, the in-plane grading is optimized such that the minimum amount of reinforcement is used to satisfy certain mechanical performance constraints. The in-plane FG clamped plates showed a 45% average saving in the reinforcement amount compared to homogenous plates, while for simply supported plates the saving strongly depends on the problem nature and varies from 4% to 45%. For stiffened plates, the in-plane grading of the stiffeners led to a saving that can reach up to 200%. The reliability analysis showed that both homogenous and FG plates have the same level of uncertainty in the global responses. Also, the non-linear analysis indicated that both plates will in general behave similarly

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Electronic Thesis or Dissertation
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Aerospace engineering
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