Date of Award

6-1994

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Anthony N. Palazotto, PhD

Abstract

An analytical study is performed to determine the dynamic response, natural frequencies and mode shapes, of deep composite cylindrical shells, including the effect of through the thickness shear strain. The DSHELL finite element program is used to predict the first four natural frequencies and the results are compared to a reference using the Galerkin technique. The program was extended to problems considering simply supported-free boundary conditions. As is well know, the free boundary is rather difficult to represent using the Galerkin technique approach. The mode shapes are created by plotting a surface-contour plot of the eigenvector output from DSHELL.

A linear, free vibration analysis was performed on two composite panels in which damping effects were assumed negligible. The analyzed panels are made of graphite/epoxy (Gr/Ep) material, having different ply orientations. The first panel, used as a baseline in this study, has an arclength, longitudinal length, and radius of curvature of 12 inches, 11 inches, and 12 inches respectively. A [0°/-45°/+45°/90°]s ply orientation under the simply supported-free boundary condition was considered. Comparisons between this baseline panel, using DSHELL, with previous holographic experimentation and analytical studies ( STAGSC- 1 finite element program was previously incorporated ) were found to correlate well. The percent difference was observed to be less than 8% in all cases. Also, it was found that accurate modeling of the composite shell panel was dictated by the natural frequencies and mode shapes. From this study, four nodes have to be positioned per each half sine wave formed in the eigenvectors.

For the second panel, the curvature and the span to thickness ratio were varied in order to measure effects on two ply orientations, [0°/90°]s and [-45°/+45°]s, under two boundary conditions, all edges simply supported and simply supported-free. The result showed that, as the shell becomes deeper, the frequency becomes smaller.

Also, findings show that as curvature increases, the natural frequencies for both laminates increases. The effect of increasing the thickness was more evident at the shallower end of the composite shell. The shear effect was evident for small values of span to thickness ratios and large curvature under the two boundary conditions studied. The percent difference between DSHELL and the Galerkin technique was generally less than 10% in all cases compared. For this study, DSHELL proved to be a very useful engineering tool.

AFIT Designator

AFIT-GAE-ENY-94J-2

DTIC Accession Number

ADA280689

Comments

The author's Vita page is omitted.

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