Abstract
Numerical and experimental tests were performed on three thin-wall carbon fabric/epoxy cylinders with end flanges, and their vibration characteristics were compared. Two different laminates with [(O°)]-2 ply and t(0)]3-3 ply configurations were used. All cylinders were fabricated using four gore sections per ply. One of the two 3-ply configurations was fabricated with the gore sections butted together, and the other with the sections overlapped approximately 6 mm. There was very little difference in the natural frequencies from tests with butted or overlapped ply joints. However, there was a 1-20% difference in natural frequencies between the finite element analysis (FEA) and test results for the 3-ply cylinders over the frequency range 88 to 577 Hz. The 2-ply configuration had overlapped ply joints and a 0.50 mm thick PTFE/copper substrate adhesively bonded to the outside. In this configuration there was approximately a 7% difference in natural frequencies between the FEA and test results. The effect of the added mass of the substrate in the test samples had a greater influence on the modal analysis than the assumption of a continuum at the overlapped ply joints. The mode shapes for each of the cylinders were comparable for all configurations tested. Damping increased by 12-38% over most of the frequency range for the 3-ply overlapped compared to the butted ply joint configuration. Damping in the 2-ply overlapped joint cylinder with PTFE/copper substrate showed a 48-93% (depending on frequency) increase over that of the 3-ply overlapped joint cylinder. An increase in damping for both 3-ply configurations and the 2-ply configuration was attributed to increased matrix shearing as a result of changes in mode shape, increased warping with mode shape, and the resultant increase in internal strain.
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