A COMPARISON OF FINITE-ELEMENT AND TEST-RESULTS ON THE DYNAMIC CHARACTERISTICS OF BUTTED AND OVERLAPPED PLY LAMINATED CYLINDERS

Numerical and experimental tests were performed on three thin-wall car bon fabric/epoxy cylinders with end flanges, and their vibration chara cteristics were compared. Two different laminates with [(0 degrees)],- 2 ply and [(0 degrees)(3)-3 ply configurations were used. All cylinder s were fabricated using four gore sections per ply. One of the two 3-p ly configurations was fabricated with the gore sections butted togethe r, and the other with the sections overlapped approximately 6 mm. Ther e was very little difference in the natural frequencies from tests wit h butted or overlapped ply joints. However, there was a 1-20% differen ce in natural frequencies between the finite element analysis (FEA) an d 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 m m thick PTFE/copper substrate adhesively bonded to the outside. In thi s configuration there was approximately a 7% difference in natural fre quencies between the FEA and test results. The effect of the added mas s of the substrate in the test samples had a greater influence on the modal analysis than the assumption of a continuum at the overlapped pl y joints. The mode shapes for each of the cylinders were comparable fo r all configurations tested. Damping increased by 12-38% over most of the frequency range for the 3-ply overlapped compared to the butted pl y joint configuration. Damping in the 2-ply overlapped joint cylinder with PTFE/copper substrate showed a 48-93% (depending on frequency) in crease over that of the 3-ply overlapped joint cylinder. An increase i n damping for both 3-ply configurations and the 2-ply configuration wa s attributed to increased matrix shearing as a result of changes in mo de shape, increased warping with mode shape, and the resultant increas e in internal strain.