Vibration of Cantilevered Graphite/Epoxy Plates With Bending-Torsion Coupling

The effects of laminate unbalance on the natural frequencies and mode shapes of cantilevered Graphite/Epoxy plates with bending-torsion stiffness coupling has been examined. Unbalanced laminates of the form [θ ₂ /0] _s were studied. A Rayleigh-Ritz analysis was performed to determine the sensitivity of the accurate prediction of the lowest three natural fre quencies to the choice of assumed mode shapes. To serve as a reference, a finite element analysis was performed, using a general anisotropic plate element, and a series of experiments were performed. The results showed that five modes, two bending, two torsional and one chordwise, were required in the Rayleigh-Ritz formulation to determine the first three modes accurately. The presence of chordwise curvature in the torsion modes, even for plates with high aspect ratio, has a significant effect on the results and must be included in the model. Plates with significant bending- torsion coupling also require a second torsion mode to obtain a reasonable estimate of the second bending mode.