THE NATURAL FREQUENCIES OF ROTATING COMPOSITE BEAMS WITH TIP SWEEP

This paper presents an experimental-theoretical investigation of the i nfluence of tip sweep on the natural frequencies of rotating aluminum and composite solid-section beams. An in-vacuo rotor test facility was used to test the beams for their vibration characteristics. Induced-s train actuation via piezoceramic elements was used to excite the beams , and strain gauges were used to measure the response of the beams. Th e theoretical frequencies were calculated using a finite-element struc tural model in which the beam had one elastic axis for the straight po rtion and another elastic axis for the swept portion. Nonlinear transf ormation relations were used to connect the elastic axes of the straig ht and swept segments of the beam. Natural frequencies of the beams we re obtained by carrying out Linearized free vibration analysis about t heir deformed states. For better accuracy in the prediction of these f requencies, graded finite-element mesh with finer mesh at the junction of straight and swept segments of the beam was used. Good correlation between experiment and theory was achieved for these beams. Modeling the sweep as an offset of the center of gravity from the assumed strai ght elastic axis was found to be inadequate for predicting the natural frequencies of swept tip beams.