VIBRATION CHARACTERISTICS OF COMPOSITE I-BEAMS WITH ELASTIC COUPLINGS UNDER ROTATION

This paper presents a free vibration analysis of composite I-beams with couplings under rotating environments. A linear analysis based upon Vlasov theory was developed to obtain coupled flap-lag-torsion equations of motion for I-beams made out of general composite laminates. Constrained warping and transverse shear effects were included. These equations were solved using Galerkin’s method. Significant influence of constrained warping and bending-torsion coupling on natural frequencies was observed. In order to provide a selective validation of the theory, graphite-epoxy and kevlar-epoxy symmetric I-beams were fabricated using an autoclave molding technique and tested in an in-vacuo rotor test facility for their vibration characteristics. Induced-strain actuation with the help of piezo-ceramic elements was used to excite the rotating I-beams. Strain gages were used to measure the response of these beams over a range of rotational speeds up to 1000 RPM. Good correlation between theory and experiment was achieved. A 1200 percent increase in torsional frequency due to constrained warping occurs for graphite-epoxy beams with slenderness ratio of 18.