Experimental-theoretical investigation of the vibration characteristics of rotating composite box beams

Abstract

This paper presents a theoretical-cum-experimental study of the free vibration characteristics of thin-walled composite box beams with bending-twist and extension-twist coupling under rotating conditions. The governing equations in generalized displacements were derived using a Newtonian approach. The composite structural model in the derivation used a solid-section approach and contained transverse shear-related couplings and appropriate cross-section warping. The free vibration characteristics of composite box beams were determined by the Galerkin method. In order to validate the theory, glass-epoxy, kevlar-epoxy and graphite-epoxy symmetric and antisymmetric box beams were fabricated using an autoclave molding technique, and tested in an in-vacuo rotor test facility for their vibration characteristics. Beam excitation in the rotating condition was effected by means of induced-strai n actuation with the help of piezoceramic bending elements. Strain gages were used to measure the response of the first three modes over a range of rotational speeds up to 1000 rpm. It was determined that the experimental frequencies and mode shapes correlated satisfactorily with the theoretical results. It is shown also that bending-shear coupling influences the flexural vibration frequencies of antisymmetric box beams significantly. Extension-shear coupling, on the other hand, does not influence the flexural-torsion vibration frequencies of symmetric box beams significantly.