A Study on Flexural-Torsion Coupling Vibration of Fiber Composite Beams

It is shown that the principal axis of elasticity (abbreviated to PAE) can be rotated from the structural axis by giving a specific fiber orientation or stacking sequence of a fiber composite beam. The theoretical results for PAE obtained by the use of the laminated plate theory agree with the experimental results for PAE of GFRP and CFRP laminated cantilever beams in the static flexural and torsional tests. It is illustrated from the flexural-torsion analysis and the static test that the angle of torsion at the free end of the beam is zero when the center of gravity of the beam with an eccentric mass coincides with the PAE. The natural frequencies of a beam involving an eccentric mass can be predicted by solving the characteristic equation of a simplified vibration equation of two degree-of-freedom system. The flexural-torsion coupling effects are discussed by using the coupling coefficient in the equation. Solving the vibration equation subjected to the sinusoidal excitation, it is proved that the torsional amplitude of the free end of the beam is zero when the center of gravity is on the PAE. The experimental results of the sinusoidal excitation test agree with the analytical solution of the vibration equation.