Outer Effects On The Bending Vibration Band Gap Of Phononic Crystal Beams

Phononic crystals have vibration band gaps, which make them have numerous engineering application prospects in vibration control. Generally, the band gaps are unchangeable after the structural and material properties of the phononic crystal are determined. It is necessary to develop a new kind of phononic crystals with tunable band gap which would be changing with outer effects, and it will extend the application range of the phononic crystal. In this paper, beams, widely used in the engineering structures, are taken as objects and the phononic crystal beams are designed to research the effects of the outer factors on the bending vibration band-gaps. The effects of twisting moment and magnetic field are involved, which can influence the structural and material properties of phononic crystal.The effects of the twisting moment are researched on the bending vibration band gaps of the phononic crystal beam which composed of steel and epoxy, and three results are gained. Firstly, by the effects of the twisting moment, the vibration in the y direction induces the bend modes in x direction, which induce resonant modes in the band gap. Secondly, for the vibration in the y direction, the main parts of the vibration at the edge frequencies of the band gap are in the y direction, but the main parts of the vibration at the resonant frequencies in the band gap are in the x direction. Finally, the twisting moment makes the angles between the direction of the vibration and the y axis change with frequency. The relative larger phase change appears at the resonant frequency within the band gap. The vibration is in the y direction but the response is in the x direction.A phononic crystal beam is manufactured composed of aluminum and Magneto-Rheological Fluid (MRF). And the effects of the magnetic field are researched on modulating the bending vibration of the beam by experiment. And the dynamics of the beam is simulated with finite element method. The magnetic field's effects are analyzed on beams of different material and structural parameters, such as matrix and scale of bulk of matrix and MRF. It has been found that the rigidity and damping coefficients of the beam increase with the increasing of the intensity of magnetic field. Therefore the beginning frequency of the bending vibration band gaps increase with the increasing of the magnetic field's intensity, which makes the magnetic field effective in restraining the bending vibration. And with the increasing of elastic module of matrix of the phononic crystal beam, the magnetic field's effects on the band gap become more unconspicuous. As well as the magnetic field's effects on the beam would become more distinct as the scale of the bulk of MRF to matrix is increasing.In summary, the band gaps of phononic crystal beams can be modulated effectively by outer twisting moment and magnetic field. And the modulation effects can be optimized by select appropriate material and structural parameters. The research results in this paper are meaningful in application of the phononic crystals in vibration control.