Abstract
Periodic structure is wildly used in metamaterial design in different fields. It has great potential in NDE and SHM fields due to different features, like focusing, bandgap, direction manipulation, and mode selection. First fundamental torsional mode T(0,1) can be focused by adding periodic structure based on phononic crystals and gradient index refraction. In the present study influence of the periodic structure with different element shape on torsional wave is discussed. Eigenfrequency analysis was performed for different configurations of the periodic structure by using the finite element method and floquet boundary condition. Dispersion curves for the torsional wave were obtained as an analysis result. Propagating wave creates a local resonance which leads to the bandgaps between modes and the first torsional mode T(0,1) becomes dispersive. The influence of the configuration on the dispersion curves is shown. Additionally mentioned that negative group velocity can be achieved.
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