In this research, we study the topological effect in both 1D and 2D metastructures consisting of chiral-shape prismatic tensegrity units. The unique axial-torsional motion introduces coupled local resonance which produces the needed Dirac degeneracy for the topological states at low frequency. A multi-resonantor design is also proposed for additional Dirac cones which can be opened for mutiple non-trivial bandgaps. Further research shows that topological phase transition can be also achieved through the adjustment of chirality. Finally, prestress control on the topological interface states is studied in both 1D and 2D cases.
Lightweight engineering structures often suffer from environmental vibration that is difficult to suppress due to its low frequency and multiple polarizations. The emerging field of metastructure offers a practical solution for the lowfrequency vibration reduction without introducing extra isolators that have gigantic size and heavy weight. In this research, 3D printed subwavelength-scale microstructures are embedded into a honeycomb structure to form a lightweight metastructure which can suppress vibrations with different polarizations at targeted frequencies. Moreover, by simply rotating the fabricated resonators from horizontal embedment into vertical embedment, the bandgaps as well as the vibration isolations can be easily switched for different vibration sources. The multi-polarization vibration suspensions have also been demonstrated with strategically positioned resonators following interval and segment arrangements. Finally, metastructures with quasi-zero dynamic stiffness are designed to achieve the ultra-low frequency vibration isolation while maintaining their lightweight.
In this presentation, a lightweight metastructure is designed based on the prismatic tensegrity structure which enables uniquely coupled compressional and torsional waves. A prismatic tensegrity structure consists of elastic bars and cables with pre-stress to provide its stiffness and therefore, has very high strength-to-weight ratio. A theoretical model with coupled compressional-torsional stiffness matrix is developed to study the band structure of the proposed metastructure. Microstructure designs based on both Bragg scattering and local resonance mechanism are investigated for vibration isolations in different targeted frequency ranges. It is noticed that unit cell with opposite chirality can lead to broadband isolation for both compressional and torsional vibrations. Interesting wave mode mixing and selective wave mode transmission phenomena are also studied based on the proposed theoretical model. Moreover, tunable wave propagations and vibration suspension are achieved by two approaches: (i) harnessing the geometrically nonlinear deformation of the periodical tensegrity prisms under global torsional or/and compressional loads to achieve large-range and coarse adjustment of the band structure; (ii) modifying the pre-stress in the tension cables with active components, such as hydraulic actuators, for small-range and fine adjustment of the band structure. The proposed tensegrity metastructure could be useful for various engineering applications in the fields of space and civil engineering where high strength-to-weight ratio as well as broadband vibration suspension are in a high demand.
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