Research On Bandgap And Transmission Characteristics Of Metamaterial Sandwich Structures

Lightweight sandwich structures form a class of structural elements of practical importance in various fields of engineering applications due to their superior properties.However,the violent vibration is generated thanks to their low dynamic inertia when these materials are subjected to excitation.The investigations of new methods and theories to solve this contradiction between good mechanical properties and high vibration performance of lightweight sandwich structures become increasingly important.In light of the emerging field of phononic crystals and acoustic metamaterials in recent years,a novelty approach to isolate the vibration of structures precisely in a specific frequency range has been provided.Based on the theories of phononic crystals and acoustic metamaterials,the mechanisms of local resonance are extended to the design of lightweight sandwich structures to achieve vibration reduction and isolation.The main work and research results are as follows:A novel pyramidal truss core metamaterial beam with embedded internal mass-spring resonators is designed and its superior low-frequency vibration insulation performance is investigated.The infinite pyramidal truss core beam is modeled by Timoshenko beam model and the dispersion analysis is conducted to predict the bounds of the bandgap.For a finite pyramidal truss core metamaterial beam with specific boundary conditions,frequency responses of the structure are obtained numerically and experimentally to show the bandgap behavior.The results obtained by the three methods are consistent with each other.From the results,it is seen that the location and width of the bandgap can be selected by tailoring the natural frequency of the resonators,the inclination angle of the truss and the mass ratio of the resonators and face sheets.More numerical examples are further analyzed and it is found that the pyramidal truss core metamaterial beam with multi-frequency resonators can achieve much broader bandgaps than that the original single frequency pyramidal truss core metamaterial beam,although the two systems have the same host beam structure,lattice constant and total resonator masses in each unit cell.A multifunctional metamaterial is proposed for vibration suppression by integrating membrane-mass structures that can be used as locally resonant metastructure into a square honeycomb sandwich structure.The finite element method is employed to calculate the band structure and the transmission spectra.The formation mechanisms of the locally resonant bandgaps are investigated via the analysis of the mode shapes of the membrane-mass resonator and face plate in a unit cell.The effects of the location of the attached mass on the bandgap property and an improved model called bilayer membrane-mass structure are also discussed.Results show that the proposed multifunctional metamaterial exhibits an excellent vibration suppression performance,as well as a significant tunability.Moreover,a specimen of the proposed metamaterial is fabricated and experimental measurements are performed,and the results obtained by experimental measurements are consistent with the numerical predictions before.The metamaterial sandwich structures proposed in this paper are multifunctional metastructure integrating these advantages of lightweight sandwich structures and the acoustic metamaterial,such as being light-weight,having high-strength,vibration suppression,low cost and fast construction.It is hoped that such solutions will have a certain reference value for the application of acoustic metamaterials in the vibration attenuation and sound insulation of lightweight sandwich structures.