| Metamaterials are novel materials appearing since the 21 st century because of their designability and extraordinary physical properties which are not exhibited by natural materials.Recently,scientists introduced structural buckling behavior into metamaterial design and constructed a new class of mechanical metamaterials with extraordinary properties,namely shape-recoverable variable stiffness metamaterials,which have broad applications in the fields of vibration isolation,noise reduction,and energy absorption.However,the mechanical properties of multistable metamaterial is unique and hard to adjust accurately once fabricated,which can not adapt to the application needs of multiple environments.To overcome the challenge,a modular multistable metamaterial is designed in this thesis,and a regulation mechanism for the mechanical properties is established.The dispersion relation of the modular multistable metamaterial and elastic wave propagation characteristics in it with different configurations are analyzed.The research content is mainly divided into the following parts:(1)The deformation of a curved beam under axial load is systematically investigated and an approximate solution for the deformation path of the curved beam is obtained.Considering the bistable characteristics of the curved beam,the force-displacement relationship of the curved beam after compression-bending deformation is predicted.The influence mechanism of the variation of geometric parameters on the mechanical properties of the curved beam is analyzed,which provides a theoretical basis for the design of multistable metamaterials and the adjustment of their mechanical properties.(2)Drawing on the connection characteristics of "mortise and tenon" structure,a tristable microstructure composed of variable-width bi-beams frame and middle-bar is designed.Based on the variation of force-displacement relationship of the curved beam after compression-bending deformation,the mechanism of regulating the mechanical properties of tristable microstructure by reducing the length of middle-bar is proposed.The effectiveness of the regulation mechanism is verified by theoretical calculation and simulation.(3)In order to match the size or properties for different requirements of applications,the tristable microstructures are modified as basic modules and assembled into modular multistable metamaterials.By virtue of 3D printing technology,the multistable metamaterials of three rows and five columns are fabricated and tensile tests are carried out.The regulable multistable mechanical properties of the structure are verified by simulation.The results show that the modular multistable metamaterial have seven stable states.By shortening the middle-bar by 8.16%,the threshold of negative stiffness and the total displacement can be effectively increased by 219% and 209%,respectively.(4)For the modular multistable metamaterial,the dispersion relation with different middle-bar lengths and different stable states are analyzed by finite element method.The influence of elastic wave transmission characteristics in finite period structures by different middle-bar lengths and stable states is investigated.The results show that complete band gap and local directional band gap exist in structurally modular multistable supermaterials.The differences of the midde-bar length and stable states have a weak influence on the complete band gaps,but the local band gaps is significantly affected by the two factors. |
