Fabrication And Properties Of Three-dimensional Anti-chiral Auxetic Metamaterials

In the past 20 years,a new material design concept has been widely concerned by researchers.This new material design method is different from the traditional material design method.It no longer focuses on the components of materials.Instead,it achieves the special properties that the traditional materials do not have through the structural design.This kind of new material is called metamaterials.The concept of metamaterials comes from optics and electromagnetics at first,and then extends to acoustics,thermology and mechanics with further studies.In this paper,we focus on the auxetic mechanical metamaterials.Different from ordinary materials,auxetic metamaterials have negative Poisson's ratio,that is,when they are stretched(compressed)in one direction,they will also expand(contract)in other directions.This unique property comes from the reasonable design of the structure.Generally speaking,the generation of auxetic properties is mainly based on re-entrance structure,chiral structure and rotational rigid structure.In this paper,the two-dimensional anti-chiral auxetic structure is extended to threedimensional through certain rules.It is modeled in Solid Works,and the solid structure is manufactured by 3D printing method.The finite element simulation software COMSOL Multiphysics is used to simulate the mechanical properties,the phononic bandgaps and the transmission spectrum of the structure.In addition,the mechanical and acoustic properties of the solid structure are tested by the mechanical test machine in the laboratory and the transmission spectrum test system built by ourselves,and are verified with the simulation results.It has been proved theoretically and experimentally that the three-dimensional anti-chiral auxetic metamaterial studied in this paper has adjustable negative Poisson's ratio and wide phononic bandgaps,and the phononic bandgaps can be tuned through the entire Brillouin zone under external force,showing adjustable vibration isolation performance.The metamaterial has potential applications in motion protection,vibration isolation,noise reduction,and external force sensing.The specific contents of this paper are as follows:1.The three-dimensional structure is designed by using certain principles on the basis of a kind of two-dimensional anti-chiral metamaterial,and the CAD model is carried out in Solid Works.Three structural parameters and two dimensionless parameters are introduced to characterize the design of the three-dimensional structure.Through 3D printing technology,the solid model is made.We have manufactured samples with high precision and small size,and samples with low precision and large size to meet the needs of different tests.Finally,in order to realize the remote application of force and control of the three-dimensional structure,we worked together with other researchers and synthesized a kind of magnetic photopolymer resin,and three-dimensional samples with magnetism are manufactured through 3D printing.2.The mechanical simulation and test of the three-dimensional anti-chiral auxetic metamaterial are carried out by Shimadzu universal test machine and COMSOL Multiphysics.The results show that negative Poisson's ratio results from the unique deformation mode of the structure under external force.With different structural parameters,the Poisson's ratio can change from-0.45 to 0.35.This means we can use different parameters to meet different application requirements.In addition,we also study the static and dynamic mechanical properties of the structure.3.In order to study the acoustic properties of the three-dimensional anti-chiral auxetic structure,we study the vibration isolation and noise reduction properties of the structure from two aspects of phononic bandgap and transmission spectrum.Finite element simulations and experiments are carried out for double check of the results.Theoretical and experimental results show that the structure has wide phononic bandgaps,and the acoustic waves whose frequency are in the bandgap region can be effectively absorbed by the structure.In addition,when the structure is subjected to external forces,the boundary of the phononic bandgap will shift downwards or upwards.Because the structure has negative Poisson's ratio,the variation is through all high symmetry points in the Brillouin zone,resulting in a full bandgap tuning.The reason of bandgap shifting under external force is explained by the analysis of vibration modes of the bandgap boundaries.The tunable wide phononic bandgaps of the three-dimensional anti-chiral auxetic structure make it suitable for applications like vibration isolation and noise reduction.