Design,Fabrication And Properties Investigation Of Auxetic Metamaterials

Mechanical metamaterials are one of the research hotspots at present.Varies novel phenomena and physical properties have been found in this area recent years.As an important category of mechanical metamaterials,auxetic metamaterials demonstrate negative Poisson's ratio due to the geometry and deformation mechanism of artificially designed microstructures.Thus a series of unique mechanical properties can be realized in this material.The existence of auxetic metamaterials provides a powerful tool for us to manipulate the deformation of material.The research on auxeticity is attracting more and more attention since it has subverted traditional understanding on the shape change of material under stress and brought a series of fancy mechanical effects,making it have wide application perspective,For the moment,auxetic metamaterials can be made by introducing re-entrant structure or rotational structure.This thesis is mainly focused on the study,both theoretically and experimentally,in the design,fabrication and mechanical properties of auxetic metamaterials.We have talked about the design of 3D auxetic metamaterials based on three kinds of models,the fabrication based on 3D printing technology and properties investigation on reversibility,strength and elastic wave propergation.1.Design for three categories of auxetic metamaterials have been analyzed by theory and finite element approach.They are re-entrant structure,chiral structure and rotational rigid structure.Auxetic metamaterial based on 3D modified double arrowhead has been designed and simulated,anisotropic auxetic property has been found and Poisson's ratio reaches-1,1.3D anti-chiral model has been designed base on 2D chiral model,it shows rotational shape change in its microstructure and isotropic auxetic behavior has been found.Its Poisson's ratio can be tuned through changing structural parameters which reaches-0,5 in simulation.3D truss structure base on Ron-Resch origami pattern has been designed for rotational rigid structure,which can show shock and bend resistance.2.Three kinds of primary 3D printing technology has been analyzed,all of them have been used to do fabrication experiments for auxetic metamaterials.For fused deposition method,ABS has been used to fabricate 2D metamaterials.For selective laser sintering/melting,nylon,Sn alloy and titanium have been used to fabricate 3D anti-tetra-chiral auxetic metamaterial.For stereo lithography apparatus,micrometer scale 3D printing system has been used.3D anti-chiral model has been fabricated successfully with 20p,m precision.3.The properties of 3D auxetic metamaterial based on anti-tetra-chiral model has been analyzed by theory,simulation and experiment.Simulation shows that the maximum stress of 3D anti-chiral structure,whose deformation is induced by rotation,is an order of magnitude smaller than traditional re-entrant structure.Mechanical tests demonstrates that nylon and titanium sample have good reversibility(99%)and high strength(12.2MPa)respectively.Analysis for deformation mechanism shows that its reversibility comes from the bending of all beams by rotational deformation,large amount of strain energy can be stored in the beams and release when stress being withdrawn.Poisson's ratio has been tested by digital video extensometer,and nylon sample shows stable auxeticity(-0.44)during compression.We have calculated the phonon band structure of 3D anti-chiral model with different structural parameters,results show wide elastic wave bandgap can be adjusted by changing structural parameters.