Structural Design And Mechanical Behaviors Of Negative Poisson’s Ratio Metamaterials

Negative Poisson’s ratio materials are mechanical metamaterials with high strength and stiffness that expand in the transverse direction when subjected to longitudinal tension and contract in the transverse direction when subjected to longitudinal compression.Due to its excellent mechanical properties,negative Poisson’s ratio materials have been widely used in the biomedical,aerospace,automotive and defense industries.In this thesis,twodimensional and three-dimensional negative Poisson’s ratio structures of different cell sizes were designed and prepared using selective laser sintering as a preparation method.The out of plane compression performance of negative Poisson’s ratio structures and their energy absorption characteristics are investigated by a combination of experiments and finite element simulations.The compressive deformation process and damage failure modes of the structure are discussed,and the configuration of the structure is optimized to improve its mechanical properties and energy absorption characteristics.The specific studies are as follows:Analysis of the micromorphology of the parent material powder before and after 3D printing to reveal changes in the state of the parent material and its potential defects,as well as the potential impact it may have on the printed specimen.Surface roughness and interfacial shear strength tests were carried out on specimens prepared by different printing methods to reveal the influence of the printing method on the basic mechanical properties of the specimens.The basic performance parameters of the formed specimens were obtained through tensile testing,and their failure modes and intrinsic damage mechanisms were analyzed based on fracture morphology,providing a basis for subsequent research on the compression performance of negative Poisson’s ratio structures.The two-dimensional inner concave negative Poisson’s ratio structures with different cell dimensions were designed and prepared.Out of plane compression performance tests and finite element simulations were carried out to investigate the effects of geometric parameters such as the internal concave angle of the structure and the thickness of the rod on the compression performance,deformation behavior and its failure mode.The intrinsic mechanism of structural damage evolution is revealed and the compressive energy absorption properties of the structure are characterized.Based on the above research,a twodimensional curved beam structure with negative Poisson’s ratio is proposed by optimizing the configuration of the load-bearing weak region of the structure,and the optimized structure is verified and analyzed.Based on the two-dimensional inner concave negative Poisson’s ratio structure,a threedimensional inner concave negative Poisson’s ratio structure with different cell parameters was designed.Out of plane compression tests and finite element simulations were carried out to investigate the effects of geometric parameters such as the internal concave angle of the structure and the thickness of the bar on the compression performance,deformation behavior and its failure mode.Based on the above research,two improved structures,a threedimensional curved beam negative Poisson’s ratio structure and a three-dimensional curved edge negative Poisson’s ratio structure,were proposed to optimize the configuration of the load-bearing weak region of the structure,and the optimized structures were verified and analyzed.The test results show that the three-dimensional curved edge negative Poisson’s ratio structure has better deformation resistance and energy absorption properties than the three-dimensional curved beam negative Poisson’s ratio structure.