Design And Mechanical Property Of Compression-rotation Threedimensional Negative Poisson’s Ratio Structure

Materials with Negative Poisson’s ratio(NPR)are,usually periodic arranged structures,a kind of mechanical metamaterials possessing counterintuitive deformation behavior.They contract under uniaxial compression and expand under uniaxial tension,which is quite a contrast to conventional materials.Because of the unique deformation behavior,metamaterials with NPR have many excellent mechanical properties that conventional materials do not possess,such as better compressive strength,fracture toughness and energy absorption capacity,which make them the research hotspot for many domestic and foreign researchers.Most of the research work at present focuses on two-dimensional NPR metamaterials and the three-dimensional NPR metamaterials rarely found in the literature are mainly built by rotating the unit cell in two-dimensional NPR metamaterials out of plane.Besides,little research was reported on three-dimensional NPR metamaterials with novel unit cell structures.In this paper,a family of compression-rotation three-dimensional NPR metamaterials are designed based on the cross chiral NPR honeycomb,and one representative structure of them is selected for systematic study.The main results achieved in this thesis work are as follows:Taking the two-dimensional NPR metamaterial consisting of a cross chiral honeycomb as the research object,the theoretical formulas for its effective elastic modulus and Poisson’s ratio are derived.Then the influence of honeycomb geometric parameters on the effective elastic constants is analyzed via finite element simulation.The study shows the difference between the results from theoretical formula and those from finite element simulation is small,which verifies the correctness of the theoretical formulas.Based on the rotation deformation mechanism of the cross chiral NPR honeycomb,the three-dimensional NPR metamaterials with a family of compressionrotation unit cells constructed by vertically combining structures in different forms of cross chirality are designed.The theoretical formulas for effective elastic constants of the representative structure are derived,and finite element simulation is carried out to analyze the influence of geometric parameters on the effective elastic constants and to verify the theoretical formulas.Then three types of stiffness-reinforced structures for the representative cell structure are designed and their effective elastic modulus and stiffness enhancement efficiency are analyzed.The results show that each structure has its own excellent effect of stiffness enhancement.The impact mechanical properties of the compression-rotation three-dimensional NPR metamaterial are also studied in this work.The deformation mode and negative Poisson’s ratio effect of the structure under low,medium and high velocity impact are studied by means of finite element simulation method.The results show that the lower the impact velocity is,the more obvious the negative Poisson’s ratio effect is,and the deformation is more uniform and sufficient.The densification strain and platform stress of the structure with different relative density under different velocity impact are analyzed,and the corresponding empirical formulas are obtained based on the finite element simulation results.In addition,the energy absorption capacity of the structure is also studied.The compression-rotation three-dimensional NPR structure designed in this study is shown to have a good negative Poisson’s ratio effect.The work enriched the existing NPR structure configuration and will provide some promising insights into the design of NPR structures in the future.