Research On Quasi-Static And Impact Crushing Properties Of Non-Positive Poisson’s Ratio Structures

The metamaterials with non-positive mechanical indexes have attracted great attentions due to the unique mechanical properties,among them non-positive Poisson’s ratio structures have become hot issues in recent years.Non-positive Poisson’s ratio structures generally include negative Poisson’s ratio,zero Poisson’s ratio and tunable Poisson’s ratio structures,the lightweight and fuctional design of strcutures need to be carried out accrding to the specific requirements in enginnering practice.The studies on non-positive Poisson’s ratio structures still have many shortages currently,firstly is the immaturity of theoretical analysis for complex curved negative Poisson’s ratio structures;secondly is the lack of systematic research on design and defoamation modes of 3D zero and tunable Poisson’s ratio structures,especially the inherent relations between structural parameters and mechanical properties;thirdly is the insufficient mechanical performances of negative Poisson’s ratio structures compared with traditional materials due to the large porosity and bending deformation mechanism,so the enhancement of stiffness and strength is worth noting;fourthly is the combination of non-positive Poisson’s ratio structures and other non-positive mechanical indexes to realize multifunctional expansion.In view of these points,this thesis focuses on the quasi-static and impact crushing properties of several nonpositive Poisson’s ratio structures,the main works are as follows:(1)The 2D double-U auxetic honeycomb(2D DUH)structure is proposed based on the straight double arrow-head configuration and the theoretical models are constructed to predict the Young’s modulus and Poisson’s ratio of 2D DUH structure.The experimental and numerical methods are also used to study the quasi-static,dynamic and local impact behaviors and energy absorption performances of 2D DUH structure.The results indicate that the curved configuration can reduce local stress concentration,enhance the auxetic effect and improve mechanical properties.(2)The 3D Aux Hex lattice structure consisting of auxetic re-entrant and hexagonal components is proposed which can achieve zero Poisson’s ratio deformation in tranverse directions.The theoretical models for Young’s modulus,Poisson’s ratio and collapse plateau stress are established.The experimental and numerical methods are also used to study the quasi-static,dynamic crushing behaviors and energy absorption performances of 3D graded Aux Hex structures.The investigations show that the 3D zero Poisson’s ratio structure c an realize enhanced mechanical properties,and the poaitive graded structure presents better energy absorption performances.(3)Based on the Poisson’s ratio complementary mechanism,the 3D hybrid double arrow-head(3D HDA)structure is proposed by combining the convex and concave quadrilateral components.Theoretical models for elastic constants of 3D HDA structure are established,the experimental and numerical are used to study the quasi-static,dynamic crushing behaviors 3D HDA structures and reveal the inherent relations between Poisson’s ratio effect and energy absorption performances.The results indicate that the hybrib structure presents higher energy absorption level when the Poisson’s ratio trends to the value of zero for quasi-static and dynamic lowvelocity crushing;while for the dynamic high-velocity crushing,the influences of Poisson’s ratio effect have almost disappeared..(4)Based on the double arrow-head truss-lattice(DATL)structures,3D auxetic double arrow-head plate-lattice(3D DAPL)structures are proposed by connecting the adjacent nodes with plates to improve the stiffness and strength.The experimental and numerical methods are used to study the quasi-static and dynamic impact crushing properties of 3D DAPL structures.The results indicate that the plate-lattices can improve the stiffness,strength and impact energy absorption performances.(5)Based on the traditional elastic snapping element,the 2D snapping negative Poisson’s ratio and negative stiffness(2D SNPS)structure is proposed.The influences of geometrical parameters on mechanical properties are studied and the effects of snapping behaviors on impact energy aborption are also discussed.The bi-material configuration is introduced into 2D SNPS structure to achieve negative/zero/positive thermal expansion deformation by adjusting the initial stable status of curved beams.