Microstructure Effects Of Dynamic Response Cellular Materials With Negative Poisson's Ratio

Negative Poisson's ratio cellular materials have a wide range of application prospects in the fields of national defense and civil use owing to its unique deformation characteristics and potential multifunctional integrated design advantages.How to establish the relationship between the cell micro-topology and its macro-dynamic response characteristics,and realize the multi-objective optimization design of negative Poisson's ratio cellular materials has been one of the frontier issues during the academic researches.In this thesis,the innovative design of the micro-topological structure with negative Poisson's ratio cellular materials is used as the original point for research.Based on the principle of bio-inspired and the concept of Poisson's ratio gradient distribution,the calculation models of negative Poisson's ratio cellular materials with different cell configurations are established.Moreover,effects of micro-structure on impact dynamic response of negative Poisson's ratio cell materials under internal impact load are investigated.The specific research content is followed as:1.Based on the one-dimensional "shock" model,the key evaluation indicators for measuring the dynamic response characteristics of Negative Poisson's ratio cellular materials with different micro-topological structures under in-plane impact loading are obtained.The critical impact velocity,dynamic plateau stress,and densification strain of cell materials are mainly studied.In addition,comprehensive performance indicators such as average dynamic Poisson's ratio and internal energy distribution coefficient are creatively introduced to achieve dynamic characteristics of cell materials comprehensive evaluation.2.Based on the design of re-entrant hexagonal honeycombs and concept of mechanical metamaterials,a bio-inspired negative Poisson's ratio re-entrant arc-shaped honeycomb structure model is proposed to reduce the maximum initial peak stress and maintain good crushing load consistency.The effects of cell micro-topology on the deformation behavior,dynamic impact stress and energy absorption characteristics of re-entrant arc-shaped honeycombs under in-plane impact loading are studied.Under the impact of low and medium velocities,the bio-inspired re-entrant arc-shaped honeycomb also shows a significant negative Poisson's ratio effect.Different from the traditional re-entrant hexagonal honeycomb,the maximum peak stress of the bio-inspired re-entrant arc-shaped honeycomb is obviously reduced at the same impact velocity,and it presents good crushing load consistency.Based on the one-dimensional shock wave theory,empirical formulas for the dynamic plateau stress of bio-inspired re-entrant arc-shaped honeycombs are also given.The theoretical calculation results are in good agreement with the finite element results.3.A energy absorption structure model with composite Poisson's ratio graded honeycomb is proposed.The explicit dynamic finite element method is employed to study the dynamic response characteristics and specific energy absorption.The effects of Poisson's graded distribution with honeycomb structure on macro-deformation,dynamic plateau stress,crushing load consistency and energy absorption capacity under different constant impact velocities are mainly discussed.The research results show that the designed composite Poisson's ratio graded honeycomb can realize the complementary advantages of different Poisson's rat io energy absorption structures.By reasonable selection of the micro-structure and length of each segment,the dynamic plateau stress and crushing load efficiency with the composite Poisson's ratio graded honeycomb structure are significantly improved,and the amplitude of impact stress fluctuations is significantly reduced,which can effectively improve and control the energy absorption efficiency of the honeycomb structure.