Study On Dynamic Crushing Performances Of Auxetic Cellular Materials Under Microstructure Control

Due to their unique large deformation characteristics,excellent designability and potential multifunctional integrated advantages,auxetic cellular materials have huge application potential in lightweight design of crashworthiness structures and adjustable energy absorption.With the further research on the impact dynamic behavior of auxetic cellular materials,it is found that cellular structures still have shortcomings in adapting to the local impact of modern upscale equipment,safety protection under complex service environments and dynamic behavior control strategies.Therefore,it is significant to study the controllability of the dynamic behavior with auxetic cellular materials under impact load.From the perspective of impact dynamics,a combination of theoretical analysis and numerical simulation is applied to explore the microstructure failure mechanism and dynamic performance adjustable design of periodic auxetic cellular structures under impact loads.The specific research content is followed as:(1)From the bionic structure design,three kinds of bio-inspired hierarchical honeycombs are established by introducing an arched structure at the traditional square honeycomb node.The non-linear dynamic finite element method is applied to investigate the dynamic crushing performances of the bio-inspired hierarchical honeycombs under in-plane impact.The influence of different cell topology and multi-material layout on crushing load uniformity and specific energy absorption is discussed in detail.The research results show that impact velocity will affect the negative Poisson's ratio effect of the re-entrant hierarchical honeycomb.Reasonable selection of cell topology and multi-material layout can effectively control and improve crushing load uniformity and specific energy absorption.In addition,the semi-empirical formula for the plateau stress of different bio-inspired hierarchical honeycombs are given,which can accurately predict the dynamic bearing capacity of the bio-inspired hierarchical honeycomb during the crushing.(2)According to the concept of functional gradient,a hierarchical gradient auxetic honeycomb model is proposed.The influence of cell microtopology structure and gradient arrangement on the dynamic deformation behavior,crushing load uniformity and energy absorption capacity of the gradient negative Poisson's ratio honeycombs under in-plane impact is studied.It is found that the dynamic Poisson's ratio of the gradient honeycomb depends on the impact velocity and the topology of honeycomb layer.Reasonable selection of the arrangement with the honeycomb layer can significantly improve the dynamic plateau stress and crushing load uniformity of the gradient auxetic honeycomb,and control the specific energy absorption of the auxetic structure.(3)Based on the design concept of mechanical metamaterials,combined with microstructure failure mechanism and impact performance enhancement mechanism for materials,the in-plane reinforced negative Poisson's ratio structure is proposed.By establishing an in-plane reinforced composite honeycomb model with the same relative density,the effects of gradient arrangement and microstructure parameters on the average dynamic Poisson's ratio,deformation mode and crushing load uniformity with composite honeycombs are discussed.The deformation mode and Poisson's ratio of the in-plane reinforced composite honeycombs are related to the inclination angle,honeycomb layer arrangement and impact velocity.Placing the honeycomb layer with a small inclination angle at the impact end can reduce the peak stress of the composite honeycomb,enhance the impact load efficiency,and then improve the crushing load uniformity.Furthermore,a semi-empirical formula for the plateau stress of the in-plane reinforced composite honeycomb is also given,and the theoretical calculation results are in good agreement with the finite element results.