The In-plane Compressive Mechanical Behavior Of Metallic Hierarchical Honeycomb Structure

Porous materials are widely applied to national defense and civil field,such as aeronautics and astronautics,automobile,and protective engineering,duo to its superb properties,for instance,low density,high specific stiffness,strength,impact resistance,soundproof,low thermal conductivity and so on.The natural porous materials have been used for thousands of years,artificial porous metal materials gradually appear in engineering,such as aluminum honeycombs and metal foams,their static and dynamic mechanical properties have been studied thoroughly and extensively.Recently,some researches indicate that a hierarchical porous material formed by introducing a hierarchical structure into a porous material has the advantage of increasing the strength and energy absorption performance of the porous material.Different kinds of hierarchical honeycombs can be formed through appreciate selection and design of its first order structure and second order structure,and different types of combinations show different mechanical properties,so hierarchical honeycombs have a very good designability.In this paper,a self-similar structural design method is used to establish single-layer(SH)and multi-layer(MH)second-order self-similar regular hexagonal honeycomb structures,and their mechanical behavior under in-plane quasi-static and impact loads is investigated by the finite element simulation and theoretical studies,respectively.According to the results of numerical simulation,the deformation mode,plateau stress and energy absorption characteristics were analyzed.Based on their deformation modes at different speeds,the corresponding static and dynamic theoretical models were established,and the deformation mechanisms of single-layer and multi-layer self-similar regular hexagonal honeycomb structures in in-plane compression were analyzed,formula of plastic collapse plateau stresses under different deformation modes are obtained.The results of theoretical analysis are in good agreement with numerical simulations.The results show that the single-layer second-order self-similar regular hexagonal honeycomb structure exhibits a deformation mechanism which includes a first-order cell wall shortening,rotation and second-order cell collapse when compressed in-plane.The research shows that the multilayered second-order self-similar regular hexagonal honeycomb structure has a distinct two-stage characteristic when compressed in a quasi-static plane,its stress-strain curve has two stages.With the increase of impact velocity,the deformation modes of single-layer and multilayer second-order self-similar regular hexagonal honeycomb structures gradually change from quasi-static mode to impact mode.Comparing the plastic collapse stress and the specific energy per unit mass of a traditional regular hexagonal honeycomb structure,a single-layer second-order self-similar regular hexagonal hierarchical honeycomb structure and a multi-layer second-order self-similar regular hexagonal hierarchical honeycomb structure with the same relative density,it is found that the multilayered second-order self-similar positive hexagonal honeycomb structure is superior to the former two,and this advantage decreases with the increase of the impact velocity and the change of the deformation mode.