Mechanical Response Of Origami-inspired Foldcore Under Quasi-Static Impact

Sandwich structures are widely used in the field of aerospace and transportation.The aircraft usually works in moist environments,and the sealed hexagonal honeycomb core prevents the condensed moisture from being discharged,which greatly reduces the mechanical properties of the honeycomb structure over a long period.Recently origami-inspired foldcore has been widely studied due to the the existence of open channels which can avoid the problem of moisture accumulation.In addition,it also greatly reduces manufacturing costs by folding sheet material into a three-dimensional structure.However,origami foldcores usually possess inferior energy absorption under compression load.Therefore,avoiding moisture accumulation and improving the energy absorption of foldcore are the ongoing challenges.This thesis provides the possibility to solve the above-mentioned problems by studying the energy absorption characteristics of new foldcores.First,this thesis analyzes the geometry of pyramid foldcore and proves the existence of open ventilation channels.The mechanical performance of the pyramid foldcore subjected to quasi-static compression and shear,respectively,have been studied experimentally,numerically,and analytically.The deformation mechanism of the pyramid foldcore in each loading scenario has been revealed,and the effects of geometric parameters on mechanical properties have been obtained through parametric analysis.It is found that the deformation mode of foldcores would not change within the proposed parameter range.Moreover,a theoretical model has been established to estimate the shear energy absorption of the foldcore.In comparison with the commonly adopted square honeycomb,Miura-ori,and Eggbox foldcores,the compressive energy absorption of the pyramid foldcore has been increased by 73%,342%,and 130%,respectively.Upon shear loading,the shear energy absorption of pyramid foldcore has been increased by 34% and 2483%,respectively,compared to the Miura-ori and Eggbox.and has been decreased by 11%,compared to the square honeycomb.The mechanical properties of the three-dimensional graded Miura-ori foldcore are studied in the second part of this thesis.Firstly,this thesis analyzes and calculates its geometry,base area,and relative density and then studies the effect of parameter on the mechanical properties of foldcore.When the foldcore is compressed in the x-direction,the existence of x-directional and z-directional gradient tends to increase the energy absorption of structure.When the foldcore is compressed in the z-direction,the existence of x-directional gradient tends to reduce the energy absorption of structure.However,the existence of z-directional gradient tends to increase the energy absorption.Comparing with the uniform Miura-ori,the model of optimal parameter can increase the energy absorption by 130%.In conclusion,the pyramid foldcore possesses high energy-absorption capacity under compressive and shear loads.The three-dimensional gradient Miura-ori foldcore can not only achieve gradient stiffness,but also possess high energy-absorption capacity.Therefore,two types of foldcores analyzed in this thesis have huge potential of application in structural core.