Study On The Influence Of Cell Wall Material’s Strain Hardening Effect On The In-plane Mechanical Properties Of Honeycombs

Honeycomb material with high specific strength and specific rigidity can absorb a large amount of energy in the event of large deformation,so these excellent mechanical properties make it widely used in aerospace,automotive and packaging engineering fields.A great deal of research about the influence of structural parameters on the mechanical properties of honeycomb has been done by experimental and numerical analysis.However,the literatures on the influence of cell wall material’s mechanical properties on the honeycomb are less.Since the strain hardening of most engineering materials appears after initial yielding,and the existing investigations have demonstrated that the strain hardening effect of the cell wall material influences the mechanical properties of the honeycomb,the concrete influence rules need to be further studied.Finite element method has very mature applications in the numerical study of honeycomb materials which overcomes the shortcomings of experimental methods.The experimental conditions are difficult to be controlled and it is difficult to collect the specimens with different material parameters.In this paper,based on the previous research models,hexagonal and regularly-arranged circular aluminum honeycombs are taken as examples.Then the influences of cell wall material’s strain hardening effect on the deformation mode,plateau stress,and energy absorption of the honeycombs under in-plane compressive loadings are investigated by numerical simulation.In order to quantify the strain hardening effect of the cell wall material,a hardening parameter,E is defined.By keeping the honeycombs’ structural parameters fixed,the cell wall material models are respectively specified as the bilinear isotropic hardening model and the ideal elastic-plastic model with different values of E.And meanwhile changing the loading velocity obtains the influence results of cell wall material’s strain hardening effec under different loading conditions.The uniaxial compression simulation results of the regular hexagonal honeycomb in the in-plane direction,show that the deformation mode in χ1 direction appears“X”shaped,“V”shaped and“I”shaped in turn with the increasing velocities;while the main deformation mode in χ2 direction is "I"shaped.With increasing value of E is from 0 to 0.1,the deformation in-plane mode is firstly shown as the local collaspe,and then the overall homogeneous deformation at the same velocity.The loading speed is lower and the trend is more obvious.Meanwhile,the plateau stress and energy absorption per unit volume of the honeycomb specimens are effectively increased.At high compression velocities,this influence of E is negligible and can be ignored.The static plateau stress is linearly related to E,and the relationship coefficients of the χi and χ2 direction are 0.7275 and 0.4858,respectively.The influence rules of cell wall material’s strain hardening effect on the regularly arranged circular honeycomb are similar to those of the regular hexagonal honeycomb.The quasi-static and transition modes follow the law of“interval deformation”.That is to say,the deformation of a certain cell in the deformation band is different from the four cells’s deformation around it.However,the strain hardening effect of the cell wall material makes the deformation of the honeycomb tend to be homogenized,and the degree of cell collapse in the deformation bands tends to be same,which results in the gradual disappearance of the“interval deformation”.The dynamic deformation mode is“I”shaped,which doesn’t change with increasing values of E.When the loading velocity is low,increasing the values of E improves the plateau stress and energy absorption per unit volume of the circular honeycomb,but the increase of the loading velocity suppresses this increase.In addition,the static plateau stress of the circular honeycomb is in a linear relationship with the value of E,and the relationship coefficient is 0.4282.The influence of the strain hardening effect of the cell wall material on the honeycombs is obvious in the static mode.The increase of loading velocity makes the influence of honeycomb inertia effect increase.In dynamic mode,the enhancement of dynamic plateau stress of honeycomb is caused by the inertia effect and the influence of cell wall material’s strain hardening effect can be neglected.To sum up,in simulating the static mechanical behavior of honeycomb materials,the hardening effect of cell wall material needs to be considered in order to improve the accuracy of the numerical model.