Numerical Simulation And Experimental Study Of The Mechanical Properties Of Three-dimensional Re-entrant NPR Honeycombs Under Compression

Negative Poisson’s Ratio honeycomb(NPRH)has special mechanical properties and is a new type of lightweight micro-structure material with broad application prospects.As a kind of NPRH,three-dimensional re-entrant honeycomb(3D-RH)has better performance than the traditional two-dimensional re-entrant honeycomb(2D-RH).With the continuous improvement of processing technology,the application prospect of 3D-RH is becoming more and more broad.Based on experiments,numerical simulations and theoretical analysis,this paper systematically analyzed the mechanical properties and deformation modes of the3D-RH under compression load.Besides,the influence of compression speed on the 3D-RH deformation modes and the influence of geometry parameters on its basic mechanical properties were studied.Firstly,3D-RH specimen were prepared manually,and quasi-static compression and dynamic compression experiments were carried out respectively.Then,3D-RH numerical simulation models were established based on the finite element method.It was found that the numerical results showed good consistency with the experimental results,which demonstrated the validity and accuracy of the established numerical models.Secondly,based on the theory of material mechanics,the theoretical solutions of the elastic modulus,Poisson’s ratio and the quasi-static compression strength of 3D-RH were derived respectively.The relative error between the theoretical solutions and the numerical solutions of the above basic mechanical properties were within 6%,which verified the accuracy of the theoretical analysis.Then,the influence of dynamic compression speed on the deformation modes of the3D-RH was studied.The results showed that with the compression speed increasing,the NPR effect of the 3D-RH was gradually weakening.Besides,the deformation modes also tent to collapse in the way of layer-by-layer.Referring to the deformation modes of the 3D-RH under dynamic compression obtained by numerical simulations,the theoretical solution of its dynamic compression strength was derived;and the relative error between them was less than7.5%,which verified the accuracy of the theoretical solution.The research results on the impact energy absorption characteristics of the 3D-RH showed that its specific energy absorption was only related to the compression speed,and had nothing to do with the geometry parameters of the 3D-RH.Finally,the influence of the geometry parameters of the 3D-RH structure on its mechanical properties was studied via numerical simulation models.The results showed that with the length of the oblique cell wall reducing or the thickness of the cell wall increasing the elastic modulus of the honeycomb material can significantly increase.Within a certain range,the re-entrant angle became larger,the NPR effect was more significant.The influence of the cell wall thickness on quasi-static compression strength and dynamic compression strength was most significant.The thicker cell wall would lead to the higher compression strength.In addition,the dynamic compression strength of the 3D-RH increased with the increase of the compression speed,and the stress strengthening effect of the structure became more significant with the decrease of the re-entrant angle or the thickness of the cell wall.