Influence Of Graded Cell Wall Thicknesses On In-plane Mechanical Properties Of Rhombus Honeycomb

The rhombus honeycombs are a kind of ideal cushioning and impact resistant material that has found the extensive applications in many fields of aerospace,biomedicine,transportation,packaging,construction,military affair and so on.The investigations on the mechanical properties of honeycomb are mainly carried out through the physical experiments or the finite element analysis by the national and international researchers.The factors affecting the performance of honeycomb are configuration parameters and loading conditions.However,the configuration parameters are not taken into consideration on the existing investigation of rhombus honeycombs.On the basis of the existing investigation,this thesis studies the relation among the in-plane mechanical properties of rhombus honeycombs and cell wall thickness,as well as the graded cell wall thicknesses under different impact velocities by numerical simulation.By using the nonlinear finite element software ANSYS/LS-DYNA,the finite element calculation model of rhombus honeycombs based on cells array is established under the dynamic loading.The results are processed and analyzed through the post-processing software LSPREPOSTD.The corresponding deformation modes,stress-strain and energy absorption curves are obtained,and the dynamic plateau stress,the energy absorption per unit mass and other values are gained through the curves are further processed.Finally,by using the data processing software Origin,the relation among these parameters and all factors is drawn.On the basis of the finite element model above,in order to study the influence of cell wall thickness,keeping the rhombus honeycombs in the condition of given expanding angle and uniform cell wall thickness,and the samples with different cell wall thicknesses are numerically calculated at four impact velocities.The deformation mode,dynamic plateau stress,and energyabsorption per unit mass are obtained,and shown in the form of chart.From the calculation results,it is shown that when the cell wall thickness is the same,the impact velocity is bigger or when the impact velocity is the same,the greater the dynamic plateau stress of honeycomb,the stronger the energy absorption capacity with the increase of cell wall thicknesses.In order to study the influence of graded cell wall thicknesses,keeping the rhombus honeycombs in the condition of given expanding angle and cell length,the sample of the finite element model contains 15 layer honeycomb cells,and the cell wall thickness for 3 layer cells is the same,forming a group,and the cell wall thickness changes in gradient.Nine kinds of gradients and four kinds of average cell wall thicknesses are selected in the thesis,the samples with different graded cell wall thicknesses are numerically calculated at four impact velocities,and the calculated results are compared with those of the rhombus honeycombs with cell uniform wall thickness.The graded cell wall thicknesses change the deformation modes of the rhombus honeycombs,and also change the shape of the response curves,which are related to the impact velocity.The stress-strain curve of the rhombus honeycombs with graded cell wall thicknesses shows piecewise deformation characteristics.When the configuration parameters are fixed,under the low velocity impact,the energy absorption per unit mass is only related to the absolute value of the gradient;with the increase of the impact velocity,the energy absorption per unit mass and the plateau stress are related to the absolute value and sign of the gradient;under the high velocity impact,the total energy absorbed per unit mass of the thickness graded honeycombs and the uniform honeycombs at the end of the compaction are close,but it is different in the process of compression,i.e.,the larger the gradient is,the larger the energy absorption per unit mass is.When the average cell wall thickness is fixed,the weaker layer(thin wall)near the impact end and the initial peak stress will be lower.Under the low velocity impact,the gradient has no obvious effect on the compressive stress of the rigid plane at the clamped end.