Study On Impact Resistance Of Three Dimensional Concave Hexagonal Structure With Negative Poisson's Ratio

Negative Poisson's ratio grid structure has good physical and mechanical properties,and has broad application prospects in vehicle,aerospace,precision manufacturing and other fields,especially its unique expansion performance,which makes it absorb more energy per unit mass under impact,which is of great value for the research of lightweight energy absorbing materials with high impact resistance.In this paper,theoretical analysis,finite element analysis and experimental methods are combined to establish the theoretical model of the relationship between the equivalent mechanical properties,mass specific energy absorption under impact load,equivalent stress,equivalent strain and size parameters of the reinforced concave hexagonal grid structure with negative Poisson's ratio,This is very important for the design of negative Poisson's ratio grid structure.For the concave hexagonal grid structure,adding reinforcing bar can obviously improve the impact resistance of the grid mechanism.In order to establish the relationship between the mesh size parameters and its equivalent mechanical properties,the geometric model of the mesh structure is established,and the expressions between the mesh size parameters and relative density,equivalent elastic modulus,equivalent Poisson's ratio and equivalent plastic collapse are derived theoretically,so as to predict the equivalent mechanical properties of the mesh structure.The finite element analysis software is used to simulate the quasi-static compression and impact of the grid structure,and the correctness of the theoretical expression of the equivalent mechanical properties of the grid structure is verified;Based on the one-dimensional shock wave theory,the expression of the stress-strain curve of the grid structure is derived,and then the expression of its mass specific energy absorption is obtained;The relationship curves of equivalent stress,equivalent strain and specific energy absorption of grid structure are studied,and the energy absorption effect under different conditions is compared.The metal 3D printing technology is used to make the negative Poisson's ratio grid experimental sample,and the quasi-static compression test is carried out.The stress-strain curve of the sample in the compression process is obtained,and the equivalent elastic modulus is calculated to verify the correctness of the simulation model.The axial impact test was carried out to observe the deformation process of the grid structure under the impact load.According to the experimental data,the equivalent stress equivalent strain curves of the grid structure with different sizes and the energy absorbed per unit mass equivalent strain curves were drawn.According to the experimental data,the second-order response surface model is established.The nsgaii algorithm is used to optimize the model to maximize the specific energy absorption and minimize the peak stress.The peak stress and specific energy absorption of the grid structure before and after optimization are compared.