Experimental Study On Anti-impact Property Of Star-shaped Metamaterial Based On 3D Metal Printing

Negative Poisson’s ratio material is a metamaterial with special mechanical properties.Usually designed as a multi-cell structure,the multi-cell material has the advantages of lightweight,impact resistance and energy absorption.Negative Poisson’s ratio effect of transverse contraction can be produced under axial compressive load.This special deformation ability and light weight and high performance make the negative Poisson’s ratio polycellular material have broad application prospects in engineering field.Because of the complex internal structure of the negative Poisson’s ratio polycellular material,it is difficult to achieve the machining accuracy by traditional machining methods.At present,many researches only stay in the stage of finite element simulation.A new type of three-dimensional negative Poisson’s ratio star-shaped metamaterial is proposed in this paper.The specimens are prepared by 3D metal printing and the dynamic impact test is carried out.At the same time,the effects of different impact speeds and design parameters on the deformation,stress-strain relationship and energy absorption characteristics of the model are investigated by combining the finite element numerical simulation.Specific research contents are as follows:(1)A three-dimensional negative Poisson’s ratio star structure design method is proposed.Based on the traditional two-dimensional negative Poisson’s ratio star-shaped structure cell,the lateral connecting rod is added to improve the stiffness.According to the deformation characteristics of negative Poisson’s ratio structure such as concave deformation and rotational deformation,a three-dimensional negative Poisson’s ratio star-shaped structure cell is designed.After arrangement and combination of three-dimensional negative Poisson’s ratio star structure cell,the three-dimensional negative Poisson’s ratio star structure overall model with stiffness optimization is obtained.Five different structure size parameter models are designed by changing the spacing between the inner concave angles and the diameter of connecting rods.(2)Dynamic impact tests of three-dimensional negative Poisson’s ratio star-shaped structure metamaterial.Fifteen three-dimensional negative Poisson’s ratio star-shaped metamaterial specimens were fabricated based on the 3D metal printing technology of selected laser melting(SLM).Drop hammer impact tests at different speeds were carried out,and stressstrain relationship and energy absorption characteristics during impact were analyzed with specimen deformation.The stress change process of three-dimensional negative Poisson’s ratio star-shaped metamaterial under impact load is divided into three stages: quasi-elastic stage,stress plateau stage,stress growth and compaction stage.The impact test results show that specimens with large spacing between the concave corners under low speed impact will produce more plastic deformation,which can effectively absorb impact kinetic energy,but are prone to transverse shear deformation.For specimens with small spacing between the concave corners,the negative Poisson’s ratio effect is obvious at the beginning of impact,and the overall structural stability is stronger under impact load.(3)Parametric analysis of impact resistance of three-dimensional negative Poisson’s ratio star-shaped metamaterials.Three-dimensional negative Poisson’s ratio star-shaped structure metamaterial numerical simulation model was established by ABAQUS finite element software to simulate dynamic impact at different speeds.Based on the impact test results,the deformation,stress-strain relationship and energy absorption properties of the model are compared and analyzed,the accuracy of the finite element model is verified,and the effects of different structural size parameters and impact speed on the mechanical properties and energy absorption of three-dimensional negative Poisson’s ratio star-shaped structure are explored.The research shows that increasing the rod diameter has significant effect on improving the impact bearing capacity and energy absorption of the structure.Reducing the spacing between the concave corners of the model is beneficial to the stability of the structure.Under the impact load,the stress rises faster and can effectively resist high-speed impact.