The Study On Axial Compression Mechanical Properties Of The Three-dimensional Compression-twist Cellular Structure

Due to its excellent mechanical and physical properties,the cellular structure can be widely used in various fields such as automotive,aerospace,medical and health,etc.It has a very broad application prospect and has become a hot spot for many researchers.The cellular structure can exhibit many special mechanical behaviors due to its variable cell shapes.Based on the twist mechanism of the two-dimensional chiral cell structure,a new three-dimensional compression-twist cellular structure(3D CTCS)was proposed.Not only dose it produce lateral contraction when axially compressed,it has a negative Poisson's ratio effect,and it also occurs lateral twist.The special phenomenon of twist makes this structure of important research value.To study the mechanical properties and deformation mechanism of the cellular structure,we must determine the geometric parameters that affect the shape of the cell.The shape of this 3D CTCS depends on the three geometric parameters of cell angle,cell length and cell thickness.The relative density of the cellular structure has a great influence on the mechanical properties of the cellular structure.Through three geometric parameters,the relative density formula is derived,and the influence of the geometric parameters on the relative density is studied.In this paper,the research on the mechanical properties of the 3D CTCS is mainly divided into three parts,namely the linear elastic properties research,compression failure,and geometric parameter gradient research.Finally,a 3D CTCS sample was produced by 3D printing technology,and an in-plane compression experiment was conducted to prove the correctness of the theoretical analysis and finite element analysis results.In the study of online elastic properties,the analytical expressions of effective Young's modulus,Poisson's ratio and twist angle are derived using beam theory,which is in good agreement with finite element calculations,and the deformation process of the cell is discussed.In order to study the influence of the geometric parameters of the cell on the mechanical properties,a finite element analysis model was established,which showed the deformation process of the cellular structure under compression.Fully considering the influence of the cell angle,cell length and cell thickness ratio on the effective Young's modulus,Poisson's ratio and twist angle,which shows that the cell angle has obvious geometric nonlinearity to the relative twist angle.For the study of the failure performance of the cellular structure,two theoretical models of elastic buckling and plastic collapse were established,and the theoretical formulas of the ultimate stress for the elastic buckling and plastic collapse were derived.By analyzing the failure conditions of this cellular structure,the only mode of failure of this structure is plastic collapse.In order to analyze the influence of various geometric parameters on the mechanical properties of the nonlinear elastic stage and prove the correctness of the theoretical analysis,a3 D CTCS axial compression failure finite element model was established.The effects of various geometric parameters on Young's modulus,twist angle and collapse stress are obtained.The functionally gradient cellular structure has superior physical and mechanical properties than the non-gradient cellular structure,so it has high research significance.In this paper,the study of the functional gradient of the cellular structure is mainly to gradient the cell angle and the cell thickness,and to establish four different ladder arrangements respectively.By establishing a finite element model,the two geometries are analyzed.The influence of parameters and gradient arrangements on the effective Young's modulus and twist angle of the linear elastic phase of the cellular structure,so as to obtain the optimal gradient arrangement and achieve the best mechanical performance.