Structural Design And Mechanical Properties Research Of Stress-matching Graded-density Lightweight Metallic Lattice Structure By SLM

The truss lattice structure is a new type of lightweight high-strength multi-functional porous structure composed of repeated arrangement of regular units.Due to its special properties such as ultra-light,high-strength,energy absorption and heat transfer,it has broad application prospects in aerospace,petrochemical,machinery,medical and other industries.However,there is a sudden change at the node of the cell because of the direct intersection of the struts,resulting in stress concentration effect,which greatly weakens the mechanical properties of the structure.Based on this,this paper takes BCC lattice structure,a typical truss lattice structure,as the research object,presents a new type of graded density lattice structure GBCC(Graded Body-Centred Cubic)for the design of BCC unit-cell struts to improve the failure mode of BCC lattice structure and improve the mechanical properties.The lattice structures with different structural parameters are compared and analyzed in theory,finite element simulation and experiment to verify the correctness of the design method.The main researches are:⑴A general finite element simulation method combining ductile fracture model and phenomenological constitutive model is established to simulate BCC lattice structures with a series of different structural parameters under quasi-static uniaxial compression.The simulation results show that the sharp corner at the node of BCC unit cell is the main inducement of stress concentration effect,which ultimately leads to the fracture of the loaded strut in the node.In addition,there is a corresponding relationship between the distribution of the damaged cell and the structural parameters of the cell.⑵In view of the stress concentration effect of BCC unit cell nodes,the graded density design of BCC cell struts is carried out to increase the angle in the cell nodes,and a new type of GBCC graded density lattice structure is obtained.Based on the classical beam theory and the law of conservation of energy,the theoretical prediction model of relative density and the theoretical force model under certain stress conditions of GBCC structure are obtained.⑶The structural parameters of BCC and GBCC are determined and the samples are fabricated.The quasi-static uniaxial compression experiments and finite element simulation analysis of GBCC and BCC samples are carried out.The experimental results show that for each group of samples with the same relative density,the initial stiffness of GBCC lattice samples is increased by 41.95%,38.20%,48.04%,and the plastic failure strength is increased by 42.25%,34.12% and 41.46%,respectively,compared with BCC lattice samples.The experimental and finite element simulation results not only show that the GBCC structure has better mechanical properties and energy absorption characteristics,but also show that the stress concentration effect and mechanical properties of lattice structure are significantly improved with the increase of the angle in the nodes.Thus,the correctness of the graded density design method proposed for the stress concentration effect at the node of lattice structure is verified,providing a reference for the design and practical engineering application of light and graded density lattice structure.