Study On Mechanical Properties And Collapse Energy Absorption Characteristics Of Porous Lattice Structures

As a new type of ultra-lightweight material with high specific stiffness,high specific strength and excellent multi-functional properties,porous material has great potential in many engineering fields,such as aerospace,high-speed transportation,medical implantation and so on.In this dissertation,the rhombic dodecahedron(RD)lattice structure is taken as the research object.In order to further improve the mechanical properties of porous lattice structure and realize the advantage of lightweight,a new type of parameterized rhombic dodecahedron(RDFV)lattice structure with variable cross-section is designed.The mechanical properties and collapse energy absorption characteristics of RD and RDFV lattice structures are studied by means of theoretical analysis,simulation and mechanical experiments.The main tasks include:(1)A more accurate theoretical representation of the relative density of porous lattice structure is established,which takes into account the influence of the fusion part of the beam.Based on Euler-Bernoulli beam theory and Timoshenko beam theory,the theoretical solutions of mechanical properties of RD and RDFV lattice structures in different directions are derived.The results show that the equivalent elastic modulus solutions of RD obtained by two kinds of beam theories are correlated.The values of Euler influence coefficient and Hooke influence coefficient in the solution of Timoshenko beam theory are the same as those of Euler beam theory,while the constant coefficient of Timoshenko influence coefficient is 1/ ? times more than that of Hooker influence coefficient,and the compound trigonometric function is equal to that of Euler influence coefficient.Among the influence coefficients of the equivalent elastic modulus solution of the RDFV structure,the functions of the variable diameter ratio and the constant section length coefficient are added,while the constant coefficient part and the compound trigonometric function part are equal to the RD lattice structure.(2)The experimental samples of 316 L stainless steel RD and RDFV lattice structures were prepared by selective laser melting(SLM)technology.The quasi-static compression experiments were carried out and compared with the theoretical and simulation results.It is verified that the mechanical properties solution based on Timoshenko beam theory has higher accuracy.According to the simulation and experimental collapse deformation process,it can be concluded that the RD and RDFV lattice structures form a deformation band along the diagonal "X" region of the structure under the coupling influence of bending deformation and shear deformation,and the overall stress of the stru cture is also distributed in the "X" region and has symmetry.During the collapse process,the bending bar of the cell structure forms a plastic hinge,which is reflected in the stress-strain curve of the platform stress stage.It is the main stage of energy absorption of RD and RDFV lattice structures.(3)The parameterized models of mechanical properties of RD and RDFV lattice structures are established,which combines the relative density and the theoretical representation of the aspect ratio of the mechanical properties by using the method of function fitting in Matlab.The results show that the equivalent elastic modulus of RDFV lattice structure with different geometric parameters is 1.4-2.2 times higher than that of RD lattice structure under the condition of the same relative density.With the increase of relative density,the multiple of lifting increases,and the degree of improvement is more obvious with the increase of diameter-changing ratio and equal cross-section length coefficient.(4)The quasi-static compression simulation of RDFV unit cell structure with different geometric parameters is carried out.It is found that with the increase of relative density,the energy absorption capacity of RD and RDFV lattice structure increases,but the energy absorption efficiency decreases.Both energy absorption capacity and energy absorption efficiency of RDFV lattice structure are obviously higher than that of RD lattice structure at the same relative density.For the RDFV lattice structure,the increase of the equal cross-section length coefficient has no obvious effect on the collapse energy absorption characteristics.With the increase of the variable diameter ratio,the energy absorption capacity and energy absorption efficiency are improved.When the variable diameter ratio is small,the effect of increasing the variable diameter ratio on the energy absorption characteristics is more obvious.