The Mechanical Properties Of Lattice Metamaterials Inspired By Crystal Microstructure

Lattice metamaterials are a kind of light-weight,multifunctional,periodically open-porous cellular materials,which has many advantages over traditional materials.Because of its effective application in various fields,it has been widely concerned by researchers at home and abroad.For this reason,this paper studies the lattice structures in detail and tries to improve its design optimization methods and analysis means.Firstly,two mechanical metamaterials,Body-Centered Cubic(BCC)and Face Centered Cubic(FCC),are obtained,which evolved from lattice metamaterials inspired by crystal microstructures,and the BCC was extended to the generalized body-centered Block(BCB).The compression characteristics and deformation mechanism of two metamaterials are studied by the combination of the both theoretical analysis and numerical simulation.Secondly,the macroscopic mechanical response of lattice structures metamaterials are investigated.Finally,based on the combined topology design method and 3D printing technology,a variety of new high-performance combined lattice structures are designed and fabricated.Through the combination of experiments and numerical simulation,their mechanical behaviors are analyzed in detail.The specific research contents are as follows.(1)The yield strength and Young's modulus of BCB and FCC are analyzed base on the static admissible field and kinematically admissible field.For BCB structure,the yield strength can be improved effectively adjusting the initial angle and horizontal angle.In addition,considering the nodal volume overlap effect and the bending/shearing effect in the theoretical analysis,the mechanical properties of the truss lattices in the larger relative density range can be better predicted.Abaqus/Standard is used for elastic analysis of lattices and compared with the theoretical model.The numerical results is in good agreement with the theoretical results.(2)The energy absorption capacity of structures depend not only on its initial yield strength and stiffness,but also on its response after yield.The plateau with stable response after yield has more potential as an energy absorber.Based on the deformation mechanism of the kinematically admissible field,the stress-strain curve of the structures is given in consideration of the elastic effect in the small strain stage and the large deformation after yielding.The simulations of the large deformation response of the structures are performed through ABAQUS/Explicit and compared with the theoretical model.Bending-dominated BCB is more inclined to Type I energy absorption mode,i.e.,the stress-strain curve presents a stable stress plateau to densification after the linear elasticity reaches the initial yield strength.But with the increase of the initial angle,BCB gradually changes from the bending-dominated deformation mechanism to the bending-stretching coupling mechanism.BCB with high initial angle shows a similar to Type II energy absorption mode,i.e.,such energy absorption modes tend to have a sharp decline in stress after a high initial yield strength,without a stable stress plateau.For stretching-dominated FCC,this kind of high connectivity structure is more inclined to stretching-dominated energy absorption mode.This response mechanism often limits the application of the structure as an energy absorber.(3)Based on the previous analysis results of the mechanical behavior of BCB and FCC,a combined design method is proposed to design a new truss lattice.According to the advantages of BCB and FCC,the combined design is expected to combine the advantages of both.The design of this new truss structure is mainly to optimize the mechanical properties of the structures,improve the response mode of the structures,improve the energy absorption efficiency of the structures,and son on.The results of numerical simulation show that the strength and stiffness of the structure along the loading direction can be effectively improved by inserting Z-pinned that parallel the loading direction in FCC.At the same relative density,the specific energy absorption of FCCBCB that embedded BCB in octahedron unit cell is better than that of FCC,and when the relative density is equal to or greater than 0.2,FCCBCB shows higher specific strength and specific stiffness.In addition,whatever base materials are selected,FCCBCB can obtain stable deformation mode with lower relative density than FCC,and has the best specific energy absorption in the studied relative density range.The combined design(FCCSC)of Simple Cubic(SC)and FCC can greatly reduce the anisotropy of structure.The anisotropic index(A)of FCCSC is close to 1 in the range of relative density studied(1.18 at 0.05 to 1.11 at 0.5),indicating that FCCSC tends to be elastic isotropic.In addition,the dynamic reinforcement term of the combined design lattice was analyzed by numerical simulation under dynamic loading at different speeds.The results show that,no matter what base materials are selected,FCCBCB exhibits the highest dynamic collapse platform stress,and the stress wave propagates fastest in FCCSC.The propagation velocity of stress wave in lattice structures are not only related to the topology of lattice structures,but also depends on the choice of base materials.Finally,the numerical simulation results are validated by experiments.In short,the mechanical properties of the structures can be macro-controlled by the combined topology design,and the reasonable design can effectively improve the carrying capacity and energy absorption characteristics of the structures on the foundation of the original structure.