Design and Mechanical Properties of Novel Lattice Structures

Author:Zheng Qing

Supervisor:jiang da zhi


Degree Year:2017





Lattice structures with lightweight and high strength have great space for engineering application and development potential in the fields of Aeronautics and Astronautics,automobiles and ships.In this thesis,anisotropy of lattice structures is systematically studied by means of theoretical analysis,numerical simulation and experimental research.The optimum design of composite lattice cylinder structure is carried out,and the scaled model of large-size lattice cylinder is put forward.The preparation process and test method of large-size composite lattice cylinder are investigated.Based on the fractal geometry theory,the mechanical properties of hierarchical lattice are deeply studied.(1)Anisotropy of the mechanical properties of lattices is related to its configuration.According to study results,the diamond lattice presents strong anisotropy in terms of stiffness and strength.Stiffness anisotropy and strength anisotropy can be adjusted through changing width of the ribs in different directions.The strength envelope of the lattice is plotted,and two failure modes,Euler buckling and material failure,are compared.Then,a theoretical optimization method is put forward for lattice cylinders,providing a theoretical basis for the lightweight design of structures with specific loading condition.(2)The stiffness and critical axial pressure of composite lattice cylinder structures are theoretically analyzed by the equivalent continuum method.The results show that there are three kinds of failure modes for lattice cylinder under axial pressure,namely,rib buckling,overall buckling,and strength failure of materials.According to the failure mode maps,large-size lattice cylinder is mainly characterized by the overall buckling failure due to its relatively small thickness.The parameter analysis,carried out through finite element model,shows that the stiffness of lattice cylinder is proportional to rib width and thickness,while the critical axial pressure and the thickness of rib have quadratic relationship.(3)Finite element model of lattice structure is established,the quantitative relationship of structure size,mechanical response and structure weight.Through responding surface method and MATLAB optimization toolbox,the lightweight design of lattice cylinder structure is realized.(4)According to the similarity theory and equation analysis,method of establishing scaling model is proposed on the base of same failure mode.The scaling model of Kagome lattice cylinder under axial compression is built,and the scaling relations of 6 independent geometric parameters(D,H,b1,b2,δ,t)are obtained.The validity of the model is analyzed and verified by finite element simulation.(5)Carbon fiber reinforced epoxy composite lattice cylinder with large size is successfully prepared by soft-mold-assisted filament winding process,and the mode and frequency of free vibration of the structure are obtained by hammering method.According to experimental results,the actual longitudinal elastic modulus of the rib is deduced.Then,axial compression test is carried on the structure,which fails due to layered fracturing of ribs.The difference of experimental values and theoretical value of axial compressive strength is about 30%.(6)Concept of hierarchical lattice is put forward,as well as its construction method,namely the plane expansion method and spatial expansion method.Its mechanical properties under different failure modes are deduced by fractal theory and observed by finite element model,with failure mode maps and strength envelope plotted.Finally,the two-order lattices of engineering plastics are prepared by 3D printing technology,and their mechanical properties are tested,validating the theoretical results.