Research On Mechanical Properties And Topology Optimization Of Graded Lattice Structures For Additive Manufacturing

In recent years,the triply periodic minimal surfaces(TPMS)have caught a lot of attention to many applications recently such as biomaterials,lightweight components with high strength and functionally graded material(FGM).The graded lattice based on TPMS is a new multi-functional structure that modifies mechanical properties via continuously changing of pore distribution.Furthermore,it can meet different practical requirements through the graded change of volume fraction.However,the traditional manufacturing method is difficult to process this new complex lattice structure.Additive manufacturing technology represented by Selective Laser Melting(SLM)is an effective way to build this structure.In this study,the specimens of network and sheet based graded lattice structures were fabricated by selective laser melting(SLM)and Ti6Al4V(TC4)metal powder material.Through experimental research,finite element analysis and theoretical analysis,The mechanical properties are studied and a gradient lattice filling strategy based on topology optimization algorithm is proposed.(1)Analysed the principle of TPMS parameter control,volume fraction calculating program,the design methods of(Gyroid and Diamond)sheet graded lattice structures are studied.(2)The effects of different cell types on the compressive mechanical properties of SLM-built TC4 graded lattice are studied.Through uniaxial compression experiment of graded lattice structure,the mechanical behavior and failure mechanism are analyzed,and the influence law of different element types on the mechanical properties of graded lattice structure,such as stress-strain curve,yield strength,elastic modulus,stress-drop and fluctuation is revealed.It is found that the sheet graded structure has higher elastic modulus,yield strength and more stable stress fluctuation than the network graded structure within the same volume fraction gradient range.The S-GG sheet graded structure has the best comprehensive performance.(3)In order to deeply analyze the deformation mechanism and stress distribution of sheet and network graded lattice structures,Johnson-Cook plastic and damage model was introduced to simulate the plastic deformation and failure behavior of materials at the post-yield stage.The simulation results showed that the compressive stress of Gyroid network graded lattice structure is concentrated in the middle region of the support rod which connects two adjacent element layers,while the compressive stress of sheet graded structure was distributed in the middle region uniformly.In addition,the energy absorption performance of Gyroid graded lattice structures was also studied.The results showed that the sheet graded structure has higher energy absorption efficiency.(4)Combined with the Solid Isotropic Material Penalty Model(SIMP)topology optimization algorithm,the filling strategies of network and sheet lattice structures were optimized,and the new lightweight cantilever beam with continuously graded filling lattice structure was successfully designed,which can provide a theoretical guidance for the current lightweight design based on porous structure filling.According to the static simulation results,it is found that the cantilever beam filled with sheet lattice structure has higher stiffness under the same total weight.In conclusion,this paper provided the design method of network and sheet graded lattice structures,obtain their mechanical properties and deformation mechanism,simulated the stress distribution of graded structure under compressive test,improved the filling strategy of lattice structure based on SIMP algorithm,obtained novel lightweight filling structure with excellent performance.It will promote the deep combination between optimal design and additive manufacturing.