Additive Manufacturing And Property Characterization Of Metal Lattice Structures

Lattice sandwich structures,which attract enormous attention and are widely used in aerospace for its advantages,such as lightweight,excellent strength and stiffness to weight,good flexibility in design,good damping and insulation properties.In this paper,lattice sandwich structures were manufactured by selective laser melting,theoretical prediction,numerical modeling and experiments for compression and three-point bending behaviors were conducted to study the effects of different structural parameters and different metal on the mechanical properties,deformation mechanism and failure modes of 3D Kagome lattice sandwich structures.Besides,it should be noted that the parts of rockets and satellites require high dimensional stability under severe temperature variation.Therefore,in order to obtain the structure integrated low coefficient of thermal expansion and low density.Invar 36 alloy can be used as the matrix material of lattice sandwich structures.To lay a foundation for the manufacture of multifunctional Invar 36 lattice sandwich structures,the effects of SLM process parameters on the microstructure and macroscopic properties of Invar 36alloy were also explored.The main conclusions are as follows:Theoretical calculation model of Kagome lattice sandwich structure parameters and its relative density,compressive strength and load capacity under different failure modes were analyzed and different strut diameters were designed.The compression and bending tests were also conducted,and corresponding stress-strain curves and load-deflection curves were obtained.The experimental curves for repetitive samples present excellent consistency,and it can be found that a slight variation in strut diameters results in a significant influence on the relative density,compressive strength and load capacity of the structure.The stress evolution and distribution of 3D Kagome lattice sandwich structures under compression and three-point bending under different structural parameters and different metal material properties were studied by finite element numerical simulation.At the moment of failure,the location where the stress distribution is concentrated（also known as a plastic hinge）will fail at the first.Under compression,for the structure with low relative density,the plastic hinge is distributed in the region near the intersection of the struts,while in high relative density,the plastic hinge is distributed in the region near the facesheets of the struts.Under three-points bending,plastic hinge also appears in different regions,for structures with low relative density,high stress level often appears in the middle of the struts under the punch,for structures with high relative density,plastic hinge appears in the intersection of struts.The Kagome lattice sandwich structures manufactured in this study were compared with the commonly used materials in engineering applications,suggesting that the Kagome lattice sandwiches provide a solution to effectively balance the strength and weight,as they present lower density than engineering alloys and higher strength than honeycombs,foams and pyramid lattice sandwich.The as-SLMed Invar 36 is dominated by fccγphase and there are some sparse bccαprecipitates,which are consistent with those of wrought Invar 36.The microstructure on the side surface is dominated by large columnar grains,while the cross-section shows a large number of small columnar grains in a melt pool,which implies that the grains grow along the maximum temperature gradient directions.The SLM process parameters for manufacture Invar 36 were explored,the optimal laser energy density is recommended to be 99.2 J/mm³,and the as-fabricated Invar 36shows the relative density of 99.5%,Vickers hardness of 1.86 GPa and yield strength of 480 MPa those are very comparable to conventionally fabricated one.The CTE of the as-SLMed Invar 36 is 1.72-1.96×10^-6℃^-1which is slightly lower than that of wrought one,due to the porosity and nickel element evaporation.