Mechanical Properties Of Stainless Steel Products By Additive Manufacturing

The efficient and reliable nodes are needed as the foundation for well-designed and realizable spatial structure.Topology optimization is an effective tool to obtain the reasonable shape design for spatial structure nodes,and additive manufacturing is an innovation to get the high-quality products of complex optimized nodes having irregular geometries.The joint application of these two technologies provides a new and effective way for the integration of design and manufacture of spatial structure nodes.However,further development and application of metal additive manufacturing technology remain hindered by a lack of thorough descriptions of mechanical properties of products.Based on the achievement that have been acknowledged,this paper introduces the metal additive technology and topology optimization technology in detail,explores the mechanical properties of the commonly used selective laser melting technology(SLM)products through experiments and data analysis,and carries out topology optimization analyses of practical engineering node design using two commercial software based on rapid casting.The main results of the study are as follows:(1)Tensile property and influencing factors of 316L stainless steel by SLMBased on a brief summary of the classification of metal additive manufacturing technology,the research progress of selective laser melting(SLM)technology is reviewed,focusing on the mechanical properties of SLM products and their main influencing factors.The basic mechanical properties of 48 selective laser-melted 316L stainless steel samples which were made by two kinds of equipment,two kinds of thickness and five directions are investigated through tensile tests.The Young's modulus of the samples ranged from 172.61 to 215.55 GPa,the yield tensile strength ranged from 446.90 to 583.47 MPa,the ultimate tensile strength ranged from 576.22 to 734.43 MPa,and the breaking elongation ranged from 20.69%to 49.56%.The yield strength and ultimate strength are much higher than the specification value of 316L steel plate and steel strip after solid solution treatment,and are both higher than the level of forging without annealing treatment.Meanwhile,the yield ratio is much higher than that of steel plate and strip treated by solid solution.The mechanical properties of samples in different groups show obvious difference.Combined with the further SEM tests and conclusions from previous researches,the main factors leading to obvious difference and the directional dependency in mechanical properties were analyzed.(2)Statistical analysis of mechanical properties of 316L stainless steel by SLMThe current constitutive model for stainless steel including modified R-O model and G-R-O model can fit the test stress-strain curves.Furthermore,SPSS software is used to analyze the statistic distribution of mechanical property indexes and the influence of equipment,directions and thickness through normality test,variance analysis and non-parametric test.The results show that the mechanical properties of the samples in different groups have obvious differences.The elastic modulus,Poisson's ratio and yield strength basically meet the normal distribution,while the ultimate strength and elongation of the corresponding plastic phase differ greatly from the normal distribution.For horizontal samples,the influence of direction can be approximately ignored,but the influence of thickness cannot be ignored.For vertical samples,the influence of equipment and direction cannot be ignored.The mean value of mechanical properties and the range of reference value with 95%guarantee rate are given,which can be used as reference for practical application.(3)Topology optimization of nodes in practice projectsTwo kinds of software(Inspire which is based on variable density and Ameba which is based on bi-directional evolutionary optimization)are used in topology optimization for outer ridge cable node and internal notochord node in the Tianquan county stadium,to explore further application of topology optimization and additive manufacturing technology in joint design of steel structure.The mechanical properties of the original and optimized nodes are then evaluated by ABAQUS.Results show that:For the nodes with large ear plate and small optimizable region in the actual project,ear plate could be abandoned and the optimization region could be increased to obtain better optimization results;Two kinds of software can significantly reduce low efficiency unit under the worst-cases of load,reduce the node weight,and obtain a reasonable and nice-looking redesigned node.