Metal Additive-Manufactured Joints For Spatial Structures:Topology Optimization

The overall complexity of spatial structures has been continuously increasing as they evolve into emerging systems and free-form geometries.This trend has also given birth to more complex forms of their joints,which must not only meet the safety requirements imposed by structural engineers,but also satisfy the aesthetic demands favored by architects.Therefore,the need for optimal design of joints in spatial structures is becoming increasingly prominent.In this respect,topology optimization represents a powerful tool.This technique allows a joint to be optimally designed under given loads and constraint conditions through material redistribution,thereby achieving the purpose of "light weight and high strength".However,the joints resulted from a topology optimization process generally feature a complex and irregular geometry difficult to materialize with traditional manufacturing methods,which in turn restricts the development of topology optimization.The advent of the metal additive manufacturing technology provides a new way to address this problem.This technology builds 3D objects through stacking metal powder layer-by-layer based on 3D model data,and therefore possesses the advantages of customizability and free-form manufacture,enabling its greater potential for materializing the optimal topology design of joints in spatial structures.Motivated by the above background and a practical engineering project,this thesis is devoted to topology optimization of metal additive-manufactured joints for use in spatial structures.First,the topology optimization software HyperWorks with the built-in OptiStruct solver is used to analyze the topology of the joint model.After establishing the topological model for the joint,a number of issues are discussed in detail,including the effects of a range of parameters on the final joint geometry,the evolution of the joint geometry throughout the optimization process,and the influence of topology optimization on the stress distribution of the joint.Then,based on the above parametric study and iterative study,the topology optimization design is applied to a practical engineering project Airmesh(the author participated in the design of Airmesh,which is a now-complete spatial truss structure employing metal additive-manufactured joints)according to the maximum stiffness criterion,with the results obtained from single-loading condition and multiple-loading condition being analyzed and compared.In addition,another topology optimization software,Inspire,which is architect-oriented,is also used to perform similar design of the Airmesh joints for two different optimization objectives.The joint geometries resulted from the above topology optimization process is then adjusted locally using PolyNURBS to generate a smoothened contour for ease in manufacture.Finally,stress analysis is conducted using Abaqus to assess the optimization effects derived from different software and optimization objectives,and to demonstrate the practical effectiveness of topology optimization.