Research On Structural Design And Mechanical Properties Of Functionally Graded Lattice Structures Fabricated By Additive Manufacturing

With the development of the aerospace field and bone tissue engineering,the performance requirements of the load-bearing structure are getting more stringent,and the development of lightweight functional structures has positive significance for current spacecraft and implants.The functionally graded lattice structure is considered to be the most suitable functional structural material due to its light weight,high strength,open pores and performance gradient changes.Since the lattice structure has a complex microstructure,it is difficult to process with traditional technology.The emergence of additive manufacturing technology has enabled the design of various lattice structures to be realized.Therefore,this subject uses additive manufacturing as the processing technology,and extensive research has been conducted on the mechanical properties of the graded lattice structure.First of all,this paper reviews the current development status of the existing additive manufacturing technology and graded lattice structure,extracts the key problems existing in the current graded lattice structure,and elaborates the specific content of this work.Aiming at the performance degradation problem of the current graded lattice structure,with the aid of numerical simulation technology,the failure mechanism of the existing structure is analyzed,and the size-graded lattice structure formed by the change of unit cell size is proposed.On this basis,considering that the mechanical properties of the graded lattice structure are related to the structure of each layer,the stiffness prediction model of each layer structure is established based on the classical beam theory,and the feasibility of the mechanical performance prediction model is verified by experiments.Then,the quasi-static compression response of the graded lattice structure is studied.Taking into account the influence of the properties of the base material on the mechanical properties of the structure,the quasi-static compression response of the graded lattice structure was studied from the two aspects of the ductile material nylon and the brittle material titanium alloy by a combination of experiment and numerical simulation.It is observed that the size-graded lattice structure has excellent load-bearing and energy absorption capabilities,and has great advantages in the application of protective devices.In order to achieve the prediction of the mechanical properties of the graded lattice structure,based on the mixture rule,the mapping relationship between the overall mechanical properties of the graded lattice structure and the structural properties of each layer is established.The experimental and numerical simulation results confirm the feasibility of the mapping relationship.Furthermore,in order to systematically evaluate the mechanical behavior of the size-graded lattice structure,the corresponding titanium alloy experimental samples were prepared by laser additive manufacturing technology,and the compression-compression fatigue test was carried out to study the fatigue behavior of the graded lattice structure.Taking into account the influence of the surface quality of the sample on the mechanical properties of the structure,the influence of the sandblasting treatment on the mechanical properties of the structure is also analyzed.It is found that the fatigue failure form of the titanium alloy graded lattice structure is a combination of ductile fracture and brittle fracture.Sandblasting can effectively improve the fatigue life of the gradient lattice structure,which provides a good reference for the improvement of the mechanical properties of the graded lattice structure.Finally,a systematic analysis of the factors affecting the mechanical properties of the graded lattice structure,including the effects of each layer structure,gradient direction,manufacturing process and post-processing.The functional structure design for tailored requirements can be better realized through reasonable structure design and process methods.Besides,numerical simulation technology was used to evaluate the engineering application potential of the structure and some follow-up extension work was carried out.