The use of lattice structures has received increasing interest in various engineering applications owing to their high strength to weight ratio. Advances in additive manufacturing technologies enabled the manufacturing of highly complex lattice structures such as triply periodic minimal surface (TPMS) models in recent years. The application of simulation tools is expected to enhance the performance of these designs further. Therefore, it is vital to understand their accuracy and computational efficiency. In this paper, modal characterization of additively manufactured TPMS structures is studied using five different modeling methods for a beam, which is composed of primitive, diamond, IWP, and gyroid unit cells. These methods include (1) shell modeling, (2) solid modeling, (3) homogenization, (4) super-element modeling, and (5) voxelization. The modal characterization is performed by using modal analysis, and the aforementioned models are compared in terms of their computational efficiency and accuracy. The results are experimentally validated by performing an experimental modal testing on a test specimen, made of HS188, and manufactured by direct metal laser melting. Finally, the relationship between the modal characteristics and volume fraction is derived by carrying out a parametric study for all types of TMPS structures considered in this paper. The complex modal characteristics of different TPMS types suggest that they can be jointly used to meet the ever-challenging design requirements using the modeling guidelines proposed in this study.
Additive manufacturing (AM), a substantial breakthrough over traditional manufacturing processes, has evolved significantly over the last few decades to meet industry demand. [1,2] It enables designers to utilize nature-inspired complex structures such as triply periodic minimal surface (TPMS) lattice structures. [3][4][5] The TPMS structures are desired and topologically ordered in many design applications due to their attractive properties, such as being lightweight and enhanced mechanical properties. [6,7] Another advantage of these structures is that their mechanical performance and functionality can be further improved by altering the thickness of given structures. [8][9][10] The quest for the ideal structure prompts new optimization proposals in the literature. Topology optimization (TO), which defines the best material distribution within the design domain, is one of the most extensively utilized optimization methods in the literature. [11][12][13] Among the various mathematical methods for TO, the solid isotropic material with penalization (SIMP), proposed by Rozvany et al., [14] gained significant attention due to its simplicity in implementation for the TO. The application of this approach to generate multiclass microstructures made of truss elements is available in the literature. For example, surrogate models for different truss-based structures are used in TO to minimize the compliance of the structure for a given volume ratio. The methodology was demonstrated on 2D and 3D case studies. [15] In another study, [16]
Graded TPMS topologies display excellent mechanical and thermal properties. Design schemes targeting optimal performance exist, but final reconstructed designs still suffer from performance degradation. To overcome this challenge, we propose an automated design framework based on the integration of a homogenization-based topology optimization scheme and a new mapping strategy. Optimized designs obtained using a modified SIMP technique are reconstructed as graded gyroid structures. Unlike mapping strategies using relative density values prior to TPMS infill, for the first time we make use of readily available adjoint sensitivities for mapping optimal densities to graded gyroid structures. Results show that the proposed framework delivers performance preserving graded designs when compared to original optimized designs obtained using OPTISTRUCT and superior performance in comparison to standard density-based mapping methods. The resulting graded design is manufactured using additive manufacturing and three-point bending tests are performed confirming simulation results and demonstrating the applicability of presented design scheme.
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