The topology optimization (TO) process has the objective to structurally optimize products in various industries, such as in biomechanical engineering. Additive manufacturing facilitates this procedure and enables the utility of advanced structures in order to achieve the optimal product design. Currently, orthopedic implants are fabricated from metal or metal alloys with totally solid structure to withstand the applied loads; nevertheless, such a practice reduces the compatibility with human tissues and increases the manufacturing cost as more feedstock material is needed. This article investigates the possibility of applying bioinspired lattice structures (cellular materials) in order to topologically optimize an orthopedic hip implant, made of Inconel 718 superalloy. Lattice structures enable topology optimization of an object by reducing its weight and increasing its porosity without compromising its mechanical behavior. Specifically, three different bioinspired advanced lattice structures were investigated through finite element analysis (FEA) under in vivo loading. Furthermore, the regions with lattice structure were optimized through functional gradation of the cellular material. Results have shown that optimal design of hip implant geometry, in terms of stress behavior, was achieved through functionally graded lattice structures and the hip implant is capable of withstanding up to two times the in vivo loads, suggesting that this design is a suitable and effective replacement for a solid implant.

One of the main advantages of Additive Manufacturing (AM) is the ability to produce topologically optimized parts with high geometric complexity. In this context, a plethora of architected materials was investigated and utilized in order to optimize the 3D design of existing parts, reducing their mass, topology-controlling their mechanical response, and adding remarkable physical properties, such as high porosity and high surface area to volume ratio. Thus, the current re-view has been focused on providing the definition of architected materials and explaining their main physical properties. Furthermore, an up-to-date classification of cellular materials is presented containing all types of lattice structures. In addition, this research summarized the developed methods that enhance the mechanical performance of architected materials. Then, the effective mechanical behavior of the architected materials was investigated and compared through the existing literature. Moreover, commercial applications and potential uses of the architected materials are presented in various industries, such as the aeronautical, automotive, biomechanical, etc. The objectives of this comprehensive review are to provide a detailed map of the existing architected materials and their mechanical behavior, explore innovative techniques for improving them and highlight the comprehensive advantages of topology optimization in industrial applications utilizing additive manufacturing and novel architected materials.

This paper investigates the mechanical behavior of additive manufactured Triply Periodic Minimal Surface (TPMS) structures, such as Gyroid, Schwarz Diamond and Schwarz Primitive. Fused Filament Fabrication (FFF) technique was utilized in order to fabricate lattice structures with different relative densities, at 10%, 20% and 30%, using Polylactic acid (PLA). The test specimens were formed by structural TPMS unit cells and they were tested under quasi-static compression. A finite element analysis (FEA) was performed in order to predict their stress-strain behavior and compare with the experimental results. The results revealed that each architecture influences the mechanical properties of the structure differently depending on the impact of size effect. The structures were designed as sandwich structures (with a top and bottom plate) to avoid significant deterioration of the mechanical behavior, due to the size effect and this was achieved at high relative densities. The Schwarz Diamond structure demonstrated the highest mechanical strength compared with the other architectures, while the Gyroid structure also revealed a similar mechanical performance. In addition, Schwarz Primitive structure showed increased energy absorption especially during plastic deformation. The overall results revealed that the integrity of the mechanical properties of the studied TPMS FFF printed structures deteriorates, as the relative density of the structures decreases.

The mechanical and dynamic behavior of FFF 3D printed polyethylene terephthalate glycol (PETG) and PETG reinforced with 20% carbon fibers is presented in this paper using several experimental tests. Compression tests, cyclic compression tests, nanoindentation, and modal tests were used as the assessment procedures. The results reveal that the addition of carbon fibers decrease as much as 66% the compressive strain, while increase the modulus and the hardness by around 30 and 27%, respectively. The loss factor and damping as calculated from the cyclic compression and models tests dropped from 17.3 to 15.4% and 13.8 to 12.3%, respectively.