## 6 Discussion  
The combination of Additive Manufacturing and Topology Optimization is rapidly advancing in recent years. The outcome optimized structures are often complicated and most times cannot be fabricated with the use of traditional manufacturing methods. More and more researchers develop new methods and algorithms to improve this section. Most of them try to evolve new algorithms and techniques that are usually based on the most well-known methods of SIM, BESO and level set. Anisotropy is not easily integrated into the general topological optimization algorithms, so to evaluate the homogenization of the topology optimized structures is an appropriated step. In the current manuscript, the SIMP method was adopted to predict the optimal material distribution within the selected cubic volume. Using different boundary conditions, two new microstructures were created as infill in Additive Manufacturing. The TO study has been executed in this paper by taking into account two selected in plane loadings. Other loading cases, if needed for every point of a loaded structure or the use of different zones for the selection of the best microstructures, could lead to the creation of functionally graded lattice structures with varying distributions. This is possible within a multiscale analysis framework [30], provided that the technological restrictions of AM support it. From the TO outcome results, we calculate that the volume mass of the initial cubic domain is reduced significantly for both microstructures. In most research manuscripts, the researchers present new methods and algorithms based on well-known TO methods to predict the material distribution more accurately and cost-effectively. However, in most cases, the proposed methods do not evaluate other characteristics of the optimized structures, such as isotropy. In the current study, in order to check the isotropy of the optimized lightweight structures, a general homogenization method was used. The proposed microstructures evaluated taking into account the isotropy with calculating the Zener ratio and modulus of elasticity. In addition, the homogenized microstructures strength has been evaluated as infill material in a cantilever model. For the homogenization study, a Representative Volume Element (RVE) was taken for each microstructure. From the results, we can observe that both microstructures have Zener ratios lower or upper to unity. The second microstructure characterized with better and smoother isotropy, and for \(\overline{\rho}\) = 0.25, the Zener ratio is equal to unity, since this Zener ratio did not change significantly. Figure 22: Strain at sB, Modulus of Elasticity, sB value and toughness of lattice structure #2 for different cell mapping angles. From the experimental results, it could be seen that, compared to the proposed lattices in the compression test, the significant differences in the stress-strain curve of both structures were the appearance of an elastic-plastic plateau after the initial elastic region and apparent strain behavior. Structure #1 has a significant increased elastic strain behavior and better elastic stability until the fracture point. The stress-strain plateau of structure #2 shows that the lattice inner bonds absorb the energy in a nonuniform way as lattice #1 (Figure 18). In structure #1, the fracture starts from the top layer of the lattice closer to the moving platform and then fails the middle layer of lattices. The bottom layer of the structures seems to not be affected during the test. On the other hand, the structure #2 failure point starts from the bottom row of the lattice, and after starting the failure of the middle row, the top row of the lattice was affected in the last. This behavior explained the different shapes of the structures, which led to vertical stresses in structure #1 and to shearing stresses in structure #2. Tensile strength tests help to evaluate and characterize the proposed lattice structures further.