# Compressive Behavior of Inconel 625 and Ti-6 Al-4V Strut Lattices Fabricated by LPBF
## 4 Discussion  
The goal of the present study was to assess the behavior of four lattice structures manufactured by LPBF from two high-performance alloys, which are used especially in the aerospace field. This study was justified because the scientific community has registered a great interest in such studies. The nTop software does not provide stress-strain curves, and the results obtained for the von Mises stress are significantly higher than those obtained experimentally. Yielding initiates when the von Mises stress reaches the uniaxial yield strength in uniaxial compression tests. Under the specified test conditions, all cell types, regardless of the manufacturing material, experienced yielding. Comparing the results of the simulations with those obtained experimentally regarding yielding, it was determined that the highest von Mises stress was recorded for the re-entrant cell type, as it had the lowest yield strength determined experimentally. The results are graphically presented in the graph in Figure 11.  
In a previous study published by the authors [37], it was concluded that the mechanical performances of lattices under flexural loads can be assessed by performing a simplified static finite element analysis in nTop. The same lattice cell types and materials used in the previous study [37] were also used in the present study; in this case, the compressive properties were studied. Regarding the tendency of the lattice types to damage under compression, a good agreement was determined between the computational and experimental results; the worst properties were recorded for the re-entrant lattice (known also as auxetic) and the best performances were recorded for the octet lattice. A similar trend was also recorded in the case of lattice flexural properties [37]. The results of the compressive behavior analysis of the lattices are consistent with those of other authors. In the present case, the simulation results show the same type of material  
Figure 11: The trendline of the yield strength and the von Mises stress, for Inconel 625 (**a**) and for Ti-6 Al-4V (**b**). failure regardless of the material selected, but experimentally, Inconel 625 is characterized by a bending-dominant mode regardless of the lattice type tested, while Ti-6 Al-4V is characterized more by a stretch-dominant mode, especially in the case of the re-entrant lattice. These modes were also identified in the review performed by [PERSON] et al. [40]. No full densification was achieved regardless of the lattice type, as the compression test ended when the 7 mm elongation was achieved, considering it was enough to characterize the material behavior. Furthermore, in the review by [PERSON] et al. [41], the maximum compressive strength of many lattice types of additive-manufactured specimens from Ti-6 Al-4V was in the range of 125-228 MPa, while the elastic modulus was in the range of 0.2-35 GPa. In our case, the average maximum compressive strength for the Ti-6 Al-4V lattice was in the range of 30.39-290.17 MPa (the lowest was for the re-entrant lattice and the highest was for the octet lattice), and between 1.74 and 4.72 GPa for the elastic modulus. [PERSON] et al. [42] also collected data from compression tests of Ti-6 Al-4V lattice structures with many cell types, orientations, and strut sizes. They observed that the maximum compressive strength can reach up to 345 MPa (a value higher than those recorded in this study but on different lattices). [PERSON] et al. [26] studied the compressive properties of functionally graded strut lattice structures with cubic and honeycomb cells manufactured by SLM from Ti-6 Al-4V alloy. They obtained the first maximum compressive strength in the range of 64-692 MPa. The same authors reported in another study [43], based on strut lattice structures with cubic and honeycomb cells with different orientations and densities, a first maximum compressive strength in the range of 14-244 MPa.