## 3 Results
### Physical Test of Uniform Lattice Structures
All the samples first experienced a beginning layer collapse in the top and bottom lattice layers, which was also present in the FEA model. While the latter continued exclusively via consecutive layer collapse over the course of the compression, the physical samples failed through shear banding in addition to layer collapse. According to [PERSON] et al. (2018), shear band formation is favoured by material concentrations around a lattice's nodes rather than its struts. Given the geometrical discretization at nodes during meshing (see Figure 12) and deviations stemming from the manufacturing technique, differences from the target thickness that cause this behaviour can occur. Despite this difference in behaviour, the reaction force levels were fairly aligned throughout the whole procedure. Figure 11: Comparison of the Simple Cubic lattice’s FEA model reaction force with models incorporating random node position deviations of up to 0.1 mm and 0.2 mm. Figure 10: (**a**) Reaction force versus displacement plots of the Simple Cubic lattice tests and simulations with uniform geometry. (**b**) Reaction force versus displacement plots of the Isortuss lattice tests and simulations with uniform geometry. Note that the result curves from the simulations are shown after filtering with an SAE J211/1 filter, but the numerical values were calculated based on nonfiltered results. Reaction force curves from the test samples were not subject to filtering. The sequences of images in Figures 13 and 14 depict the experimental behaviours of the structures compared with their Finite Element models. After surpassing the linear elastic phase, the uniform Simple Cubic lattice sample exhibits buckling beams in the second and last layers from the bottom. To compensate for the reduced height availability, the entire section is shifted forward. In the FE model, there is a more localized layer shift where only one section of horizontally oriented beams moves sideways because of buckling. Figure 12: Geometrical deviation from the target caused by the meshing procedure used to export the geometry (**a**); FE representation of cylindrical beam elements overlapping at nodes (**b**); and printed lattice geometry (**c**). Figure 13: Comparison of structural behaviour between physical testing of the Simple Cubic lattice (sample 1) (**a**) and its FEA model (**b**) at identical plate displacements of 2.5 mm, 10 mm, and 20 mm. Similar to the physical test sample, the Isotruss FEA model displays the most significant buckling response in the lowest and uppermost cell layers, where the corner beams bend outward more than in other layers. The FEA model then shows a complete layer collapse in the middle section first, while the physical model fails because of shear banding throughout the entire structure. Table 4 summarizes the total absorbed energy per sample and its specific energy absorption attained during the compression test. The Simple Cubic lattice's SEA value, as determined using the FEA model, lies 14.9% above the average results obtained from the physical tests. This is explained by the significantly higher force peak during the linear elastic region of the compression procedure, as shown in Figure 9(a) On the other hand, the SEA performance values of samples 1 and 2 of the Isotruss lattices are 1% and 12% higher than those predicted with the FEA model, whereas sample 3 only reaches 75% because of its complete loss of load-bearing capacity during the test. The absorbed energy levels are overestimated by the FE models compared with the averaged values of both lattice types. In the case of the SC lattice, this can be explained by the increased buckling strength of the FEA model since the remaining part of the curve coincides very well with the test results. If only samples 1 and 2 of the Isotruss lattice test are considered, and the third sample is discarded as an outlier, their average energy absorption amounts to 57.2 J, which comes within 8% of the value predicted by the FEA model.