PSI - Issue 41

Fabio Distefano et al. / Procedia Structural Integrity 41 (2022) 470–485 Author name / Structural Integrity Procedia 00 (2019) 000–000

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11

G7_0.05

G7_0.1

G7_0.2

Fig. 8 SEM images, unit cells fracture

G7_0.05

G7_0.1

G7_0.2

Fig. 9 SEM images, details of the fracture surface

3.5. Finite element analysis results The results of the FE analyses are shown in Fig. 10 and Fig. 11. For a better understanding, in the ID of the unit cells is included the strut diameter values. In order to compare the compressive behaviour and the failure modes of different cell shapes and sizes, the results are reported for different displacements considered as percentage value of the cell diameters. The FE models were developed by considering the true stress of the Ti6Al4V ELI alloy, thus the real ultimate stress value of 1107 MPa was considered for the representation of the Von Mises stress. The deformation behaviour of the G7 unit cell is consistent with the experimental tests. Thus, the reliability of the FE model is verified. In the G7 unit cell, for all the configurations, the collapse mode of the vertical struts is dominated by buckling. For the G7 cells with relative density 0.2, at a displacement of 25% a symmetric deformation appears. For a displacement of 50%, the inferior part collapses before the superior one. For the G7 cells with relative density 0.1, at a displacement of 25%, a symmetric deformation appears in the G7_2.1mm cell, while a collapse mode dominated by buckling of the inclined struts appears in the G7_5mm cell. At a displacement of 50%, the G7_2.1mm cell presents a symmetric deformation, while the collapse of the structure occurs in the G7_5mm cell. For relative densities of 0.1 and 0.2, all the analysed configurations do not reach a displacement of 75%, due to the collapse of the structures. The G7 cells with relative density 0.05, because of the aspect ratio low value, present buckling dominated collapse mode also in the inclined struts; this behaviour is observable at displacements of 25% and 50%, with symmetric deformation. At a displacement of 75%, the failure of the vertical struts occurs, and the stress values decrease. G7_2.9mm cell presents peak stress values at the cross nodes, while G7_7.3mm cell, with the same 0.2 relative density, presents evenly distributed stress values in the whole structure.