PSI - Issue 41

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

474

5

2.2. Experimental investigations G7 unit cell was investigated by carrying out compression test. The microlattice structures were produced via EBM, by an Arcam Q10 printer, using Ti6Al4V ELI (Grade 23) fine powder. The used titanium alloy contains reduced levels of oxygen, nitrogen, carbon and iron and its particle size distribution is between 45 and 100 μm. Three different levels of relative density were analysed: 0.05, 0.1 and 0.2. The three configurations were obtained by varying the diameter D of the cell while maintaining constant at 0.2 mm, the strut diameter t (Fig. 2). The relative densities and the dimensions of the unit cells considered are based on the features needed for the application in the biomechanical field. Therefore, the geometric parameters of the single unit cells considered to produce the specimens are shown in Table 1.

Table 1. As designed geometric parameters of the G7 unit cells G7 unit cells ρ c /ρ m 0.05 0.1 0.2 Porosity [%] 95 90 80 D [mm] 2.9 2.1 1.4 t [mm] 0.2 0.2 0.2 L [mm] 2.28 1.59 0.98 A [mm] 1.70 1.14 0.65 t/D 0.07 0.10 0.14

All the configurations analysed guaranteed six unit cells for each edge of the microlattice structure in order to avoid size effects; thus, each specimen is made of 6x6x6 unit cells as shown in Fig. 3. A top and a bottom plate with 1 mm thickness are considered for the application of the loads during experimental tests. It was experimentally verified that the presence of face-sheets does not influence failure mechanisms and compressive response of the microlattice specimens (Gümrük et al., 2013). Geometrical characteristics of the specimens are summarised in Table 2. Where 0.05, 0.1 and 0.2 represent the relative densities of the microlattice structures.

(a)

(b)

(c)

Fig. 3 Specimens: (a) G7_0.05; (b) G7_0.1; (c) G7_0.2

An INSTRON 8854 servo-hydraulic testing machine, equipped with a 250 kN load cell, was used to perform compression test at a constant cross-head speed of 1 mm/min with a preload of 5 N. Due to the repeatability of the tests, two repetitions were carried out for each specimen configuration.