PSI - Issue 41

Saveria Spiller et al. / Procedia Structural Integrity 41 (2022) 158–174 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000–000

168

11

infill raster of 90° (perpendicular). This is the highest result achieved since this infill pattern strategy introduced less porosity, in comparison with the other strategies.

Fig. 10. CT scan pictures of the internal porosity of specimens printed with different raster angles. 0°, 45° and 90° (Damon et al., 2019)

Besides the density, the most important effect on the mechanical properties is the building orientation. In several works, specimens have been printed in different layouts on the printing platform, and the mechanical properties of the sintered parts were proven to change accordingly. For example, Kurose et al. (2020) printed flat tensile specimens, on the side, and vertically. The flat and side configurations gave comparable results, while the vertical specimens failed at low loading. This is due to the alignment of the loading direction with the building direction, the weakest one (Fig. 12d), (Loh et al., 2020). Moreover, Kurose et al. (2020) explained that the residual pores are elongated on the layer plane, therefore they are detrimental when the load is applied perpendicular to the layer surface. This porosity effect was also depicted as responsible for the higher shrinkage percentage observed along the building direction.

Fig. 11. a) layouts used in Alkindi et al., (2021); b) fracture surface of specimen printed at 90° (vertical); c) fracture surface of specimen printed at 0° (horizontal); d) schematic of the stronger and weaker loading direction in 3D printed specimens, from Loh et al., (2020).

The different mechanical behavior of specimens printed at different inclinations on the building platform was also studied by Alkindi et al. (2021). In their work, a filament with a high infill percentage of 17-4 PH SS was used to print tensile specimens with the configuration reported in Fig. 11. a) layouts used in Alkindi et al., (2021); b) fracture surface of specimen printed at 90° (vertical); c) fracture surface of specimen printed at 0° (horizontal); d)