## 3 Results and Discussion
### Mechanical Properties
#### 3.2.1 Tensile Tests
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mechanical Property** & **Source** & **Sum of Squares** & **F** & **F Crit** & \(p\)**-Value** \\ \hline Yield strength & BG & 131.961 & & 750.954 & 3.885 & \textless{}0.001 \\  & WG & 10.722 & & & \\ \hline Ultimate tensile strength & BG & 131.961 & & & \\  & WG & 10.722 & & & \\ \hline Elastic modulus & BG & 74,080 & & & \\  & WG & 105,680 & & & \\ \hline Elongation at break & BG & 109.256 & & & \\  & WG & 6.856 & & & \\ \hline BG = between groups; WG = within groups; SS = sum of squares; F = F ratio; F crit = critical F ratio. & & & \\ \end{tabular}
\end{table} 
Table 2: ANOVA tests for tensile properties. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mechanical Property** & **XY** & **XZ** & & **ZX** & \\  & **Experimental** & **Experimental** & **Datasheet** & **Experimental** & **Datasheet** \\ \hline Yield strength [MPa] & 47.0 (0.6)  & 47 & 32.0 (1.5)  & 73.0 (1.3)  & 42 \\ Tensile modulus [MPa] & 2220 (54)  & 2150 & 2128 (144)  & 8.0 (0.2)  & 2.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of tensile properties of Ultem 9085 samples built according the three building directions XY, XZ, and ZX, mean values, and standard deviations (in parentheses). Superscript letters indicate statistically-homogeneous subsets ([PERSON]’s HSD test, \(\alpha\) = 0.05). samples was higher with respect to those calculated for XY and XZ samples; this implies a higher dispersion of the data. Samples after tensile tests are shown in Figure 2a-c. These images provide evidence of the different filament deposition patterns adopted for the building of samples with XY, XZ, and ZX orientations, respectively. Figure 2d-f show the fracture surfaces of the three kinds of samples. From a visual analysis it seems that ZX cross section shows lower porosity degree than XY and XZ samples. The presence of few voids can in fact be observed mainly in the region close to the interface between infill and contour (red arrows). Similarly, in XZ samples the porosities seem mainly located at the border area where infill and contour filament meet; however, the amount of observed voids seems higher than for ZX samples. Moreover, the visual inspection of XY surface fracture evidences the presence of some voids both at the interface infill/contour and in the infill area. These qualitative observations agree to the density values reported in Table 1.  
The comparison of fracture surfaces evidences some differences in the fracture behavior of samples as a function of the different building orientations. Both XY and XZ specimens, which granted the best tensile properties, showed a brittle fracture. The slightly higher UTS of XZ samples with respect to the XY ones was probably due to the different contour/infill areas ratio. The observed fracture surfaces show a rectangular shape where most of the area is constituted by the infill, and only a minority part represents the contour. In both XY and XZ samples, the filament which forms the contours is deposited parallel to sample axes and, as a consequence, in the same direction of load application. This allows filaments to strongly oppose to the load application. On the other hand, the filaments which constitute the infill are placed at 45\({}^{\circ}\) with respect to the direction of load application. In samples with XZ orientation, the contour/infill areas ratio is higher with respect to XY samples because of the contour is present on the longest side of the rectangular cross section (while in the XY samples, the contour represents the shortest side). This may explain both the higher strength and elongation of XZ specimens with respect to XY ones. Figure 2: Samples built in XY, XZ, and ZX building directions after tensile tests. Macroscopic views of samples (**a–c**) and fracture surfaces (**d–f**).