## 3 Results and Discussion
### Mechanical Characterization
#### 3.2.1 Tensile Testing  
After generating the experimental plan and collecting the response observations (Table S1) of the tensile test according to the ASTM D638 standard (UTS and Young's modulus), an ANOVA study was performed using the Design-Expert software. Randomization was used for the testing sequence, as reported in Table S1 in the Supplementary Material. The average tensile stress of the five tested samples versus displacement curves are shown in Figure 5. All the tested specimens showed brittle failure with no yielding. The UTS varied in the range between 48.99 MPa and 61.98 MPa for the two materials. [PERSON]'s modulus varied in the range between 2.05 GPa and 2.34 GPa. The measured tensile properties were similar to those reported in other papers focusing on ULTEM(tm) 9085 [16; 27; 28; 29]. [PERSON] et al. [29] showed tensile strength values varying from 46.83 MPa for flat samples to 71.03 MPa for on-edge samples. The tensile modulus varied from 1.77 GPa to 2.48 GPa. In this study, the raster orientation varied from 90\({}^{\circ}\) to 0\({}^{\circ}\). Similarly, [PERSON] et al. [28] reported tensile strength values from 31.30 MPa to 70.60 MPa. FDM(tm) samples show lower mechanical properties, in particular the UTS reduction ranges between 20-40% and the strain of about 2% [30]. These findings depend on the presence of voids and on the thermal history of the printed samples when compared to injection molded specimens. The Analysis of Variance (ANOVA) table for [PERSON]'s modulus response is shown in Table 3. Model adequacy checking on the residuals from the analysis did not show any anomaly, as shown in Figure 6 The material type (factor A) is an influential factor (\(p\)-value \(<\) 0.001) on [PERSON]'s modulus (Figure 7, Table 3) and it is involved in a significant interaction AB (\(p\)-value \(<\) 0.001) with the geometry (factor B) (Figure 8). The model appears to have a good robustness to define the observed response with a high R-squared value of 0.8368. Conversely, when the UTS response is considered as the response variable, the ANOVA analysis shows that the material and the geometry factors do not influence it (Table 4). The tensile test is actually unable to characterize the ultimate tensile strength (UTS) for the two materials, as revealed by the very low R-squared value of 0.0764 We explain this finding by considering that the tensile test for flatwise printed specimens is not as sensitive to the interlayer bonding as it is for the upright orientation case where interlayers are directly loaded. In fact, for flatwise samples the longitudinally oriented rasters can sustain applied loads. ULTEM(tm) 9085 displayed a structure with a clear distinction of the deposited filaments that are not completely bonded and melted together (Figure 9). Therefore, testing methods that account for the interlayer bonding resistance should be used to fully characterize the mechanical behavior  
Figure 5: Average tensile stress versus displacement curves. of the material. The morphological analysis of the fractured specimen reveals other features. The longitudinal rasters that were aligned along the tensile load show a deformed cross section with some yielding before failure (see green arrows), and the transverse rasters were not deformed and there were some zones where adhesive failures occurred (see red ellipses). It is important to notice that the yielding occurs locally and for the longitudinal raster only. This is not reflected in the macroscopic behavior of the samples as shown in Figure 6. Compared to other studies, the level of fiber-to-fiber fusion seems lower for the analyzed specimen [29]. Crack propagation seems to also depend on the raster orientation [31]. This analysis highlights the importance of characterizing the interlayer bonding for these samples.