## 3 Results and Discussion
### Mechanical Properties  
#### 3.2.1 Tensile Tests  
Tensile tests were performed on dog-bone specimens with building orientation XY, XZ, and ZX, respectively. The statistical experiment was carried out using the one-way analysis of variance (ANOVA) in order to evaluate the main effects of building orientations (the independent variables) on each tensile property under investigation (yield strength, ultimate tensile strength, elastic modulus, and elongation at break, which are the response variables). Specifically, the \(p\)-value which indicates the level of significance of the different factors within a statistical test is reported; it represents the probability \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Building Orientation** & **Density (g/cm\({}^{3}\))** & **Relative Density (\% of Theoretical)** & **Porosity (\%)** \\ \hline XY & 1.2389 (0.0004) & 96.40 (0.03) & 3.60 (0.03) \\ XZ & 1.2552 (0.0003) & 97.30 (0.02) & 2.69 (0.02) \\ ZX & 1.2637 (0.0002) & 97.96 (0.02) & 2.04 (0.02) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average values of densities and porosity (standard deviations in parenthesis) of printed parts for the different building orientations. of a factor affecting the mechanical properties. The significant factors are tested with \(p\)-value lower than 0.05. The statistical analysis (Table 2) revealed significant differences among building orientations for all the tensile properties under investigation; this implies that at least one of them differs from the others. The [PERSON]'s HSD post hoc test (\(\alpha\) = 0.05) was performed in order to identify which pairs of building directions are significantly different from each other. Table 3 shows the means and the standard deviations for the tensile properties such as yield and ultimate tensile strengths, elastic modulus, and elongation at break; moreover, it compares these outcomes with those present in the technical datasheet provided by Stratasys (in this case, specimens were built by using Fortus 3D printer setting default process parameters defined by Stratasys). It is evident that XZ orientation was the most performant one showing the highest values of yield and ultimate tensile strengths (UTS), elastic modulus, and elongation at break. However, pairwise multiple comparisons with [PERSON]'s HSD test revealed that UTS, tensile modulus, and elongation at break of XY samples were not significantly different with respect to those determined for XZ specimens. On the other hand, ZX samples reported statistically lower tensile properties compared to the both XY and XZ building directions. Despite the value of tensile modulus for ZX samples not being significantly different from those obtained for the other two orientations, tensile strength and elongation at break were much lower with respect to those observed for XY and XZ directions. The observed trend for tensile properties is in good agreement to that reported in the literature [10; 13; 20; 25]. A comparison between the experimental results and the mechanical properties reported in the technical datasheet (Table 3) is possible only for the best and worse performant building directions, XZ and ZX, respectively. For XZ orientation, all the measured mechanical properties were slightly higher than those stated by the manufacturer; on the contrary, this was not observed for samples printed in the ZX direction. In this case in fact, the measured properties were slightly lower than those reported in the material datasheet. Moreover, the standard deviation associated to the tensile properties of ZX