## 3 Results and Discussion
### Effect of Infill Pattern on Flexural Properties
#### 3.2.3. Fractographic Analysis  
To further investigate the flexural behavior of the specimens, the fractographic analysis was performed using SEM, as shown in Figure 12. In addition, raster angles for which  
Figure 11: (**a**) Edgewise force-extension; (**b**) stress–strain behavior of different infill patterns; (**c**) Comparison of Edgewise flexural strengths for different infill patterns.  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Pattern**} & **Max. Flexural** & **Flexural Modulus** & **Flexural Strength** & **Fracture** \\  & **Load (N)** & **(GPa)** & **(MPa)** & **Strain (\%)** \\ \hline Line & 22.6 \(\pm\) 1.25 & 0.28 \(\pm\) 0.01 & 10.1 \(\pm\) 0.70 & 6.7 \(\pm\) 0.1 \\ Triangular & 18.9 \(\pm\) 1.74 & 0.32 \(\pm\) 0.02 & 8.12 \(\pm\) 0.89 & 4.8 \(\pm\) 0.1 \\ Grid & 19.2 \(\pm\) 1.52 & 0.27 \(\pm\) 0.01 & 8.51 \(\pm\) 0.94 & 9.4 \(\pm\) 1.2 \\ Tri-hexagon & 11.1 \(\pm\) 0.90 & 0.26 \(\pm\) 0.02 & 5.01 \(\pm\) 0.56 & 5.0 \(\pm\) 0.1 \\ Quarter-cubic & 29.0 \(\pm\) 1.01 & 0.38 \(\pm\) 0.01 & 12.1 \(\pm\) 0.36 & 8.3 \(\pm\) 0.1 \\ \hline \end{tabular}
\end{table}
Table 5: Summary of Experimental results for edgewise flexural properties at different infill patterns.  
the mechanics have not been studied in detail were analyzed. For the analysis of the in-plane sample, the samples with raster angles of \(45/-45^{\circ}\) and \(75/15^{\circ}\) were analysed, whereas quarter-cubic and tri-hexagon specimens were analyzed for the infill pattern case, as depicted in Figure 12e,f. The micrographs revealed the presence of three different types of defect in the tested samples, which are categorized as delamination between consecutive layers (1), raster rupture (2) and voids or gaps (3), as shown in Figure 12. These defects, in turn, affected the fracture behavior of the samples.  
concentrations and hence the failure. The failure of individual rasters due to severe loading conditions was categorized as a raster rupture, whereas the presence of the inherent voids and gaps (3), as shown in Figure 12a,c, is due to the nature of the manufacturing process, i.e., fused filament fabrication. Although the infill density was theoretically set to 100%, some voids are still there due to the different process parameters, such as the printing speed and raster gap. These voids act as the stress raisers and stress concentration regions where the fracture can preferentially occur. Similar mechanisms have also been reported in the literature for the 3D printed polymeric materials under different loading conditions. However, in the case of \(45/-45^{\circ}\), good interlayer bonding and no periodic voids can be seen, hence providing greater strength than \(75/15^{\circ}\)[26].  
Similarly, for the quarter-cubic and the tri-hexagon, the micrographs show that the raster rupture was more drastic (along with the presence of voids) and hence the major mechanism for failure. Furthermore, the surfaces of the ruptured rasters also indicated a brittle fracture in the tri-hexagon pattern, resulting in a significant difference in the flexural load carrying capacity for edgewise samples.