## 3 Results and Discussion
### Experimental
#### 3.1.3 The Effects of Raster Angle on Anisotropy
Based on the discussions mentioned above and from the SEM images in Figure 14, it could be seen that the \(+45^{\circ}/-45^{\circ}\) raster angle shows a weak layer adhesion when printed in the longitudinal and transverse build orientations. The longitudinal build orientation also shows delamination from the perimeter layers. As the delamination happened in the interface between the perimeter and the inner core of the sample, it confirms that the poor later adhesion when the angle of the load to the polymer changes can be the main reason for the crack initiation, crack propagation, and finally failure of the part. In the transverse build orientation, the smooth fractured surface with evident air voids for \(+45^{\circ}/-45^{\circ}\) in comparison with the \(90^{\circ}/0^{\circ}\) raster angle  
Figure 13: (**a**) Tensile strength, (**b**) elongation, and (**c**) Young’s modulus values for ABS samples when the raster angle values change between \(+45^{\circ}/-45^{\circ}\) and \(90^{\circ}/0^{\circ}\). corresponds to the low layer adhesion of the layers. These air voids which are the potential failure spots in the structure are marked with red arrows and circles in Figure 14c. The uneven fracture surface of the 90\({}^{\circ}\)/0\({}^{\circ}\) with no obvious interlayer air voids suggests that the part was resisting the layer delamination, as the mechanical testing results suggest. Figure 14 is marked with yellow circles and arrows to show the unevenly broken surfaces of the printed part. The effects of the raster angle on the mechanical properties of the printed ABS samples were investigated and the results are presented in Table 4.  
Figure 15 shows the mechanical anisotropy behaviour for the longitudinal (\(\Delta\) (UTSL)) and transverse (\(\Delta\) (UTST)) build orientations printed at different raster angles. Similar downward trends for both graphs can be observed. The lowest mechanical anisotropy for the longitudinal and transverse build orientations was recorded when samples were printed at a 90\({}^{\circ}\)/0\({}^{\circ}\) raster angle, showing a value of 68% and 40%, respectively. This indicates a drop of 70% for samples printed longitudinally and 18% for samples printed transversely when switching from +45\({}^{\circ}\)/ -45\({}^{\circ}\) to 90\({}^{\circ}\)/0\({}^{\circ}\). \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multicolumn{2}{l}{**Longitudinal Build Orientation**} & & & & & & \\ \hline Raster & UTS\({}_{\text{mean}}\) & UTS\({}_{\text{SQQT Error Mean}}\) & \(\Delta_{\text{(mean)}}\) & \(\Delta_{\text{SQQT Error Mean}}\) & E\({}_{\text{(mean)}}\) & E\({}_{\text{SQQT Error Mean}}\) \\ angle & (MPa) & (MPa) & (\%) & (\%) & (MPa) & (MPa) \\ \(0^{\circ}\)/90\({}^{\circ}\) & 32 & 0.71 & 0.23 & 0.002 & 2285 & 28.06 \\ +45/ \(-\)45 & 25.36 & 0.27 & 0.32 & 0.046 & 1668 & 46.49 \\ \hline \multicolumn{2}{l}{**Transverse Build Orientation**} & & & & & \\ \hline Raster & UTS\({}_{\text{(mean)}}\) & UTS\({}_{\text{SQQT Error Mean}}\) & \(\Delta_{\text{(mean)}}\) & \(\Delta_{\text{(SQQT Error Mean)}}\) & E\({}_{\text{(mean)}}\) & E\({}_{\text{SQQT Error Mean}}\) \\ angle & (MPa) & (MPa) & (\%) & (\%) & (MPa) & (MPa) \\ \(0^{\circ}\)/90\({}^{\circ}\) & 19.03 & 0.61 & 0.22 & 0.018 & 1788 & 51.02 \\ +45/ \(-\)45 & 10.65 & 0.43 & 0.09 & 0.005 & 1747 & 77.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: UTS, \(\Delta\), and E values for ABS samples printed in the LBO and TBO at different raster angles. Figure 14: SEM images of ABS polymer printed in (**a**) the longitudinal build orientation with a +45\({}^{\circ}\)/ -45\({}^{\circ}\) raster angle, (**b**) the longitudinal build orientation with a 0\({}^{\circ}\)/90\({}^{\circ}\) raster angle, (**c**) the transverse build orientation with a +45\({}^{\circ}\)/ -45\({}^{\circ}\) raster angle, and (**d**) the transverse build orientation with a 0\({}^{\circ}\)/90\({}^{\circ}\) raster angle. 3.1.4.