## 3 Results and Discussion
### Experimental
#### 3.1.3 The Effects of Raster Angle on Anisotropy  
Two raster angles of \(0^{\circ}/90^{\circ}\) and \(-45^{\circ}/45^{\circ}\) were selected as the main angles to print samples in two different longitudinal and transverse build orientations. For the \(0^{\circ}/90^{\circ}\) setup, the second layer of the deposited filament lays on top of the first layer with the \(90^{\circ}\) opposite orientation. For the \(\pm 45^{\circ}\) orientation, the first layer and second layer have an angle of \(45^{\circ}\) with each other. Like the layer thickness, the raster angle was identified as an influential machine parameter in the assurance of the anisotropy phenomenon. Figure 12 shows the micro-CT images of samples printed with (a) a \(+45^{\circ}/-45^{\circ}\) raster angle and (b) a \(0^{\circ}/90^{\circ}\) raster angle. The micro-CT images can be a very useful and reliable asset to determine the internal structure of the printed samples without physically damaging or deforming the part. In these images, the sample printed with a \(+45^{\circ}/-45^{\circ}\) raster angle is showing a structure with potentially more evident air voids compared with the sample printed with a \(0^{\circ}/90^{\circ}\) raster angle. This could potentially influence the mechanical integrity of the sample when the part is under load. Changing the raster angle showed a noticeable influence on the mechanical properties of the printed parts. Figure 13 represents the obtained ultimate tensile strengths, elongation at breaks, and [PERSON]'s modulus values for ABS-made samples in the two build orientations--transverse and longitudinal--at two different raster angles of \(45^{\circ}/-45^{\circ}\) and \(90^{\circ}/0^{\circ}\). For the ABS polymer, the ultimate tensile strength for samples printed in the longitudinal build orientation increased by around 7 MPa when the raster angle was switched from  
Figure 11: Mechanical anisotropy (\(\Delta\) (UTSL) and \(\Delta\) (UTST)) for parts printed at different layer thicknesses. Figure 12: The micro-CT images of the ABS samples printed at (**a**) a \(+45^{\circ}/-45^{\circ}\) raster angle and (**b**) a \(90^{\circ}/0^{\circ}\) raster angle. \(+45^{\circ}/-45^{\circ}\) to \(90^{\circ}/0^{\circ}\). The literature also confirmed parts printed at \(45^{\circ}/-45^{\circ}\) had lower tensile properties than their counterparts printed at \(90^{\circ}/0^{\circ}\)[30; 31]. The same trend was also observed for samples printed in the transverse build orientation but with a larger gap of 9 MPa. The elongation at break for samples printed in the longitudinal build orientation was increased by 28% for a \(+45^{\circ}/-45^{\circ}\) raster angle, whereas the elongation at break for samples printed in the transverse build orientation dropped by 60% for the same raster angle compared to the \(90^{\circ}/0^{\circ}\) raster angle. Although [PERSON]'s modulus did not change much for the transverse build orientation, samples printed in the longitudinal build orientation dropped by 27% when the raster angle was changed from \(90^{\circ}/0^{\circ}\) to \(+45^{\circ}/-45^{\circ}\). This means that for samples printed in the longitudinal build orientation, the \(+45^{\circ}/-45^{\circ}\) raster angle, provides a less stiff structure because of their position to the applied force, whereas the \(90^{\circ}/0^{\circ}\) provides a more rigid structure when the load is perpendicular to the rasters. This could be related to the angle that the polymer filaments have to the applied force. When the orientation of the filaments is perpendicular to the direction of the force, the resistance to break comes mostly from the polymer chains and as soon as the rasters find an angle to the applied force, the layer adhesion parameters come into the equation and like the transverse build orientation, the mechanical properties of the printed samples can be affected enormously.