## 4 Influence of 3D Printing Parameters on the Fatigue Life of FFF Prints
### Raster Angle  
The raster angle is a determining factor in the tensile and flexural fatigue performance of FFF prints [20; 24; 37; 53; 55; 57; 59; 68]. It has been shown that the tensile strength of FFF prints improves by decreasing the raster angle [22]. In an ideal condition where the rasters of each layer are perfectly aligned with the axis of the applied tensile force (raster angle of 0\({}^{\circ}\)), the highest tensile strength is achieved [70; 71; 72]. In the case of flexural and compressive loading, the highest static strength corresponds with grid patterns [54] and perpendicular arrangement [73], respectively. Despite the static strength, the fatigue strength of FFF prints does not follow a particular trend against the raster orientation for all materials. In PLA prints, the raster angle of 45\({}^{\circ}\) has produced the highest tensile and rotating bending fatigue strength, while for ABS prints, 0\({}^{\circ}\) has been the optimum raster angle. For PETG prints, the highest fatigue life at high and low tensile stresses is achieved in 0 and 45\({}^{\circ}\) raster orientations, respectively. [PERSON] et al. [37] studied the tensile strength and tensile fatigue behaviour of PLA prints with different raster angles (0\({}^{\circ}\), 45\({}^{\circ}\), and 90\({}^{\circ}\)). They observed that 45\({}^{\circ}\) prints show the best fatigue performance among the studied specimens. Interestingly, while 0\({}^{\circ}\) prints had the highest UTS, they exhibited the lowest fatigue life. The highest tensile fatigue strength was also achieved for 45\({}^{\circ}\) PLA prints in the work of [PERSON] and [PERSON] [59]. The endurance limit of 45\({}^{\circ}\) prints was reported to be 10 MPa, followed by 5 and 0.5 MPa for 0\({}^{\circ}\) and 90\({}^{\circ}\) prints, respectively. [PERSON] et al. [20] investigated the tensile fatigue behaviour of notched PLA prints produced with raster orientations of 0\({}^{\circ}\) and 90\({}^{\circ}\). They observed no significant difference between the fatigue strength of the printed samples. The authors also concluded that due to implementing a high nozzle temperature (250 \({}^{\circ}\)C) and optimum printing parameters, layers were bonded perfectly, resulting in near-homogenous samples. Thus, the raster orientation did not affect the fatigue strength of the samples markedly. As reported in the literature, the optimum raster angle in ABS prints is 0\({}^{\circ}\). By comparing the S-N curves published in [55; 57; 58], it is evident that 0\({}^{\circ}\) prints possess the highest fatigue resistance, followed by 45\({}^{\circ}\) and 90\({}^{\circ}\) prints in descending order. Similarly, the flexural fatigue life of 0\({}^{\circ}\) ABS prints was higher than those of 90\({}^{\circ}\) counterparts in the works of [PERSON] et al. [69] and [PERSON] et al. [35]. ABS prints produced in the 0\({}^{\circ}\) direction resisted around 96,500 fatigue cycles as compared to less than half (-40,700) for 90\({}^{\circ}\) prints [35]. In another study, ABS prints at different raster orientations were subjected to cyclic tension for up to 10,000 cycles [53]. Although Y-aligned (0\({}^{\circ}\)) prints performed slightly better than 45\({}^{\circ}\) and X-aligned (90\({}^{\circ}\)) prints, all samples exhibited relatively similar fatigue resistance. Only one study investigated the fatigue behaviour of PETG prints in which tensile PETG specimens were 3D-printed at 0, 45, and 90\({}^{\circ}\) raster angles and were subjected to sinusoidal tensile cycles [60]. It was found that 0\({}^{\circ}\) prints perform best at high stress amplitudes, followed by