## 4 Influence of 3D Printing Parameters on the Fatigue Life of FFF Prints
### Raster Angle
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Type** & **Mat** & **Variable** & **Fixed Parameters ** & **Specimen** & **Testing Conditions** & **Results** & **Ref** \\ \hline \multirow{10}{*}{PC} & \multirow{6}{*}{Paint} & \multirow{6}{*}{Paint} & Nozzle T: 290 \({}^{\circ}\)C & \multirow{6}{*}{Tradform} & Nozzle T: 290 \({}^{\circ}\)C & \multirow{6}{*}{Tradform} & \multirow{6}{*}{Tradform} \\  & & & Platform T:145 \({}^{\circ}\)C & & & & \\  & & & Print V:28 mm/s & & & & \\  & & & Layer H: 0.254 mm & & & & \\  & & & Extrusin W: & & & & \\  & & Build & 0.508 mm & ASTM-D790 & Stress level: 20, 40, 60, & & \\  & orientation: X, & Air gap: 0 mm & and & & 80\% UTS, R = 1, & & \\  & & Y, Z & Shels: 1 & ASTM-D7774 & 0.5 & & \\  & & & Infill density:100\% & & & & \\  & & & Infill pattern: grid & & 5 Hz & \\  & & & (45\(/\)\(-\)45\({}^{\circ}\)) & & & & \\  & & & FFF printer: Stratasys & & & \\  & & & Fortus 400 mc & & & & \\ \hline \hline \end{tabular}  
* Nozzle D. nozzle diameter; nozzle T. nozzle temperature; platform T: platform (printing bed) temperature; layer H: layer height; extrusion W: extrusion width; print V: print speed; \({}^{\text{bb}}\) (+) means direct correlation and (-) means inverse correlation.  
\end{table} 
Table 2: _Cont._grid (\(45/-45^{\circ}\)) and \(45^{\circ}\) prints. At low stress amplitudes, \(45^{\circ}\) prints exhibited the highest fatigue life. It should be noted that the fatigue test was not repeated for each data point in the latter study, making it hard to justify the underlying mechanism of this behaviour. However, it can be said that in all cases, \(0^{\circ}\) and \(45^{\circ}\) prints have shown higher fatigue performance than other raster angles. In the latter study, transverse (\(90^{\circ}\)) prints had the least performance among other specimens. The effect of the raster angle on the rotating bending fatigue performance of FFF prints was studied by [PERSON] et. al. [68]. PLA and ABS were 3D-printed in round shapes as per ISO-1143 in horizontal (\(0^{\circ}\)) and vertical (\(90^{\circ}\)) orientations. All specimens were subjected to sinusoidal bending stress using a Santam rotating bending fatigue device. The fatigue resistance of all prints was reported to be higher at a \(0^{\circ}\) raster angle compared to that of \(90^{\circ}\) prints [68]. Although a particular value has not been reported as the optimum raster angle in the studies conducted so far, it can be said \(0^{\circ}\) and \(45^{\circ}\) prints perform better than \(90^{\circ}\) prints in both ABS and PLA prints when subjected to tensile and bending cyclic forces. The significance of the raster angle in compression and combined fatigue loading modes has not been investigated yet. However, it is expected that in compression, the perpendicular alignment of extruded filaments against the loading direction would result in better fatigue performance, as is the case in the static compressive strength of FFF prints. It is noteworthy to mention that the deformation mode plays a decisive role in this regard. In tension, the specimen is stretched; thus, the highest strength is achieved when the extruded filaments are aligned with the applied load. In contrast, parts tend to buckle under compressive force, so an orthogonal arrangement in which the extruded filaments are perpendicular to the applied load gives the highest compressive strength [73].