# Mechanical and Tribological Performance of Carbon Fiber-Reinforced PETG for FFF Applications
## 3 Results
However, the analysis of PETG-CF (Figure 12) shows the opposite behavior to the non-reinforced material with respect to the layer thickness, decreasing drastically as the layer thickness increases, showing a trend inversely proportional to the deviation, which allows for ensuring that these deviations cause internal defects in the parts. When examining the fracture images of the tested specimens, a brittle fracture pattern is evident in PETG (Figure 13a), representing a failure caused by the individual filament failures within the specimen. This characteristic failure mode is distinctive in Additive Manufacturing [37; 38; 39; 40]. However, in the case of the reinforced specimen, a more ductile failure is observed (Figure 13b), clearly influenced by the movement of the reinforcements within the material matrix. This effect might contribute to the alteration of the matrix's behavior and, consequently, result in a reduced elongation capacity due to the accumulation of reinforcements in critical zones of the specimen. Figure 11: Results of tensile tests (stress–strain) for PETG-CF material. In addition, most of the fractures are located in similar positions on the tensile test specimens, Figure 14. This effect can be confirmed under each combination of printing parameters (layer thickness, temperature), ensuring the uniformity of the printing conditions and the material homogeneity through the evaluation of three repeated tensile tests. A similar effect appears when the specimens are subjected to compression tests, where a strong dependence on the layer thickness appears in the case of PETG (Figure 15a). This effect is also observed in PETG and PETG-CF. Figure 7.0 Fracture behavior under tensile tests for xxx conditions in PETG and PETG-CF. Figure 7.1 Mean tensile test results (**(a)** strain; **(b)** stress) for PETG and PETG-CF material. Figure 7.2 Fracture analysis: **(a)** PETG; **(b)** PETG-CF. agrees with the study of [PERSON] et al. [16] who defined that the most influential parameter in the results is the layer thickness. It can be seen that at 0.15 mm thickness the material resists a greater stress in the elastic zone, and this decreases as the layer thickness increases. When looking at the fluence zone (or elasto-plastic transition) for the three thicknesses it seems that the change from one zone to another follows a similar pattern. However, this is not the case for the plastic zone, where the 0.15 mm thickness gives a part performance that deviates from what would be expected, decreasing drastically before it starts to grow steadily, as in the other cases. On the other hand, for the PETG-CF material (Figure 15b), the result is very similar in the elastic zone of the graph, decreasing with the increase in the thickness of the thickness used; the fluence zone is similar in the three cases, although less accentuated, predictably due to the reinforcement. The plastic zone grows steadily as the layer thickness increases, without showing a change in trend as occurs with PETG. Therefore, it can be seen that the compression result seems to be more stable in the case of PETG-CF. When the data are analyzed as a whole (Figure 16), it can be seen that in the case of PETG-CF, the results are more consistent and show better performance. Therefore, the incorporation of reinforcement improves certain properties, such as compression strength. Compression tests show similar effects in both specimen types (CF-reinforced PTEG and non-reinforced PETG). The fracture of the compression test specimens has not been  
Figure 7.3 Maximum compression test results for PETG and PETG-CF material. Figure 7.4 Compression tests (stress–strain): (**a**) PETG; (**b**) PETG-CF. detected. The deformation of the cylindrical test specimens results in the increase in the diameter size in the middle of the specimen, as shown in Figure 7.5  
Finally, an ANOVA analysis shown in Table 2 was carried out to determine the statistical influence of the manufacturing parameters of the specimens on the variables studied, resulting in the following considerations: