# Research on Basic Properties of Polymers for Fused Deposition Modelling Technology
## 3 Results
### SEM Scrap Observation After Three-Point Bending Test  
SEM observations of the surface conditions of fractures obtained after strength tests were carried out at 40\(\times\) and 250\(\times\) magnifications on samples coated (sprayed) with graphite. Reference areas located near the center of the obtained fractures were selected for testing. The SEM topography of the fracture surfaces obtained after the static three-point bending test for the selected samples is shown in Figure 23. The drawing also shows the observation areas selected for research. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{\begin{tabular}{c} **R\({}_{y}\)** \\ **Yield Stress [MPa]** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Elongation at Yield** \\ **[mm]** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **R\({}_{u}\)** \\ **Ultimate Tensile** \\ **Stress [MPa]** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Elongation at Break** \\ **[mm]** \\ \end{tabular} } \\ \hline
1. & PETG Carbon & 113.69 \(\pm\) 0.52 & 2.14 \(\pm\) 0.004 & 112.59 \(\pm\) 0.79 & 2.38 \(\pm\) 0.001 \\ \hline
2. & FiberFlex 40D & - & - & - & - \\ \hline
3. & PETG Sunlu & 36.55 \(\pm\) 0.31 & 1.66 \(\pm\) 0.020 & 2.41 \(\pm\) 0.03 & 0.22 \(\pm\) 0.005 \\ \hline
4. & HIPS Devil Design & 22.96 \(\pm\) 0.73 & 2.33 \(\pm\) 0.020 & 9.14 \(\pm\) 0.02 & 5.31 \(\pm\) 0.010 \\ \hline
5. & TPU & - & - & - & - \\ \hline
6. & PA+15 CF & 98.26 \(\pm\) 0.20 & 3.55 \(\pm\) 0.040 & 1.99 \(\pm\) 0.03 & 11.86 \(\pm\) 0.080 \\ \hline
7. & PETG 3 DAActive & 74.02 \(\pm\) 0.08 & 3.12 \(\pm\)0.020 & 70.77 \(\pm\) 0.08 & 3.35 \(\pm\) 0.060 \\ \hline
8. & PLA 3 DAActive & 66.02 \(\pm\) 0.10 & 1.56 \(\pm\) 0.050 & 1.20 \(\pm\) 0.10 & 8.48 \(\pm\) 0.150 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties obtained from three-point bending test. Figure 22: Stress–displacement curve from three-point bending test for (**a**) non-elastic polymers and (**b**) elastic polymers. On each of the observed sample fracture surfaces, the influence of the direction of the print paths on the structure and surface topography of the obtained fractures was revealed. The band structure of the resulting fractures is best revealed by observations carried out at low magnifications of 40\(\times\) to 60\(\times\). Therefore, in the case of fracture surfaces of samples without the presence of fibers in the matrix, such as PETG Sunlu, PETG 3 DActive, HIPS Devil Design, and PLA, a system of faults related to the passage of the crack front through areas of local deformation is visible on the fracture surfaces of the samples. They are formed along the (vertical) print paths. An example of a fault pattern along the (vertically arranged) print paths of the HIPS Devil Design sample is shown in Figure 24a. A similar, although less transparent, band arrangement of faults is characterized by breakthroughs in samples containing the fibers PETG Carbon and PA+1 SCF Rosa 3D. An example of the fracture surface of the PETG Carbon sample in a general view obtained at 40\(\times\) magnification is shown in Figure 24b. Faults forming extensive planes are observed on the scrap surfaces of the PETG Sunlu samples compared to the surfaces of the PETG 3 DActive samples, where they are clearly denser (Figure 25). In both samples, the transition between adjacent planes is separated by a sharply outlined edge. Moreover, numerous micro-faults are visible on the fault surfaces, creating a characteristic strition effect, and their number clearly increases at the fractures of the PETG 3 DActive samples. In both samples, the fracture characteristics are appropriate  
Figure 23: General view of sample fracture surfaces of samples after the R\({}_{\text{g}}\) bending strength test, with markings of the areas where observations were made: (**a**) PETG Carbon; (**b**) PA+1 SCF Rosa 3D; (**c**) PETG 3 DActive; (**d**) PETG Sunlu. The red area shows local deformations which are formed along the (vertical) print paths.