## 3 Results and Discussion
### Fracture Resistance Testing  
The results of fracture resistance testing are given in Figures 1 and 2. The key values are graphically represented with the box chart. The box is determined by the 25 th and 75 th percentiles. The whiskers are determined by the 5 th and 95 th percentiles. The mean value is represented with a transparent rectangle, while the separation line between the 25 th and 75 th percentiles represents the median. When the 50% infill samples are studied, there is no significant deviation in impact energy values between them, regardless of their thickness.  
If the angle at which the sample is penetrated is compared (0 degrees or 180 degrees), it is observed that the mean values of impact energy and the medians are nearly identical when the sample is impacted at an angle of 0 degrees, with a slightly higher dispersion of values for samples with a thickness of 5 mm. On the other hand, for samples tested at an angle of 180 degrees, there are fewer differences within the samples, as evidenced by almost identical box sizes. If one measurement with a significant Jump in value (3 mm at 50% infill and 180 degrees impact angle) is disregarded, it can be observed that the change in position does not have a significant impact on the values of consumed energy for fracture. Although all samples have four upper and lower layers with layers in-between filled to 50%, it is evident that upper/lower layers absorb most of the impact energy.  
Due to this conclusion, the experiment with 100% fill samples was conducted without observing the impact on the first impact surface (Figure 2). Consistency in most results was  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **Sample Mass/g** \\ \hline
100\% infill 5 mm & 5.88 \(\pm\) 0.02 \\
100\% infill 3 mm & 3.56 \(\pm\) 0.01 \\
100\% infill 2 mm & 2.25 \(\pm\) 0.01 \\
50\% infill 5 mm & 4.28 \(\pm\) 0.01 \\
50\% infill 3 mm & 2.792 \(\pm\) 0.009 \\
50\% infill 2 mm & 1.928 \(\pm\) 0.0001 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mass of printed samples.  
Figure 1: Fracture resistance of PLA FDM models with 50% infill: (**a**) impact on bottom layer, and (**b**) impact on upper layer.  
Figure 2: Fracture resistance of PLA FDM models with 100% infill.  
observed, as depicted in the diagram. Earlier research indicated that increasing the number of layers enhances strength due to a higher temperature gradient and improved diffusion between the layers [24]. Nevertheless, this may also result in distortion, interlayer cracking, and the separation of parts due to frequent heating and cooling cycles, potentially causing a decline in strength over time [25].  
It was shown by the results that the profile of 100% infill with a thickness of 2 mm should be avoided. The argument is made based on the significant data dispersion in the 100% infill profile compared to the 50% infill profile, indicating that the construction of such profiles exhibits unpredictable behavior when subjected to impact. Another extreme of different values is the thickness of 5 mm. At this thickness, a significant difference in medians was observed for the 100% full profile (4.5 J) and the 50% fill profile (2.2 J/2.4 J). The full profile was proven to be incomparably more durable and suitable for application. It can be concluded that, in terms of impact strength, samples with a thickness of 3 mm are optimal. This suggests that significant material savings can be achieved by using 50% infill without compromising the mechanical properties of the PLA sample.