## 3 Results and Discussions  
### Acoustic Emission Analysis  
Figures 4-7 show histograms of the acoustic emission parameters. Each figure provides the number of events (NoE) registered during the test, i.e., the frequency registered during the brittle events. Figures 4 and 5 show results of the AE parameters detected using S5 and S6, respectively, on fractured Group 1 samples, whereas Figures 6 and 7 show results for the same sensors, but on fractured Group 2 samples, respectively. The amplitude of sensor 5 was higher than that of sensor 6. Moreover, the range between 50 and 60 dB, which was the one characterized by the greatest number of events, in the graph concerning sensor 5 was higher than that of other ranges. The differences between the ranges flattened out slightly in the case of sensor 6. The results for Group 2 were similar to those of Group 1: amplitude was characterized by events of brittle fractures in the range of 50 dB \(<\) A \(<\) 60 dB. Moreover, for both sensors, the higher count values are in the range of bin C \(>\) 30. These results are in line with those found by [PERSON] et al. [16]. Concerning energy, the maximum occurrence was in the range 1000 eu \(<\) E \(<\) 5000 eu. In each graph, there are some samples which can be traced as outliers: in Group 1, samples S081 and especially S142 have higher occurrences than the average of the other samples. The same was the case for samples S143 and S172 (Group 2), which had higher values than the other samples or with respect to the average values. Figures 8-10 show the behavior of the AE parameters with respect to the radial (\(X_{\mathrm{R1}}\approx X_{\mathrm{R}}\)) and the longitudinal positions (\(X_{\mathrm{L}}\)) in terms of amplitude, counts, and energy for Group 1 and Group 2, respectively. The choice of using three-dimensional graphs was found to be the most adequate to define, at the same time, the dependence between the cumulative sums of amplitude, counts, and energy within the two directions of the wooden beam. Figure 4: Number of events (NoE) registered during brittle fracture for Group 1 recorded by sensor 5. Each sample is identified by an ID number “Saxxy” corresponding to the number of slices (xx) and the count of the produced sample in the slice (y). (**Top**) amplitude; (**Middle**) counts; (**Bottom**) energy released by the fracture. Figure 5: Number of events (NoE) registered during brittle fracture for Group 1 recorded by sensor 6. Each sample is identified by an ID number “Saxxy” corresponding to the number of slice (xx) and the count of the produced sample in the slice (y). (**Top**) amplitude; (**Middle**) counts; (**Bottom**) energy released by the fracture. Figure 6: Number of events (NoE) registered during brittle fracture for Group 2 recorded by sensor 5. Each sample is identified by an ID number “Sscy” corresponding to the number of slice (xx) and the count of the produced sample in the slice (y). (**Top**) amplitude; (**Middle**) counts; (**Bottom**) energy released by the fracture. Figure 7: Number of events (NoE) registered during the brittle fracture for Group 2 recorded by sensor 6. Each sample is identified by an ID number “Sscy” corresponding to the number of slice (xx) and the count of the produced sample in the slice (y). (**Top**) amplitude; (**Middle**) counts; (**Bottom**) energy released by the fracture. Figure 8: Three-dimensional graphs: x-axis—radial position X\({}_{\rm R}\) (mm); y-axis—longitudinal position X\({}_{\rm L}\) (mm); z-axis—cumulative sum of the amplitude, i.e., \(\Sigma\)AA (dB). (a) Group 1, S5; (b) Group 1, S6; (c) Group 2, S5; and (d) Group 2, S6. Figure 9: _Cont._  
Figure 10: Three-dimensional graph: x-axis—radial position \(X_{\rm R}\) (mm); y-axis—longitudinal position \(X_{\rm L}\) (mm); z-axis—cumulative sum of the energy, i.e., \(\Sigma\)AE (eu). (**a**) Group 1, S5; (**b**) Group 1, S6; (**c**) Group 2, S5; and (**d**) Group 2, S6.