# Investigation of Acoustic Emission of Cracks in Rails under Loading Close to Operational
## 3 Results and Discussion
It should also be noted that there is a significant difference in the AE parameter values corresponding to defective and defect-free specimens. At the maximum load value equal to 45 kN, the number of AE hits recorded per loading cycle for defect-free specimens is, as a rule, no more than 20 AE hits per loading cycle. In contrast, for defective specimens, the AE hits rate, as a rule, turns out to be 1.5-2 times higher. The amplitude distribution quantile q0,9 for specimens with a defect is 4 dB higher than for defect-free specimens, which increases the proportion of high-amplitude signals in the data sample. However, for specimens with different crack locations and for different crack lengths, a pronounced difference in the AE data is not observed; Figure 11 shows the variability plots, which show the scatter of the AE parameters for different locations of cracks. Analysis of the data depicted in Figure 11 shows that for groups of specimens with different locations of the crack, the intragroup dispersion turned out to be greater than the intragroup dispersion. Therefore, the location of the crack does not affect the reliability of its detection by the AE testing. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Defect Location** & **Specimen** & \multicolumn{3}{c}{**Average Number of Hits**} & \multicolumn{3}{c}{**Quantile q0,9**} \\ \hline  & & 15 kN & 30 kN & 45 kN & 15 kN & 30 kN & 45 kN \\ \hline  & R1 & 1 & 9 & 21 & 50.8 & 50.2 & 50.9 \\ \cline{2-8} no defect & R2 & 3 & 13 & 11 & 52.2 & 53.5 & 54.9 \\ \cline{2-8}  & R3 & 2 & 13 & 18 & 52.6 & 54.3 & 53.3 \\ \cline{2-8}  & R4 & 3 & 12 & 23 & 52.0 & 52.8 & 54.4 \\ \hline mean & & 2.3 & 11.8 & 17.5 & 51.9 & 52.7 & 53.4 \\ \hline  & R5 & 3 & 24 & 45 & 51.3 & 53.9 & 56.3 \\ \cline{2-8} web & R6 & 4 & 7 & 37 & 52.3 & 57.1 & 57.5 \\ \cline{2-8}  & R7 & 4 & 11 & 44 & 53.3 & 57.7 & 58.2 \\ \cline{2-8}  & R8 & 2 & 12 & 39 & 52.5 & 58.3 & 59.6 \\ \cline{2-8}  & R9 & 2 & 19 & 34 & 53.7 & 57.5 & 60.3 \\ \hline mean & & 3.14 & 16.43 & 41.00 & 52.71 & 56.86 & 58.36 \\ \hline  & R10 & 2 & 14 & 29 & 49.9 & 55.4 & 56.9 \\ \cline{2-8} web-head & R11 & 2 & 33 & 47 & 53.2 & 55.1 & 57.8 \\ \cline{2-8}  & R12 & 2 & 9 & 32 & 51.9 & 55.4 & 56.9 \\ \hline mean & & 2.0 & 18.7 & 36.0 & 51.7 & 55.3 & 57.2 \\ \hline  & R13 & 2 & 31 & 36 & 52.5 & 59.1 & 59.8 \\ \cline{2-8} web-foot & R14 & 5 & 14 & 19 & 52.6 & 57.7 & 59.7 \\ \cline{2-8}  & R15 & 4 & 12 & 33 & 52.6 & 58.1 & 59.4 \\ \hline mean & & 3.7 & 19.0 & 29.3 & 52.9 & 58.3 & 59.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Values of AE parameters obtained during testing. Since the presence of a crack leads to the appearance of AE signals of greater amplitude and duration, most clearly, AE data corresponding to defective and defect-free specimens differ in the correlation graph showing the relationship between the AE hits duration and its amplitude. Three areas can be distinguished on the correlation plane. Area 1, corresponding to the noise of the loading machine and contact friction, is empty (excluding the intersecting part of regions 1 and 2, which corresponds to region 2) since these types of noises are filtered parametrically and mechanically due to the introduction of damping pads made of acoustic felt. In region 2, signals of low amplitude and duration are localized, which can be identified as structural noise of rail steel caused by the presence of non-metallic inclusions and deformation of the cementite network in the material structure. The signals associated with the development of a crack are localized in region 3. In this region, there is a pronounced difference in the graphs corresponding to defective and defect-free specimens. Table 4 shows the values of the parameter N\({}_{3}\) corresponding to the number of indications in area 3 of scatterplots (Figure 12) for defective and defect-free samples. Analysis of the data given in Table 4 shows that the values corresponding to defective and defect-free specimens differ significantly from each other.