## 3 Results  
### AE Source Study Results  
To determine the parameters of the AE source, cyclic tension tests were performed on samples of dissimilar welded joints. Defect-free specimens and specimens with diffusion interlayers of different thicknesses were examined. A total of 16 samples were tested, including 4 defect-free samples (not subjected to additional heat treatment) and 4 samples with different heat treatment modes, with diffusion interlayers of different decarburized interlayer thicknesses of 145, 225 and 600 \(\upmu\)m.  
From the point of view of AE data, the cyclic loading of samples is a stationary process with a constant level of AE activity. Figure 8 shows the dependences of AE activity on time for a specimen of a dissimilar welded joint without diffusion interlayers and with diffusion interlayers of an average thickness of 225 \(\upmu\)m. In all experiments, the AE activity was quite low since the nature of loading of the specimens corresponded mainly to the region of elastic deformation. The average value of activity in the test series changed insignificantly in the range from 0.18 to 0.52 imp/s, with a tendency to rise up with an increase of the diffusion interlayer thickness. The presence of diffusion interlayers also influences the values of the AE hit amplitudes. When loading the welded joint samples with diffusion interlayers, the amplitude level was 40-50 dB, while when testing the defect-free samples, the AE hits mainly had an amplitude of less than 40 dB. The values of the AE hit amplitude over time are shown in Figure 9: Figure 9 corresponds to the results of testing a defect-free specimen, and Figure 9 corresponds to testing a specimen with a diffusion interlayer of about 225 \(\upmu\)m thickness. Figure 7: Photo of process pipeline (**a**) and the time realization of stationary noise (**b**). The values of AE activity and the level of AE hit amplitudes differed significantly for defect-free samples and samples with diffusion interlayers, but no direct correlation was found between the thickness of the diffusion interlayer and the values of AE parameters. Table 6 shows the average values of AE activity and the quantile 95% order of amplitude distribution. When analyzing the distribution of AE hit amplitudes, it was found that the presence of diffusion interlayers leads to a qualitative change in the type of AE hit amplitude distribution. For specimens without diffusion interlayers, the distribution corresponds to the exponential law, which is confirmed by the value of the determination coefficient R\({}^{2}\) > 0.92. For specimens with diffusion interlayers, the nature of the amplitude distribution acquires a power-law character and corresponds to the Gutenberg-Richter law. The minimum value of the determination coefficient R\({}^{2}\) for distributions corresponding to specimens with diffusion interlayers is 0.93. Figure 10a shows examples of amplitude distributions for defect-free specimens, and Figure 10b shows the specimens with interlayers of different thicknesses. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type of Specim**} & \multirow{2}{*}{**Defect Free**} & \multicolumn{3}{c}{**With Diffusion Interlayers**} \\ \cline{3-5}  & & **-145 \(\mu\)m** & **-225 \(\mu\)m** & **-600 \(\mu\)m** \\ \hline AE activity, 1/s & 0.12 & 0.38 & 0.52 & 0.43 \\ Quantile 95\% of amplitude distribution, dB & 34.3 & 41.2 & 44.1 & 43.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: AE parameters of specimens of dissimilar welded joints under cyclic loading. Figure 8: AE activity for a defect-free sample of a dissimilar welded joint (**a**) and for a sample with diffusion interlayers (**b**). Figure 9: AE impulse amplitudes for a defect-free sample of a dissimilar welded joint (**a**) and for a sample with diffusion interlayers (**b**). To form a description of the AE source parameters, it is rational to use the averaged non-normalized distribution of AE impulse amplitudes, which gives an idea of both the process activity and the AE hit amplitude values.