## 3 Results and Discussion  
The samples were subjected to tension until failure. In the process, acoustic emission was recorded. In all the samples, the failure occurred in the metal free from welds, which is why the mechanical properties of the plates rather than those of the welds were measured. Since strengthening technologies were mainly applied to the welds, and it was from the welds that AE signals were recorded, the authors decided that the results of processing AE information should be compared not with the results of static failure tests, but with the results of fatigue tests in samples being fractured along the welds. The experiment produced an array of acoustic emission data, which was processed according to the method described above for finding concentration and kinetic indicators (Table 1) at the stage of uniform fracturing in the elastic deformation zone. This zone was chosen as a zone of correct stress, since it corresponds to uniform stress in the range of operating stresses of a given material in a real object in many industrial areas. The results of recording the key AE parameters at the stage of elastic wave radiation are shown in Figure 3.  
Figure 2: Functional scheme of loaded device 1—sample; 2—transducers of acoustic emission (TAE); 3—universal testing machine; 4—control unit; 5—computer for load management; 6—preamplifier of AE signals; 7—AE signals processing unit; 8—computer for registration of AE signals. The limits of the uniform fracturing period were found by comparing the results of failure simulation (Equation (2)) with a constantly increasing stress and the experimental results of recording AE parameters (Equation (1)), under the condition that \(\xi\) and \(C(t)\) are proportional (\(k_{AE}\) = const). Figure 4 shows an example of finding the limits of the uniform fracturing period. For each of the samples at this stage, such parameters were found as the values of the concentration and kinetic strength indicators using the formulas from Table 1, MMSE (Measured Area under the Rectified Signal Envelope), which corresponds to energy (according to the energy and statistical approach to AE testing) [33,34], the average value of the amplitude, the number of pulses, and AE activity. To assess how informative the proposed method is, a correlation analysis was performed, where the correlation was found between the resulting values of concentration and kinetic indicators and traditional AE indicators (number of pulses, MARSE, etc.) and the number of cycles to failure of welded joint samples during fatigue tests, which were obtained using similar samples from the same material and the same strengthening technologies [35]. The results are shown in Table 2. The service life of the samples was calculated using Equation (5), with the value of the working stress being taken in the range of 50 to 100 MPa, as this is the average working stress in various industrial areas. Figure 3: Key AE indicators as functions of time at the stage of elastic deformations, where (**a**) is an untreated sample, (**b**) is a sample after heat treatment, (**c**) is a sample after beveling, (**d**) is a sample after ultrasonic treatment. Table 2 shows that the heat-treated samples have the highest number of pulses, activity, and MARSE, which means that there is a lot of noise and it is impossible to assessing strengthening quality using these parameters. In addition, these parameters have a positive correlation with service life, which goes against their physical significance. However, the proposed concentration and kinetic indicators make it possible to assess strengthening quality by factoring in the influence of noise, which proves their resistance to destabilizing factors. The negative value of the correlation coefficient describing the relationship between the concentration and kinetic criteria and the service life corresponds to all previously obtained results, demonstrating the stability of the relationship, which cannot be said about traditional criteria, including MARSE [33].