## 5 Conclusions  
We have studied the possibility of isolating acoustic emission data from the model background signal which was used to simulate the performance of an industrial rotary equipment. A useful signal (AE pulse) was obtained in the experiments on uniaxial compression of CFRP samples with continuous recording of acoustic emission signals. It was found that in all types of samples the amplitude of the AE signal monotonically increases with time, and the activity of acoustic emission (before the fracture) reaches 800-900 pulses per second. It is shown that, despite the predominance of low-amplitude pulses in the total mass of recorded signals, the medium- and high-amplitude AE pulses are recorded long before the fracture time, starting from the middle of the first stage of the acoustic emission activity in each of the experiments. This effect enables us to develop an algorithm for isolating useful AE pulses (induced by damage accumulation in the composite part) against the background of a noise-like signal. We have demonstrated (even taking into account the high amplitude of the background signal) that the AE signals comprising of 5, 10, 20% of all signals can be reliably detected long before the \"actual\" fracture onset. Analysis of the acoustic emission data obtained for all three types of materials shows that all single pulses can be divided into three groups with respect to the maximum of frequency spectrum: low-frequency pulses with the maximum of frequency spectrum in the range of 200-350 kHz, medium-frequency pulses with the maximum of frequency spectrum of about 420 kHz, and high-frequency pulses with the maximum of frequency spectrum more than 500 kHz. Two of these four groups were observed in the experiments on uniaxial  
Figure 16: Relative detection time for the AE pulses comprising of 5, 10, and 20% of all the reliably detected pulses in each of the laboratory experiments (uniaxial tension of the woven laminate sample cut along the warp and weft directions (**a**) and the unidirectional CFRP sample cut along the fiber direction (**b**) at various background signal intensities). tension of CFRP samples (these are low- and medium-frequency groups). The characteristic frequencies of spectrum maximum for these groups are 320 and 420 kHz, respectively. The remaining two groups are located in the high frequency region (above 500 kHz) and are represented by a large number of recorded pulses. Therefore, we can conclude that high-frequency AE pulses can be associated with the sources such as interlayer shear and delamination. The useful signal was isolated against the background of noise by analyzing two typical cases: separation of a time-localized useful signal from a continuous background signal and isolation of a time-localized useful signal against the background of periodic local acoustic pulses. The strategy proposed for the first case requires sequential implementation of the following procedures:  
* Frequency filtering of the original signal with a high-frequency filter having a cutoff frequency of 200 kHz. * Isolation of single AE impulses with a maximum amplitude that exceeds the maximum amplitude of the background signal by 5 dB. The strategy developed for the second case involves:
* Decomposition of the signal into empirical modes and construction of the first of these modes. * Separation of single AE impulses from the entire data volume. * Multiparameter cluster analysis of a complete set of single pulses; the cluster associated with pulses in which the background acoustic pulse prevails (the case when the amplitude of the superimposed AE pulse is much less than the background acoustic pulse) is excluded from consideration. Conceptualization, O.P. and I.P. ; Investigation, I.P., A.P. and O.P. ; Methodology, I.P. and A.P. ; Formal analysis, I.P. and O.P. ; Project administration, O.P. ; Writing original draft, I.P., O.P. and A.P. ; Writing--review&editing, O.P., I.P. All authors have read and agreed to the published version of the manuscript.