PSI - Issue 28

L.R. Botvina et al. / Procedia Structural Integrity 28 (2020) 2118–2125 L.R. Botvina et al. / Structural Integrity Procedia 00 (2019) 000–000

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The dependence of the relative area of the damaged surface S * on the deformation corresponds to a power relation with indexes equal to 3.8 and 2.4 for 15Cr2MnMoV steel and low-carbon steel, respectively, which show that the rate of damage development in 15Cr2MnMoV steel was higher than in low-carbon steel. 3.3. Dependences of acoustic emissions parameters on the relative number of cycles Figure 4 shows the dependence of the acoustic parameters estimated during the tension on the relative number of pre-loading cycles.

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Fig. 4. Dependences on the relative number of cycles of the average values of the AE intensity, the total number of acoustic signals Σ N A E , the slope coefficient γ (a, b) and the total energy of AE signals Σ E AE and the fracture energy (c, d) for specimens from 15Cr2MnMoV (a, c) and low carbon steel (b, d) It follows from the figures that the given acoustic parameters decrease with the relative number of cycles, although at N/N f =0, 5 in the graph of Fig. 4, b, obtained for low-carbon steel, there is an increase in some acoustic characteristics that correlate with a similar increase in the cumulated energy of AE signals and the fracture energy estimated by the area under the deformation curves (Fig. 4, d). Similar increase in the acoustic and fracture energies at N/N f =0, 5 is also observed for 15Cr2MnMoV steel (Fig. 4, c). The reason for this increase may be due to changes in the processes of cyclic hardening and softening of steel during pre-сycling. Analysis of the amplitude distributions of acoustic events for both steels (Fig. 2, e, f) plotted for each of the selected in Fig. 2 stages of damage development showed a twofold decrease in the b AE -value parameter at the final stage of fracture at N/N f =0.7 compared to a cyclically undeformed specimen. At the other stages, its values change slightly, but at the third stage, at which the ultimate strength of the material is reached, for all tested specimens, they exceed