PSI - Issue 36

Sergiy Bezhenov et al. / Procedia Structural Integrity 36 (2022) 356–361 S. Bezhenov / Structural Integrity Procedia 00 (2021) 000–000

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Fig. 1. (a) medium carbon steel; (b) low-alloy steel; (c) Ni-based alloy; (d) Ti-based alloy.

Di ff erences in the elements of the microstructure of the near-surface and central zones of the material of the samples of the studied materials after their surface hardening were not recorded. However, the method of etching pits revealed an increased density of dislocations directly near the surface of the hardened sample. Only a small number of them were observed in the near-surface zone of the sample without surface strengthening. A feature of the AE research technique is the step change of cyclic loads of products with exposure duration at each level. The maximum stresses were exceeded by 20-30 % endurance limit. The AE count rate was taken as the informative parameter of AE signals, which were recorded in the frequency band from 0.2 to 2.0MHz. The Fig. 2 schematically shows the method of non-destructive testing to obtain the AE characteristics of a particular product, which is combined with the results of its own further fatigue tests. Here, the points illustrating the stepwise increase in load are marked with 50MPa. The duration of cyclic stresses at each load level of the products did not exceed the duration of the incubation period of fatigue failure. Thus, during the AE control, each object of study remained within the stage of non-localized destruction.

Fig. 2. Scheme of step-by-step AE testing of products with their subsequent fatigue testing.