PSI - Issue 36

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

360

5

Fig. 3. Generalized scheme of the AE characteristics of structural materials having di ff erent technological inheritance.

The Fig. 3 presents a generalized scheme of AE characteristics of products with di ff erent technological inheritance according to the AE model of cyclic degradation of materials named above. It was established that the dependences of the AE count rate on the relative cyclic stresses for materials of di ff erent classes have identical features. First, it is a phasing that manifests itself in an abrupt change in the growth rate of AE activity of the material after reaching a certain value of the relative stresses of the cycle. Secondly, it is a significant change in the AE activity of a particular material after ultrasonic treatment at each of the recorded stages of loading. At the stage of microyielding, as well as at the stage of deformation hardening, there is an increase in the rate of growth of the total AE count. However, the ratio of the duration of these stages changes: in the samples after surface hardening, the microyielding stage is prolonged, and the deformation hardening stage is reduced.

Table 3. Mechanical properties of the samples investigated under the high-cycle fatigue conditions.

σ ∗∗ AE , MPa

n AE ( II )

n AE ( III )

γ

N ′ , cycles

material

N

H

N

H

N

H

N

H

medium carbon steel

10 20

2.277 2.365 5.127 2.444

2.662 2.732 8.773 3.890

7.766 8.056 15.38 7.113

9.339 11.09 26.32 11.32

265 330 490 455

330 375 635 580

1.075 1.091 1.082 1.090

1.076 1.080 1.087 1.086

low-alloy steel

heat-resistant Ni-based alloy deformable Ti-based alloy

100 200

The results of AE studies, which are summarized in the Table 3 allow to connect the abscissa of the breaking point of the cyclic AE characteristic with the value of the endurance limit by following relation 3 with a relatively stable coe ffi cient of proportionality γ :

σ − 1 = γ · σ ∗∗ AE

(3)

Thus, the evaluation of the limit state of power plants in conditions of HCF can be carried out based on the results of non-destructive AE control. This enables assessment of the e ff ectiveness of the technological measures aimed at increasing the life of parts of the power plants, based on non-destructive AE control.