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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turbine engine, which requires long-term tests to verify the results of calculations, is acute. Elements of such complex power plants are operated in a wide range of power and temperature regimes, which requires the use of materials of di ff erent classes. The task becomes much more complicated if we take into account the e ff ect of strengthening operations Petukhov (2006), as well as the e ff ect of aggressive environment Yasniy et al. (2017). Taking into account various operational, constructional and technological factors only by calculation methods does not provide the necessary accuracy of forecasting the mechanical behavior of products in conditions of fatigue McEvily (2010); Tsyban’ov et al. (2020). Unfortunately, it is not possible to completely abandon long-term fatigue tests Pisarenko et al. (2014), and the material and time costs of such tests are obvious. Therefore, the development of methods for assessing the damage of structural materials of di ff erent classes on large bases of periodic load according to non-destructive methods of control remains relevant. One of the promising areas for assessing the technical condition of products operated in conditions of high-cyclic fatigue (HCF) is the use of non-destructive methods of control, in particular, the method of acoustic emission (AE) Skalskiy and Andreykiv (2006); Hudramovich et al. (2017). However, due to the di ffi culty of determining the real stress-strain state of the local volumes of material responsible for its destruction, it still remains problematic to es tablish a relationship between the degree of deformation of structural material and AE parameters under given load conditions. The purpose of the work is to study the possibility of estimating the limit state of materials of di ff erent classes with di ff erent technological heredity in the conditions of HCF on the basis of data of preliminary non-destructive testing by the AE method. The following research methods were used in the work: micro structural studies on a scanning electron microscope; estimation of dislocation density by digestion pits method; test for high-cycle fatigue by console bending; acoustic emission testing under cyclic loads. The first three of these methods constituted a standard research procedure. The details of AE control will be discussed below. The custom-designed model samples of di ff erent classes of materials made of medium carbon steel, low-alloy steel, heat-resistant Ni-based alloy, deformable Ti-based alloy were investigated. The chemical composition and mechanical properties of the studied materials are given in the Table 1. The microstructure of the studied materials is shown in Fig. 1. 2. Methods and materials

Table 1. Chemical composition and mechanical properties of the investigated materials.

composition, %

material

σ B , MPa

σ 0 . 2 , MPa

Al

C Cr

Cu Fe

Mn Mo Ni

Si

Ti

medium carbon steel

- -

0.46 -

-

base 0.54 - base 0.55 -

- -

0.23 - 0.25 -

665 980

370 780 815 690

low-alloy steel

0.38 1.00 -

heat-resistant Ni-based alloy 0.6 -

21.0 0.37 0.46 0.29 -

base 0.31 2.60 1200

deformable Ti-based alloy

6.4 -

-

-

-

-

3.3 -

0.3 base 980

The samples with di ff erent technical condition of the surface were investigated. The investigation included, first of all, examination of the samples after standard technological processing ( N ). Secondly, the samples subjected to superficial ultrasonic hardening ( H ) have been studied.