PSI - Issue 30

V.P. Gulyaev et al. / Procedia Structural Integrity 30 (2020) 40–44 Gulyaev V.P., Petrov P.P., Stepanova K.V. / Structural Integrity Procedia 00 (2020) 000–000

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The width of the atomic planes lines (220) of the samples and the standard at Wolf - Bragg reflection angles is 2 θ = 124.24 degrees. The diffraction lines profiles were obtained at the points of sample effective part from 2 and 3 batches of steel samples (see Fig. 2). 3. Results and discussion The FWHM broadening values of diffraction lines profiles of surfaces of 09G2S steel samples cyclically deformed at different levels of the maximum cycle stress σ max obtained by X-ray in 2009 are listed in column 3 of table 2. Changes in the FWHM broadening of the diffraction lines profiles of elastically deformed samples relative to the FWHM of the reference (unloaded) one indicate, that the external cyclic load causes microstrains of the substructure, in accordance with Rekomendacii (1988), and researches carried out by Botvina (2008) and Klevtsov (2006). A decrease of the FWHM broadening values at cyclic loading with a maximum stress σ max = 0,9 σ 0,2 shows the completion of distinct microplastic strain stage of substructure elements.

Table 2. FWHM broadening of the diffraction lines profiles after cyclic loading and long-term storage for 10 years.

FWHM

Number of Measurements

2019 After long-term storage

2009 After cyclic loading σ max

9 (standard samples)

σ max =0

0,55 … 0,57 1,02 … 1,41 0,89 … 1,24 0,58 … 0,83

- -

9 9

σ max =0,5 σ 0,2 σ max =0,7 σ 0,2 σ max =0,9 σ 0,2

0.12 … 0.162 0.15 … 0.20

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In 2019, the diffraction lines profiles of the effective parts of steel 09G2S samples cyclically deformed in 2009 and stored under normal conditions were obtained on Rigaku Ultima IV diffractometer. X-ray was conducted at the same 3 points illustrated in Fig. 1a along the central axial line of the samples effective parts from 2 and 3 batches cyclically loaded in 2009 with maximum cycle stresses, cycle amplitudes σ max = 0,7 σ 0,2 and σ max = 0,9 σ 0,2 . The FWHM broadening values are listed in table 2. The FWHM broadening of samples with different levels of maximum stresses σ max , measured immediately after cyclic deformation in 2009, indicate that the greatest accumulation of microdeformations of substructure elements of 09G2S steel is observed in the range of cycle stresses close to σ max = 0.5 σ 0.2 . Perhaps this experimentally confirms the linearity of the accumulation of substructure fracture up to a given stress level. 4. Conclusions It was found that the experimentally determined values of the FWHM broadening of the diffraction lines profiles, measured in 2009 immediately after cyclic deformation of 3 groups of laboratory samples of 09G2S steel with 3 different levels of maximum cycle stresses σ max = 0.5 σ 0.2 , σ max = 0.7 σ 0.2 , σ max = 0.9 σ 0.2 , significantly decrease after holding for a long storage time in an unstressed state. Long-term storage of samples subjected to cyclic loading with maximum cycle stresses σ max not exceeding the yield strength σ 0,2 of 09G2S structural pipe steel promotes the stress strain state relaxation (see table 2). This obvious fact to some extent contradicts the theoretical principles of the fatigue damage accumulation. Thus, further investigation is necessary to explore the issue in detail. Acknowledgements This work was supported by Larionov Institute of Physical and Technical Problems of the North Federal Research Center "Yakut Scientific Center of the Siberian Branch of the Russian Academy of Sciences", and funded by Ministry of Science and Education of Russian Federation, Project III.28.1.1 in the frames of Program for Basic Research of the Siberian Branch of Russian Academy of Sciences.