PSI - Issue 59

Ivan Pidgurskyi et al. / Procedia Structural Integrity 59 (2024) 314–321 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The studies were carried out for an energetically stable crack shape a/c = 0.786, for which the SIF along the contour is practically the same. The following levels of single overloads were modeled: Q OL = 1.67; 1.8; 2.0 and 2.2, which were combined with the cyclic stresses of the main cycle σ = 120; 150; 187.5; 200 MPa. The stress ratio in all cases was R = 0.25. It was established (Fig. 8) that increasing the overload level Q OL leads to increase in the number of delay cycles N D . It was also found that with smaller SIF ranges, retardation N D is longer and, conversely, when the SIF range increases, retardation decreases. Such regularities are observed for each level Q OL .

Fig. 8. Dependence of the crack growth retardation N D after single overloads of different levels on ΔK A (steel 09Mn2Si).

The obtained results of simulation of the influence of the main cycle SIF range on the surface crack growth retardation in low-alloy steel 09Mn2Si after an overload Q OL = 2.0 were compared with the data obtained during the development of surface and through-thickness cracks in structural steels at the same overload Q OL = 2.0 (Fig. 9). Based on these results, the N D – ∆ K trend was constructed (Fig. 9).

N , cycle

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1 – е xp. 2 - Panasiuk (1990) 3 - Robin et al. (1983) 4 - Song and Shieh (2004) 5 - Pokrovskii et al. (1996) 6 - Kishimoto et al. (1989)

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ΔК , а

Fig. 9. Dependence of the number of delay cycles N D on the range of the main cycle ∆ K for structural steels at the overload factor Q OL = 2.0.

Therefore, an increase in the range of SIF leads to a decrease in the number of delay cycles N D both for 09Mn2Si 09Mn2Si steel and for other structural steels, which is consistent with the analysis (Skorupa (1998)). This feature must be taken into account when assessing the durability of structures and their elements. Conclusions The main regularities of the effect of overloading on the surface fatigue crack growth retardation in low-alloy steel 09Mn2Si under uniaxial tension of the plates were investigated. It was found that for an energetically stable