PSI - Issue 77

6

Klusák Jan et al. / Procedia Structural Integrity 77 (2026) 432–439 Klusák Jan, Kozáková Kamila, Seitl Stanislav / Structural Integrity Procedia 00 (2026) 000–000

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Fig. 5. Critical distance curves for S460 NL (a), S690 QL (b), and S960 QL (c) steels (smooth polished samples) This state can also be expressed in terms of (theoretical stress concentration factor) which represents stress amplification due to geometry, and (the fatigue notch factor) which corresponds to the actual impact on the fatigue life of material. is always less than or equal to (Liao, et al., 2020). However, here ≥ for =0 . This fact indicates that the surface inequality plays a significant role in fatigue life determination. This is apparent mainly from Fig. 3(c), where the S-N curve for smooth and polished samples is far above the curve for notched samples. For this reason, as-machined samples were also tested and evaluated. Figure 6 shows the dependence of based on the S-N curve for as-machined smooth samples. Similar surface quality of smooth and notched samples leads to more reliable results. The critical distances =0 only occur for long fatigue lifes, where even small defects play a significant role.