PSI - Issue 77

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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and the predicted notch (Kozáková, et al., 2024). Nevertheless, knowledge of the critical distance remains crucial for predictions.

Nomenclature D

the narrowest diameter of the specimen geometrical stress concentration factor critical distance of a model notch number of cycles to failure r radius of notch a stress amplitude an nominal stress amplitude of notched specimen a s nominal stress amplitude of smooth specimen σ yn ��� ( ) K t K f l m N f fatigue notch factor

average stress over the critical distance at a notched specimen

2. Testing specimens To determine the critical distance from the experimental data, it is necessary to measure two sets of S-N curves. One set should be of smooth specimens and the other of specimens with a model notch. The fatigue lifetime of other notches can then be predicted based on these curves. This paper uses six different notch radii. Table 1 shows the notches radii and corresponding stress concentration factors = max / nom . Fig. 1 shows the basic geometry of the smooth and notched specimens for ultrasonic fatigue testing. Table 1. Notches used for fatigues testing. Notch radius r (mm) 3 1.5 0.8 0.4 0.2 0.1 K t (-) 1.47 1.8 2.23 2.87 3.74 4.78

Fig. 1. Smooth and notched specimens for ultrasonic fatigue tests