PSI - Issue 68

Jan Klusák et al. / Procedia Structural Integrity 68 (2025) 660–665 Jan Klusák, Kamila Kozáková/ Structural Integrity Procedia 00 (2025) 000–000

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determined for particular N f . When we calculate the critical distance for whole range of number of cycles to failure, we obtain the dependence of l cr on N f (Fig. 2).

Fig. 2. The critical distance l cr of the calibration notch.

3. Fatigue life prediction of notched specimens Based on the knowledge of the critical distance l cr , the fatigue life of different notches can be predicted. It has been shown that the critical distance depends not only on the number of cycles but also on the notch radius (Kozáková and Klusák, 2024). For this reason the critical distance used for the predictions of different notches is modified by the ratio of stress concentration factors. p = cr ∙ tm tp (4) where K tm and K tp stand for the stress concentration factors of the model notch and the predicted notch respectively. Fig. 3 shows curves of the critical distances l p of different predicted notches.

Fig. 3. The critical distance l cr of the calibration notch (red) and the critical distances l p of predicted notches (blue).

The prediction of fatigue life is performed as an inverse task to the procedure of l cr determination. For a predicted notch we have the distribution of SED (from the numerical solution of the geometry and for arbitrary level of loading), see the left part of Fig. 4. From the distribution we can read the average value of the SED over the whole cross section ( ( / ) and over the critical distance of the predicted notch ( > @ . The value of is obtained from Eq. 4 for particular number of cycles to failure . For the same the value is known from the fatigue − curve of the smooth specimen. Finally the level of SED of the predicted notch is given by the following relation: ! "# ( f ) = !$ ( f ) ∙ %&' ! " %&)* ( # + (5)