PSI - Issue 68

Martin Nesládek et al. / Procedia Structural Integrity 68 (2025) 527–533

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Martin Nesládek et al. / Structural Integrity Procedia 00 (2025) 000–000

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Papuga et al., 2023; Zaeimi et al., 2024) but also in predicting segments of the S-N curve with fewer specimens (Fargione, 2002; Lipski, 2016; Matušů et al., 2023) than conventional fatigue tests, such as those outlined in ASTM E739-10 (ASTM 1981). The temperature increase during cyclic loading, utilized by this method, is known as the self-heating (SH) effect (Meneghetti, 2007; Torabian et al., 2017). This phenomenon, which is significantly influenced by testing frequency, load amplitude, and stress ratio, typically occurs in three phases if the tests are run to specimen failure – see Fig. 1a. For the fatigue limit evaluation, it turns out that the most important role plays the stabilized temperature increase Θ , which when plotted for different stress amplitudes in the diagram in Fig. 1b constructs the so-called SH curve. By leveraging the fact that the specimen's test temperature stabilizes well before failure, a step test procedure (Fig. 2a) can be implemented. In this method, a single specimen is subjected to multiple stress amplitude levels in successive blocks, with each block running for enough cycles to ensure temperature stabilization. This greatly Fig. 1. (a) Schematic evolution of temperature during constant-amplitude cyclic loading leading to specimen failure at ! cycles. (b) Construction of the self-heating curve from stabilized temperature increases at various stress amplitudes and localization of fatigue limit σ "# .

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Fig. 2. (a) Schematic illustration of the step-test procedure. Fatigue limit evaluation approach by (b) (La Rosa, 2000), (c) (Luong, 1998) and (d) (Matušů et al., 2024).