PSI - Issue 68

J.A. Ziman et al. / Procedia Structural Integrity 68 (2025) 1159–1165 J.A. Ziman et al. / Structural Integrity Procedia 00 (2025) 000–000

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the quadratic fit parameter and R 0 the electrical resistance without a change in temperature. Equation (8) was used to determine the temperature-corrected electrical resistance R corr . (7)

(8)

3. Results 3.1. Fatigue life prediction considering higher test frequencies The LITs were carried out at ambient temperature with a starting stress amplitude σ a , start of 180 MPa and a load increase Δσ a of 5 MPa per step. The step length was set to 1.8·10 5 cycles for both test frequencies. Figure 4a shows the cyclic deformation curves of the change in temperature ΔT and the change in temperature-corrected electrical resistance ΔR corr . The frequency effect can evidently be shown in terms of an increased lifetime of the specimens. Besides that, a transition of the first material response towards higher stress amplitudes can be derived (220 MPa at 80 Hz and 240 MPa at 260 Hz). The increased lifetime as a result of increasing test frequency is caused by a more pronounced limitation of dislocation mobility, which in turn lead to a delay regarding the material degradation, Jenkin (1925). Using the procedure proposed in 2.1 according to Weber et al. (2023), all exponents and coefficients required for calculating a S-N curve according to StressLife were determined. The CATs used for this purpose are shown and discussed in more detail in 3.2 to correlate their progression with the investigated reduction of the surface residual stresses σ ES . The S-N curve based on the change in temperature-corrected electrical resistance is shown in Figure 4b for both testing frequencies.

Fig. 4. (a) Cyclic deformation curves for load increase tests (LIT) for frequencies f = 80 Hz and 260 Hz; (b) S-N curves according to StressLife based on temperature-corrected electrical resistance ΔR corr for frequencies f = 80 Hz and 260 Hz.