PSI - Issue 68

Robert Szlosarek et al. / Procedia Structural Integrity 68 (2025) 1173–1180 Robert Szlosarek et al./ Structural Integrity Procedia 00 (2025) 000–000

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Fig. 3. total strain fatigue life diagram with data of Nitzsche et al. (2024). The raw data of the experiments were analyzed at eleven points of the lifetime. The obtained parameters for ′ and ′ were approximated by a polynomial function of third order. Fig. 4 shows the values and fitted functions for both datasets.

Fig. 4. (a) parameter ′ with the corresponding fitting function; (b) parameter ′ with the corresponding fitting function. Using these functions, the lifetime of all performed experiments was determined with the computational framework. Fig. 5 shows the gained stress amplitude and damage over the cycles for representative tests of swaged X2CrNiCuN17-6-4 with a total strain amplitude of 0.8 % and 0.6 %. The graph of the stress amplitude shows a constant value up to a damage value of 0.01. This was implemented to prevent numerical instabilities. Furthermore, the stress amplitude varies in dependency of the damage value as it was observed in the experiment. This represents a significant difference to the approach with the values taken at half of the lifetime. Furthermore, the stress amplitude with the functions for ′ and ′ does not match the experimental data perfectly. Since the values for ′ and ′ are fitted by a set of seven experiments, the resulting curve is an average value out of all input data. Resulting from the nonconstant stress amplitude, the progression of the damage curve is also nonlinear.