PSI - Issue 57

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Jan Papuga et al. / Procedia Structural Integrity 57 (2024) 79–86 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 2. Left: Fatigue results including the regression analysis by the Kohout-V ěchet S -N curves. Right: Fatigue strength ratio  and the ratio between fatigue strengths on axial channel for in-phase and out-of-phase load regimes across various interpolated lifetimes.

Table 2. Parameters of the K&V formulas and the statistical evaluation of the regression fit. Parameter Push-pull Torsion In-phase Out-of-phase a 5294 1205207 196277789 1691  -0.355 -0.795 -1.285 -0.258 B 10275 103645 63451 11844 C 187443 328189 150601 454792 R 2 0.965 0.986 0.970 0.950 s logN 0.182 0.182 0.318 0.230 s S 8.250 3.363 5.835 6.942

3. Multiaxial fatigue analysis Multiaxial tension torsion fatigue experiments were run to show the response of the AM material to the questions postulated by Papuga et al. (2019 and 2021): How the various fatigue strength criteria behave if the same stress amplitudes on both applied load channels are applied in the in-phase and the out-of-phase combination? Which load regime at the same stress amplitudes causes higher damage? Paper by Papuga et al. (2021) highlighted that it is better to perform such analyses on thin-walled specimens to decrease the potential effect of the non-constant duration of the crack growth phase on this basic question. It also showed that to highlight the potential effect of phase shift between the tension and torsion load channels, brittle materials could be more interesting. The brittleness of the material was assessed by Papuga et al. (2019, 2021) via the fatigue strength ratio  =  FS /  FS , which compares the fatigue strengths in fully reversed push-pull  FS and in fully reversed torsion  FS . Fatigue strength ratio  across various interpolated regions is provided in Fig. 2, right. It is obvious that for different fatigue lifetimes it reaches values from 1.1 (i.e., close to brittle response) to 1.35, where it approaches the common ductile response. 3.1. Analyzed criteria From many various fatigue strength criteria, see Papuga (2011) or Papuga et al. (2022), four criteria were chosen: • Quadratic Critical Plane criterion (QCP) as defined by Papuga and Halama (2019) to represent the typical critical plane criterion; • LZ (Liu-Zenner) integral criterion - Zenner et al. (2000); • Dang Van (1973) criterion (DV) using the hydrostatic stress together with the maximum shear stress amplitude, because it represents the most often implemented solution in commercial fatigue solvers [13];