PSI - Issue 75

S.S. Penkulinti et al. / Procedia Structural Integrity 75 (2025) 1–9 Author name / Structural Integrity Procedia (2025)

7

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, ( ( , )) / , ( ( , ))

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(13) It was found that =2.36 for the case of local-analysis carried out on the LoF defect population. The same procedure was applied to the results from non-local analyses. A similar surface response was obtained, with the minimum and maximum fatigue strengths obtained for =0° and =90° , respectively. However the anisotropic factor value has decreased to =1.42 . Similar results were also obtained for the gas pore population, with = 1.27 for local analysis, and = 1.11 for the non-local analysis. The decrease in the values observed for gas pores, as compared to LoF defects, can be attributed to the spherical symmetry of the gas pores that minimizes stress concentration directionality. Note however that the anisotropic factor does not reach a value of 1 as for a perfect ideal sphere. In addition, all results suggest that the anisotropy in the fatigue behavior is reduced when the non-local parameter increases. This can be interpreted by considering that the non-local parameter is correlated to the El-Haddad parameter 0 , as detailed in the work of Taylor (1999), 0 being the critical defect size below which defects have no impact on the fatigue resistance. In other words, the use of a high value in the numerical model should correspond to a material with a high 0 value and therefore a limited sensitivity to defects. Consequently, one would expect a lesser impact of defects on the computed fatigue resistances and therefore on the fatigue anisotropy when is increased. Fig. 4 shows empirical cumulative distribution functions (ECDF) of the fatigue strengths obtained from the different defects loaded in the critical direction ( =0°) and the non-critical direction ( =90°) , for the case of local analysis. In agreement with the low anisotropic factor for gas pores ( = 1.27) , there is limited impact of the loading direction on the gas pore fatigue strength distribution. For the LoF defect population, one can see that increasing the polar angle not only increases the mean fatigue strength but also the scatter of the results. It is worth noting that despite an increase in the mean fatigue resistance, low fatigue strengths similar to that of the critical orientation can still be obtained with =90°. Yet, a practical implication for part designers is that a component subjected to tensile loading should be positioned on the build plate so that the loading direction coincides with an horizontal direction in order to limit the impact of defects on the fatigue resistance.

Fig. 4: Distributions of the fatigue strengths associated to critical ( =0°) and non-critical ( =90°) directions. Local analysis (from Penkulinti et al. (2025)).