PSI - Issue 53

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Rainer Wagener et al. / Procedia Structural Integrity 53 (2024) 151–160 Author name / Structural Integrity Procedia 00 (2019) 000–000

Fig. 3: Comparison of the local stress state of the nominal CAD-geometry and the scanned “real” additively manufactured geometry including local defects like pores and surface roughness.

The stress distribution in the part of CAD-geometry is as expected. A stress concentration occurs in the notch root and with increasing distance to the root the stress decreases. On the defect-loaded realistic side the same global stress distribution occurs but, due to the pores, local stress distributions are superimposed. In contrast to the continuous and closed highly stress volume in case of the CAD-geometry, several stress hotspots occur in the real geometry. Furthermore, using the same stress level for both models in order to derive the highly stress volume (HBV) according to Kuguel (1961), Sonsino et al. (1995) and Sonsino et al. (1997) and neglecting the jagged volume in case of the real geometry (sum of all local volumes), the resulting HBV – where volumes down to 90 % of the maximum stress are included – differ. Within the nominal design side a volume of HVB = 0.2073 mm³ will be calculated, but this volume reduces to HBV = 0.1203 mm³ in the realistic side. A factor of about 1.7 between both highly stress volumes will have a noticeable impact on the calculated fatigue strength. A consequence of the multiple stress hotspots is a movement of the crack position. In the ideal geometry it is located in the notch root. Due to the imperfections like pores in the AM structure as a result of the exposure strategy, the fatigue relevant stress hotspot is shifted in the built direction. This movement depends on the material and its tendency to pore formation. Therefore, it can be influence by the exposure strategy. Finally, it has to be stated that impact of this movement of the stress hotspot and its influence on the fatigue behavior has been proved by the test results of different materials and exposure strategies. 4. Influence of the exposure strategy on the fatigue strength of notches So far it has been shown that in case of notches parallel to the built direction the local microstructure and defect distribution in the notch geometry is influence by the up- or down-skin orientation. The resulting distribution of defects is depicted in Fig. 4. schematically.