PSI - Issue 17

Radomila Konečná et al. / Procedia Structural Integrity 17 (2019) 138 – 145 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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behavior. Since the peak stress and fatigue crack initiation occur at the notch root, the geometrical deviations between design intent and actual geometry are examined there. Fig. 4 compares the semicircular notch with the notch of Type B specimens. The build direction does not affect the entire notch geometry because it is obtained by sequential layer contouring. Contour width, process parameters and system accuracy may explain slight deviations observed.

Fig. 4. Effective semicircular notch in Type B specimen (white dotted curve is theoretical 2-mm radius circle).

Fig. 5 groups together three notch views taken from specimens that share the common build direction shown by the arrow. In these cases, large global deviations from notch circularity are apparent, the most evident being for the Type C and Type A- specimens while the Type A+ specimen is macroscopically close to circular.

Fig. 5. Effective semicircular notch in three types of specimens (white broken curve is theoretical 2 mm radius circle).

As mentioned before, however, it is the local quality at the notch root that is critical for the fatigue behavior. Therefore, Type C notch is globally poor but its notch root is not too different from the theoretical geometry because the layer-by-layer fabrication locally does not introduce significant stair-stepping of the surface, see also the magnified view in Fig. 6a.