PSI - Issue 24

7

Lorenzo Bergonzi et al. / Structural Integrity Procedia 00 (2019) 000–000

Lorenzo Bergonzi et al. / Procedia Structural Integrity 24 (2019) 213–224

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which corresponds to the average minimum layer thickness of a single layer pass for DMLS. This approach is highly conservative, since grain are usually smaller Yan, Xiong, and Faierson (2017).

Table 3. Obtained geometrical ratios and recommended ones. Recommended value ⁄ > 3 ⁄ > 0.5 % B ⁄ ≥ 1.25 ? > % + 1.5, % Obtained value 15.00 0.71 1.50 15 > 12.66

3.1. Stress intensity factors: round fillets vs spline Stress intensity factor ( D ) comparison between round fillet and spline curve is offered in Figure 4: in particular ASTM E8M Type I, ASTM E8M type V and ASTM E8M sheet type, different MaCh3D round fillet radiuses and spline are reported. It is possible to see how spline profile determines the lowest of the stress concentrations factor, expressed according to Eq. 5. D = $$ % ⁄ (5) % = ' % ⁄ (6) Where $$ is the stress along specimen axis, whilst % is defined according Eq. 6, ' being the reaction force on the middle plane of the specimen determined from FE model.

Figure 4. Stress concentration factor (Kt) for ASTM specimens, MaCh3D fillet radii and spline.

3.2. Contact force distribution along specimen profile Since spline fillet influences the shape of specimen head, it was important to verify that contact behavior during load application remained unchanged in respect to the full size MaCh3D specimen. To do so, spline profile started at the same location along the edge where full-size round fillet begins. In this point, where there is a change in curvature, main contact between the sample and the seat happens. This behavior was maintained also for miniaturized specimen, achieving good accordance between contact force maximum as determined for full size and mini specimen with spline profile, as shown in Figure 5 (a) where contact forces were normalized respect the maximum value, whilst in Figure