PSI - Issue 37

G. Macoretta et al. / Procedia Structural Integrity 37 (2022) 632–643 G. Macoretta, B. D. Monelli / Structural Integrity Procedia 00 (2019) 000 – 000

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3.3. Tensile tests Per each ser of process parameters, the average values of the parameters describing the static tensile behavior of the material are reported in Fig. 10. The adoption of the A1 and A2 doesn’t introduce a reduction in the material yield and ultimate strength, which resulted to be even increased by these process parameters. The same occurred for the elastic modulus of the material. On the other side, the elongation at fracture (A%) resulted to be significantly affected, passing from values of about 44% to 20% in the case of the A2 process parameters. Despite the increase in the material porosity and surface roughness, the fatigue strength of the specimens produced by adopting the parameters A1 and A2 resulted to be lower but comparable to the baseline value, Fig. 8. The Wöhler curves, calculated according to the ASTM E739 standard, resulted to be almost parallel within the investigated cycles range, pointing out a uniform fatigue life reduction regardless of the stress level. If evaluated at a fatigue life of 1 million cycles, the reduction in the fatigue strength produced by the A1 and A2 sets is equal to 11% and 4% respectively. Despite having a slightly higher surface roughness and pore aspect ratio, the specimens printed by adopting a greater meltpool aspect ratio, A2 set, presented a higher fatigue strength and a lower scatter in the fatigue life than the A1 ones, which on the other side presented the pores with the greater area. It suggests that a limited number of bigger defects played a more important role than a series of smaller defects, which don’t produce a stress concentration significantly greater than the one occurring in the baseline specimens. Different behaviors could be observed in presence of a machined surface or of the standard aging heat treatment aimed at the precipitation of the γ ’ and γ ’’ phases. 3.4. Fatigue tests

Fig. 7. Static mechanical behavior of the tested specimens