PSI - Issue 34

Dario Santonocito et al. / Procedia Structural Integrity 34 (2021) 211–220 D. Santonocito et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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(a)

(b)

(c)

Fig. 7. Fatigue limit assessment by Thermographic Method. The temperature trend is reported vs. the applied stress level.

4.4. Fracture surfaces

After static and fatigue tests the fracture surfaces have been evaluated through an optical microscope. In Fig. 8a, is reported the fracture surface of a specimens failed during static tensile test. The fracture surfaces show a ductile failure, with very limited plastic deformations. A series of defects is clearly visible, due to the lack of powder melting. The defects have a circular shape with an average diameter of 0.175 mm. Fatigue fracture surfaces show a smoother profile, typical of a brittle failure (Fig. 8b). Defects due to the lack of powder melting, with an average diameter equal to the one of the static cases, have been found. The circular defects can act as initiation sites for plastic deformations that would lead the specimen to failure, both under static and fatigue load.