PSI - Issue 3

G. Zucca et al. / Procedia Structural Integrity 3 (2017) 553–561 Author name / Structural Integrity Procedia 00 (2017) 000–000

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3.2. Electronic Microscopy Fracture surface FESEM observation showed four different morphologies (letters A to D in Fig. 11) for four different stage of crack propagations.

Fig. 11: Overview of fracture surface.

The initial point of fracture is located in the A zone (red region of the Fig. 11) where, at high magnification it is possible to observe two corrosion pit (red dotted lines in Fig. 12)

Fig. 12: Corrosion Pits.

Fig. 13: First Fatigue Region.

In the B and C zone is possible to notice the clear presence of fatigue mechanism: it originally proceeds from the initiation to the upper side tilted of about 45° (B zone Fig. 13), than it changes its path from the left to the right (C zone Fig. 14), following the hinge shape and the enlargement of its resistant section.