PSI - Issue 3

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

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Author name / Structural Integrity Procedia 00 (2017) 000–000

In particular, the rear hinge portion affected by the fracture (red arrow in Fig. 7) was carefully removed in order to obtain a small piece. This was done to facilitate the observation/assessment of the fracture. In order to obtain both fractographic and metallographic specimens two cuts were executed following the dotted red lines in Fig. 7.

Fig. 7: Cuts on Rear Hinge.

Fig. 8: Rear Hinge Fracture Analysis.

Optical microscopy on the crack showed two different morphologies:

 the first, surrounded by the dotted red line in (Fig. 8), is basically flat and has an extension of about 5 mm in the direction of fracture propagation. It showed a smooth and bright grain, without relevant plastic deformations (Fig. 8).  the second one was characterized by dull and coarse grain (dotted yellow line in figure Fig. 8), typical of silky fracture surface due to an instantaneous phenomenon. Taking into consideration the first part, following the radial marks until convergence, it is possible to recognize the initial point of fracture (Fig. 9). Observing this region from the outside it is possible to note lack of external protective layer near the initiation (dotted red circle in Fig. 10).

Fig. 9: Initial Point.

Fig. 10: External layer damage at the crack initial point.