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

Fig. 14: Second Fatigue Region.

Fig. 15: Ductile Fracture Region.

At the end of the fatigue region in the D zone, the crack showed also dimples and micro-voids (Fig. 15). These are typical evidences of unstable propagation phase in a fatigue mechanism, when the reduction of the resistant section produces fracture areas characterized by overload morphology, ASTM (1994). In addition, FESEM examination allowed to measure distance between each mark, obtaining a mean value of 1µm which suggests a high cycle fatigue mechanism. 3.3. Chemical Analysis ICP-OES and EDS analysis were carried out in order to confirm both alloy (AA7075) and anodized protection layer in compliance to the design requirements provided by the OEM. Results show a complete conformity, ASM (1993), (Fig. 16 and Fig. 17).

Fig. 16: EDS Spectrum of Alloy.

Fig. 17: EDS Spectrum of Coating.

3.4. Microstructural Analysis and Hardness Test In order to gain further information about material characteristics possibly affecting the development of investigated cracks, a microstructural examination by polishing and etching with Keller reagent was performed on two sections of the hinge: