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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 near crack cross section  crack cross section

Internal microstructure near the crack showed the typical features of the aluminum alloy AA7075 with thermal treatment T7351 (Fig. 18), compatible with the expected technical specifications. The etching highlights an oriented microstructure, heat solution treated, Nicodemi (2000), with clear precipitates on the grain boundaries. A pattern of 10 indentations HRB gives the mean value of 78 and a standard deviation of 1. No microstructural alterations were found, ASM (2004). In addition, metallographic analysis of the edges of the same specimen showed an irregular thickness of the external protective layer, with zones characterized by lack of the layer itself and or presence of corrosion pit. Moreover, metallographic section of the crack shows a corrosion pit phenomenon, with the deepest one of about 100 µm and the total absence of anodized protection layer (Fig. 19).

Fig. 18: near crack cross section.

Fig. 19: crack cross section.

3.5. Finite Element Analysis A FEA model was performed in order to obtain a qualitative stress map around the crack region. Geometry 3D model of hinge was reproduced using design drawings and real item measurements. 96363 tetrahedrons elements were applied to provide the suitable mesh for mathematical model (Fig. 20).

Fig. 20: Geometry.

Fig. 21: Load Conditions.