PSI - Issue 3

9

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

561

Fig. 26: Hinge of a similar aircraft.

In addition, numerical model showed that is necessary a stress concentrator (i.e. corrosion pit) to obtain a stress value above fatigue limit for AA7075 in the region where fatigue started. Conclusion Hinge failed because of fatigue cracks due to corrosion pit phenomena generated by an incorrect surface protection. Although the investigated parts had been visually inspected for the presence of corrosion, as scheduled by the maintenance manual, that did not prevent from the occurred hinge failure, probably because of the limited reliability of a simple visual exam not able to detect incipient cracks under the worn painting layer. For these reasons, following the investigation, a more reliable Non-destructive Test was recommended; in details, an Eddy Current inspection of the MLG door hinges was issued in order to prevent other similar incidents. References

Aerospace Specification Metals Inc., 27 12 2016. [Online]. http://asm.matweb.com/search/GetReference.asp?bassnum=MA7075T73. ASM, 2004. Metals Handbook, in Atlas of microstructures of industrial alloys, 8th edition, p. 251.

ASM, 1993. Specialty handbook, in Aluminum and aluminum alloys. ASTM, Case Studies for Fatigue Education, Ralph I. Stephens, 1994. Gugliotta, A., 2002. Introduzione alla Meccanica della Frattura Lineare Elastica, Torino: Levrotto & Bella,. Nicodemi, W., 2000. Acciai e leghe non ferrose, Zanichelli. Vergani, L., 2006. Meccanica dei Materiali, Milano: McGraw-Hill.