Fatigue fracture of a nose landing gear in a military transport aircraft
Introduction
Landing gears are usually subjected to severe environmental conditions, such as temperatures, climates and operational situations such as runway conditions among others. Several works showed fracture in landing gear in parts such as cylinder attachment lugs manufactured from aluminium alloy [1], landing gear assembly manufactured in a die forging aluminium alloy [2] and nose landing gear structure [3] among others. This paper analyses the rupture of a nose landing gear of a military transport aircraft, EMB 121 – Xingu, which collapsed during take-off procedure. Since this component is considered to be critical to aircraft safety, the Brazilian Air Force requested a failure analysis investigation.
Section snippets
Experimental examination
Chemical analysis results are shown in Table 1. A comparison of its composition within the range of commercial alloys available indicated that the material is a microalloyed vanadium steel. The as-received failed landing gear component is shown in Fig. 1.
The experimental procedure consisted in the characterisation of fracture aspects of the failed nose landing gear. Visual examination was carried out by means of unaided eye and stereoscopy. Fractographic examinations were made using a Leo
Results and discussion
The crack surface was initially observed with the unaided eye (Fig. 2) and stereoscopy. The fractured nose landing gear showed surface corrosion as shown in Fig. 3, Fig. 4. Stereographic microscopy showed clearly the fatigue fracture surface, as well as paint in the fracture surface (Fig. 5). Paint in the fractured surface indicates that the microcracks were not identified during previous maintenance process.
In order to analyse the different fracture aspects involved, a SEM was used. Fig. 6
Conclusions
The initial crack growth in the landing gear was due to fatigue. A secondary initiation site was also observed and corrosion pits were identified, suggesting that corrosion was the main cause of fatigue initiation. The paint mark with 1-mm depth approximately in the fractured surface suggests that the crack was not identified during previous maintenance. Thus, a non-destructive test such as high-quality dye penetrant inspection is recommended to detect cracks.
Acknowledgements
Thanks are due to Mr. Jefferson Rodrigues Tavares and Mr. Rogério Duque Gonçalves.
References (3)
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Aircraft landing gear failure; fracture of outer cylinder lug
Eng Fail Anal
(2002)