EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Failure analysis of aircraft structural components is critical in an industry where safety is of supreme importance. INTA provides technical support in failure analysis and accident investigation to the Spanish Civil and Military Aviation Accidents Investigation Commissions in order to prevent future incidents. This paper presents an incident study where a Piper aircraft was involved. During takeoff, two supports from the right main landing gear were fractured, forcing the aircraft to land.
Chemical, microstructural and mechanical characterization were carried out on samples of the supports material. It was determined that they corresponded to an aluminium alloy type ASTM A356.0 T6 with dendritic microstructure and a casting aluminium alloy type ASTM A535.0 with equiaxial grains from the front and rear supports, respectively. Although both alloys were in accordance with the manufacturer specifications, the high porosity in addition to the shrinkage cavities, which appeared in the manufacturing process, led to a decrease in the material strength.
Visual observation of the two supports indicated that the fractures were located in its central part, which has the thinnest section, in the trunnion connection area. The loads application was in the direction of the landing gear axis, causing a bending force on the part.
Fractographic and metallographic studies were carried out by optical and scanning electron microscopy. The fractographic characters showed that the front support fractured instantaneously due to static overload, as a result of one or more abrupt landing attempts and, as a consequence, the rear support broke just afterwards, being a secondary failure.
It was concluded that the fracture mechanism was produced by bending static overload, with a very high speed load application, practically instantaneously.