"FATIGUE FAILURE IN A LIGHT AIRCRAFT PROPELLER"
FATIGUE FAILURE IN A LIGHT AIRCRAFT PROPELLER Silva, O.M.M.1; Lourenço, N.J.2; Graça, M.L.A3;; Franco, L.A.L4 1 Instituto de Aeronáutica e Espaço, Brasil -email@example.com 2 Instituto de Aeronáutica e Espaço, Brasil - firstname.lastname@example.org 3 Instituto de Aeronáutica e Espaço, Brasil - email@example.com 4 Instituto de Aeronáutica e Espaço, Brasil - firstname.lastname@example.org A light aircraft experienced an in-flight propeller separation accompanied by a loss of power leading to an emergency landing. After landing the propeller was disassembled and sent to analysis in order to investigate the root cause of the failure. In-flight separation of a propeller is potentially dangerous and unfortunately frequent in aviation environment around the world as can be seen in literature. An in-flight separation may be due to impacts on propeller surface resulting plastic deformation and leading to fatigue . This kind of failure is called FOD (foreign object damage) and is current in others components such compressor blades [2,3]. Another frequent failure is due to corrosion which leads also to fatigue failure . In our experience with aircraft maintenance around Brazil frequently we see aircrafts with propellers in a very poor state. Maintenance programs are object of federal regulation and mandatory. The investigation of an accident or incident plays an important role in safety management and may reduce losses of lives. In this work visual examination was carried out initially by means of unaided eye and stereoscopy. Fractographic examinations were made using a Leo 435VPi - Oxford scanning electron microscopy (SEM). Metallographic examination was made using a Leica - DMRXP optical microscope (OM). The as-received fractured propeller is shown in Figure.1. Figure 2 shows the propeller surface with impact marks. Fracture surface, Figure 3 and Stereograph examination, Figure 4 showed a flat surface with beach marks. The crack surface was examined using a scanning electron microscope (SEM). SEM analysis of the fracture surface at initiation area is showed in Figure 5. A SEM, Figure 6, at fracture initiation area showed fatigue striations. A metallographic section was taken perpendicular to fracture. The polished section was examined in the unetched condition and showed plastic deformation at the fatigue initiation site, Figure 7. The cause of the fracture was fatigue. The fatigue nucleated at plastic deformation due to impact on propeller surface. We suggest that a more accurate visual analysis of propellers may help to identify damaged surfaces and prevent accidents. Acknowledgements: The authors thank the Centro de Investigação e Prevenção de Acidentes Aeronáuticos (CENIPA and DPAA/CTA) of Brazil for financial support of this work. References:  M.C. Kushan, S.F. Diltemiz and İ. Sackesen. Failure analysis of an aircraft propeller . Engineering Failure Analysis. Volume 14, Issue 8, December 2007, Pages 1693-1700. ,  L. Witek M. Wierzbińska and A. Poznańska. Fracture analysis of compressor blade of a helicopter engine. Engineering Failure Analysis. Volume 16, Issue 5, July 2009, Pages 1616-1622. N.J. Lourenço, M.L.A. Graça, L.A.L. Franco and O.M.M. Silva. Fatigue failure of a compressor blade. Engineering Failure Analysis Volume 15, Issue 8, December 2008, Pages 1150-1154.  H-C Lee, Y-H Hwang and Tae-Gu Kim. Failure of aircraft propeller assembly. Engineering Failure Analysis. Volume 11, Issue 3, June 2004, Pages 305-312. Figure 1: Section of the propeller as-received. Figure 5: Initiation crack site. Figure 2: Propeller surface (Trailing edge) showing impact marks. Figure 6: Striations at initiation crack site. Figure 3: Fracture surface. Figure 7: Section showing an impact from foreign object. Figure 4: Impact mark.