Investigation of a Boeing 747 wing main landing gear trunnion failure |
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| Affiliation: | 1. Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000, PR China;2. Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730,000, PR China;1. College of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, PR China;2. State Key Laboratory of Metastable Materials Science & Technology, Yanshan University, Qinhuangdao 066004, PR China;3. Shenyang Liming Aero-Engine Group Corporation Ltd, Shenyang 110043, PR China;1. University of Rome “ROMA TRE” Engineering Department, Via della della Vasca Navale 79, 00146 Rome, Italy;2. Fraunhofer IWM, Woehlerstrasse 11, 79108 Freiburg, Germany;3. Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD, USA;4. Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, England;5. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-4040, USA;1. Chair of International Production Engineering and Management of University of Siegen, Paul-Bonatz-Straße 9 -11, 57076 Siegen, Germany;2. Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University, Campus-Boulevard 30, 52074 Aachen, Germany;3. Chair of Production Engineering of E-Mobility Components, RWTH Aachen University, Campus-Boulevard 30, 52074 Aachen, Germany |
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| Abstract: | A loud noise was heard from the vicinity of the port wing landing gear during pushback of a Boeing 747-300 from the terminal at Sydney (Australia) airport. Inspection showed that one of the wing landing gear trunnion fork assemblies had failed. Detailed investigation revealed that the trunnion had failed by fatigue cracking. Deep machining grooves were found at the root of an internal radius that had not been shot-peened as required, and a chemical surface process during manufacture had resulted in shallow intergranular attack at the bottom of these grooves. It is probable that the critical cracking started from some of these grooves. In addition, the wall thickness at the failure location was significantly less than the minimum required in the drawings.Since the deep machining grooves, the lack of peening and the intergranular attack were all consequences of manufacturing, the fatigue cracking probably started shortly after the component entered service. This implies that fatigue cracking was present during all the trunnion overhauls, but was not detected by non-destructive inspections during the overhauls. Quantitative fractography was used to produce a crack growth curve based on fracture surface markings thought to represent the overhaul timings. The crack growth curve suggested that the fatigue cracking was large enough to be detected by inspection during the last overhaul, if not the one before. However, it was probably not easy to detect the cracking. This investigation therefore highlights the difficulties that can be encountered when inspection is the last (or only) line of defence against failure owing to unexpected manufacturing deficiencies. |
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| Keywords: | Ultra high strength steel Landing gear Fatigue Shot peening Non-destructive inspection Quantitative fractography |
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