DISCONTINUITIES-INSERVICE-CORROSION+stress+fatigueREVB-Nov-10-2019.pptx - IN-SERVICE CONDITIONS \u2022 Failure and degradation of components may result


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IN-SERVICE CONDITIONS Failure and degradation of components may result from a variety of causes even if no defects (discontinuities) are initially present. Discontinuities/Defects that occur due to overstress (over loading), fatigue, excessive temperatures, corrosion, erosion or a combination of these items can be called service defects/discontinuities which may render the component rejectable . Defects found would be considered flaws or discontinuities that would or could interfere with the ability of the material or part to perform its service satisfactorily i.e. not all discontinuities are defects.
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Examples of the complexity of in-service failures due to multiple discontinuity sources Niansheng et al [13] studied a leakage failure of a brake nave on a landing gear, finding that rough machining marks and incomplete protective coatings initiated a crack, which further propagated by transgranular stress corrosion . Eliaz et al. [14] investigated the cracking of the main landing gear of a cargo aircraf , finding it to be caused by abusive grinding during an overhaul. The grinding caused localized overheating, which altered the martensitic structure of the material, leading to thermally induced cracks. Bagnoli et al. [15] studied the fatigue failure of a landing gear swinging lever, which turned out to be caused by abnormal silicon concentration of the material due to the manufacturing process of the part during the forging stage. Barter [16] studied the failure of the wing landing gear trunnion fork assemblies of a Boeing 747-300 aircraf. Analysis of the failure showed that deep machining grooves were present as a consequence of poor shot peening , this along with a chemical surface process during manufacture resulted on intergranular attack at the bottom of the grooves, causing cracking and failure of the part. Handbook of Materials Failure Analysis with Case Studies from the Aerospace and Automotive Industries 2016, Pages 167-190 Chapter 8 - Suspension and landing gear failures Author Edgar A.Ossa, MarcoPaniagua According to reported cases of failure of landing gear system parts, they can be divided into metallurgical, environmental, design, processing, and overload failures where corrosion has played a role in many of these failures.
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SERVICE CONDITIONS EFFECTING AND CAUSING IN-SERVICE DISCONTINUITIES AND FAILURES Over Loading Temperature Fatigue, COD and movement Corrosion Oxidation Rate of Corrosion Corrosion Protection Stress Corrosion Corrosion and In-Service Cracking, fatique – discontinuities : excellent resource on all types, with images and descriptions of how occurring and where found https:// petrowiki.spe.org/PetroWiki website link provided as an additional free resource for student information with all content from Petroleum engineers handbook and society. The content in this units slides are not from this source.
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