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Fatigue Fracture of an Aluminum Main Support Bridge for a Helicopter 直升机铝制主支撑桥疲劳断裂
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c9001600
V. Champagne
{"title":"Fatigue Fracture of an Aluminum Main Support Bridge for a Helicopter","authors":"V. Champagne","doi":"10.31399/asm.fach.aero.c9001600","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c9001600","url":null,"abstract":"\u0000 This paper summarizes the results of a failure analysis investigation of a fractured main support bridge made of 7075 aluminum alloy from an army helicopter. The part, manufactured by “Contractor IT,” failed component fatigue testing while those of the original equipment manufacturer (OEM) passed. Metallurgical data collected during this investigation indicated that the difference in fatigue life between the components fabricated by IT and by OEM may be attributable to a difference in dimensions at the web where fatigue crack initiation occurred. The webs of the two OEM parts examined had cross-sectional thicknesses significantly larger than the web cross-sectional thicknesses of the IT components. Recommendations included changing the web reference dimension of 0.38 in. to include a tolerance range based upon a fracture mechanics model. Also, the shot peening process should be controlled especially at the critical areas of the web, to assure complete coverage and proper compressive residual stresses.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"335 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122333903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Analysis of a Helicopter Blade Fatigue Fracture by Digital Fractographic Imaging Analysis 直升机叶片疲劳断裂的数字断口成像分析
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c9001144
R. Mcswain, R. Gould
{"title":"Analysis of a Helicopter Blade Fatigue Fracture by Digital Fractographic Imaging Analysis","authors":"R. Mcswain, R. Gould","doi":"10.31399/asm.fach.aero.c9001144","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c9001144","url":null,"abstract":"\u0000 A helicopter was hovering approximately 10 ft above a ship when one spar section failed explosively. Visual inspection revealed a crack had progressed through one member of a dual spar plate assembly at a fold pin lug hole. The remaining spar plate carried the blade load until the aircraft was landed. The helicopter main rotor blade spar fracture was analyzed by conventional and advanced computerized fractographic techniques. Digital fractographic Imaging Analysis of theoretical and actual fracture surfaces was applied for automatic detection of fatigue striation spacing. The approach offered a means of quantification of fracture features, providing for objective fractography.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134424156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Cracking of Aircraft Pylon Strut 飞机挂架支柱开裂
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0006413
{"title":"Cracking of Aircraft Pylon Strut","authors":"","doi":"10.31399/asm.fach.aero.c0006413","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0006413","url":null,"abstract":"\u0000 Examination of a 7075-T6 aluminum alloy pylon strut revealed cracks in two locations on the ears of the strut. Because the part was still intact, the cracks had to be forced open so that the fractures could be examined. Scanning electron microscopy (SEM) of the opened cracks showed that the crack surfaces were covered with a mud crack pattern suggestive of stress-corrosion cracking (SCC). The T6 temper is susceptible to SCC. It was concluded that cracking of the strut could have been aggravated by the hard landing experienced by the aircraft. The strut, however, contained stress-corrosion cracks which were present before the landing. It was recommended that an inspection for SCC be made of all pylon struts with a similar service life.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132881804","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Fatigue Fracture of Aluminum Alloy 7178-T6 Aircraft Fuel-Tank Floors 7178-T6铝合金飞机油箱底板的疲劳断裂
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0046227
{"title":"Fatigue Fracture of Aluminum Alloy 7178-T6 Aircraft Fuel-Tank Floors","authors":"","doi":"10.31399/asm.fach.aero.c0046227","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0046227","url":null,"abstract":"\u0000 The floors (fabricated from aluminum alloy 7178-T6 sheet, with portions of the sheet chemically milled to reduce thickness) of the fuel tanks in two aircraft failed almost identically after 1076 and 1323 h of service, respectively. Failure in both tanks occurred in the rear chemically milled section of the floor. An alkaline etch-type cleaner was used on the panels before chemical milling and before painting. Various tests and measurements indicated that the aluminum alloy used for the fuel-tank floors conformed to the specifications for 7178-T6. Low power magnification, fractographs taken with a scanning electron, and optical microscopic examination of the milled sections revealed extensive pitting on both sides of the floors. Evidence found supports the conclusions that the floors failed by fatigue cracking that initiated near the center of the fuel-tank floor and ultimately propagated as rapid ductile-overload fractures. The fatigue cracks originated in pits on the fuel-cell side of the tank floors. The pits were attributed to attack caused by the alkaline-etch cleaning process. Recommendations included monitoring of the alkaline-etch cleaning to avoid the formation of pits and careful inspection following alkaline-etch cleaning, to be scheduled before release of the floor panels for painting.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132111099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Failure of an Oil-Line Subassembly Because of Poor Welding 由于焊接不良导致油管组件失效
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0047636
{"title":"Failure of an Oil-Line Subassembly Because of Poor Welding","authors":"","doi":"10.31399/asm.fach.aero.c0047636","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0047636","url":null,"abstract":"\u0000 Several elbow subassemblies comprising segments of oil-line assemblies that recycled aircraft-engine oil from pump to filter broke in service. The components of the subassemblies were made of aluminum alloy 6061-T6. Two subassemblies were returned to the laboratory to determine cause of failure. In one, the threaded boss had separated from the elbow at the weld. In the other, the failure was by fracture of the elbow near the flange. The separation of the threaded boss from the elbow was due to a poor welding procedure. Crack propagation was accelerated by fatigue caused by cyclic service stresses. The fracture of the second elbow near the flange was caused by overaging during repair welding of the boss weld. Satisfactory weld penetration was achieved by improved training of the welders plus more careful inspection. Repair welding was prohibited, to avoid recurrence of overaging from the welding heat. Additional support for the oil line was installed to reduce vibration and minimize fatigue of the elbow.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133991333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Aircraft Attachment Bolt Failure 飞机附件螺栓失效
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0091644
{"title":"Aircraft Attachment Bolt Failure","authors":"","doi":"10.31399/asm.fach.aero.c0091644","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0091644","url":null,"abstract":"\u0000 During a routine inspection on an aircraft assembly line, an airframe attachment bolt was found to be broken. The bolt was one of 12 that attach the lower outboard longeron to the wing carry-through structure. Failure occurred on the right-hand forward bolt in this longeron splice attachment. The bolt was fabricated from PH13-8Mo stainless steel heat treated to have an ultimate tensile strength of 1517 to 1655 MPa (220 to 240 ksi). A water-soluble coolant was used in drilling the bolt hole where this fastener was inserted. Investigation (visual inspection, 265 SEM images, hardness testing, auger emission spectroscopy and secondary imaging spectroscopy, tensile testing, and chemical analysis) supported the conclusion that failure of the attachment bolt was caused by stress corrosion. The source of the corrosive media was the water-soluble coolant used in boring the bolt holes. Recommendations included inspecting for corrosion all the bolts that were installed using the water-soluble coolant at the spliced joint areas, rinsing all machined bolt holes with a noncorrosive agent, and installing new PH13-8Mo stainless steel bolts with a polysulfide wet sealant.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132720097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Failure of Nose Gear Door Bolts 前齿轮门螺栓失效
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0006432
{"title":"Failure of Nose Gear Door Bolts","authors":"","doi":"10.31399/asm.fach.aero.c0006432","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0006432","url":null,"abstract":"\u0000 A failed 25 x 32 mm (1 x 1 in.) cadmium-plated 1040 carbon steel countersunk head type nose gear door securing bolt with a common screwdriver slot was examined. Fracture originated at a thread root and propagated across the cross section. The topography of the fracture was excessively rough and more granular than would be expected from pure mechanical fatigue. This indicated an allied corrosion mechanism. Cracks other than the one leading to failure were observed. Metallographic examination of the bolt cross section showed many cracks typical of stress-corrosion damage. It was concluded that the bolt failed by a combination of SCC and fatigue. It was recommended that aerospace-quality fasteners meeting NAS 7104, NAS 7204, or NAS 7504 be used to replace the currently used fasteners.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"116 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132852425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Use of Electron Fractography to Diagnose Cracking in an AISI 4340 Nose Landing Gear Cylinder 用电子断口学诊断AISI 4340前起落架气缸裂纹
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c9001538
J. A. Scott
{"title":"Use of Electron Fractography to Diagnose Cracking in an AISI 4340 Nose Landing Gear Cylinder","authors":"J. A. Scott","doi":"10.31399/asm.fach.aero.c9001538","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c9001538","url":null,"abstract":"\u0000 Examination of a cracked nose landing gear cylinder made of AISI 4340 Cr-Mo-Ni alloy steel proved that the part started to fail on the inside diam. When the nucleus of the stress-corrosion crack was studied in detail, iron oxide was found on the fracture surface. A 6500x micrograph revealed this area also displayed an intergranular texture. One of a group of small grinding cracks on the ID of the cylinder nucleated the failure. Other evidence indicated the cracks developed when the cylinder was ground during overhaul.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125998585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Fatigue Fracture of an Aircraft Wheel Half That Was Initiated at a Subsurface Defect 某型飞机轮毂半部分由次表面缺陷引起的疲劳断裂
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c0047169
{"title":"Fatigue Fracture of an Aircraft Wheel Half That Was Initiated at a Subsurface Defect","authors":"","doi":"10.31399/asm.fach.aero.c0047169","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c0047169","url":null,"abstract":"\u0000 The flange on an outboard main-wheel half (aluminum alloy 2014-T6 forging) on a commercial aircraft fractured during takeoff. The failure was discovered later during a routine enroute check. The flange section that broke away was recovered at the airfield from which the plane took off and was thus available for examination. Failure occurred after 37 landings (about 298 roll km, or 185 roll miles). Examination of the fracture surfaces revealed that a forging defect was present in the wall of the wheel half. The anodized coating showed distinct twin-parallel and end-grain patterns between which the fracture occurred. The periphery of the defect was the site of several small fatigue cracks that eventually progressed through the remaining wall. Rapid fatigue then progressed circumferentially. Metallographic examination using Keller's reagent showed that the microstructure was normal for aluminum alloy 2014-T6 and the hardness surpassed the minimum hardness required for aluminum alloy 2014-T6. An abrupt change in the direction of grain flow across the fracture plane indicated that the wall had buckled during forging. This evidence supported the conclusion that the wheel half failed in the flange by fatigue as the result of a rather large subsurface forging defect. No recommendations were made.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127711955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Use of Electron Fractography to Dianose Stress-Corrosion Cracking of an AISI 4340 Nose Landing Gear Cylinder 用电子断口分析AISI 4340前起落架气缸应力腐蚀开裂
ASM Failure Analysis Case Histories: Air and Spacecraft Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.aero.c9001542
J. A. Scott
{"title":"Use of Electron Fractography to Dianose Stress-Corrosion Cracking of an AISI 4340 Nose Landing Gear Cylinder","authors":"J. A. Scott","doi":"10.31399/asm.fach.aero.c9001542","DOIUrl":"https://doi.org/10.31399/asm.fach.aero.c9001542","url":null,"abstract":"\u0000 A nose landing gear cylinder made from AISI 4340 Ni-Cr-Mo alloy steel was found cracked and leaking, causing partial depressurization. Investigation revealed the crack to be a stress-corrosion type, judging by the 6500x electron fractograph. It had started in a region of concentrated, large non-metallic inclusions near the chromium-plated ID of the cylinder. Also, there were breaks in the chromium plate and pits in the underlying base metal. The cylinder had been in service for 18,017 h, and 5948 h had passed since the first and only overhaul. Substandard plating of the ID at this time ultimately resulted in pitting of the metal. The combination of surface pitting and stress concentration at the nearby inclusions resulted in stress-corrosion cracking.","PeriodicalId":326464,"journal":{"name":"ASM Failure Analysis Case Histories: Air and Spacecraft","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130149771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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