26 Budynas-Nisbett:Shigley's ll.Failure Prevention 6.Fatigue Failure Resulting ©The McGraw-Hill Mechanical Engineering from Variable Loading Companies,2008 Design,Eighth Edition Fatigue Failure Resulting from Variable Loading 263 Medium-carbon steel (ASTMA186) 30 dia Flange (1of2) Fracture (a)Coke- r wheel (c) Figure 6-7 Fatigue failure of an ASTMA186 steel double-flange trailer wheel caused by stamp marks.(a)Cokeoven car wheel showing position of stamp marks and fractures in the rib and web.(b)Stamp mark showing heavy impression and fracture extending along the base of the lower row of numbers.(c)Notches,indicated by arrows,created from the heavily indented stamp marks from which cracks initiated along the top at the fracture surface.(From ASM Handbook,Vol.1 1:Failure Analysis and Prevention,ASM International,Materials Park,OH 44073- 0002,fig 51,p.130.Reprinted by permission of ASM Intemational,www.asmintemational.org.) Figure 6-8 Aluminum alloy 7075-T73 .94 Rockwell B 85.5 Aluminum alloy 7075-T73 755 landing gear torquearm 10.200 assembly redesign to eliminate fatigue fracture at a lubrication hole.(a)Arm configuration, original and improved design [dimensions given in inches). Fracture b)Fracture surface where (1of2) arrows indicate multiple crack origins.(From ASM -Primary-fracture Handbook,Vol.11:Failure Lubrication hole surface Analysis and Prevention,ASM 1.750-in.-dia Lubrication hole International,Materials Park. 0.090-in.wall OH440730002,fig23, p.114.Reprinted by permission of ASM in International www.asminternationol.org.) 3.62 dia Secondary fracture Original design Improved design Detail A (a侧Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition II. Failure Prevention 6. Fatigue Failure Resulting from Variable Loading 266 © The McGraw−Hill Companies, 2008 Fatigue Failure Resulting from Variable Loading 263 Figure 6–7 Fatigue failure of an ASTM A186 steel double-flange trailer wheel caused by stamp marks. (a) Coke-oven car wheel showing position of stamp marks and fractures in the rib and web. (b) Stamp mark showing heavy impression and fracture extending along the base of the lower row of numbers. (c) Notches, indicated by arrows, created from the heavily indented stamp marks from which cracks initiated along the top at the fracture surface. (From ASM Handbook, Vol. 11: Failure Analysis and Prevention, ASM International, Materials Park, OH 44073- 0002, fig 51, p. 130. Reprinted by permission of ASM International ®, www.asminternational.org.) Aluminum alloy 7075-T73 Rockwell B 85.5 Original design 10.200 A Lug (1 of 2) 25.5 4.94 Fracture 3.62 dia Secondary fracture 1.750-in.-dia bushing, 0.090-in. wall Primary-fracture Lubrication hole surface 1 in Lubrication hole Improved design Detail A (a) Figure 6–8 Aluminum alloy 7075-T73 landing-gear torque-arm assembly redesign to eliminate fatigue fracture at a lubrication hole. (a) Arm configuration, original and improved design (dimensions given in inches). (b) Fracture surface where arrows indicate multiple crack origins. (From ASM Handbook, Vol. 11: Failure Analysis and Prevention, ASM International, Materials Park, OH 44073-0002, fig 23, p. 114. Reprinted by permission of ASM International ®, www.asminternational.org.) Medium-carbon steel (ASTM A186) (a) Coke-oven-car wheel Web 30 dia Flange (1 of 2) Fracture Tread Fracture