Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM...
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Transcript of Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM...
![Page 1: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/1.jpg)
Brittle Fracture
“You can observe a lot just by watchin’.”
Yogi BerraAll graphics from ASM Metals Handbook unless otherwise noted
![Page 2: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/2.jpg)
Case Study:Paseo Bridge – Kansas City
• The Bridge– Suspension bridge– Built in 1957– Carries I-35, I-29, & US-71– Crosses Missouri River – Major artery north of K.C.
• 94,000 vehicles/day
![Page 3: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/3.jpg)
Case Study: Paseo Bridge – Kansas City
• The problem– Expansion joint
misalignment (23 Jan 03)• Deck rose 9 inches above
approach on one end• 1 inch step on another
– Guardrails snapped– Bridge closed for 2 weeks
![Page 4: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/4.jpg)
Case Study: Paseo Bridge – Kansas City
• What happened?– Cause(s)– Mitigating circumstances
• How should it be fixed?– Who will perform repairs?
• Who is at fault?– State/City/Contractor?
• What are the ramifications?– Cost– Inconvenience– Other bridges
Deck Approach
![Page 5: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/5.jpg)
Case Study: Paseo Bridge – Kansas City
![Page 6: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/6.jpg)
How Material Breaks?
• Ductile vs. brittle fracture• Principles of fracture mechanics
– Stress concentration• Impact fracture testing• Fatigue (cyclic stresses)
– Cyclic stresses, the S—N curve– Crack initiation and propagation– Factors that affect fatigue behavior
• Creep (time dependent deformation)– Stress and temperature effects– Alloys for high-temperature use
![Page 7: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/7.jpg)
Fracture
Separation of a body into pieces due to stress, at temperatures below the melting point.
Steps in fracture:– crack formation– crack propagation
Depending on the ability of material to undergo plastic deformation before the fracture two fracture modes can be defined - ductile or brittle
Ductile fracture - most metals (not too cold):Extensive plastic deformation ahead of crackCrack is “stable”: resists further extension unless applied stress is increased
Brittle fracture - ceramics, ice, cold metals:Relatively little plastic deformationCrack is “unstable”: propagates rapidly without increase in applied stress
Ductile fracture is preferred in most applications
![Page 8: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/8.jpg)
Sequential tearing of bonds
Brittle Fracture
strength
% elongation
f < 1%
![Page 9: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/9.jpg)
Brittle Fracture (Limited Dislocation Mobility)
No appreciable plastic deformationCrack propagation is very fastCrack propagates nearly perpendicular to
the direction of the applied stressCrack often propagates by cleavage –
breaking of atomic bonds along specific crystallographic planes (cleavage planes)
![Page 10: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/10.jpg)
Brittle Fracture
• Cleavage occurs primarily in BCC and HCP crystals
• Only in FCC materials at low temp• Cleavage occurs with in grains on specific
planes
[010]
[001]
[100]
![Page 11: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/11.jpg)
Brittle Fracture
![Page 12: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/12.jpg)
Brittle Fracture
• Macroscopic• Flat fracture face• Little/No necking• “Crystallized” fracture
surface
![Page 13: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/13.jpg)
Brittle Fracture• Low-Magnification• “Chevron Marks”• Chevrons point back to origin
![Page 14: Brittle Fracture “You can observe a lot just by watchin’.” Yogi Berra All graphics from ASM Metals Handbook unless otherwise noted.](https://reader034.fdocuments.us/reader034/viewer/2022051401/56649d085503460f949d9ebe/html5/thumbnails/14.jpg)
Brittle Fracture
• Microscopic (SEM)• “River Pattern”• Crack progressed
“downstream”• These are not fatigue
striations! (How can you tell?)