Lecture 6 Creep Failure
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Creep Failure
Transcript of Lecture 6 Creep Failure
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Creep failure
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Diffusion creep
•
bulk crystaldiffusion
d
grain boundarydiffusion
d
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Dislocation creep
glide
glide
climb
Diffusion assisted climb important:
climb
1. Annihilation:
poof !
2. By passing obstacles:
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Dislocation Climb:
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Stress Relaxation
total = el + pl = 0 so el = - pl
el = / E and pl = c = A n (@ cont. T)
-n d = - A E dt
1-n | =- A E t |0
. .
. .
. .
time
time
p
el
o
t
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Tertiary creep :
c
time
tertiary creep
Creep damage starts
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Creep Failure
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Design against creep (metals)
• Minimize T / Tmelting
to slow diffusion, climb, and creep.
• Arrange for large grain sizes to slowdiffusion.
• Use precipitates (oxide particles) and solid solutions to slow dislocations.
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