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Creep and Fatigue

by dental guy
Tags: creep, fatigue
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dental guy
Sep25-08, 02:45 AM
P: 6
What is the difference between dynamic creep and fatigue?
How are they tested?
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Sep25-08, 07:01 AM
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Creep is permanent deformation over time; fatigue is crack propagation over time. Both occur due to applied loads and both can lead to failure. Creep is characterized by looking at the elongation of the sample; fatigue, by elongation of the crack.
Sep25-08, 07:11 AM
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FredGarvin's Avatar
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In a nutshell...

Creep is a constant stress situation that is below yield. It is extremely prevelant in higher temperature conditions. Creep is usually tested with a wire of a given size that has a constant load and the elongation is measured over time. Be careful not to mistake creep with stress relaxation.

Fatigue is due to cyclic/alternating loading that can be at any stress level. The loading is repeated until the number of cycles imparted causes failure. This is expressed in S-N curves for particular materials. A material is usually said to have an infinite fatigue endunce limit if it can withstand 10^6 cycles at the particular alternating stress level.

I'll have to look up the particular ASTM specs on each test.



dental guy
Sep25-08, 11:28 PM
P: 6
Creep and Fatigue

If we have to perform experiment on polymers with cyclic loading, then will it be categorised under fatigue and not creep?
Sep26-08, 06:31 AM
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FredGarvin's Avatar
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That would be a fatigue type of test. It depends on your outcome and what you are measuring to be able to call it a fatigue test. Are you going to take the samples to failure?
dental guy
Sep26-08, 07:38 PM
P: 6
Thanks fred,
We do not want to take it to failure. We are interested in change in dimension , if it occurs, say after 12-15 millions cyles.
Aug4-11, 12:22 AM
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