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Creep and Fatigue

  1. Sep 25, 2008 #1
    What is the difference between dynamic creep and fatigue?
    How are they tested?
     
  2. jcsd
  3. Sep 25, 2008 #2

    Mapes

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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.
     
  4. Sep 25, 2008 #3

    FredGarvin

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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.

    Creep:
    http://www.engineersedge.com/material_science/creep.htm
    http://www.nuc.berkeley.edu/thyd/ne161/jlrhoads/creep.html

    Fatigue:
    http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kelly/fatigue.html
    http://en.wikipedia.org/wiki/Fatigue_(material)
     
  5. Sep 25, 2008 #4
    Thanks,
    If we have to perform experiment on polymers with cyclic loading, then will it be categorised under fatigue and not creep?
     
  6. Sep 26, 2008 #5

    FredGarvin

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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?
     
  7. Sep 26, 2008 #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.
     
  8. Aug 4, 2011 #7
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