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Low cycle fatigue, Coffin's law

  1. Apr 20, 2016 #1
    1. The problem statement, all variables and given/known data
    Hi, I require some assistance using coffin's law.
    I have the strain range and cycles to failure but need coffins slope- 'c'.
    C2 can then be found after the other values are known.

    2. Relevant equations
    Where Δε^pl is plastic strain range, N is the cycles to failure and C2 and c are constants.

    3. The attempt at a solution
    I have the strain range and cycles to failure data in excel. No problems here.
    It seems from the above graph that coffins slope-c is the slope of the Log(stress amplitude) and Log(cycles to failure) regression line.
    So I use excels slope function and get -0.05

    The textbook and other sources say this value is usually +0.5.

    using the 'c' I attained in the equation results in lower cycles to failure for lower strains, the opposite of what is expected.

    Thanks for any help you can offer.
  2. jcsd
  3. Apr 25, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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