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Homework Help: Material fatigue and stress

  1. Jan 4, 2004 #1
    Could you please explain what each of the following symbols stand for:

    I have worked out that da is the crack length
    i have worked out that dN is the number of cycles
    Are both of these correct?

  2. jcsd
  3. Jan 4, 2004 #2


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    What you have is a simplified model of the rate of crack propagation:

    [tex] \frac{da}{dN} = A\Delta K^m [/tex]

    2*a is the crack length (not da), N is the number of cycles (not dN).

    ΔK is the stress intensity factor range:

    [tex] \Delta K = Y\sqrt{\pi a}(\sigma_{\rm max} - \sigma_{\rm min}) [/tex]

    (Y is a crack geometry factor).

    A and m are empirical constants (found by plotting log(da/dN) versus log(ΔK)).
  4. Jan 5, 2004 #3
    Thanx for the help.
  5. Jan 5, 2004 #4
    One more thing

    you said that Y is a crack geometry factor, how do you find the crack geometry factor??
  6. Jan 5, 2004 #5


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    It depends on the shape/aspect ratio of the crack. Hopefully, there is a table or explanation in your textbook. Here's a page I found with a bunch of them that might help:

    http://www.ems.psu.edu/~green/436-8C.pdf [Broken]
    Last edited by a moderator: May 1, 2017
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