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Yielding stress

  1. Dec 9, 2009 #1
    as depicted in the diagram below
    stress-strain.JPG
    the stress strain for an alloy with an average nucleus size of 100 micron
    find
    1)the modulus of elasticity for the alloy
    2) the yielding stress


    for 1) i assume that the red line is meant to be at 0.0005 therefore
    E=dσ/dε=100e6/0.0005

    E=200Gpa

    for 2) i dont know what i can do, all that i do know is that the slant of the line from ε=0.002 to the point of σy is equal to 200Gpa (from the E i found before), but how can i use this to find the stress, i do not know the strain for σy, since i was given the nuclesu size i think i must somehow use that, but how??
     
  2. jcsd
  3. Dec 9, 2009 #2

    chemisttree

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    Ignore the 100 micron nucleus info. The sample yields where there is a deviation from a linear stress/strain relationship, right?
     
  4. Dec 9, 2009 #3
    but how can i use that information, when you say a deviation from stress strain relationship, do you mean a deviation from the young modulus? i dont think that thats true, is there not a small portion where the line is not linear but before yielding?
    even on the graph there is a portion between the linear section and the point marked as 2 with the green line
     
  5. Dec 9, 2009 #4
    i think i need to use the imaginary linear line that starts at 0.2% and rises to yielding stress at a slant equal to E
     
  6. Dec 10, 2009 #5

    Mapes

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    Agreed.
     
  7. Dec 10, 2009 #6
    now i assume that the apropriate strain for the yielding stress is 0.003, is that correct?

    σ/0.001=E=200Gpa

    σ=200MPa

    is this correct? according to the graph it cannot be
     
  8. Dec 10, 2009 #7

    Mapes

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    It's simpler than that. The convention is to use the stress where the 0.2% offset line meets the actual stress-strain curve.
     
  9. Dec 10, 2009 #8
    but i dont know the function of the actual curve, do you mean the linear section,
    where
    σ=200Gpa*ε
    (ε=0.002)

    σ=400MPa

    dont think thats what you mean,

    how can i find the curve after the linear section?
     
  10. Dec 10, 2009 #9

    Mapes

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    You read it off by eye.
     
  11. Dec 10, 2009 #10
    is there no way to calculate it?
     
  12. Dec 12, 2009 #11
    Last edited by a moderator: May 4, 2017
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