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Homework Help: Force-Elongation Graph

  1. Nov 29, 2009 #1
    Evening all,

    I have a Force vs. Elongation graph of a specimen (Aluminium). From this I need to derive the values of Young's Modulus, Yield Stress, Yield Strain, Ultimate Tensile Strength and so forth.

    I assumed this was fairly straight forward, but when I tried calculating the UTS, my answer was way way off of what it should roughly be.

    The calculation I tried is as follows:

    The maxima of the curve was 53.5kN and the A0 of the specimen was 76.9mm2.

    UTS = F/A0 = 53500 / 76.9x10-6 = 695.7MPa

    The answer should be around the 69GPa mark.

    Any ideas where I'm going wrong? I get similar results when trying to calculate any other values from the graph.

    Many thanks.
  2. jcsd
  3. Nov 29, 2009 #2


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    Staff Emeritus
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    695.7MPa (~100 ksi) is about right for Al. That's pretty strong for Al.

    69 GPa would be about right for the elastic (Young's) modulus.
  4. Nov 30, 2009 #3
    Thanks for the reply. Made a mistake in my post in saying Young's Modulus should be around 69GPa rather than say that the UTS should be around 400MPa? So I guess it's really not that far off.

    I also calculated Youngs Modulus but got around 13GPa which seems very low.
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