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Homework Help: Youngs Modulus for Steel

  1. Feb 19, 2010 #1
    1. The problem statement, all variables and given/known data
    I was given the problem to try experimentally find youngs modulus for normalized steel but when i did the equation the value i got was about 33 GPa. It is supposed to be around 200 isnt it? I cannot figure out what is wrong, am i missing something or is the measured data probably wrong? these values were all measured experimentally and in a bit of a hurry so it could be that, that is causing the problem, but i cant see howthe result could be thrown so off...

    heres the data anyway

    Test piece original length: 25mm
    Diameter: 3.52mm -- cross sec area:9.73mm^2

    and the graphs attached , looking at the one for normalized steel, but also tried it with tempered steel with similiarbad results

    2. Relevant equations

    Youngs modulus -> dStress/dStrain

    3. The attempt at a solution

    i took 2 points at x=1.28mm, y = 9600 N and x=1mm, y = 6000 N

    [ (9600/9.73*10^-6) - (6000/9.73*10^-6) ] / [ (1.28/25) - (1/25) ] = 33.035 GPa

    I know i probably didnt read the values off the graph very accurately but I didnt expect the answer to be so far off because of that.

    Attached Files:

    Last edited: Feb 20, 2010
  2. jcsd
  3. Feb 19, 2010 #2


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    Clancy, welcome to PF! You have the right equation. The graph appears to be a plot of force vs. deformation. Did you interpret it correctly? Please show your work so someone can check your math.
  4. Feb 20, 2010 #3
    Be sure to take points in the straightline section of the curves. This is where the definition Youngs modulus = dStress/dStrain is defined. I cannot see you have taken the correct points. Be sure to claculate strain with respect to its original length.
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