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Homework Help: I have this real graphic from a tensile test

  1. Apr 29, 2015 #1
    1. The problem statement, all variables and given/known data
    How can I calculate the ultimate stress? (I refere to the stress that it's in the green rectangle). I have a real graphic, I have two deformations, (it was 2 test, from the same material) and only one stress. The orange curve is Stress versus unit deformation 1, and the gray one is stress vs. deformation 2 . The blue one is the average between the deformation 1 and 2 vs Stress. The REAL graphic from I want calculate this, it's in the last part of the post


    2. Relevant equations

    3. The attempt at a solution

    I know that fracture stress is in the red rectangle. I know that the graphic in the last part of the curves, it's illogic (because the deformation "decrease") but the stress is ok, because is the real fracture stress

  2. jcsd
  3. Apr 29, 2015 #2
    I don't think the red rectangles are the fracture stresses. When the specimens failed the testing machine probably rebounded and since the machine is most likely calibrated using a strain gauge it gave you some negative displacement values. Not sure why an increased load was measured but I would be attempted to ignore these values.

    Also the blue curve does not look like the average of the two curves to me.
  4. Apr 29, 2015 #3
    Thank you for your opinion
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