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Homework Help: Load-Elongation Curve

  1. Feb 22, 2016 #1
    1. The problem statement, all variables and given/known data
    I have done a tensile test.
    Now that remains to do is create a table where the elongation (in mm) is shown at a specific load (in kN).

    I had two plates that I put through the tensile test.
    Both of them were 165 mm before the test.
    After measuring after the test, the first has been stretched to 178 mm and the other has been stretched to 188 mm.

    The problem I am having is that the supposed elongation doesn't seem to add up.

    2. Relevant equations
    Not an equation but the graph of the load-elongation curve.

    3. The attempt at a solution

    The graph has been drawn at a running speed of 1:2 mm.
    I assumed the x-axis would be the elongation.
    All I had to was draw a line down from the needed loads and multiply by because it's on a 1:2 mm scale.

    However, the first one (the tall one), if I drew a line straight down at the end and measure the difference between start and end. It seems to be 5.2 mm, multiplied by two gives me 10.4 mm.
    The actual elongation has been (178-165) = 13 mm. 10.4, 13 mm, it's still a difference.
    The second one however seems to be 5.6 mm, multiplied by two gives me 11.2 mm.
    It is actually (188-165) = 23 mm.
    Now, that is a bit too big of a difference to me.

    I have no idea what I'm doing wrong. Am I going into it with a completely wrong mindset?
    I just can't seem to figure out how to read the elongation at a load.
    Last edited: Feb 22, 2016
  2. jcsd
  3. Feb 24, 2016 #2
    I figured it out. I misread the explanation.
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