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Homework Help: Making since of a graph

  1. Mar 25, 2008 #1
    View attachment instructionsaj1.bmp
    here is what I've obtained


    View attachment dataaj1.bmp


    Increasing (με) (μin/in) and decreaseing (με) (μin/in) are both STRAIN
    [Increasing σ (psi)] and decreaseing σ (psi) are both STRESS]

    My question is. From the directions above, is it asking for a plot of Stress vs Strain or a Stress-Strain curve. And in either case. How many. Should I pool all the data together for one plot or for two? Or is it asking for both a plot and a curve?

    further down it asks for: "use data from the most linear portion of the curve to calculate Modulus of the alloy using the following stress-strain equation (recall that the Modulus is the slope of the linear portion of the stress-strain curve, so the equation is the slope of a line)

    To me this says to use a stress-strain curve. But why did it ask for a stress vs strain plot? I've spent way too long trying to interpret the directions.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 25, 2008 #2

    Tom Mattson

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    Staff Emeritus
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    Gold Member

    You should make a stress-strain plot for the increasing loads, and a separate stress-strain plot for the decreasing loads. You are then asked whether the curve that best fits the data is linear. If so, then indicate such. If not, then identify the largest interval over which the data are approximately linear, and find the line of best fit (this is a necessary step in determining the modulus).
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