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Help with data from tensile test

  1. Mar 17, 2013 #1
    Hi

    Just got the data from a tensile strength test on a axle we did in school.

    Before it broke:
    http://i.imgur.com/1ddrZ7j.png

    The data :

    https://www.dropbox.com/s/xf5m8m8gyco561n/data.txt

    column 1: the displacement in mm

    column 2: the force in kN


    I'm supposed to plot a stress strain diagram like this http://i.imgur.com/qdoHBse.png


    My matlab code:


    Code (Text):

       
        load data.txt

        %diameter 4 mm
        d=4;
        cross_section_area=pi*d^2/4;

        Length=140;

        displacement=data(:,1);
        force=data(:,2);

        for i=1:length(displacement)

            stress(i)=force(i)/cross_section_area;
        end
        stress

        for i=1:length(force)
            strain(i)=displacement(i)/Length;
        end
        strain



        plot(strain,stress)
     
    I'm supposed to filter the original data a bit but I have tried but i don't get nothing simular to the desired graph. Can anyone help me

    Edit : Its aluminum 6082 T6
     
    Last edited: Mar 17, 2013
  2. jcsd
  3. Mar 17, 2013 #2

    nvn

    User Avatar
    Science Advisor
    Homework Helper

    Huumah: Did your rod break suddenly, right at the end of the rod? Perhaps you had a stress concentration, because you did not provide a large fillet at the rod ends?

    Aside from that, something seems amiss in your rod dimensions. If the diameter of the rod shown in your photograph is 4 mm, then its length (the small portion) cannot be 140 mm. Check the dimensions of your rod carefully. What were the exact dimensions of the small portion of your rod, before applying force to it?

    Furthermore, if your rod is really 4 mm in diameter, then if it is Al 6082-T6, it would break at approximately 3.7 kN, not the values listed in your data file. Something seems amiss.

    By the way, although this will not change the shape of your plot, do not forget to convert the force to newtons (N), by multiplying your force by 1000.

    Also, in post 1, you said column 1 in your data file is displacement (mm). Then why does the value in column 1 virtually never change? There appear to be three columns in your data file. Therefore, what is column 3, in your data file?
     
    Last edited: Mar 17, 2013
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