Hollow circular tube versus hollow rectangular shaft

  1. Mar 30, 2011 #1
    Sportnut:
    If I am using exact same aluminum material, with exact same thickness of gauge and I construct a 4ft long hollow circular tube that is 1" diameter, and I also construct a 4ft long hollow rectangular shaft that is 1" square, which would be more resistant to bending?
     
  2. jcsd
  3. Mar 30, 2011 #2

    Bill_K

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    Hard to say, but the circular pipe would resist bending equally in all directions. Whereas the square pipe would be great in horizontal and vertical directions but would quickly fail if you tried to bend it along a diagonal (making it diamond-shaped)
     
  4. Mar 30, 2011 #3
    Thanks Bill. I appreciate your response.
     
  5. Mar 30, 2011 #4

    AlephZero

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    The square tube would be stiffer because more of the material is further from the centerline.

    The stiffness ratio (from the second moments of area) is (1/12) / (pi/64) = about 1.7

    Post #2 is wrong. The square tube is also equally stiff for bending in any direction, though this is not so "obvious" as it is for a circular tube.
     
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