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Homework Help: Solid mechanics problem

  1. Feb 23, 2010 #1
    Basically, my problem is small part of a bigger assignment, but I'm completely stuck at this point. This is really a math problem, but I figured I'd post it here anyway considering I might have misunderstood the physics.

    1. The problem statement, all variables and given/known data

    A vertical pipe is subjected to a axial force of 1089N and an Mb of 600Nm. The maximum stress in the pipe is not to be larger than 150MPa.

    I am to find the relation between di and do (di/do), where di is the inner- and do is the outer diameter of the pipe (which is part of a bigger construction.)

    2. Relevant equations

    von Mises theorem, but there are no sheer stresses in the pipe.


    sigma=F/A+Mb/Wb+Mv/Wv. However Mv is zero in this case.

    3. The attempt at a solution


    -> 150e6=1089/[(pi/4)*(dy^2-di^2)+600/(pi/32dy)*(dy^4-di^4)

    I can't seem to find a method to isolate di/dy from this equation, mainly because of the single dy in the Wb for circular pipes. Any help would be appreciated. If something is unclear don't hesitate to ask.
  2. jcsd
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