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External pressure on cylinder

  1. May 16, 2017 #1
    Hello,
    This is a real simple question but I am having a hard time to answer it.
    We have cylinder with outer Radius Ro, Inner Radius Ri. Internal pressure = 0.
    External pressure = to be find.
    Material is Nylon.

    I would like to know:
    External pressure Po at which the tube/cylinder will go under deformation given Yield strength.

    How do i find the external pressure on a rod- Given it is not a pressure vessel?
    Should i use the collapse pressure formula OR Radil stress formula assuming Internal pressure Pi to be zero?

    upload_2017-5-16_14-28-21.png
     
    Last edited: May 16, 2017
  2. jcsd
  3. May 16, 2017 #2
    There is nothing in the problem statement to indicate that there is an external pressure at all. Please re-read what you wrote and add whatever is missing.
     
  4. May 16, 2017 #3
    Thanks,
    I re-wrote the question
     
  5. May 16, 2017 #4
    This "simple problem" is really not simple at all, and may still be undefined. I see two options to pursue here:
    1) You can assume absolutely perfect axial symmetry and consider only simple compression of the material.
    2) You can also recognize that there is the potential for the cylinder wall to buckle, thus collapsing in an asymmetric form.
    For the first option, get a theory of elasticity book and dig in to problems in cylindrical coordinates.
    For the second option, the wall thickness becomes critical, and I doubt that the problem can be solved in general (with no specification on the wall thickness).
     
  6. May 16, 2017 #5
    What are you assuming about the nature of the stress-strain curve for nylon, and in particular, do you have a well defined yield point? Nylon is not a "nice" engineering material like say, steel, so everything is a bit iffy about this problem.
     
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