Buckling of cylindrical shells 1

[mechengr09]

I am trying to calculate the critical buckling load for a thermoplastic cylindrical shell under compressive pressure load. I have E,K at temperature for the material.What formula can I use to roughly estimate the critical load?

 

[rb1957]

it depends on the geometry of the section ...
first you need to calculate (L/rho) ...
if this is large, Euler is appropriate.
if this is small, because t/D is samll, then you've got a column that will cripple before it "Euler" buckles.
if it is small because L is small, then probably (maybe?) the column will fail at Fcy.

somewhere along the line you'll need to research "Johnson-Euler" columns; this is an analytical technique for cutting off Euler at the crippling stress (the maximum achievable in the real world.

good luck

 

[mechengr09]

Thanks for the reply. Can give guidance/links to references on the equations to use for Euler/Johnson.

 

[rb1957]

it in lots of texts ...

basically it says the maximum allowable stress is the section crippling stress (Euler as you know goes on to infinity) and uses a parapbola tangent to the Euler curve with the vertex at (L/rho = 0, Stress = Fcc). by a quirk of math, the tangency point is at Fcc/2, so this is the maximum for Euler to be valid.

the difficult part is calculating the crippling stress. What's your section like ? D, t, L, fixity

 

[mechengr09]

The section is a T. I have found some references to Euler/Johnson but applicable to steels. Still trying to look for something that will apply to polymers.

Thanks for your responses.

 

[rb1957]

sorry, but how is a Tee like a "cyclindrical shell".

Euler/Johnson isn't only applicable to steel , we use it for Al as well. that said, it may be more valid for metals as opposed to polymers. if you've got E, do you also have fcy (which could be the same as fty) ?

if the legs of the Tee are thin (b/t > 10) consider reinforcing them with lips.

do you plan on testing ?