Hi all,(adsbygoogle = window.adsbygoogle || []).push({});

i hope that i am in the right forum.

As you see in my topic i have a problem with Roark's formula especially for elastic stability of plates and shells.

The formula i got a problem with is the following:

If you have the book:

sixth edition: page 689 table 35 formula 15.

or

seventh edition: page 735 table 15.2 formula 15.

if you dont have the book:

"thin walled circular tube under uniform longitudinal compression" (ends not constrained)

formula:

stress = (1/root(3))*(Young's Modu / (1-poissons ratio²) *( t / r )

where

r = radius of tube

t = wall thickness (i hope...)

"Tests indicate an indicate buckling stress of 40 - 60% of this theoretical value"

So on i got an indicate stress of 1363 N/mm² by using a wall thickness equal 1.5 mm,

radius 139.82, steel with E = 210000 N/mm² and Poissons ratio = 0.3.

Even with 40% of this stress i got approx. 545 N/mm² anyway.

So I need 714 kN to buckle this tube.

With: force = stress * area

area = (radius² - (radius - t)²)PI

It seems a bit too much for me.

Could anyone help me with my doubts? I helpful link would be very nice too.

What other material properties will influence my buckling tube in a relevant way?

I thank you in advance

Matt

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# Roark's formulas for stress and strain

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