- #1
matthias_t
- 1
- 0
Hi all,
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 don't 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
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 don't 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