Subject: Re: How do you calculate the strength of aluminum pipe?

From: [email-masked] (Michael John Hide)
Date: Wed, 24 Apr 1996 04:37:56 GMT

[email-masked] (Alex Burmester) wrote:

>Will someone share the equation for the strength of aluminum tubing?

>Specifically, a short tube supported at both ends and loaded in the 
>middle by a rope slung over the tubing.

>Factors would be wall thickness, length and diameter.

>Just a good estimate is all I need, nothing fancy and let's
>assume 6061-T6 aluminum.

>Thanks much,

>Alex.
Use the engineers bending formula  M/I=f/y . Where  M =moment ,   I
=momertof inertia ,f =allowable stress [say 1% proof] , and y=
distance to neutral axis  .most of this stuff is available in
handbooks
    mike

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From: PAUL <[email-masked]>
Date: Sun, 28 Apr 96 10:12:45 -0500

>Factors would be wall thickness, length and diameter.
 
Excerpt fromStructural Aluminum Design by Reynolds Aluminum:
A thube or pipe under external pressure tends to fail in the plastic range or
in the elastic range, depending on the wall/diameter ratio. In the plastic
range the collapsing pressure is the deciding factor.In the elastic range the
collapsing pressure is go
verned by the t/D ratio, the length of the tube and the modulus of elasticity.
In computing the failure of pressure of a tube both must be checked.:
 
[A                            let's try this again....
p=2 x t x f(compressive strength of material in PSI) over Outside Diameter,
where "t"= wall thickness and "p""=collapsing pressure. this calcuates plastic
range
elastic range:
If a certain D/t ratio is exceeded, the tube tends to collapse. if the length
of tube is: L (more than or equal to)2.45D (square root of)d/2t ...in.
 
Critical collapsing pressure:
p=2E/1-m2 (t/D)(to the 3rd)   Where L=length, E=Modulus of elasticity,
m=Poisson's ratio of .33  .
My apologies for the unformed formulae, but it's hard to get the notation
right. There are more if you find that this does not answer your question. An
actual tube size might help! Good Luck!
Paul

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From: [email-masked] (Stephen Gaudio)
Date: 30 Apr 1996 03:58:41 GMT

In article <[email-masked]>,
>Just a good estimate is all I need, nothing fancy and let's

how are you supporting the ends? (is bending supported? is there
	internal stress?)
what is the ratio of length to diameter? (is shear small?)
what is the ratio of thickness to avg diameter? (will it buckle?)

is the rope constrained to stay at the midpoint? if not, it may
move during service and lead to differing loading conditions.
if so, is the integrity of the aluminum at stake?

a blind application of stress = My/I can lead to incorrect answers.
it's just one component of the overall stress tensor which just will agree with
reality if the tube is fairly long, thick-walled and statically
determinate.

steve.