Aluminum Tube Failure

Is this what you mean?:

Exactly!

Exactly the picture, or exactly the force determined by experiment?

I meant the Picture,
And Thanks for the mathwork, sounds good t me.

WOOOOOHH!!!!!

I did a quick check on the bending stress and it appears that this will fail in bending before buckling.

It is getting closer to home time here so I will have to confirm, but can you give the exact grade and heat treatment of the aluminum you have?

Pretty brittle stuff,

one of two alloys either 6061-T6 or 6063-T832

Thanks

Alright, using a yield strength of 39,000 psi (6063-T832); [6061-T6 has a typical yield of 40,000 psi].

You will see yielding at 67 lbs with a deflection at the free end of just under 1".

(a far cry from buckling failure of 650 lbs)

This also takes into account the usual disclaimer (codes, dynamics, safety factors ........)

May I ask what this is for?

Yielding will just be starting at 67 lbs but that will not be failure.

S = π(d⁴ - d_i⁴)/32d = 0.06186 in³

Z = (d³ - d_i ³)/6 = 0.082475 in³

^{Assuming Fy = 39000 psi,}

First yielding at M = S*Fy = 2412"#, so P = M/36 = 67#

Fully plastic at M = Z*Fy = 3216"#, so P = M/36 = 89#

Of course, this assumes that the smaller HSS with the fixed end is capable of taking a moment of 1.333*3216 = 4290"#.

Perhaps it would be wiser to make the fixed end tube larger and thicker than the other one. That way you would get a little more 'meat' where you need it most.

I read the OP again. The fixed end piece is a solid rod, not a tube, so it will be adequate.

I'm not mechanical, but this is kind of interesting.

To what extent is the failure dependent upon the fit being "near perfect" (stress probably distributed AROUND PIPE DIAMETER better) vs. "sloppy fit" (stress probably concentrated on knife edge contact at end of one or both tubes)?

Would cutting the end of the tube at an acute angle (tops in) distribute stress better than a 90 degree end cut? I'm out of my area here, but it seems like the buckle would start on one side of the tube and migrate around the diameter of the tube. Distributing the force around the tube with a slanted cut seems like it would require a larger portion of the tube to fail before the fatal buckle.

Bruce