Minimum bend radius / strain limit for thick aluminum extrusion

[LocutusScientific]

We are bending a 7" wide, 3/4" thick 2024-T3 aluminum extrusion up by 25 degrees with a 12.5" bend radius. We are concerned that the material will be damaged at the bend due to the high strain, such as from introduction of cracks that will result in fatigue failure in operation. I see a lot of references for minimum bend radius for thin sections but nothing much above 1/2" thick materials. Are there any references or rules of thumb for bending plates this thick?

More fundamentally, what would I look for in terms of a strain limit? A max strain that is some percentage of the published elongation at break?

 

[dvd]

You will eventually get fatigue failure with aluminum -

 

[rb1957]

how about heat after bending ?
What is the profile of the extrusion ? You may have more difficulties maintaining the section through the bend.
How close are you to the 1/2" thk min bend ?
The machine to do this bend will need to be quite large ... the forces would be significant.

What's the application ? bridge component ? facia ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[drawoh]

LocutusScientific,

There are all sorts of handbooks and websites showing the minimum bend radii of various aluminium alloys. Aluminium 2024[‑]T3 is just about the hardest material you can bend. I would look for another solution.
[ul]
[li]Can you extrude the actual bent shape?[/li]
[li]As noted above, can you heat treat after bending?[/li]
[li]Do you need the high strength material? Sheet metal shops bend 5052[‑]H32. 5086 is the strongest as-welded grade of aluminium. Either material will be stronger at the bend than 2024[‑]T3 with cracks in it. [/li]
[li]Is this a super lightweight design requiring exotic material? Is your structural shape optimal? Why not machine from billet, or assemble from riveted sheet metal? [/li]
[/ul]

--
JHG

 

[LocutusScientific]

The bend is towards the tip of a 100" long, 3/4" thick extruded fan blade. Heat treating after bending is an option, as is other alloy considerations. This is an existing product with 2024-T3 currently in use. For now I am looking for a way to evaluate what would be the maximum amount we can safely bend this without damage. I'm currently running some nonlinear FEAs to get a better idea of what the strain will look like during the operation.

 

[rb1957]

I suspect that the loads on such a thing will be way more significant than the forming stresses. If you're doing a model you may want to bench mark by bending 0.063" thk sheet with a bend rad of 3t (ie something quite typical).

But a stress relieve heat treat should remove any question. Better (by far) would be the HT to O condition bend then HT to T42.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[LocutusScientific]

I like the benchmark idea. I can look at the strain on thin bent plates that follow recommended minimum bend radii to see how they compares with my thicker plate.