Determining point of permanent deformation in aluminum pieces

[PostFrameSE]

I have some unique aluminum shapes that I need to determine at which point they will have been stressed beyond their yield point. I can't just test one as we're designing this part and don't really want to get a die made just to do some testing.

When doing calculations like that, can I use the full yield strength, or do I need to use .6Fy or something like that? The shapes are quite non-symmetrical with some areas that are thin enough that they could buckle prematurely I suspect. Any thoughts?

Thanks.

 

[Ron]

What is the alloy and tempering; and is there any welding?

 

[PostFrameSE]

I'm considering using 6105-T5, and there is no welding.

 

[civilperson]

Solve for the extreme fiber yielding, for local buckling and for LTB, least value controls.

 

[Ron]

If you don't have mill certificates on the aluminum, you'll have to use the published average yield or the minimum yield for 6105-T5 material.

Agree with civilperson on the parameters to check, but include torsional considerations since your section is assymmetric.

 

[PostFrameSE]

Thanks,

I'm probably in over my head on this as I don't have the Aluminum Design Manual nor the money to spend on just this one problem. I've calculated my moment of inertia and section modulus of this, but the local buckling is what's throwing me.

To over-simplify, I have a double U-shaped piece that will be used as a beam (sliding door vertical). The legs of one of the U-shapes are going to be pinned at 24" o.c. to framing members but the other U-shaped piece is pretty much free to buckle. Obviously, it really helps my moment of inertia to get that material away from my centroid, but I fear that it's too slender and would yield far too quick.

I'm wondering if it would be too simplistic and conservative to just leave off that extended piece so that I don't need to concern myself with the LTB or local buckling. Unless somebody would like to see a picture of what I'm trying to accomplish and offer further thoughts, I'll probably just go that route.

Do extruders generally have people on staff to solve these sorts of problems?

Thanks.

 

[Ron]

Extruders offer little to no help. They won't even compute section properties for you!

Post a photo so we can see what the section looks like, and the loading parameters.

 

[PostFrameSE]

Thanks Ron. Hopefully I attached this correctly. On my drawing you'll see I gave the section properties that I think are applicable. The thickness of that bottom "backwards L-shape" is .10". You'll see as well that I put some screws showing where some 2.5" members will be framing into this vertical. Those fasteners will be spaced 24" o.c.

This piece is actually a vertical sliding door rail, where extruded "girts" will frame into that 2.5" area. This piece will have wind load applied to it bending it about the X-axis. I feel that the bottom portion of this piece (which will actually just be a trim to cover the end of the exterior cladding) though it adds significantly to the section properties, in reality will not behave very well due to local buckling concerns.

Any thoughts would be appreciated.