determining point of permanent deformation in aluminum piece

huangyhg

determining point of permanent deformation in aluminum piece
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.
what is the alloy and tempering; and is there any welding?
i'm considering using 6105-t5, and there is no welding.
solve for the extreme fiber yielding, for local buckling and for ltb, least value controls.
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.
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   
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.
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"