2014 T6511 extrusion plastic bending LT

[bf109g]

Hello all.

Anybody have a reference for 2014 T6511 extrusion plastic bending in the LT direction? Everything I see is for the L direction.

Since Ftu is the same for both the L and LT directions, could I use the charts for the L direction and reason it that way?

Thanks.

 

[rb1957]

try AR-MMPDS-01, fig 3.2.1.0(g) ... shows an unsurprising (?) drop in LT as the thickness increase (compared with L direction)

 

[bf109g]

Agreed, but I have thinner sections (<.5). I also have data that show the LT values in MMPDS not as S basis, but as A basis.

I'm just asking for a sanity check for using the L plastic bending curves for LT for sections less than .5 thick.

 

[rb1957]

the AR-MMPDS-01 data is S-basis (for thickness > 0.125"), i'd use that. If you've got A-basis numbers for thicker sections you could compare with the S-basis in AR-MMPDS-01.

I gotta say that i'm alittle suspicious of plastic bending in the LT direction of an extrusion ...

 

[bf109g]

As am I. I just don't have a good comfort factor without some testing.

I'm looking at cargo system restraint components.

My solution is to move things around on the pallet to get the reaction loads down. The Douglas layout centered the locks on the pallet sides. The config I'm working on pushed everything forward so that I'm getting a high load on the aft most side restraint when I have an aft CG.

Of course, this config has been around for 20 years, so there's going to be squawking and gnashing of teeth. Not to mention the inertia load factors were pulled out of the air with no check of available load factor data. And shear due to bending was calculated as V/A... Kind of hard to go back to mahogany row and say this thing's AFU.

 

[rb1957]

agreed, though just because something has been in service for upteen years doesn't make it complaint ... it might only mean that the installation hasn't been subjected to the certification loads, (presumably 9g crash).

something to consider might be that if you're section is going plastic (ie above linear bending) would another loadpath become active ?

it can be a struggle to make something that has been around for donkey's years "correct", but that's why we get paid the big bucks ! ... keeping other people's a$$es out of the fire

 

[bf109g]

Knowing the pain of changing the floor layout, I'm going to suggest fabbing the part from 7075 T651 plate in the future. That gives me positive margins all around.

I could live with the 2014 extrusion, provided the assembly is installed per the Douglas layout.