Stress question for the gurus

I have a simple question about some stress values used in an analysis I'm reviewing. Here's the material values the analysis is working with:

AL 7075-T6511 extrusion-

Ftu = 78 ksi Fcy = 70 ksi Fbru = 140 ksi (e/D = 2.0)

Where'd this Fbru come from? Brittle rupture? And how can it be higher in value than the ultimate tensile stress?

In other parts of the analysis I've seen Fbu... is this the same as Fbru? I don't like the idea of brittle rupture being the criteria for a stress analysis. I'd much rather it be yield stress for loading that will be encountered more than once (i.e. not a crash).

Thanks in advance for any insight! Dave

Reply to
David Harper
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No brittle rupture is involved with either.

Fbru is the ultimate bearing strength for a lug (e/D = 2.0 here). Fbu is the ultimate bending strength. It's a plastic bending allowable.

The NASA Structures Manual, vol 1 covers these subjects.

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For Lugs look in section B2. See sec B4.5 for plastic bending.

Reply to
Jeff Finlayson

You're welcome.

Very similar information is avialble in popular aerospace text, Design and Analysis of Aerospace Structures by Bruhn.

Reply to
Jeff Finlayson

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