Air show 787

[Flieger]

Originally Posted by island911

"Composites fail progressively, not all at once like metals."

say wuhaa...?

Well, the first part is true in certain situations. Mostly bending of beams- if you apply a constant strain rate on an Instron machine you will see the load drop in stair steps and hear each ply break one by one, especially if there are unidirectional plies in more than one orientation.

If you just pull on a coupon of uni all you see is the load go up and then BANG! then splinters flying at you.

[surflvr911sc]

Wife's office, and I'm a bit proud.

Not bad for a girl that had to pay for college and flying lessons with what she earned from waiting tables, and then flying for the US Air Force. What a journey it's been.

[Head416]

I hope she's been practicing barrel rolls!

[wdfifteen]

Originally Posted by Scott Douglas

And therein lies the problem, they broke.
Unlike the B-52 example where they deformed.
Composites aren't very forgiving when pushed past the limit. It's catastrophic failure.

Neither is aluminum. The limit is the limit, and when you pass it, you're screwed. Carbon fiber composites have high stress/weight so you can build in a higher stress limit at the same weight. A broad plastic region in the stress/strain curve gives you a nice safety zone if you wish to ignore design limits, but a strain limit is still a strain limit. Just pay attention to design limits and there won't be a problem not matter what the material.

[wdfifteen]

Originally Posted by gordner

They all break them, it is required. That wing vastly out performs the B52 wing structurally, not breaking is not all there is to it. Composites fail progressively, not all at once like metals.

I've done a lot of testing of carbon fiber composites. They don't fail progressively, they fail catastrophically. That doesn't mean a carbon fiber STRUCTURE has to fail catastrophically, it just has to be designed with the modulus of CFCs in mind.