Re: Question for aero engineers.

David J. Gall

Right on, Jay. Just like wood. There's also a question of stabilization and substrate strength in a composite sandwich structure. It is possible (but NOT likely in this case) that the added thickness is needed because the chosen substrate (foam) is not quite strong enough in compressive strength (or small enough in cell size in some cases) to prevent buckling of the nominal laminate in compression, so the laminate is thickened in order to provide more of its own stiffness as a resistance to buckling. Lots of goodies to consider in this business!!!

David J. Gall

----- Original Message -----
From: Jay Scheevel <scheevel@...>
Date: Wed, 29 Sep 2004 01:10:03 GMT
To: Q-LIST@...
Subject: Re: [Q-LIST] Question for aero engineers.

David writes:
You probably answered your own question. Good work!
I agree. But, probably the reason for the question is that this behavior
is the opposite of most non-composite structural materials.
In most composite laminates put into compression there is a tendency for
small voids in the bonding material to form into unstable tension cracks.
In this case laminates will generally fail by fibers separating along
these propagating cracks allowing the fibers to buckle. When put in
tension, these same voids are not prone to forming tension cracks and
laminates will fail by fibers stretching to failure longitudinally (or
tearing). Overall, in compression, the laminate strength is more strongly
controlled by the integrity of the bonding material and in tension it is
more strongly controlled by the integrity of the fibers, thus the
difference in failure strengths and the need for beefing up the
compressional laminate relative the the tensional one.
Jay Scheevel Tri-Q, still building

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