RE: [PSUBS-MAILIST] Carbon Fiber

["Wade Carson" <wacarson@interchange.ubc.ca>]

Anthony,

I think that the reason that most composite materials are frowned upon for
1ATM subs is that the strength of the material can vary so much in each
different specimen and because manufacturing plays such a critical role in
their strength.  Even conventional materials such as steel or aluminum have
variance in their strength depending on the size, location, and direction of
cracks in the material (and there are always cracks in the material, unless
you grow yourself a gigantic single crystal chunk like those used in
airplane turbine blades).  This is one of the reasons for safety factors and
testing.  Composite materials are even worse for this problem because it is
much more difficult to spot or test for cracks and stress concentrations can
appear due to tiny bubbles that occur in manufacturing.
Anyways, the point is that you could build a hull with a safety factor of
two and it might fail, and then you could build a hull with a safety factor
of three and it might still fail, and then you could build a hull with a
safety factor of two again and it might pass but you would have no idea by
how much.  So the bottom line is, it could be done but it would be a risky
venture from a safety standpoint and from a financial standpoint.  You would
have to have a very high safety factor and then test it to yield and operate
it at much less than the test depth and then continue to test it at
somewhere close to the yield depth periodically in case any new cracks had
developed (I guess that's not much different than the procedure for a
conventional hull but I would increase all the margins).  Some of the other
guys could probably tell you better than me whether these trade-offs are
worth the advantage of having a carbon fibre hull or whether the added risk
of a more unpredictable material is still within the realm of sanity.

Wade

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of
TeslaTony@aol.com
Sent: Sunday, August 13, 2000 12:46 PM
To: Personal_Submersibles@psubs.org
Subject: [PSUBS-MAILIST] Carbon Fiber


I have read about using Fiberglass and how easy it is to work, but I have
also heard that it is not that great to use for a sub hull since it would
have to be ambient instead of 1ATM.
Now my question is: Could Carbon Fiber be used for a 1ATM sub? It's far far
stronger than Fiberglass, about as easy to work and probably a bit stiffer
to
boot, so it makes me think that it could be used for a 1ATM sub unless I am
missing something here.

Anthony