Re: [PSUBS-MAILIST] Carbon Fiber

[TeslaTony@aol.com]

In a message dated 8/13/00 2:14:16 PM Pacific Daylight Time, 
wacarson@interchange.ubc.ca writes:

> 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
>  
Hmmm....I wonder if I could grow a crystal into the shape of the hull I 
need.....

Anthony