Re: [PSUBS-MAILIST] Carbon Fiber

["Karl Fuller" <fullerk@voyager.co.nz>]

Tony,
Just a little on what I know about carbon fiber as I know of in association
with America's Cup yachts (now New Zealand's Cup twice ;-) )
I agree with the comments made about the inconsistent strengths of carbon
fiber lay ups but not saying it shouldn't be used for this reason. The
methods to achieve success are not simple and to be used successfully,
requires careful engineering and years of experience form how I understand
it.
One of the bigger historical problems with carbon fiber, is delamination
problems. A way to avoid this are to use epoxy resins and to do as much of a
continuous lay-up as possible, in one go so you get a chemical bond between
layers.
As I understand it, you would not need an autoclave but an oven to 'bake'
the hull as they do with the yachts.
Reworking carbon fiber is a huge problem. You can only cut it with metal
working tools like a grinder. It will very quickly blunt many metal working
tools. Also if it is a structural change, unlike steel (where a join can be
close to 100% of the parent metal although aluminum is about 60%) you will
have problems creating strong joint bonds, requiring considerable tapered
overlays, once again, with potential delamination problems.
Galvanic action in seawater is a big consideration as most metals will
sacrifice to it, aluminum literally fizzes away, I have seen and repaired
the results. Keels have dropped off yachts, due to this.
You can use polystyrene to make your molds and later melt it out with a
solvent. There should be not heat problem with epoxy resin unless you have a
particularly volumous area of resin, going off at once.
Mixing ratios for epoxy resin are critical. There are so many part A
molecules to bond with part B and if the mix is slightly incorrect, you end
up with unbonded free molecules, not contributing to the structure strength.
Polyester resin does not have this problem but is inferior in strength, sets
very fast and is cheaper but I wouldn't recommend it.
It has been mentioned that there could develop stress or other cracks in
carbon fiber. Carbon fiber, although immensely strong for it's weight, is
also extremely brittle. When a carbon fiber mast breaks on an America's Cup
yacht, they have to replace all the ropes/lines as the deck gets showered
with fine glass like shards which cut hands to pieces. I think it would be
like most other materials in that if your have have where stress is
concentrated, you must avoid sharp corners and radiate stress away from
stressed areas otherwise it will crack like any other material and may give
less indication of it doing so, than steel. You can test for cracks like
steel, using dye penetrants, magnetic penetrants (I'm fairly sure) and of
course x-rays, as you may have to for a surveyed steel hull anyway.
Like steel, if you get the design accepted for construction, you may have to
have regular inspections during the construction process, cores samples may
need to be taken etc. Also, you may have to build it a heat and humidity
controlled environment which you would want to do to some extent anyway.
Like the Firestone tires, bonding between layers, requires strict humidity
levels.
Whoever sells you the carbon fiber and resin may require certain conditions
to be kept or want to waive their responsibilities as well, as do paint
manufacturers.

I personally would still consider using carbon fiber but I would seriously
weigh it against Pat's suggestion of using a steel inner hull and glass
outer shell, to create the efficient shape you require. You can put ballast
tanks, bottles, dropweights, pipes etc., between the skins. Also you can
have the frames on the outside and use them to support the glass skin,
saving internal room as well. I agree with Paul that it is strong enough and
would unmanned, test the sub to certain depths, periodically, to be assured
of it's continued integrity. Perhaps even treat it has you would your ports,
accepting they have a limited life, like aircraft frames.

When you mentioned the hull shape for your sub Tony, I got the impression
you where implying an out of round sectional shape athwart ships ? If this
were so, you would be constructing a hull that has very difficult to
calculate design compression problems. The reason you never see an out of
round hull, is the danger of collapse due to the shape. Hope you didn't mean
this as upon finding you, you might end up looking  indistinguishable from
your spirulina swamp rebreather !( Swamp breather food :-( )

I also would like to have on any info on comparative carbon fiber to steel,
information you Paul or anyone has. Thanks in advance.

I'm totally open to any comments on what I've written.

Regards, Karl.

--- Original Message -----
From: <TeslaTony@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Monday, August 14, 2000 1:12 AM
Subject: Re: [PSUBS-MAILIST] Carbon Fiber


> In a message dated 8/13/00 8:57:07 PM Pacific Daylight Time,
> vulcania@interpac.net writes:
>
> > A few more thoughts regarding composits versus steel for use in
submarines:
> >
> >  If you want to certify your boat, the pressure hull will have to be
made of
> >  steel to meet the regs, won't it?
>
> Yeah, but what are the advantages to getting it certified? I'm not
planning
> on using it for commercial purposes, although if I need to sell it I could
> have a few problems.....
>
> >  People say "fiberglass is lighter", but is that what we really want?
Subs
> >  displace a lot of water, and generate a lot of buoyancy.  They need to
be
> >  heavy to overcome this.  Steel is perfectly suited in this regard.
> Wouldn't
> >  a composite hull need to be extraordinarily thick to be heavy enough to
> >  counteract displacement buoyancy?  And then, wouldn't a steel hull of
> >  identical outside dimensions and displacement, but with thinner walls,
have
> >  a greater and more useful inner volume available for occupants,
components,
> >  and such?
>
> Actually I think that lighter _is_ better since I want to have one or more
> drop weights, and it's nice to be able to lose as much weight as possible
if
> you have to surface fast.
>
> >  Some say composits are easier to work with, but I don't know if that's
> true.
> >  If carbon fiber needs a pressurized autoclave to cure properly; and in
any
> >  case we've got to make extensive masters and molds; and then go through
the
> >  labor of casting up and sanding down, I'm not all that sure it would be
> >  easier.
>
> Renting a pressurized autoclave is probably cheaper than getting a shop to
> make an elliptically shaped steel hull that can handle the proper depths,
and
> using a foam core system might help with shaping the material (which might
be
> a problem if it has to be heated, but that's why I asked you guys, isn't
it?).
>
> >  And then again, Chris brings up the valid issue of cost per square yard
of
> >  material.  Shop around, and steel is pretty reasonably priced.
>
> Unfortunately there are three steel suppliers in my local area, one only
does
> "1018" (very soft steel, no good for a sub), the other two are junkyards
that
> I refuse to do business with unless I absolutely have to.
> Now I could always order my stuff directly from the manufacturer, but how
> much would 1000+ lbs. cost to ship? I think the autoclave and the
composites
> are starting to look cheap....
>
> >  The basic tooling and manufacturing methods used when working steel are
> >  pretty modest, really.  It's great stuff, and fun to work with.  And
for
> >  those few pieces you can't form yourself, there are shops that will do
it
> >  for you.
>
> After doing some blacksmithing I got pretty hooked on steel, although my
> equipment consists of one coal-fired antique wagonback forge, a 55# cast
iron
> anvil, misc. hammers, chisels, punches and stands, better for making
swords
> than subs (or plowshares).
>  As for someone else being able to make one of the hulls I want...I dunno,
> it's elliptical, 10+ feet long, 4- or 5- feet wide and a little flattened,
> not exactly sure how flat it will be though, and I have never seen any
> equipment yet that can do something like that yet, nor have I seen
anything
> like it either.
>
> >  If anyone is inclined toward composits because of an aversion to
working
> >  with steel due to a lack of training or equipment,   I suggest get into
> >  metal fabrication.  It's not as intimidating as it looks; and once
people
> >  start working in steel, my experience is they usually come to like it
quite
> >  a bit.
> >
> >  VBR,
> >
> >  Pat
> >
>
> Hey, maybe one of you guys can prove me wrong about Carbon Fiber or other
> Composites being cheaper and easier for me to use in the long run, you
would
> make me one very happy man (especially since I don't know where to get
> composites in the first place).
>
> Anthony
>