Re: [PSUBS-MAILIST] Carbon Fiber

["D. Blake" <dblake@bright.net>]

Hi Karl:
Thanks for the info,  very thought provoking.  Tony's mention of a flattened
protion of hull had me kinda wondering also in terms of strength
calculation.  Some time ago on the design website, we kicked around the idea
of a two-man sub similar in design to  the SM 80/2 illustrated at:
http://www.globalsubmarines.com/sm02.htm   This particular sub makes use
of--what appears to be--two 2:1 ellipsoidal encaps welded together to form a
sort of 'flyingsub', or saucer-shaped pressure-hull.  Very cool design; but
unfortunantly, has depth limitations due to the flattened shape.  Of course
this could be overcome by providing support in the middle or centerline, but
the question still begs: how to mathmatically determine the strength?
Later,
Big Dave

-----Original Message-----
From: Karl Fuller <fullerk@voyager.co.nz>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Monday, August 14, 2000 12:12 PM
Subject: Re: [PSUBS-MAILIST] Carbon Fiber


>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
>>
>