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Re: [PSUBS-MAILIST] Fiberglass Hull
On Jan 27, 2007, at 10:37 AM, Mark Roberts - Harbortronics wrote:
One guy per the link points out a very important thing with regards
to fibers.... they can be very strong in tension, but have
effectively no compressive strength. To my mind, that's a show
stopper right there.
A show changer, true... but not necessarily a show stopper. All one
has to do is put the casing of the pressure vessel under tension,
rather than compression.
How?
As a thought experiment, imagine a soccer ball. Let's replace the
seams with steal beams, and the skin with fiberglass... but allow the
fiberglass to bow inwards. The fiberglass under tension will transmit
the compressive force to the steel framework which can resist it
under compression and bending forces.
One could make a cylinder similarly... take a hexagonal lattice, roll
it up, etc.
Chuck
----- Original Message -----
From: Brent Hartwig
To: personal_submersibles@psubs.org
Sent: Saturday, January 27, 2007 4:34 AM
Subject: RE: [PSUBS-MAILIST] Fiberglass Hull
Doug,
I'm not qualified to answere your questions about fiberglass
composite sub hulls under external pressure, but here is a
interesting thred about just that sort of thing. Here is the link
and a small quote from the discussion that has the most meat in it.
http://www.eng-tips.com/viewthread.cfm?qid=174497&page=1
"Spend some time looking through ASME III (Unfired Pressure
Vessels) for vessels under external pressure. And keep in mind
that if you intend to operate at 100 ft (~45 psi) that you'll want
a hefty margin against any kind of pressure boundary buckling
failure. Think in terms of emergency recovery time from a depth
overshoot if you experience horizontal control plane malfunction
while descending at some speed and down angle when nearly at your
maximum operating depth.
I may be able to find a more specific ASME reference for you, but
for a number of reasons I don't think I can provide any hints as
regards a design collapse depth, so you're on your own there.
Norm
arto (Mechanical)
12 Jan 07 9:46
also look under ASME PVHO (Human occupancy) & Sec. X {fiber
reinforced plastic) pressure vessel codes"
end quote
In the past I saw a web site for a deep diving live aboard
submarine project called the Neptune. They were working on a design
for a carbon fiber pressure hull that they claimed could be used
down to 6000 meters. The web site waswww.neptunesubmarines.com but
it's a dead link now. I was put onto this site originally by a web
site for the Perendev magnetic motor. At one time I thought it
might be a great motor for subs in general but there is some
serious greed problems with the owner of the company. Neptune
Submarines were wanting to put the Perendev magnetic motor in there
live aboard submarine to replace a nuclear type power source. Maybe
someone here knows what happened to this Neptune Submarines group
out of Switzerland? Here is a pic of there submarine design.
http://img224.imageshack.us/img224/7608/24243158bk0.jpg
Regards
Brent
From: djackson99@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Fiberglass Hull
Date: Fri, 26 Jan 2007 00:35:40 -0500
I know it's an old topic but I have mostly ignored the previous
post regarding fiberglass because I never thought I was going to
give it a second thought. ...wrong again.
1) Did anyone ever come up with a way to calculate even a ball-park
working depth given all, or at lease some of the variables for
fiberglass construction? If so can you point me in that direction?
2) I know that the externally loaded working psi for a non-
reinforced cylinder is lower than it's internal working psi. That
makes even more scene to me when thinking about the alignment and
tensile strength of glass or carbon fibers compared to their
compression strength. However it seems that there would be a ratio
that could be used to estimate the reduction in loading ability.
Would that be true? For example if pipe section is rated for
1000psi, could it's external load psi rating be stated as x% lower,
say 20% lower, based on the type of material?
Thanks --Doug J
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