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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