[Date Prev][Date Next]
[Chronological]
[Thread]
[Top]
Re: [PSUBS-MAILIST] Viewport Toughness
I'm only pulling from what I've read and my own thoughts. If you can get
Stachiw's book, it is very good. And look in places like ASM or ASTM for
more info on glass and acrylic.
I guess its up to defining strength. Glass has a high modulus meaning it is
brittle. This means that a material under tensile loads does not experience
much change in length with a given stress before it fails. Materials like
this typically don't experience much (if any) plastic flow, they go right to
failure.
Under ideal conditions glass would be able to withstand a high degree of
uniform stress. Is it stronger, maybe? That depends on the application. For
a sub, strength means that you want something that will withstand a given
stress. And be able to absorb kinetic energy; take a bump, and not fail. An
example of kinetic energy is an impact test like the Gardner test done by
ASTM. When a material is impacted by something the stress spikes, sometimes
out of the materials elastic region. Outside this region the material will
be plastically deformed meaning it cannot return to its original shape
(advanced notice). Acrylic has a lower modulus then glass and can withstand
localized over stressing because of its ability to transfer energy thought
itself.
In order for glass to take a bump and not fail the peak stress cannot pass
the yield point. As said earlier, after this point there really isn't a
plastic region only immediate failure. Yes, you could make a port out of
glass but localized stress from, an imperfection in the material, or in the
seat/seal, or from being bumped is magnified and can easily peak the stress
past the yield point. What about mounting to the flange, will the fastening
system introduce more localized stress?
Acrylic is clearer, more forgiving, lighter (guess), easier to work with and
gives you advanced notice before potentially killing you.
Cost is another factor, like with forming and machining. Can you machine a
conical of flat surface on a glass port? You can grind one, but its
expensive. Can you drill holes in glass, yes but its expensive.
There has been a lot of testing on glass, and it was determined that other
materials are better suited for sub windows and research went in that
direction. While glass has other uses which acrylic is a poor candidate.
Acylic isn't perfect either, but comparatively it is better than glass. Here
is an article I found on the accident with Rich Slater as mentioned in
Busby. He uses the word "glass" but means acrylic.
http://www.faultline.org/place/2002/12/helvarg1.html
Adam
----- Original Message -----
From: "Brian Cox" <ojaibees@ojai.net>
To: <personal_submersibles@psubs.org>
Sent: Friday, October 10, 2003 1:25 AM
Subject: Re: [PSUBS-MAILIST] Viewport Toughness
> I have a question about using a glass dome, wouldn't a thick glass dome
actually stronger than acrylic? But it would not be able to be used because
of it propensity to shatter under certain types of stresses. Adam ?
>
> Brian Cox
>
> ----- Original Message -----
> From: "Adam Lawrence" <adteleka@in-tch.com>
> To: <personal_submersibles@psubs.org>
> Sent: Monday, October 06, 2003 7:30 AM
> Subject: Re: [PSUBS-MAILIST] Viewport Toughness
>
>
> > From what I have read, when a viewport breaks it starts by extruding
itself
> > into the flange and then final failure is like a shotgun going off.
Also,
> > failure initiates on the inside surface, where the acrylic is in
tension.
> > Test it, that's the only way you'll know!
> >
> > Adam
> >
> >
> > ----- Original Message -----
> > From: "pierre&marie" <poulin.carrier@videotron.ca>
> > To: <personal_submersibles@psubs.org>
> > Sent: Monday, October 06, 2003 5:49 AM
> > Subject: [PSUBS-MAILIST] Viewport Toughness
> >
> >
> > > Hi People!
> > >
> > > I've been to a house building show here in cold Canada and there was a
> > boot
> > > that sold "unbreakable" windows for thief.
> > >
> > > They say that there technologie can change a normal window into a
bullet
> > > proof window.
> > >
> > > The basic of that method is to put a high resistance thin plastic film
> > that
> > > stick on the window. Almost like a windshield. You should see me
comming
> > > from now... I asked if we can put that film on acrylic and the said
yes.
> > >
> > > Do you think that this could be helpful for psubs? It would not
augment to
> > > strenght of the viewport but if it break it could prevent water from
> > comming
> > > inside the sub or prevent the viewport from imploding?
> > >
> > > Comments?
> > >
> > > Pierre "Viewport Strenghtener Technicien" Poulin
> > >
> >
> >