[PSUBS-MAILIST] buoyancy

[Sean T. Stevenson via Personal_Submersibles]

I didn't mean to imply that composites are necessarily bad for the application, but rather that they are not easily predictable. Composite hulls usually require verification of theoretical results by physical testing.  As for the theory, fiber reinforced matrix composites usually exhibit properties which are weighted averages of the individual component properties in proportion to their volume fractions, but they have failure modes which homogeneous isotropic materials do not, particularly with respect to buckling, delamination, and brittle fracture. Additional variables such as average length of fiber, the order of consecutive principal fiber orientations, layer thickness and so forth all have an effect on the ultimate part performance, making composite failures less predictable.  That said, there have been a number of commercially successful composite pressure hulls, but there is a significant amount of work involved in validating them.

Sean


On November 11, 2015 2:25:41 PM MST, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean,I just put it through the Deep Sea Power & Light program whichhas
>basic geometries & a materials list with epoxy / fiberglass.I had spent
>a lot of time a couple of years ago, researching the building
>of a fiberglass 1atm sub. The E glass / epoxy combination was the
>best(including price) for compressive strength.Those carbon fiber
>pressure vessels are wound so a different kettle of fish.Graham Hawke
>did a carbon fiber wound submarine pressure hull at one stage.They do
>have carbon fiber masts which are both under compression & tension,so
>the compressive strength can't be too bad.Alan 
>From: Hugh Fulton via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: 'Personal Submersibles General Discussion'
><personal_submersibles at psubs.org> 
> Sent: Thursday, November 12, 2015 8:44 AM
> Subject: Re: [PSUBS-MAILIST] buoyancy
>   
>Sean,
>We have a New Zealand developed programme for design that is widely
>used in
>the pacific islands where Kiwis (NZ'ers) are involved. It covers
>piping,
>fabrication, ditch digging, construction of most things.  It is called
>"TLAR".  No guarantees go with it.
>Hugh 
>
>
>
>-----Original Message-----
>From: Personal_Submersibles
>[mailto:personal_submersibles-bounces at psubs.org]
>On Behalf Of Sean T. Stevenson via Personal_Submersibles
>Sent: Thursday, 12 November 2015 8:26 a.m.
>To: Personal Submersibles General Discussion
>Subject: Re: [PSUBS-MAILIST] buoyancy
>
>Alan, how did you do that calculation?  What layer count, thickness,
>component volume fractions and principal fiber orientations did you
>use?
>
>Sean
>
>
>On 2015-11-11 12:15, Alan James via Personal_Submersibles wrote:
>> Hank,
>> I did a quick calc on a sphere of nominal dimensions made of epoxy / 
>> fiberglass.
>> With external pressure it had a depth of 4347ft, with internal
>3785ft. 
>> I should have posted the results in psi, but you get the picture.
>> The big thing to me would be that if you ruptured it by hitting 
>> anything, or so it failed, you would go down like a lead balloon.
>> Alan
>
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