Re: [PSUBS-MAILIST] Isn't 'Mini book review.' anymore--pressure t est

[Dan h <machine@epix.net>]

I think I read where this type of test is done with the hull completely
flooded with liquid instead of air.  Water!   A tube is
connected through the pressure chamber wall  and into the sub full
of liquid.  The other end of the tube is connected to a graduated
vessel on the outside of the chamber.  As the pressure in the chamber
increases the hull is squeezed and fluid is pushed from inside the hull
into the graduated vessel.  You simply read the change in the volume
of liquid in relation to the increase in pressure in the chamber and plot
it.  When your plot starts ot go nonlinear, your at the end of the
elastic limit.  No computer necessary.  Reading fluid rather
than air, you got an exact easy reading.

Dan H.

AndrePevestorf@aol.com wrote:

In einer eMail vom 12.04.2002 17:30:52 (MEZ) - Mitteleurop. Sommerze schreibt Asmyth@changepoint.com:
 
 

I'm referring to a thin tube that allows you to track air flow out of the hull as the hull compresses.

Does that mean that the proceed from the assumption that a hull with a whatever shape and a material with a linear elastic behavior (for the first time) will contract under external pressue with a linear increase of the inner pressure due to the linear decrease of the inner volume? (if the hull is definitely sealed)
Hmm... sounds like a brilliant idea indeed.
With "stress gauges" (DMS in german) there is the problem that you have to know were the critical stresses will appear.
Tracking the decrease of the inner volume needs no special consideration of the stiffeness distribution in the hull structure. It works well even when the hull is really strong and only the hatch (or something other) works like a drumhead.....

Unfortunately it doesn´t work while the sub is manned... I guess that the fact that our lungs burns O2 to CO2 will also influence the micro-pressure..but I´m not sure about the practical consequence. If you use also CO2 absorbers I´m relatively sure that this will disturb any exact pressure tracking.
...maybe the passengers have to brath consequently from a closed circuit (rebrather)

With this procedure any nonlinear reaction to a linear increasing of the pressure will be a sign for problem. increase the inner pressure with a higher ratio then the deep ----> some parts of the structure got weak. If the inner pressure increase continualy while the deep is the same there could be a leak an water runs into the hull....

conclusion: very good method for preventing the hull for demage or lose. But needs a fine deep sensor and a very fine pressure sensor and a computer to get the curves in realtime.. or a quick pen ....

If wether it´s work in a boat on a lake or sea is just an other quest.

Thanks you for that good idea!

A.