Re: [PSUBS-MAILIST] Sphere

["Sean T. Stevenson" <cast55@telus.net>]

david cutajar wrote:

> I'd like to know a good source for spheres also. And
> other than FEMA on a cad system (Solidworks etc.) I am
> unsure how to acurately predict failure.
>
> On a sphere, because of it's simple shape, I would
> think that the falure calculation should be somewhat
> simple. That is, without bulkheads probably.
>
> -David Cutajar
>  
From ABS Rules for building and classing underwater vehicles, systems 
and hyperbaric facilities:

****************

Section 6

23   Spherical Shells Under External Pressure

23.1   Shell Geometry

D       mean diameter
D_i    inner diameter
D_o   outer diameter
R_o   outer radius
t         shell thickness

23.3   General

The limit pressure for spherical shells is to be obtained from the 
following equation:

P_cs / P_ys = 0.7391 * [ 1 + ( P_ys / (0.3 * P_es ) ) ^ 2 ] ^ -1/2      
for P_es / P_ys > 1
P_cs / P_ys = 0.2124 * P_es / P_ys                                       
           for P_es / P_ys <= 1

where

P_ys = ( 2 * sigma_y * t ) / R_o
R_o = the nominal outside radius of the spherical shell
P_es = ( 2 / ( sqrt ( 3 * ( 1 - nu ^ 2 ) ) ) ) * E * ( t / R_o) ^ 2

The maximum allowable working pressure is given by:

P_a = P_cs * eta , where eta = 0.67.

****************

In the above equations, sigma_y, E and nu are the material properties:  
yield strength, elastic modulus and Poisson's ratio respectively.

Note that this will give you appropriate working pressure, and not crush 
depth as you asked, but hopefully this is useful.

-Sean





************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 311
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************