Re: battery boxes

[Dick Morrisson <rmorrisson@unidial.com>]

A little more detail to the explanation Phil gave.

John Shawl stated he was able to get a better "crush depth" by adding cardboard
rings to the outside of the plastic bottle.  Phil said the rings had to be
attached or it would be the same as if they weren't there.  Contradiction?  I
don't think so!  Read on.

When a vessel is under compressive load, the diameter starts to decrease.  If
the vessel is thin walled like a coke bottle, the wall will buckle long before
any significant decrease in diameter (i.e. circumferential length).  When the
wall buckles, some of it collapses in, but!! another part has to extend out to
maintain the circumferential length.  It goes "oval" for a moment before
actually collapsing.  This is where the external rings help to forestall
buckling (by helping to prevent the "oval"ing) and therefore the "crush depth"
goes up a little.  Good example John.

If the vessel is designed like a sub should be (and Phil has many to his
credit), the bending stiffness of the wall prevents buckling until about the
same point as the wall fails in compression.  At this point the circumferential
length has decreased significantly and the "oval"ing will not be enough to get
much, if any, help from the ring stiffeners (they will just hang on the
outside).

So, if you are designing implosion resistant coke bottles, add snug cardboard
rings, if you are designing subs, make sure you have 100% continuous welds
between rings (stiffeners) and the hull.

Dick Morrisson


Phil Nuytten wrote:

> Hi, Jon:
>         Re: slipping external rib/ring stiffeners over a cylinder to
> increase the cylinder's depth capability: External rings MUST be attached
> to the cylinder; then, as the cylinder tries to buckle under load, it has
> to 'drag' the rings with it . . if the rings are not physically attached to
> the cylinder, the cylinder doesn't know that they're there.
>
> Regards
> Phil Nuytten