T3D Re: underwater housings

["Gregory J. Wageman" <gjw@xxxxxxxxxx>]

Bob Wier wrote:

>I'm a bit surprised at this since generally materials have higher
>compressibility ratings than expandability (I forget the technical
>terms - it's been too long since I took strength of materials!).

It isn't an issue of the material's tensile strength.  It's the
housing's resistance to deforming that matters.

For an intuitive example, consider how easy it is to crush an empty
tin can flat.  On the other hand, think how difficult would it be
for you to burst that same can open from the inside.  In the bursting
case, the material itself (or a seam if it isn't a continuous piece)
must give way.  In the crushing case it need only deform, assuming
the contents are compressible (e.g. air).  This is a function of
rigidity, not tensile or compression strength.

        -Greg


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