[PSUBS-MAILIST] hatch

[Sean T. Stevenson via Personal_Submersibles]

These sorts of problems tend to require some FEA, as the straight shell calculations only account for the circumferential stresses and not the bending introduced into a hatch lip. That said, 0.875" is reasonably thick, and if you model such a dished head, faced off normal to the centre of curvature, turned to eliminate the acute outside edge and grooved for an o-ring, then the minimum distance between the corner of the o-ring groove and the outer shell surface will give you a reasonable approximation of the shell thickness to use for calculation, but then means that the hatch will be significantly heavier than it needs to be.

A deeper dish leads to less bending stress (and less extraneous material) but increases volume and decreases bearing area.  There's probably an optimum tradeoff.

Sean


On August 6, 2015 10:05:31 AM CDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Hi Sean,I was thinking about making a hatch from a single piece of
>dished material instead of the typical dome welded to a ring etc.   I
>have a tank head that is 7\8 thick 516-70  .  I was thinking about
>cutting a disk from it at the apex and simply machining a flat land
>with o-ring groove.  Is this a good or bad idea and would you be able
>to calculate the failure depth if I measure the depth of dish and
>dia.Hank
>
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