<html><head></head><body><p dir="ltr">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.</p>
<p dir="ltr">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.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On August 6, 2015 10:05:31 AM CDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px"><div id="yui_3_16_0_1_1438873234788_2375">Hi Sean,</div><div id="yui_3_16_0_1_1438873234788_2375" dir="ltr">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.</div><div id="yui_3_16_0_1_1438873234788_2375" dir="ltr">Hank</div></div><p style="margin-top: 2.5em; margin-bottom: 1em; border-bottom: 1px solid #000"></p><pre class="k9mail"><hr /><br />Personal_Submersibles mailing list<br />Personal_Submersibles@psubs.org<br /><a
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