[PSUBS-MAILIST] hatch

[hank pronk via Personal_Submersibles]

Sean,Thank you, just a thought, it would be 16 lb heavier, but very easy and quick to fabricate.  I could build it and clamp it to Gamma's hatch and do a depth test without risk to other parts.Hank 


     On Thursday, August 6, 2015 9:32 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
   

 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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