[PSUBS-MAILIST] epoxy domes

Thu Aug 4 13:41:10 EDT 2022

Hi Sean. The creep issue may be moot if we stick with Hemispheres and ultimately a 60 inch full sphere.  The optics are unbelievable and better than acrylic. At least looking at the two side by side.  We are happy to destroy domes and ports because they are dirt cheap to make.  Also it’s fun as hell to do this. 
Hank

Sent from my iPhone

> On Aug 4, 2022, at 10:04 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> A few concerns, the most obvious of which is the lack of an extensive body of test data for epoxy resin in this application, in comparison to that of PMMA (acrylic), and of course that the use of epoxy resin in this application is not covered or sanctioned by any of the design guides, other than where "novel" designs are addressed in the language. This loophole makes such unusual designs possible, at the expense of somewhat onerous testing requirements, which include full scale destructive testing.
> 
> That said, what specific epoxy product are you testing?
> 
> The comparable epoxy product which I am familiar with is MG Chemicals 832WC, linked here: 
> https://www.mgchemicals.com/products/potting-compounds/epoxy-potting/clear-epoxy-resin/
> 
> The technical data sheet for this product indicates a glass transition temperature of 33°C for this resin, which makes me suspect that sustained load creep will be a problem, even if the specified yield and ultimate failure strengths are sufficient.
> 
> I also wonder about the refractive index of the cured resin. This is not indicated on the data sheet, but could give rise to visual distortion if it is too far removed from that of water and acrylic.
> 
> Interesting concept. Curious to know what you discover.
> 
> Sean
> 
> -------- Original Message --------
> On Aug. 4, 2022, 05:48, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:
> 
> Hi all,
> A friend has asked me to help him make a dome using epoxy casting resin.  I tried to discourage him, but his arguments have merit.
> I had him make a sample piece 2 inches thick and big enough to start testing.  The sample is amazingly clear.  I started by cutting and machining sample strips for bend testing as well as one pice to set out in the sunlight and one piece is stored in the shop.  So far to my surprise the epoxy machines as well as the acrylic and the comparison bend test with acrylic were also a surprise also.  Both the acrylic and epoxy had the same strength resisting bending and returning to normal.  I measured the bending movement with my magnetic base dial gauge and they were within .010 inch of each other.  The acrylic sample broke before the epoxy, by a good percentage.  I will repeat this test several times, but we are now making ports that will fit in my port testing chamber and do many pressure cycles and destruction tests.  This will give us a base line against acrylic.  If it works out we will make a small 2 inch thick by 24 inch dome and pressure test that.  Fingers crossed.
> Hank
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