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Bolt Through Fiberglass, Shear Load - Design Help Needed

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Even though the Carbon group in the periodic table contains Tin and lead - 'Carbon is classified as an element in the 'non-metals' section which can be located in groups 14,15 and 16 of the Periodic Table. Non-metallic elements exist, at room temperature, in two of the three states of matter: gases (Oxygen, Hydrogen & Nitrogen) and solids (Carbon, Phosphorus, Sulfur and Selenium).'

Thank you Wikipedia  :clap:

Sparky --  In the aerospace industries it is common to "lay-up in" various bushings and nutplates to take critical shear loads in "fiberglass lay-ups.  These are (usually) 400 series CRES (read: stainless steel) components heat treated to (at least) Rc45.  If a through bolt is your desire, then merely a T-Bushing set should do the trick.  The main thing to remember is that you want to maximize the OD and thickness of your T-bushings.

Thanks for all the ideas. Initially I had been thinking about embedding a SS plate in the layup. But I have great concerns about water migrating in between the materials over time and causing damage that won't be detected before it is extensive. The different thermal expansion rates also cause me to worry about burying a plate in there.

Lew may have hit on one of my own candidate ideas, if I understand properly what a T-Bushing would be.

I'm thinking to create a pocket on the back side, in which the bushing would sit with some play. On the other side a washer would complete the sandwich arrangement and allow it ro pivot.

I'll have to include some sketches later when at my computer. It's too difficult on a phone.

Sparky -- The T-Bushings I am familiar with have a knurled cylinder for the thickness of the lay-ip, a T-head on one side (call it 2.5X the diameter of the knurled body), and a light slip fit to a washer on the other side.  The knurled body is a very lighy finger-press to the hole.  The knurls are coated with epoxy for installation.  Does this help?

You can buy a thing called a "big head" fasteners, it's basically a bit of perforated stainless with a nut welded to it, bond this to the existing grip with epoxy, then laminate over it creating a captive nut.

Alternatively, bond on a piece of tufnol, whale or 10G40 would be my grade of choice here, the drill and tap it once the adhesive has set. Tufnol will give a better bond to epoxy than s/so, and is non conducting, so no galvanic corrosion


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