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The Click-Bond company has faxed me a test report on the ultimate tensile load capability of their stud fasteners. (For those of you unfamiliar with these devices, they are on page 107 of the 1999-2000 Aircraft Spruce catalog.)
The test they ran was on the cold (-60 F) temperature limits of three different adhesives, but the room temperature results are relevant to us. They used CS125-1420-CR fasteners which are a 1/4-20 stud made of stainless, where the head of the stud is encapsulated into a fiberglass disc about the size of a 25 cent piece. However, the attachment of the stud to the disc is identical to the CS-1032-CR fastener, which is the 10-32 thread version I use.
The ultimate load capability of studs bonded to composite surfaces (as opposed to aluminum surfaces), loaded axially (i.e. normal to the surface, as though you were trying to pull the stud off the surface), was just over 300 pounds. The failure mode was delamination of the fiberglass disc (ripping the stud out of the base) rather than a bond failure (pulling the disc off the surface). The failure load when bonded to a metal surface was higher, for reasons that were not discussed.
Of course, the glue you use has to be capable of handling the 300 pound load as well. If you use double-stick tape you'll pull the entire thingy off the surface. But our epoxy should have substantially more than 300 psi capability in tension.
I use Click-Bond studs for Adel clamps holding hydraulic lines (and someday, antenna and electrical wiring). This test data tells me that's just fine. I was considering using them to anchor rudder cables to the firewall -- this test data tells me that's a bad idea.
Normal design practice is for cockpit-mounted items to stay attached with a 40G load applied in any direction. The theory is that 40G is the limit for human survivability, and it would be a shame to survive a 30G impact only to be killed by something breaking loose in the cockpit and crunching your head. This tells me that if I use "Click Studs" to mount anything in the cockpit, I need one for each 7.5 pounds of stuff.
- Rob Wolf
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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