"Michael Koblic" wrote in message
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"Ed Huntress" wrote in message
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When you're bonding metal with strong adhesives, it's good to keep the
peel-strength/cleavage-strength issue in mind. That's one weakness of
those adhesives in metalwork. As an aside, this is what rivet-bonding is
all about in making aircraft wings. If you look at how the rivets are
placed it's clear that they're not being used for the sake of their shear
strength, as aircraft rivets normally are. They're there solely to keep
the edges of the wing skins from lifting and starting a peel failure.

--

Through trial and much error I found techniques of increasing a glue bond
strength that work for me (this is probably what proper engineers learn in
the first semester). Just changing the shape of the joint ever so slightly
I find the glue holds so much better (a cylinder glued to a flat vs.
cylinder recessed by a few thou *into* the flat - does not have to be a
particularly good fit, either. Also works for improving soft solder joint
strengths. Then there is less clean up then when using high temp
soldering - but that is another story!). Since I discovered the joys of
press fit (now that I have the machinery to produce one) things are even
better. But there is no way around it in this case and I shall have to
defeat the pesky peel some other way :-)

--
Michael Koblic,
Campbell River, BC

Yes, your cylinder example is a good one. In the first case there is a big
cleavage load. If you recess the flat to provide a shallow "socket" for the
cylinder, you have a shear load where they overlap, and that's where
adhesives are very strong.

A good example is the chassis of the Lotus Elise, which is also used in the
Tesla electric sports car. The chassis is made of tubular aluminum
extrusions that are bonded together with epoxy. The joints are
plug-and-socket types, or very close to plugs and sockets, in which almost
all of the load is in shear. Where there's no peel or cleavage,
metal-to-metal bonded joints can be stronger than the parent metal itself.

--
Ed Huntress