On Wed, 11 Jul 2018 20:16:33 -0700, Jeff Liebermann
wrote:

On Wed, 11 Jul 2018 13:48:47 -0500, AMuzi wrote:

I think the question isn't so much 'has the tube's ultimate
strength been diminished?' but rather 'is it yet strong
enough for expected application?'.

Nope. I'm not trying to measure if the tubing is strong enough.
Assuming identical lengths of tubing, I wanted to see if the presence
of a Rivnut significantly changed the tension required to bend or
break the tubing when compared to the identical tubing that did not
have a Rivnut inserted. If I'm able to pull hard enough, I should be
able to eventually break both tubes. If they break at the same
tension, then I'll declare the Rivnuts are safe to use. If there's a
substantial difference in tension, then I'll declare the Rivnuts
weaken the frame.

I'd think it obvious that any hole drilled laterally into a tube would
have an effect on the bending strength of the tube. The question
wouldn't be whether the rivnut changed the strength of the tube but
whether the tube was strong enough with the rivnut installed in the
tube.




In theory and in absolute yes the tube is less strong. In
practice, from Santana ExoGrid tandems to Bianchi thinwall
tempered aluminum models, to their carbon bikes, rivnuts are
not a failure point.

Where are the Rivnuts installed on these machines? Water bottle
holders? The pictures don't show much detail:
https://www.google.com/search?q=Santana+ExoGrid+tandem&tbm=isch&
https://www.google.com/search?tbm=isch&q=bianchi+aluminum
--

Cheers,

John B.