On 7/12/2018 11:54 AM, Jeff Liebermann wrote:
On Thu, 12 Jul 2018 00:41:36 -0700, John B. Slocomb
wrote:
Then, of course, the question arises as to what is a significant
difference? Someone mentioned a bit ago about deciding that a TIG
welded frame joint was strong enough to work, ignoring that a properly
made sweated joint is always much stronger.

Bicycle tubes and thus frames, are not all of the same strength.
Columbus XCR material has an ultimate tinsel strength of 1350 MPa
(195,800 PSI), Nobium is 1050 (152,289 PSI) and 25CRMO4 is 80 MPa
(116,030 PSI).

One can only speculate on the effects of drilling, oh say, a quarter
inch rivnut hole in a (approximately) 200,000 psi strength tube and
doing the same thing in a tube roughly half the strength?

Good point. I plan to use the weakest possible steel tubing as
excavated from the junk pile. I think it unlikely that I'll find any
manner of exotic metals or even double butted tubing. At this time,
all I care about is that the two tubes are reasonably identical.

If you really proceed with this, you should understand that under static
loads, low strength steels are largely unaffected by stress risers.
Their ductility enables microscopic high stress areas to yield and
distribute stress away from the discontinuities.

High strength steels are usually less ductile, so stress risers are more
of an issue. All steels are affected by stress risers in fatigue situations.


--
- Frank Krygowski