Originally Posted by
DannoXYZ
It's not technically "fatigue" in the metallurgical sense since you never ever really stress a frame close enough to its yield-strength to do work-hardening anyway. I suspect what happens is that the tubing themselves are fine, but you end up with lugs and brass that ends up with microscopic cracks. I've cut apart old steel frames and have found a lot of corrosion in the lugged joint itself where there once was full-contact with brass.
So yeah, old steel frames do get softer from A LOT of empirical evidence. However, HOW that softness develops is arguable and certainly is not metal "fatigue". "Frame fatigue" is a more accurate way to describe it perhaps.
Ok, Danno, this begins to sound like the failure of solder joints after extensive thermal shock cycling. The beryllium copper leads are ductile enough that they will not be stressed, but the solder joint itself can easily be undergoing plastic stress cycles, fatiguing, and cracking after only 25 cycles, if the design is very badly wrong. The circuit has not failed, nor has the part or the wiring board, but the joining was not strong.
Road Fan