On Thursday, April 8, 2021 at 10:49:48 AM UTC-7, wrote:
On Thu, 8 Apr 2021 05:43:43 -0700 (PDT), Tom Kunich
wrote:

Jeff, try picturing threading a Kevlar inner cable through the outer. Now how
would you expect to do that?
Two ways. Pull or push. For pull, I would run a metal wire through
the cable housing, attach to Kevlar fiber with glue, and pull on the
metal wire. For push, I would glue a wad of cotton to form a shuttle
on the end of the Kevlar fiber. A conical dart shape should work.
Insert the shuttle into the cable housing and blow it through housing
using compressed air.
https://en.wikipedia.org/wiki/Cable_jetting
As a real engineer I have some ideas that could work but why when
stainless steel is more than sufficient. Jay is a lawyer and not a
mechanic. We all know that he broke a cable probably because he
overtightened it at the derailleur and broke the strands.
We all don't know that. You might, but we don't.
Stainless is extremely good at weather resistance but very bad at
pressures that overload the molecular bond of the material.
Pressure? Stainless is excellent in compression (also known as
pressure) but might have problems in tension or torsion.

Broken molecular bonds? Lots of ways to do that but none seem to be
found in a brake cable:
https://www.google.com/search?q=break+molecular+bonds
In general, one needs to input sufficient energy to beak the molecular
bond, usually forming ions or different molecules. Maybe Jay exposes
his brake cables to ionizing radiation, which is known to break
molecular bonds. Perhaps you could re-write your description of metal
fatigue failure in a manner expected from a "real engineer"?

People who pretend to be engineers are tiring. You have already told us that you only rarely ride a bicycle anymore so perhaps you might want to explain what you're even doing on this group?