There have been strong doubts over ACI spokes at times, but I don't believe all professional wheel builders stress relieve properly anyway, no matter how popular they are.
yup to both.
Re ACI spoke quality; I have occasionally seen spokes (including ACI ones) with duff bends. If you look under a x20 microscope (or a really good magnifying glass) you can see that the forming die used to make the bends was allowed to wear (and/or gall) such that the inside of the elbow bends isn't always smooth like it should be.
This can make some or all of the spokes extremely vulnerable to cracking at that point, via fatigue. I say 'some' because it can be pot luck if the resultant warty lump on the inside of the elbow bend is a nascent crack or not; the material on the inside of the bend should yield in compression as the bend is made and this can be a somewhat random process if the abutting surface isn't smooth; you may or may not get a 'fold-over', and if you do it is as good as having a crack...
The other thing that can cause similar 'fold-over' on the inside of the bend is if the steel itself is full of (relatively large) sub-surface inclusions. I stopped buying cheap galvanised spokes in about 1983 when I realised that I had bought a duff batch and that is why my spokes were breaking. A little metallography (samples mounted in Bakelite, ground back to the spoke centreline, polished to ~3um, etched in Nital, magnification x100 when photographed) clearly showed a 'fold-over' on the inside of the bends. I was alerted to this when the front wheel I'd built had uneven sized flanges (but no dish to speak of) and yet the spokes on one side just kept on breaking no matter what I did, whilst the other side were pleasingly robust....
Re Plug1n's wheels; high initial tension + service stresses may have caused the spokes to settle a little (bend yielding and flange deforming, typically) in service. Backing the tension off would then lessen the rate of fatigue damage; according to some models of fatigue damage, there are contributions from both the cyclic stress variation (which won't vary much with mean tension anyway)
and the mean stress. The severe initial conditions would certainly seek out any spokes with imperfections. By contrast had the wheels been built normally and stress-relieved properly, it is possible that any minor imperfections would have been caused to yield locally (during the overload) which then leaves them with a (relatively) compressive residual stress around them when at the service load. This can mean that even spokes with minor imperfections (which are always a possibility) will last OK.
FWIW most spokes will fail in straight tension between 250kgf and 300kgf; in the absence of stress concentrations and residual stresses, a spoke tensioned to about 100kgf ought to have an essentially infinite fatigue life, since it ought not see cyclic stresses (or mean stresses) above the fatigue limit.
NB regarding spoke tension variations; the issue with these is not breakage of the spokes per se, it is more that
a) the slackest ones may have nipples that start to unscrew by themselves and/or
b)the tightest ones (esp on the DS rear) may be tight enough that the rim may be vulnerable to cracking.
BTW when Brandt wrote his book, rims were either single-wall or shallow double wall; in either case the upper limit for spoke tension (summer/California use) is set by the rim 'pringling' (which is a type of Euler buckling). However modern (deep, wide, stiffer) rims are not tension-limited in the same way, but are liable to crack if they are sprayed with nasty salty winter road water whilst loaded with high spoke tension.
It is pretty easy to chase down radial high spots too zealously and in the process end up with a few spokes that are too tight; it is often better to accept that the rim does have a little bump in it if that results in more acceptable spoke tension.
cheers
