Quoted message said:Old Crow or was it Wild Turkey said:Quoted message said:>Thinking back on it, I supposed that the second spoke
>popping could have been the result of the two spills I
>had on Saturday, but given the fact that the lady
>apparently (and I see this only because I saw lateral
>movement and she saw radial movement while spinning the
>wheel -- which resulted in her working on it some more)
>did not do a good job truing the wheel, I'm not so
>certain.
Quoted message said:Quoted message said:That should not compromise spoke life although it might
damage the rim so that it cannot be made as true as a new
one, or maybe not at all if it was collapsed, but that
should not affect spoke life. Spoke life is shortened by
not stress relieving and from kinks caused by foreign
objects against them to cause kinks.
Quoted message said:It's not the just kink, it's the stress riser caused by a
sharp object damaging the surface on impact. If just a
kink was sufficient, every crossed spoke would fail, as
would every "corrected line" spoke that you advocate.
Explain how that would be so. There needn't be any plastic
flow or gouging in a kink to cause failure.
by definition, for the material to take any permanent set,
there has to be plastic deformation. whether that be caused
by bending or something sharper like chain gouge or pedal
strike is open to circumstance.
Quoted message said:My reference to a kink is one induced by, for instance, a
wheel collapse in which a spoke is doubled back on itself
or one in which the wheel fell on an unoccupied pedal and
got snagged by a projecting part in a crash. These are
sharp bends in the middle of a spoke. Ones that cannot be
straightened by anything but a hammer and smooth surface
to fatten the kink, and even then it is doubtful to be
durable. In effect an unsupported "elbow".
understood, but there are two types of "sharp" bend. the
bending that has a comparatively large radius like a
straightened paper clip, or the minor bend which has a very
small radius like a chain gouge. the smaller the radius, the
greater the stress concentration & the greater fatigue
propensity. the large radius bend induces similar effects in
the material to "correcting the line".
Quoted message said:Quoted message said:Quoted message said:Even smooth bends have practically no effect on spoke
life. Replacement spokes must often be bent to insert
them into the hub. The main thing is to stress relieve
them after truing. That's what assures durability for
high quality spokes.
Quoted message said:Interesting qualification - that high quality spokes
assure durability. Can it therefore be inferred that you
don't feel confident that "stress relief" has the same
magical properties of infinite fatigue life on poor
quality spokes? If so, what would be the differentiator?
I see you didn't live in the days of Stella and Robergel
spokes from which I discovered the benefits of stress
relieving.
but i'm not too old to still find wheels with these spokes
at swap meets.
Quoted message said:These spokes broke after such short duty that a large
statistical trend was discernable by stress relieving
although that did not stop spoke failures entirely. It
was with the advent of DT spokes that truly durable
spokes became available. Now there are several brands
that work well.
yes, there are now several brands that work well. but their
long life is not the product of "stress relief"; it's the
fact that in the 70's, it became economic to mass produce
vacuum degassed steels. ultra-clean materials like this are
substantially more fatigue resistant because this process
virtually eliminates inclusions, thereby removing a
significant source of fatigue initiation.
a traditional steel for example may have half the fatigue
limit in the transverse axis of a rolled sheet compared to
its longitudinal axis. the same alloy composition, but
vacuum degassed, may have very similar fatigue limits in
both orientations. when first seen, the observation of this
effect sparked a hunt for explanation. electron microscopy
subsequently confirmed fatigue initiation at tiny inclusions
previously thought to be insignificantly small.
Quoted message said:
As I have described here often, spoke wire must be ductile
enough to withstand cold forming yet retain a sufficiently
high yield strength to resist fatigue failures at normal
spoke loadings. This had not been so before DT spokes so
there is where you should look for the answer. Redaelli,
Berg, and Prym spokes also did not survive long even with
stress relieving although it extended their service life.
Quoted message said:It's interesting how you're so very careful with your
claims; when challenged you fall back on your personal use
of just one brand of top quality spoke, as if it were
proof across the whole mechanical/materials spectrum.
You create these characterizations of thin air to your
liking. Every so often someone with your attitude shows up
here on wreck.bike to attack what has been discovered
about bicycle parts apparently trying to defend myth and
lore from days gone by. I can't see any other goal but
then you never said what you believe is the cause of
failures. Instead of beating around the bush and
insinuating and alluding to some agenda, how about stating
what it is you believe is occurring.
what causes failures is well known. it's what alleviates
them that seems to be the issue here. all that "stress
relief" achieves is a wheel that is fully bedded in before
riding. spokes do not therefore loosen and others do not
therefore carry disproportionate load. in that respect, the
practice referred to as "stress relief" is a good thing, and
thoroughly to be commended. but the business of fatigue
mitigation itself is achieved in the spoke manufacturers
factory, not the wheel builders bench.
the explanation of "local yielding" you've presented as
theory on how to eliminate fatigue is unfortunately built on
some gross misconceptions. you assert that the steel in
spokes exhibits the same properties as mild steel, i.e. the
exhibition of yield and deformation without work hardening
as a method of reducing residual stress. reality is,
stainless steel spoke wires /do/ work harden immediately
from yield, as the real-life spoke stress/strain graphs in
the back of your book show. "stress relief" therefore has
the ability to not only continue increasing the dislocation
density of the material [which /increases/ lattice stresses]
at any point where it does yield, [/if/ it yields, and
that's conjecture], but to also activate slip bands and
initiate cumulative damage effects.
the closest analogy to your explanation is something called
"coaxing" where a component is progressively loaded and
fatigue limits improved, but unfortunately, this effect is
only present in materials that exhibit strain aging.
stainless steel is not one of them.
so, you want to know my agenda? update your book and get rid
of the glaring materials theory errors! and please include
the differential spoke tension formula for dished wheels
while you're at it.
Quoted message said:
Jobst Brandt [email hidden]
