Ben C wrote:
On 2008-04-23, Peter Cole wrote:
Ben C wrote:

I think jim's point is that no-one has shown that spoke fatigue starts
on the inside of the bend significantly (or at all) more often than it
starts on the outside.
"jim beam" doesn't correct his spoke lines. He will have a moment under
normal load. That will likely be larger than any residual stress
contribution.

The presence of moment under normal load is my preferred likely
candidate for what causes most spoke failures.

And in fact part of what Jobst calls "residual stress" is I believe
just a convoluted description of moment under load.

no, he's completely unclear on either concept.



He says that when you put the bend in the elbow of an outbound spoke the
bend can't spring back because the flange is in the way but is held
there by spoke tension. He calls that "residual stress", which is
confusing, but that's what he calls it.

it's not confusing, it's just plain wrong. see above.



For that to be possible there must be quite a bit of moment, since spoke
tension is not high enough to hold a bend in an elbow that is close to
flush with the flange. Overloading reduces that tension by bending the
elbow and/or deforming the hub and reducing the moment. Jobst says
instead overloading deforms the fibres or something and relieves the
"residual stress". But it is actually basically the same thing (although
I think Jobst denies the hub can possibly deform at this point).

That is my conclusion from all the discussions I have read about this on
RBT. Residual stress deserves mention as a possible mechanism that may
also be involved, but no more than that.

why bother to muddy the water with something not observed to be the
case? if we want to discuss irrelevancies, let's discuss stress
corrosion cracking and hydrogen embrittlement as well!



Beam is right: straight-pull spokes are a better design. On the other
hand with aluminium hubs and quality steel spokes breakages are rare
these days so it's not really as big a problem as a casual reader of RBT
might take it for.

The evidence we would expect to see for residual stress being a factor
just isn't there.

Having said that many people (who aren't jim beam) don't scrutinize the
broken spoke carefully through a magnifying glass, but just chuck it in
the trash, so we wouldn't know.
People like Jobst & I are at a disadvantage from a "forensics" angle --
we don't break spokes, so have no samples to analyze.

I thought Jobst did used to break them before he started
stress-relieving.

and he failed to correlate his use of the new breed of spoke, made of
fatigue resistant vacuum degassed stainless steel, with prolonged life,
instead attributing it to the process he "invented" [copied] instead.
that kind of, er, "oversight" might be good for selling books to those
with insufficient scientific or engineering background, but it's just
plain insulting to those who do.



"jim beam" seems to have plenty. Follow his faith-based analysis if
you want.

I know you don't really want to be a troll. Fight the urge.