QBP wheels

Quoted message said:

Ben C said:

Quoted message said:

Ben, for those with background in mechanical design, most of what
Jobst says regarding stress relief in spokes is easily understood,
and pretty obviously correct.

I understand the idea, and it is reasonable. And as you say later,
credit to Jobst for thinking of it. But I don't believe we can say more
than "it may be a factor in some failures."

I think that statement is far too limited. And I think most people
with extensive background in mechanical design principles would also
think it's too limited.

If you're going to bring up the idea of extensive backgrounds in
mechanical design principles then I think you should try to indicate
what in particular that background teaches that alters the argument.

[...]

Quoted message said:

Quoted message said:

They are difficult to detect, but not impossible, and that doesn't
change the fact that do you have to actually detect them before you can
claim that they are a factor, rather than just a possible factor.

Not at all. If:

1) you had a situation known to normally produce residual stresses in
parts that routinely failed by fatigue, and

2) you applied techniques known to cause stress relief in those parts,
and

3) you observed a significant improvement in fatigue life,

If. But that hasn't been done in any kind of even vaguely scientific
way. All we have is a couple of anecdotes.

Quoted message said:

then it doesn't require the actual detection or measurement of those
residual stresses to logically conclude they were an important factor,
and are now lessened or eliminated.

Lack of evidence that you would expect to find if the hypothesis is true
is also a factor.

Jim Beam keeps asking: do spokes break more often in regions of high
tensile residual stress? I missed the post where someone explained
either that they do or that they don't or that we don't know or that it
doesn't make any difference.

Quoted message said:

Yes, I understand there could be confounding factors. But IMO, what
we see here are fairly desperate attempts to come up with _some_ way,
_any_ way, to suggest that stress relief either doesn't exist, or
doesn't work. In view of the logic behind it and the evidence in
favor of it, neither the effort nor the motivation make much sense to
me.

It comes down to exactly what the claim is that's being made. I'm sorry
but I think Jobst states it far too strongly. He is always saying:
residual stress breaks spokes, spokes break if you don't stress-relieve,
loose spokes break because they aren't properly stress-relieved, etc.
etc.

If I've misinterpreted his position, fine, but it is not willful
minterpretation and I don't have anything against Jobst personally.

But I can understand why people get angry with him, because failure to
distinguish clearly between hypothesis and fact is bad science, and that
is a serious matter. It might not be necessary to call him names, but it
is necessary not to let him off the hook.

Ben C? said:

jim beam said:

Quoted message said:

Ben C? writes:

> All I'm disagreeing with here is the position that residual stress is
> known to be the only or the primary cause of broken spokes.
>
Those are your words, not mine. Willful misinterpretation often
arises from a poor defensive position in a discussion.

so present /evidence/ for your position!!! you've never done that.
/evidence/ is easily defended against "misinterpretation".

As far as I can tell, Jobst is now admitting there is no evidence and
saying that neither does he claim that residual stress is known to be
the only or the primary cause of broken spokes.

Of course residual stress is not the only or primary cause of broken
spokes. Build a wheel with residual stress in the spokes, but then put
the wheel in storage in an inert atmosphere at a constant moderate
temperature with no load other than its mutual gravitational attraction
to the earth. How long will the spokes last?

Quoted message said:

He could have fooled me, and it would be better if he could come out and
clarify his position with more definiteness rather than by an
implication wrapped in an insult. But on the whole it's progress.

Well, there are other factors that can cause broken spokes, such as FOD
in the spokes (e.g. sticks when riding on trail), having the chain go
into the spokes, damage by airline baggage handlers, etc. Neither
Brandt's stress relief theory nor "beam's" better materials contention
will prevent these type of spoke failures. If spoke fatigue failures are
NOT occurring, then these external damage factors may well be the
primary cause of spoke failure.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth