Spoke Fatigue Study

Peter said:

Quoted message said:

I see you chase every iota to death. I suppose for readers such as you
I should have qualified that as for most skilled humans other than
stunt riders, it is essential in riding no-hands.

There was no indication in the article by Jones that riding the URB1
with a counter-rotating wheel took extraordinary skill or extensive
practice and training sessions. From his description it appeared that
he got on the modified bike and was able to successfully ride it
no-handed although he found it more difficult than a regular bike.

His conclusion was that in addition to the steering forces created by
gyroscopic effects there is also a steering force due to the bike's
geometry. The relative magnitude of these forces has been discussed in
previous threads, but by declaring gyroscopic effects to be essential
you imply that the force due to the steering geometry is insufficient -
contrary to what Jones found.

For many people, riding a bike no-hands seems to require too much skill
even with the assistance of the gyroscopic effect.

There are 2 mechanisms that cause a bike to steer in the direction it is
leaned: front-end geometry (trail, caster, "flop"😉, and gyroscopic
effect. The gyroscopic effect is proportional to speed. Riding a bike
no-hands is much more difficult at low speeds where the gyroscopic
effect becomes minimal, it's not necessary to build special bikes to
demonstrate this, just ride slowly. The skills for low-speed no-hands
riding are more like those for track stands, something I can't do even
though I'm proficient at no-hands riding at normal speeds.

It's also simple to demonstrate the strength of the gyroscopic effect.
Just grasp a front wheel by the quick release and give it a spin --
tilting the wheel will cause a strong turning force. The strength of the
force is proportional to both the wheel spin rate and the tilt rate,
factors which make no-hands steering at high speeds extremely sensitive.

I really don't understand why some people are making this complicated
when it is so easy to demonstrate and should be familiar to anyone who
has ridden a bike for any length of time. I guess it's all in the spirit
of trying to "catch" Jobst in some kind of minuscule inconsistency --
seems more legal than technical -- and a bit creepy.

In article said:

So even if the entire length of spoke had residual stress, and you
brought the tension beyond yield, the curve would be flatter and the
peak stresses would be reduced. Bringing the spoke back to the same
average tension would result in lower peak stress.

We don't need to rely on the fact that local yielding only affects a
small portion of spoke, which is what the rest of the explanations
assume. When Benjamin's spoke elbows bent, the average tension had to
reduce significantly. So I can't understand the argument that yielding
doesn't change the average tension significantly, and your comment that
"the other 300mm of spoke having elasticity to make it look more like a
constant tension." If the changes due to yielding are small, then yes, I
can understand. But it seems we have evidence to the contrary.

We don't need to rely on local yielding being on a small
portion of the spoke, _if_ you have some means present to return the
final tension to what it was before the yielding. If the whole length
does have yield, then yes, the average tension will change.

But it's important to realize the extent of where the effect
actually happens. The peak residual stresses in a spoke are at the
elbow from its forming, and stress relief will be most apparant there,
while the straight section of spoke experiences no real effect.

Imagine marking a line on the spoke at the boundary between the
elbow and the straight section of the spoke. The reduction of tension
you're envisioning happens in the elbow if this mark is held in the
same place before and after stress relieving. But, what holds this
line? Just the elbow, and the straight section of spoke.

The elbow isn't pulling as hard as before, while the straight
section is - it'll pull the mark outwards towards the rim. As this
mark moves, the elbow tension increases, while the tension of the
straight section decreases, until some happy balance is met.

As this mark moves, the tension of the elbow increases much
faster than the straight-section tension decreases, the relative rates
proportional to the relative lengths.

If you estimate the elbow as being 3mm worth of wire in a 300mm
spoke, then the final effect on tension is about 1% of what you would
get looking at the elbow alone. It's not zero, but it's tiny.

-Luns

Luns Tee said:

In article said:

So even if the entire length of spoke had residual stress, and you
brought the tension beyond yield, the curve would be flatter and the
peak stresses would be reduced. Bringing the spoke back to the same
average tension would result in lower peak stress.

We don't need to rely on the fact that local yielding only affects a
small portion of spoke, which is what the rest of the explanations
assume. When Benjamin's spoke elbows bent, the average tension had to
reduce significantly. So I can't understand the argument that yielding
doesn't change the average tension significantly, and your comment that
"the other 300mm of spoke having elasticity to make it look more like a
constant tension." If the changes due to yielding are small, then yes, I
can understand. But it seems we have evidence to the contrary.

We don't need to rely on local yielding being on a small
portion of the spoke, _if_ you have some means present to return the
final tension to what it was before the yielding. If the whole length
does have yield, then yes, the average tension will change.

[snip good stuff]

Quoted message said:

If you estimate the elbow as being 3mm worth of wire in a 300mm
spoke, then the final effect on tension is about 1% of what you would
get looking at the elbow alone. It's not zero, but it's tiny.

Thanks again, Luns. I appreciate your time and patience.

I understand what you're saying. I'm right with you if the spoke is
straight. But I'm not sure what part the elbow plays.

As I see it, the elbow is supported on one end by the hub, and the other
end of the elbow is pulled on by the tension in the spoke (duh!). The
short side of the elbow is a cantilever beam. So I expect the inside of
the elbow to see high stress when the spoke is tensioned, ignoring any
residual stress from manufacture.

Credit to Carl Fogel for the original version:

_______________/|
/ | |
/ . . . | |
/ . __________| |
| . / /---\ \|
| . | ^ | |
| . | | | | <- hub flange
| . | |
| . | high stress concentration at apex

When you squeeze the spokes, the inside of the elbow may yield simply
because of that stress concentration. When that elbow yields, a small
strain at the apex of the elbow may translate into a fair amount of
displacement at the spoke/hub interface. So the elbow straightens
somewhat, dropping the tension, but the only part that was yielded was
the inside curve of the elbow.

If the elbow straightens significantly (as seen in Benjamin's photos),
then the tension drops when you stress relieve. Bringing the tension
back up to its previous level will return some of the stress
concentration back to the inside of the elbow.

I don't know how to calculate the final stress after all of that
manipulation. I have a foggy idea that if the loss in tension is not
complete, then the resulting stress concentration at the elbow is less
than it was before the stress relieving.

--
Dave
dvt at psu dot edu

In article <[email hidden]>,

Jim Smith said:

Michael Press said:

In article <[email hidden]>,
Jim Smith <[email hidden]> wrote:

[...]

Quoted message said:

I just now flipped through the third edition of the book and did not
see any attempt to provide evidence for stress relieving beyond the
general statement in the introduction that the techniques were arrived
at guided by engineering principles and results. Based on that and the
comments I have seen here, it seems to go something like this: "I was
suffering broken spokes, I started 'stress relieving' my spokes, they
stopped breaking." This fits my definition of "anecdotal" as it is
based on personal experience and takes the form of a short account of
an interesting incident.

Flipping through led you to publish your findings that Brandt's
book provides only anecdotal evidence for the efficacy of
temporarily increasing the tension on the spokes of a tensioned
and trued wheel. After you have read for comprehension come back
and tell us what you have found.

You know, it would help to expidite things if you would just provide
the edition and page number where it can be found. Is ther some
reason you don't want to do that?

Yes, because it would be of no use to you. Reiterating, you
"flipped through the third edition of the book." I asked what you
discovered after reading it for comprehension. I never offered to
read it for you.

Scientific discourse is founded on experiment. A researcher
reports an experiment and the results he obtained. Other
researchers reproduce the experiment and obtain their results.
Have you done the experiment? Several people both in this forum
and outside have, and reported their results.

--
Michael Press

Michael Press said:

In article <[email hidden]>,
Jim Smith <[email hidden]> wrote:

Quoted message said:

Quoted message said:

You know, it would help to expidite things if you would just provide
the edition and page number where it can be found. Is ther some
reason you don't want to do that?

Scientific discourse is founded on experiment. A researcher
reports an experiment and the results he obtained. Other
researchers reproduce the experiment and obtain their results.
Have you done the experiment? Several people both in this forum
and outside have, and reported their results.

I am ready to read. Where can I find the experimental summary and/or data
for the experiments you rely on for your thesis. I am also ready to
wholeheartedly agree, should that be evident from that material. Thanks
ever so much.
--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

PS : that's Einstein saying that, not me. Why do you think he's right, if
you do ... ?

Michael Press said:

In article <[email hidden]>,

Jim Smith said:

Michael Press said:

In article <[email hidden]>,
Jim Smith <[email hidden]> wrote:

[...]

> I just now flipped through the third edition of the book and did not
> see any attempt to provide evidence for stress relieving beyond the
> general statement in the introduction that the techniques were arrived
> at guided by engineering principles and results. Based on that and the
> comments I have seen here, it seems to go something like this: "I was
> suffering broken spokes, I started 'stress relieving' my spokes, they
> stopped breaking." This fits my definition of "anecdotal" as it is
> based on personal experience and takes the form of a short account of
> an interesting incident.

Flipping through led you to publish your findings that Brandt's
book provides only anecdotal evidence for the efficacy of
temporarily increasing the tension on the spokes of a tensioned
and trued wheel. After you have read for comprehension come back
and tell us what you have found.

You know, it would help to expidite things if you would just provide
the edition and page number where it can be found. Is ther some
reason you don't want to do that?

Yes, because it would be of no use to you. Reiterating, you
"flipped through the third edition of the book." I asked what you
discovered after reading it for comprehension. I never offered to
read it for you.

Scientific discourse is founded on experiment. A researcher
reports an experiment and the results he obtained. Other
researchers reproduce the experiment and obtain their results.
Have you done the experiment? Several people both in this forum
and outside have, and reported their results.

Hmm, I have seen this sort of evasive nonsense somewhere else around
here, now if I could only remember where...