spoke fatigue troll

jim beam said:

http://www.flickr.com/photos/38636024@N00/1346747861/

your homework assignment is to annotate the above showing the location
of the neutral plane, and to indicate the residual stress profile across
the section.

How's this: http://i29.tinypic.com/27y4bd4.jpg

Red: tensile residual stress
Blue: compressive residual stress
Green: neutral

Based on the link Peter posted

http://www.lanl.gov/contour/beam.html

Although I'm not sure if they're using negative (blue) to mean
compressive (I am) or which way they're bending their beam.

Ben C said:

jim beam said:

http://www.flickr.com/photos/38636024@N00/1346747861/

your homework assignment is to annotate the above showing the location
of the neutral plane, and to indicate the residual stress profile across
the section.

How's this: http://i29.tinypic.com/27y4bd4.jpg

Red: tensile residual stress
Blue: compressive residual stress
Green: neutral

Sorry, I'm an idiot. Attempt 2:

http://i26.tinypic.com/2jeqq7a.jpg

Ben C said:

jim beam said:

http://www.flickr.com/photos/38636024@N00/1346747861/

your homework assignment is to annotate the above showing the location
of the neutral plane, and to indicate the residual stress profile across
the section.

How's this: http://i29.tinypic.com/27y4bd4.jpg

the revised one is better!

Quoted message said:

Red: tensile residual stress
Blue: compressive residual stress
Green: neutral

Based on the link Peter posted

http://www.lanl.gov/contour/beam.html

that's not a profile appropriate here [but peter cole never plays it
straight] - it's a beam machined from thick section and the residual
stress profile is completely different from bent wire. here's a better one:
http://www.ncnr.nist.gov/AnnualReport/FY1999/residual.pdf

bear in mind, that is not severely bent like a spoke elbow, but it's a
much more relevant residual profile.

Quoted message said:

Although I'm not sure if they're using negative (blue) to mean
compressive (I am) or which way they're bending their beam.

for a written description, try this:
http://groups.google.com/group/rec.bicycles.tech/msg/af080b93a59cca03

"cccTCttt", severely bent wire, is closer to appropriate.

naturally, if residual stress is an initiator, you expect fatigue to
start and grow from a point of high tensile residual. that's why, with
a coil spring, where there is a high tensile skin residual, and where
you have high skin torsion load that coincides, you do indeed observe
fatigue to initiate in the high tensile region. that's why thermal or
mechanical stress relief is so important in that application.

but with a spoke, the fatigue is observed to be independent of any high
residual zone [because there's minimal applied loading there], and
indeed independent of either tensile or compressive minor residuals.
therefore the largest concern is applied load, and thus its origination
is in the design, not the material processing.

jim beam said:

Ben C said:

jim beam said:

http://www.flickr.com/photos/38636024@N00/1346747861/

your homework assignment is to annotate the above showing the location
of the neutral plane, and to indicate the residual stress profile across
the section.

How's this: http://i29.tinypic.com/27y4bd4.jpg

the revised one is better!

Quoted message said:

Red: tensile residual stress
Blue: compressive residual stress
Green: neutral

Based on the link Peter posted

http://www.lanl.gov/contour/beam.html

that's not a profile appropriate here [but peter cole never plays it
straight] - it's a beam machined from thick section and the residual
stress profile is completely different from bent wire. here's a better one:
http://www.ncnr.nist.gov/AnnualReport/FY1999/residual.pdf

bear in mind, that is not severely bent like a spoke elbow, but it's a
much more relevant residual profile.

It looks like I guessed right that blue is compressive and red is
tensile.

The profiles look similar but for the thicker beam, the regions of
highest residual stress are nearer the centre of the beam. They
alternate in the same sort of way, but it's as though the effect is sort
of rippling out and becoming weaker by the time you get to the edge.

Fatigue can start in the interior, but there are more things to get it
started on the exterior, like surface imperfections. So you would think
tensile residual stress at the exterior would be the biggest problem--
as the coil spring has.

[...]

Quoted message said:

for a written description, try this:
http://groups.google.com/group/rec.bicycles.tech/msg/af080b93a59cca03

"cccTCttt", severely bent wire, is closer to appropriate.

That looks more like the bar-- regions of highest T (bright red) and C
(dark blue) nearer the interior.

Quoted message said:

naturally, if residual stress is an initiator, you expect fatigue to
start and grow from a point of high tensile residual. that's why, with
a coil spring, where there is a high tensile skin residual, and where
you have high skin torsion load that coincides, you do indeed observe
fatigue to initiate in the high tensile region.

that's why thermal or mechanical stress relief is so important in that
application.

but with a spoke, the fatigue is observed to be independent of any high
residual zone [because there's minimal applied loading there]

Are you saying spoke fatigue usually starts in the region of high
tensile loading-- i.e. the outside of the bend for outbound spokes? I
thought no-one really knew where it started because we haven't looked at
enough failed spokes.

For outbound spokes the small compressive residual on the outside of the
bend will mitigate fatigue (if only a little bit).

For inbound spokes it won't though-- they get a tensile loading on the
inside of the bend in use, where there is the small tensile residual.

Although not the highest region of tensile residual, it still might
accelerate fatigue that starts on the surface due to a surface
imperfection. I think that's Cole's point.

That all sounds reasonably logical provided one is careful not to make
unfounded claims about how significant that tensile skin residual on the
inside of inbound spokes is compared to other factors (which to be fair
Cole doesn't).

I doubt very much that it is very significant at all, but if it were,
how about this for a wheel-building technique:

Take 18 of your 36 spokes and bend their elbows inwards to about 75
degrees (you might have to go to 65 and let them spring back).

Then bend them back out to 90 degrees (you might have to go 95 or 100
and let them spring back).

They now should have compressive residual stress on the insides of the
elbows. Perfect! Use them for the inbound spokes. The other 18 should be
good to go out of the box for the outbound spokes.

Then whatever you do DON'T stress-relieve and ruin everything.

Since there is now compressive residual stress on all spokes protecting
you from fatigue, I predict that they will last even longer than usual--
at least 600000 miles.

Ben C said:

jim beam said:

Ben C said:

On 2008-04-26, jim beam <[email hidden]> wrote:
> http://www.flickr.com/photos/38636024@N00/1346747861/
>
> your homework assignment is to annotate the above showing the location
> of the neutral plane, and to indicate the residual stress profile across
> the section.
How's this: http://i29.tinypic.com/27y4bd4.jpg

the revised one is better!

Quoted message said:

Red: tensile residual stress
Blue: compressive residual stress
Green: neutral

Based on the link Peter posted

http://www.lanl.gov/contour/beam.html

that's not a profile appropriate here [but peter cole never plays it
straight] - it's a beam machined from thick section and the residual
stress profile is completely different from bent wire. here's a better one:
http://www.ncnr.nist.gov/AnnualReport/FY1999/residual.pdf

bear in mind, that is not severely bent like a spoke elbow, but it's a
much more relevant residual profile.

It looks like I guessed right that blue is compressive and red is
tensile.

The profiles look similar but for the thicker beam, the regions of
highest residual stress are nearer the centre of the beam. They
alternate in the same sort of way, but it's as though the effect is sort
of rippling out and becoming weaker by the time you get to the edge.

yup.

Quoted message said:

Fatigue can start in the interior,

that's /ultra/ rare.

Quoted message said:

but there are more things to get it
started on the exterior, like surface imperfections.

almost /all/ failures start at the exterior.

Quoted message said:

So you would think
tensile residual stress at the exterior would be the biggest problem--
as the coil spring has.

indeed. and on spokes too.

Quoted message said:

[...]

Quoted message said:

for a written description, try this:
http://groups.google.com/group/rec.bicycles.tech/msg/af080b93a59cca03

"cccTCttt", severely bent wire, is closer to appropriate.

That looks more like the bar-- regions of highest T (bright red) and C
(dark blue) nearer the interior.

theoretical bar, not actual. the actual on that test was somewhat skewed.

Quoted message said:

Quoted message said:

naturally, if residual stress is an initiator, you expect fatigue to
start and grow from a point of high tensile residual. that's why, with
a coil spring, where there is a high tensile skin residual, and where
you have high skin torsion load that coincides, you do indeed observe
fatigue to initiate in the high tensile region.

that's why thermal or mechanical stress relief is so important in that
application.

but with a spoke, the fatigue is observed to be independent of any high
residual zone [because there's minimal applied loading there]

Are you saying spoke fatigue usually starts in the region of high
tensile loading-- i.e. the outside of the bend for outbound spokes?

either inside or outside, but definitely a region of high loading
[caused by bending].

Quoted message said:

I
thought no-one really knew where it started because we haven't looked at
enough failed spokes.

who hasn't? just go to a bike shop and ask them to save some for you.

Quoted message said:

For outbound spokes the small compressive residual on the outside of the
bend will mitigate fatigue (if only a little bit).

theoretically, yes, but in practice they break pretty evenly both ways.

Quoted message said:

For inbound spokes it won't though-- they get a tensile loading on the
inside of the bend in use, where there is the small tensile residual.

Although not the highest region of tensile residual, it still might
accelerate fatigue that starts on the surface due to a surface
imperfection. I think that's Cole's point.

peter cole is just fixated on the fact that because there may be a
residual stress, there will definitely be fatigue. which is not the
case here because it's not observed to be initiating in that high
residual zone.

Quoted message said:

That all sounds reasonably logical provided one is careful not to make
unfounded claims about how significant that tensile skin residual on the
inside of inbound spokes is compared to other factors (which to be fair
Cole doesn't).

I doubt very much that it is very significant at all, but if it were,
how about this for a wheel-building technique:

Take 18 of your 36 spokes and bend their elbows inwards to about 75
degrees (you might have to go to 65 and let them spring back).

Then bend them back out to 90 degrees (you might have to go 95 or 100
and let them spring back).

They now should have compressive residual stress on the insides of the
elbows. Perfect! Use them for the inbound spokes. The other 18 should be
good to go out of the box for the outbound spokes.

Then whatever you do DON'T stress-relieve and ruin everything.

but you can't. if you don't overload/stabilize/"stress relieve", the
wheel will go out of true in a few miles as the spokes bed in to the hub
holes. you can prove that to yourself next time you build.
particularly rears.

Quoted message said:

Since there is now compressive residual stress on all spokes protecting
you from fatigue, I predict that they will last even longer than usual--
at least 600000 miles.

easier to just use a fatigue resistant material in the first place, or
better yet, use straight pull spokes.

jim beam said:

Ben C wrote:

[...]

Quoted message said:

Quoted message said:

For inbound spokes it won't though-- they get a tensile loading on the
inside of the bend in use, where there is the small tensile residual.

Although not the highest region of tensile residual, it still might
accelerate fatigue that starts on the surface due to a surface
imperfection. I think that's Cole's point.

peter cole is just fixated on the fact that because there may be a
residual stress, there will definitely be fatigue. which is not the
case here because it's not observed to be initiating in that high
residual zone.

Well I think you're right about that.

But I'm not sure Peter Cole has claimed the presence of residual stress
means there will definitely be fatigue (premature fatigue that is-- that
there will be fatigue in cyclically loaded aluminium is as certain as
death and taxes).

But Brandt _does_ appear to claim that residual stress causes spoke
failure and that stabilization works by stress-relieving. That's a step
too far for me.

Ben C said:

jim beam said:

Ben C wrote:

[...]

Quoted message said:

Quoted message said:

For inbound spokes it won't though-- they get a tensile loading on the
inside of the bend in use, where there is the small tensile residual.

Although not the highest region of tensile residual, it still might
accelerate fatigue that starts on the surface due to a surface
imperfection. I think that's Cole's point.

peter cole is just fixated on the fact that because there may be a
residual stress, there will definitely be fatigue. which is not the
case here because it's not observed to be initiating in that high
residual zone.

Well I think you're right about that.

But I'm not sure Peter Cole has claimed the presence of residual stress
means there will definitely be fatigue (premature fatigue that is-- that
there will be fatigue in cyclically loaded aluminium is as certain as
death and taxes).

But Brandt _does_ appear to claim that residual stress causes spoke
failure and that stabilization works by stress-relieving. That's a step
too far for me.

the thing for me is that it's not like he couldn't go out and acquire
evidence if he really believed it to be true. hard data is where it's
at, not assertion based on fundamental misconception such as the belief
that he can eliminate fatigue from a material with no fatigue endurance
limit.

Ben C said:

jim beam said:

Ben C wrote:

[...]

Quoted message said:

Quoted message said:

But Brandt _does_ appear to claim that residual stress causes spoke
failure and that stabilization works by stress-relieving. That's a step
too far for me.

the thing for me is that it's not like he couldn't go out and acquire
evidence if he really believed it to be true.

Agreed. If it were anyone else they would say, "I know maybe residual
stress is a factor", and people would say "yes, interesting, perhaps",
discuss it a bit, and move on.

But because it's Brandt's pet herring it refuses to die and people go
around believing that "residual stress causes spoke failure".

This is particularly ironic as Brandt is himself the proud slayer of the
previous generation's myth and lore.

Before you catapult from your ad hominem to a broader indictment of the
engineering skills on this forum, you might (at least) familiarize
yourself with what Jobst actually wrote on the subject.

Residual stresses do exist, but they are only one part of the picture.
The debate (here) on this issue has evolved from a denial that residual
stresses existed, to an acceptance that they did, but played no part in
spoke fatigue, to now claiming they may play a minor role. All this is
rather beside the point.

The technique Jobst describes in his book is called "stress relief", not
"residual stress relief". Obviously, residual stress is added to
operational stress to predict fatigue. When a wheel is laced and
tensioned, some areas may be operating near yield. By momentarily
overloading, those areas will yield, and upon removal of the overload,
the (operating) stress will be lowered. That's all. There will be no
effect on any area other than one that's close to yield. That's all he says.

It is impossible to predict, given the various combinations of hubs and
spokes; forming and bending histories, exactly where the critical stress
areas are. There may not even be any. But we can not be sure of that. We
do know that if there are any tension stresses close to yield -- from
all the various sources: residual, spoke tension, bending moment, stress
raisers -- those critical stresses (and only those stresses) will be
lowered and the fatigue life will be improved. Jobst describes this as
"correcting the spoke line at the microscopic level". I don't think I
can improve upon that description.

And for the record, Jobst's book recommends correcting the spoke line
(carefully, and only when needed) after the wheel has been tensioned.
Also, peak residual stresses may exist on the surface after a bend (it
depends on the depth of the plastic/elastic transition) as described
here: http://www.doitpoms.ac.uk/tlplib/beam_bending/plastic.php

Also, "direct pull" spokes have been around for a hundred years or so,
like almost all current "innovations", there are reasons for their
historical lack of popularity.

Finally, the "Mavic method" and cruder versions of stress relief have
been around for many years. Jobst never claimed to have invented wheel
stress relieving, only to have explained it and devised a better way to
do it. As for the claim that the benefit of these exercises is only to
provide "bedding in", I'd think it should be obvious (even after
building only a few wheels) that the final stresses in a wheel are
something of a [censored] shoot, not guaranteed to be improved or worsened by
bedding in.

All this straw man bashing could be avoided by simply reading the book.
Do you critique all books without reading them?

In article <UFnRj.2152$Zs1.2046@trndny07>,

Peter Cole said:

Finally, the "Mavic method" and cruder versions of stress relief have
been around for many years. Jobst never claimed to have invented wheel
stress relieving, only to have explained it and devised a better way to
do it. As for the claim that the benefit of these exercises is only to
provide "bedding in", I'd think it should be obvious (even after
building only a few wheels) that the final stresses in a wheel are
something of a [censored] shoot, not guaranteed to be improved or worsened by
bedding in.

Jobst once spoke of being in a bicycle shop in Italy where
the guy building the wheel put the tensioned wheel on the
floor and stood on it. This was in the days before spokes
became much better.

--
Michael Press

Peter Cole said:

Ben C said:

jim beam said:

Ben C wrote:

[...]

Quoted message said:

> But Brandt _does_ appear to claim that residual stress causes spoke
> failure and that stabilization works by stress-relieving. That's a step
> too far for me.
the thing for me is that it's not like he couldn't go out and acquire
evidence if he really believed it to be true.

Agreed. If it were anyone else they would say, "I know maybe residual
stress is a factor", and people would say "yes, interesting, perhaps",
discuss it a bit, and move on.

But because it's Brandt's pet herring it refuses to die and people go
around believing that "residual stress causes spoke failure".

This is particularly ironic as Brandt is himself the proud slayer of the
previous generation's myth and lore.

Before you catapult from your ad hominem to a broader indictment of the
engineering skills on this forum, you might (at least) familiarize
yourself with what Jobst actually wrote on the subject.

Residual stresses do exist, but they are only one part of the picture.
The debate (here) on this issue has evolved from a denial that residual
stresses existed, to an acceptance that they did, but played no part in
spoke fatigue, to now claiming they may play a minor role. All this is
rather beside the point.

The technique Jobst describes in his book is called "stress relief", not
"residual stress relief". Obviously, residual stress is added to
operational stress to predict fatigue. When a wheel is laced and
tensioned, some areas may be operating near yield. By momentarily
overloading, those areas will yield, and upon removal of the overload,
the (operating) stress will be lowered. That's all. There will be no
effect on any area other than one that's close to yield. That's all he says.

It is impossible to predict, given the various combinations of hubs and
spokes; forming and bending histories, exactly where the critical stress
areas are. There may not even be any. But we can not be sure of that. We
do know that if there are any tension stresses close to yield -- from
all the various sources: residual, spoke tension, bending moment, stress
raisers -- those critical stresses (and only those stresses) will be
lowered and the fatigue life will be improved. Jobst describes this as
"correcting the spoke line at the microscopic level". I don't think I
can improve upon that description.

And for the record, Jobst's book recommends correcting the spoke line
(carefully, and only when needed) after the wheel has been tensioned.
Also, peak residual stresses may exist on the surface after a bend (it
depends on the depth of the plastic/elastic transition) as described
here: http://www.doitpoms.ac.uk/tlplib/beam_bending/plastic.php

Also, "direct pull" spokes have been around for a hundred years or so,
like almost all current "innovations", there are reasons for their
historical lack of popularity.

Finally, the "Mavic method" and cruder versions of stress relief have
been around for many years. Jobst never claimed to have invented wheel
stress relieving, only to have explained it and devised a better way to
do it. As for the claim that the benefit of these exercises is only to
provide "bedding in", I'd think it should be obvious (even after
building only a few wheels) that the final stresses in a wheel are
something of a [censored] shoot, not guaranteed to be improved or worsened by
bedding in.

All this straw man bashing could be avoided by simply reading the book.
Do you critique all books without reading them?

As on many other occasions, you make a much more reasonable case than
Jobst.

I find little to disagree with in the above.

Recently I said I thought stabilization mostly worked by bending the
spokes but in some cases may also work by deforming the hub. daveornee's
recent pictures, which are very similar to those posted long ago by jim
beam, tip things a bit towards hub deformation in my mind. But I think
it still may be a bit of both and that it depends what hub and spokes
you're using.

I am not criticizing the book. I did not mention the book. I am talking
about Jobst's posts here, from which I have got the distinct impression
of a misleading emphasis on residual stress as a cause of spoke failure.

But as I have better things to do than go around digging up references
to prove this, to be fair I probably shouldn't have written what I did.

Michael Press said:

Quoted message said:

Finally, the "Mavic method" and cruder versions of stress relief
have been around for many years. Jobst never claimed to have
invented wheel stress relieving, only to have explained it and
devised a better way to do it. As for the claim that the benefit
of these exercises is only to provide "bedding in", I'd think it
should be obvious (even after building only a few wheels) that the
final stresses in a wheel are something of a [censored] shoot, not
guaranteed to be improved or worsened by bedding in.

Quoted message said:

Jobst once spoke of being in a bicycle shop in Italy where the guy
building the wheel put the tensioned wheel on the floor and stood on
it. This was in the days before spokes became much better.

Mara was a small man who wore flexible rubber soled athletic shoes
with which he carefully walked around on the spokes of a new wheel
after tensioning, and turning the wheel over to do the same on the
other side. His comment was "makes the wheel last a long time" as my
Italian speaking friend translated. This was in Florence Italy and
Mara was Gastone Nencini's mechanic.

Jobst Brandt

Ben C said:

Recently I said I thought stabilization mostly worked by bending the
spokes but in some cases may also work by deforming the hub. daveornee's
recent pictures, which are very similar to those posted long ago by jim
beam, tip things a bit towards hub deformation in my mind. But I think
it still may be a bit of both and that it depends what hub and spokes
you're using.

Holes typically deform as shown in the pictures. Just from eyeballing
those, it looks like about 0.5mm. Taken over an elbow length of 6mm,
that works out to a (rough) angle change of 5 deg. The depth of deform
should be less than linear with spoke tension, so the nominal 50% over
load of stress relief should represent less than a third of the depth.
Even that amount will reduce the spoke tension significantly (full spoke
tension = 0.75mm). Stress relief may reduce problems with tension loss
caused by spokes bedding in, but it's unlikely that has any impact on
spoke fatigue failure. There isn't even a plausible hypothesis for that.

Bottom line is that the deformation, both the majority that comes from
initial tension as well as whatever smaller contribution that may come
from over loading, doesn't predict the direction or degree of bending
stress in the tensioned spoke. The residual stresses may be beneficial
or harmful, the beauty of the over loading method of stress relief is
that you don't have to know all that, it will just improve things if
they're bad and not change things if they're not.

Obviously, if an outbound spoke has a noticeable bow away from the
flange after tensioning, it has a bending stress that will create
additional tension. Less obviously, a spoke that was pulled flat from
initial tension might have just as much bending tension. You can't just
look at a laced and tensioned wheel and diagnose stress levels by
inspection.

Quoted message said:

I am not criticizing the book. I did not mention the book. I am talking
about Jobst's posts here, from which I have got the distinct impression
of a misleading emphasis on residual stress as a cause of spoke failure.

As I said before, these threads have gone through an evolution that
began with a denial of the presence of residual stress and have morphed
into a grudging admission with the dismissal for irrelevance. Residual
stresses are present, they may or may not be a factor in any given spoke
failure, but that's impossible to know without knowing all the operating
stresses. No postmortem is going to tell you whether the failure was
caused by a raiser, bending stress, residuals or any combination
thereof. All you do know is that stress relief will mitigate harmful
stresses from any/all of those causes.

These (endless) arguments follow the same pattern. Something is taken
out of context and a straw man is created. Like spoke tension and wheel
strength. The FEA leaves no doubt about what happens when a wheel is
overloaded, it doesn't matter that an unspoked rim will support body
weight without collapsing, the loads we're talking about are the several
g's that happen when the wheel hits a pothole, that's when strength
becomes important. Normally tensioned wheels loose spoke tension at
about the same magnitude of deflection as rim damage starts, looser
tension will mean impact damage will happen earlier. As the loaded area
of the rim becomes slack, the rim looses lateral stiffness while still
under compression and therefore is susceptible to buckling. Instead of
focusing on those important issues the threads degenerate into a
critique of spoke bed cracking, despite the fact that this is a problem
for only a few rims and the straw man is raised that Jobst advised
builders to exceed manufacturer's specs. When several sources are found
that confirm the anodization fatigue connection, all that is dismissed
with talk of anisotropy and extrusion flaws -- factors (obviously) still
there whether anodization is or is not.

For the last time, Jobst didn't say that spoke fatigue is caused
exclusively from residual stress, nor that spokes should be tightened
beyond published limits. He only said that stress relief reduces harmful
stresses and that, for a particular type of rim (with explicit caveats),
the maximum spoke tension as determined by buckling margin could be
found with the same process.

In article <[email hidden]>,

Ben C said:

On 2008-04-28, Peter Cole <[email hidden]> wrote:

[...]

Quoted message said:

As on many other occasions, you make a much more reasonable case than
Jobst.

Yeah, ain't he an unreasonable curmudgeon.

Quoted message said:

I find little to disagree with in the above.

Oh, bless you.

Quoted message said:

Recently I said I thought stabilization mostly worked by bending the
spokes but in some cases may also work by deforming the hub. daveornee's
recent pictures, which are very similar to those posted long ago by jim
beam, tip things a bit towards hub deformation in my mind. But I think
it still may be a bit of both and that it depends what hub and spokes
you're using.

I am not criticizing the book. I did not mention the book. I am talking
about Jobst's posts here, from which I have got the distinct impression
of a misleading emphasis on residual stress as a cause of spoke failure.

You criticize what you do not fully apprehend.
"distinct impression of a misleading emphasis
on residual stress as a cause of spoke failure"
is no basis for advancing categorical denials
of what is clearly laid out. Good people here
have spoon fed you all the details repeatedly,
and you spit up as would an unruly child. Get
a grip, exert yourself, and be man.

Quoted message said:

of a misleading emphasis on residual stress as a cause of spoke failure"

Quoted message said:

But as I have better things to do than go around digging up references
to prove this, to be fair I probably shouldn't have written what I did.

These better things are to promote unsupported assertions
contrary to well supported findings? Do some work on your
own. You presume too much upon the good will advanced to you.

--
Michael Press

Michael Press said:

In article <[email hidden]>,
Ben C <[email hidden]> wrote:

[...]

Quoted message said:

Quoted message said:

I am not criticizing the book. I did not mention the book. I am talking
about Jobst's posts here, from which I have got the distinct impression
of a misleading emphasis on residual stress as a cause of spoke failure.

You criticize what you do not fully apprehend.
"distinct impression of a misleading emphasis
on residual stress as a cause of spoke failure"
is no basis for advancing categorical denials
of what is clearly laid out. Good people here
have spoon fed you all the details repeatedly,
and you spit up as would an unruly child. Get
a grip, exert yourself, and be man.

Rubbish. And I make no apology for refusing to swallow anything I've
been "spoon fed".

You know what's great about this thread? It finally
names the true cause of spoke failure. It's right
in the subject header. It's the spoke fatigue troll.
He hides under cattle guards and reaches up
and grabs your spokes when you aren't looking.
That's why your hub flanges get deformed - it's
that damned spoke fatigue troll yanking on them.

Ben
You have to admit it's a better explanation than
some on RBT.

Peter Cole said:

Ben C said:

Recently I said I thought stabilization mostly worked by bending the
spokes but in some cases may also work by deforming the hub. daveornee's
recent pictures, which are very similar to those posted long ago by jim
beam, tip things a bit towards hub deformation in my mind. But I think
it still may be a bit of both and that it depends what hub and spokes
you're using.

Holes typically deform as shown in the pictures. Just from eyeballing
those, it looks like about 0.5mm. Taken over an elbow length of 6mm,
that works out to a (rough) angle change of 5 deg. The depth of deform
should be less than linear with spoke tension, so the nominal 50% over
load of stress relief should represent less than a third of the depth.
Even that amount will reduce the spoke tension significantly (full spoke
tension = 0.75mm). Stress relief may reduce problems with tension loss
caused by spokes bedding in, but it's unlikely that has any impact on
spoke fatigue failure. There isn't even a plausible hypothesis for that.

Well my hypothesis (which perhaps you don't regard as plausible 🙂 is
that this bedding in reduces the bending moment on the spoke.

It doesn't matter whether the spoke bends or the hub deforms. The result
is a spoke closer to the flange so less moment.

Quoted message said:

Bottom line is that the deformation, both the majority that comes from
initial tension as well as whatever smaller contribution that may come
from over loading, doesn't predict the direction or degree of bending
stress in the tensioned spoke.

I don't understand what you're saying here. Surely for all spokes the
effect of hub deformation is going to be to reduce moment on the elbow?

[...]

Quoted message said:

As I said before, these threads have gone through an evolution that
began with a denial of the presence of residual stress and have morphed
into a grudging admission with the dismissal for irrelevance. Residual
stresses are present, they may or may not be a factor in any given spoke
failure, but that's impossible to know without knowing all the operating
stresses. No postmortem is going to tell you whether the failure was
caused by a raiser, bending stress, residuals or any combination
thereof.

You would expect to see more failures starting in the regions of tensile
residual stress (i.e. inside of inbound spokes) if residual stress from
manufacturing is a factor.

There are other factors of course, but there ought to be a statistical
bias.

[...]

Quoted message said:

These (endless) arguments follow the same pattern. Something is taken
out of context and a straw man is created. Like spoke tension and wheel
strength. The FEA leaves no doubt about what happens when a wheel is
overloaded, it doesn't matter that an unspoked rim will support body
weight without collapsing, the loads we're talking about are the several
g's that happen when the wheel hits a pothole, that's when strength
becomes important. Normally tensioned wheels loose spoke tension at
about the same magnitude of deflection as rim damage starts, looser
tension will mean impact damage will happen earlier. As the loaded area
of the rim becomes slack, the rim looses lateral stiffness while still
under compression and therefore is susceptible to buckling.

I follow your account of that. But I reserve judgment on whether a
tightly spoked wheel's rim may yield before its spokes go slack.

Quoted message said:

Instead of focusing on those important issues the threads degenerate
into a critique of spoke bed cracking, despite the fact that this is a
problem for only a few rims and the straw man is raised that Jobst
advised builders to exceed manufacturer's specs.

Fogel was probably right when he said there were no manufacturer's specs
in those days, and that the method of going to the taco point and back a
bit was good advice for the rims of the day.

It is worth pointing out though that that is not a suitable method for a
modern deeper-section Mavic rim. I'm not claiming Jobst ever said it
was, but the details get lost and people over-tension their rims.

I probably would have myself if it hadn't been for jim beam's
explanations of why it causes fatigue.

Quoted message said:

When several sources are found that confirm the anodization fatigue
connection, all that is dismissed with talk of anisotropy and
extrusion flaws -- factors (obviously) still there whether anodization
is or is not.

That is a much harder one to call. Some of these debates can be well
understood with basic mechanics and understanding of stress/strain and
S-N curves, which are simplified macroscopic views of how materials
behave.

But the effects of anisotropy and anodization on fatigue life is getting
much deeper into the structure of metals. Yes we know in the most
general terms they both can be factors but that's a long way from
understanding it enough to know how to apply it to bicycle rims.

On Apr 29, 2:49 am, "[email hidden]" <[email hidden]>

Quoted message said:

You know what's great about this thread?  It finally
names the true cause of spoke failure.  It's right
in the subject header.  It's the spoke fatigue troll.
He hides under cattle guards and reaches up
and grabs your spokes when you aren't looking.
That's why your hub flanges get deformed - it's
that damned spoke fatigue troll yanking on them.

Ben
You have to admit it's a better explanation than
some on RBT.

This is the reason you need to learn to bunny-hop cattle guards. You
don't let the troll grab your spokes.

Ben C said:

On 2008-04-28, Peter Cole <[email hidden]> wrote:

Quoted message said:

Well my hypothesis (which perhaps you don't regard as plausible 🙂 is
that this bedding in reduces the bending moment on the spoke.

It doesn't matter whether the spoke bends or the hub deforms. The result
is a spoke closer to the flange so less moment.

Quoted message said:

Bottom line is that the deformation, both the majority that comes from
initial tension as well as whatever smaller contribution that may come
from over loading, doesn't predict the direction or degree of bending
stress in the tensioned spoke.

I don't understand what you're saying here. Surely for all spokes the
effect of hub deformation is going to be to reduce moment on the elbow?

No. Hole deformation will change the elbow support angle slightly. It
will always enlarge the angle, if the angle was too big to begin with,
it will increase the moment. If the angle was initially too small, the
angle may be improved, but there still may be a bending stress.

Quoted message said:

Quoted message said:

As I said before, these threads have gone through an evolution that
began with a denial of the presence of residual stress and have morphed
into a grudging admission with the dismissal for irrelevance. Residual
stresses are present, they may or may not be a factor in any given spoke
failure, but that's impossible to know without knowing all the operating
stresses. No postmortem is going to tell you whether the failure was
caused by a raiser, bending stress, residuals or any combination
thereof.

You would expect to see more failures starting in the regions of tensile
residual stress (i.e. inside of inbound spokes) if residual stress from
manufacturing is a factor.

There are other factors of course, but there ought to be a statistical
bias.

Who says there is or isn't? If spokes are bowed at the flange and the
spoke line is not corrected, the bending forces introduced as the spoke
is tensioned will swamp any residual stresses. Those spokes will
generally fail at the outside of the bend. There are those who refuse to
correct a bad spoke line then cite these failures as evidence of the
irrelevance of residual stress. It's comical, really.

Quoted message said:

[...]

Quoted message said:

These (endless) arguments follow the same pattern. Something is taken
out of context and a straw man is created. Like spoke tension and wheel
strength. The FEA leaves no doubt about what happens when a wheel is
overloaded, it doesn't matter that an unspoked rim will support body
weight without collapsing, the loads we're talking about are the several
g's that happen when the wheel hits a pothole, that's when strength
becomes important. Normally tensioned wheels loose spoke tension at
about the same magnitude of deflection as rim damage starts, looser
tension will mean impact damage will happen earlier. As the loaded area
of the rim becomes slack, the rim looses lateral stiffness while still
under compression and therefore is susceptible to buckling.

I follow your account of that. But I reserve judgment on whether a
tightly spoked wheel's rim may yield before its spokes go slack.

Jobst did an FEA. It's in the book. A similar FEA is here:
http://www.astounding.org.uk/ian/wheel/3c_rim.html

A loaded spoked wheel doesn't deform into a uniform oval, it develops a
flat spot. As the length of the flat spot grows (with increasing load)
the bending stress on the rim increases. When that stress reaches a
critical value the bend is permanent. The rate at which the flat spot
grows with load is related to the initial spoke tension. That's it. That
you can ride around on a loosely spoked wheel doesn't say anything about
what happens when it meets a pothole.

Quoted message said:

Quoted message said:

Instead of focusing on those important issues the threads degenerate
into a critique of spoke bed cracking, despite the fact that this is a
problem for only a few rims and the straw man is raised that Jobst
advised builders to exceed manufacturer's specs.

Fogel was probably right when he said there were no manufacturer's specs
in those days, and that the method of going to the taco point and back a
bit was good advice for the rims of the day.

It is worth pointing out though that that is not a suitable method for a
modern deeper-section Mavic rim. I'm not claiming Jobst ever said it
was, but the details get lost and people over-tension their rims.

I probably would have myself if it hadn't been for jim beam's
explanations of why it causes fatigue.

Again, if you haven't read the book then you don't have a leg to stand
on. You're just repeating a misquote. Jobst (correctly) refers people to
his book. That's the "advice" you should take. The "details" don't get
"lost" if you buy the book.

Quoted message said:

Quoted message said:

When several sources are found that confirm the anodization fatigue
connection, all that is dismissed with talk of anisotropy and
extrusion flaws -- factors (obviously) still there whether anodization
is or is not.

That is a much harder one to call. Some of these debates can be well
understood with basic mechanics and understanding of stress/strain and
S-N curves, which are simplified macroscopic views of how materials
behave.

But the effects of anisotropy and anodization on fatigue life is getting
much deeper into the structure of metals. Yes we know in the most
general terms they both can be factors but that's a long way from
understanding it enough to know how to apply it to bicycle rims.

Nonsense. The "defenses" of anodizing boil down to an assertion that the
rim extrusions are so crappy that it doesn't matter if they take an
additional reliability hit from anodizing. If you have to derate spoke
tension below what all the other wheel components can tolerate just to
prevent socket cracking then you've just got weak sockets. Of course if
you don't understand the benefit of high spoke tension you don't think
you've given anything up.

Peter Cole said:

Nonsense. The "defenses" of anodizing boil down to an assertion
that the rim extrusions are so crappy that it doesn't matter if they
take an additional reliability hit from anodizing. If you have to
derate spoke tension below what all the other wheel components can
tolerate just to prevent socket cracking then you've just got weak
sockets. Of course if you don't understand the benefit of high
spoke tension you don't think you've given anything up.

I have a collection of things I don't throw away in my basement where
they are not in the way. Among these I have more than 40 rims from
the days of tubulars and subsequent MA-2 clinchers that were discarded
in wheelbuilding sessions held at my place when riders took care of
their own equipment. None of these rims has cracks, none were
anodized and all had 36 spoke sockets and eyelets. These include
Fiamme, Super Champion, Nisi, Weinmann, and Mavic rims.

The Nisi rims (tubulars) used steel flat washers and had no eyelets.
To work with them was a pain because loose washers at times got lost
in the rim. For this a glob of rim glue was put inside the hollow
section of the rim and the washer rattled around until it got stuck.

Since then Solomon bought Mavic and changed their focus on how rims
should be made. Today we read about the results in this newsgroup
often.

Those were the "good old days" but then I still have enough MA-2 rims
to keep me rolling for a long time.

Jobst Brandt