Butted vs. straight-gauge spokes

[Jobst Brandt]

Wayne T Dunlap writes:

>>>> Weight savings is an extra bonus. The real reason is that a wheel with DB spokes will be more
>>>> durable, not necessarily stronger.

>>> If the straight gauge is stronger wouldn't it be more durable than double butted under heavy
>>> loads?

>> If... but they are not, because their ends, where they fail, are identical for both types of
>> spoke, having the same cross section. The swaged spoke having been made from a straight gauge
>> spoke blank.

>> Fatigue is a process by which a metal is torn apart by repeated loading much lower than that
>> needed to forcefully break the part. Therefore, it is not rupture strength but rather stress
>> levels under cyclic loading that cause spokes to fail. That is why stress relieving is highly
>> important in building durable wheels.

> So, essentially what you are saying is that the fact that the middle of a double butted spoke is
> thinner, it allows it to flex and take the stress off the ends of the spoke where most spoke tend
> to break. But wouldn't the fact that the middle of a double butted spoke flexes more than a
> straight gauge, cause the middle section to fatigue more and, therefore, cause more mid section
> breakage?

No. That spokes do not break in their slender mid sections is well established. Failure occurs at
stress concentrating features where the spoke is not uniformly loaded and where it has corners in
which stresses are naturally higher. An analogy would be a uniformly wide hallway that makes a right
angle turn with a stream of people walking in the same direction. Congestion at the corner is
inevitable as is stress concentration in a spoke's threads, elbow, and head.

To visualize an extreme example, cut 10cm from the middle of a spoke and replace it with a coil
spring with a stiffness of 200lbs/inch of stretch. Instead of tightening the spoke by turning the
spoke nipple, stretch the spring an inch and attach it to hooks on the cut ends of the spoke. This
tensions the spoke to 200lbs. Deflecting that spoke under the usual loads (causing a length change
of 0.003-0.005") would cause less than 1lb change in spoke load instead of 50lbs or more.

By adding elasticity, swaging spokes emulates that function.

Jobst Brandt [email protected] Palo Alto CA

 

[Ajames54]

On Wed, 12 Feb 2003 16:33:08 GMT, [email protected] wrote:

SNIP
>
>No. That spokes do not break in their slender mid sections is well established. Failure occurs at
>stress concentrating features where the spoke is not uniformly loaded and where it has corners in
>which stresses are naturally higher.
SNIP

>
>Jobst Brandt [email protected] Palo Alto CA

Kind of a question kind of a statement... Would not the extra cold working of the spoke in forging
the head and then bending the spoke also be a factor in why spokes break at the head?

 

[Jobst Brandt]

A? James writes:

>> No. That spokes do not break in their slender mid sections is well established. Failure occurs at
>> stress concentrating features where the spoke is not uniformly loaded and where it has corners in
>> which stresses are naturally higher.

> Kind of a question kind of a statement... Would not the extra cold working of the spoke in forging
> the head and then bending the spoke also be a factor in why spokes break at the head?

No. DT has the spoke wire delivered cold worked to its maximum strength. Further cold working does
not increase tensile strength. This is one of the features of DT spoke material. It has the highest
yield strength of spokes I tested yet it has the greatest ductility.

As I have often pointed out, stress relieving is essential to durable wheels. The stresses that are
relieved by this process are ones remaining from spoke forming as well as ones introduces during
wheel building. There is a whole book on this subject.

http://www.avocet.com/wheelbook/wheelbook.html

Jobst Brandt [email protected] Palo Alto CA

 

[Tom Nakashima]

Interesting to see a German Language Edition of the Bicycle Wheel. Did you translate this yourself?
And have you got any response from the Deutschland who have used your book to build a wheel? -tom

<[email protected]> wrote in message news:[email protected]...
>
> As I have often pointed out, stress relieving is essential to durable wheels. The stresses that
> are relieved by this process are ones remaining from spoke forming as well as ones introduces
> during wheel building. There is a whole book on this subject.
>
> http://www.avocet.com/wheelbook/wheelbook.html
>
> Jobst Brandt [email protected] Palo Alto CA

 

[Ajames54]

On Wed, 12 Feb 2003 17:19:42 GMT, [email protected] wrote:

>A? James writes:
>
>>> No. That spokes do not break in their slender mid sections is well established. Failure occurs
>>> at stress concentrating features where the spoke is not uniformly loaded and where it has
>>> corners in which stresses are naturally higher.
>
>> Kind of a question kind of a statement... Would not the extra cold working of the spoke in
>> forging the head and then bending the spoke also be a factor in why spokes break at the head?
>
>No. DT has the spoke wire delivered cold worked to its maximum strength. Further cold working does
>not increase tensile strength. This is one of the features of DT spoke material. It has the highest
>yield strength of spokes I tested yet it has the greatest ductility.

I was thinking more along the lines of Cold Work Embrittlement .. years ago I did some microsections
on spokes (an admittedly small sample) and the grain structure showed a significant amount of cold
work in those areas.

But since I have no idea what alloys they use or what specs they buy them to I will defer ..

 

[Sheldon Brown]

Jobst Brandt wrote:

>>Some materials suffer more from stress reversals but steel is interested in the stress change and
>>the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are. See also:
>>
>>http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
>>http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm

In the second of these references, I found:

"In monolithic materials, it has been observed that tensile mean stresses are detrimental
and compressive mean stresses are beneficial to fatigue life in comparison to a base of zero
mean stress."

There has been some controversy on this list about the observed greater durability of quick release
axles vis-a-vis solid axles, and this would seem to support those of us who maintain that QR axles
are less prone to breakage than solid ones, despite having less material.

Sheldon "Vindicated By NASA" Brown +--------------------------------------------------+
| Cynic: A blackguard whose faulty vision sees | things as they are, not as they ought to be. |
| --Ambrose Bierce |
+--------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Jobst Brandt]

Tom Nakashima writes:

http://www.avocet.com/wheelbook/wheelbook.html

> Interesting to see a German Language Edition of the Bicycle Wheel. Did you translate this
> yourself? And have you got any response from the Deutschland who have used your book to build
> a wheel?

It got a good reception back when Avocet still had a distributor in Germany but that has reduced to
a trickle of sales, even though Amazon.de lists it.

I wrote the translation but had a bikie friend in Germany look after the syntax and grammar. It is
written in the same style as the English in which I try to live up to Richard Feynman's axiom:

"If you can't explain it in plain English, then you probably don't understand it yourself."

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

A? James writes:

>>>> No. That spokes do not break in their slender mid sections is well established. Failure occurs
>>>> at stress concentrating features where the spoke is not uniformly loaded and where it has
>>>> corners in which stresses are naturally higher.

>>> Kind of a question kind of a statement... Would not the extra cold working of the spoke in
>>> forging the head and then bending the spoke also be a factor in why spokes break at the head?

>> No. DT has the spoke wire delivered cold worked to its maximum strength. Further cold working
>> does not increase tensile strength. This is one of the features of DT spoke material. It has the
>> highest yield strength of spokes I tested yet it has the greatest ductility.

> I was thinking more along the lines of Cold Work Embrittlement ... years ago I did some
> microsections on spokes (an admittedly small sample) and the grain structure showed a significant
> amount of cold work in those areas.

As I said, their steel is the most ductile and that's what makes it so robust. Swaging the
midsections is trivial compared to rolling threads and forming heads.

> But since I have no idea what alloys they use or what specs they buy them to I will defer.

So even if you knew the alloys, what would that do to your assessment and comments you might be
holding back?

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

Sheldon Brown writes:

>>> Some materials suffer more from stress reversals but steel is interested in the stress change
>>> and the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are.
>>> See also:

http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm

> In the second of these references, I found:

> "In monolithic materials, it has been observed that tensile mean stresses are detrimental and
> compressive mean stresses are beneficial to fatigue life in comparison to a base of zero mean
> stress."

> There has been some controversy on this list about the observed greater durability of quick
> release axles vis-a-vis solid axles, and this would seem to support those of us who maintain that
> QR axles are less prone to breakage than solid ones, despite having less material.

That doesn't apply to axle steel and the difference between QR axles and solid ones is structurally
minimal, the material (bore) lying in the neutral axis. I am fairly sure that the QR axles are
better material. My rear axle failures resulted from horizontal slot dropouts which give no fore and
aft bending support to the axle. "Vertical" dropouts support the forward circumference of the jam
nut and therefore, support most of the bending load from chain tension, the one that generally
causes fatigue failures. That is why these dropouts occasionally fail on the right* side.

* = 'drive side'

Jobst Brandt [email protected] Palo Alto CA

 

[Paul Kopit]

Would the manner that the spokes were swaged make any difference? The Wheelsmith spokes taper more
abruptly than the DTs.

What is the purpose of making the spoke thicker again at the nipple end?

 

[Sheldon Brown]

Jobst wrote:

>>>>Some materials suffer more from stress reversals but steel is interested in the stress change
>>>>and the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are.
>>>>See also:
>>>
>
> http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
> http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm

I responded:

>>In the second of these references, I found:
>
>
>>"In monolithic materials, it has been observed that tensile mean stresses are detrimental and
>>compressive mean stresses are beneficial to fatigue life in comparison to a base of zero mean
>>stress."
>
>
>>There has been some controversy on this list about the observed greater durability of quick
>>release axles vis-a-vis solid axles, and this would seem to support those of us who maintain that
>>QR axles are less prone to breakage than solid ones, despite having less material.

Jobst answered in part:

> That doesn't apply to axle steel

Why not?

Sheldon "Curious" Brown +------------------------------------------+
| So we'll go no more a roving |
| So late into the night, |
| Though the heart be still as loving, |
| And the moon be still as bright. |
| |
| For the sword outwears its sheath, |
| And the soul wears out the breast, |
| And the heart must pause to breathe, |
| And Love itself have rest. |
| |
| Though the night was made for loving, | And the day returns too soon, | Yet we'll go no more a
| roving | By the light of the moon. | --Lord Byron |
+------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Wayne T]

"A Muzi" <[email protected]> wrote in message news:[email protected]...
> > > Wayne T Dunlap writes:
> > > >>> I've always used 14 gauge straight gauge 36 spoke wheels on my touring bike because I was
> > > >>> told that these spokes are more dependable under touring loads. Now it sounds like most
> > > >>> posters here feel that double butted wheels are at least as strong or maybe stronger. My
> > > >>> builder who is converting my bike to cassette and will be rebuilding my rear wheel, feels
> > > >>> that I should go with double butted. I weigh a little under 180. Used to go up to 195, but
> > > >>> no more. Since the front wheel doesn't need to be rebuilt, it will remain 14 gauge
> > > >>> straight gauge 36 spoked wheel. What is the primary reason for double butted wheels? I
> > > >>> would think weight savings. How much savings would that be?
> > >
> > > >> Weight savings is an extra bonus. The real reason is that a wheel with DB spokes will be
> > > >> more durable, not necessarily stronger.
> > >
> > > > If the straight gauge is stronger wouldn't it be more durable than double butted under heavy
> > > > loads?
>
> > <[email protected]> wrote in message
> > news:[email protected]...
> > > If... but they are not, because their ends, where they fail, are identical for both types of
> > > spoke, having the same cross section. The swaged spoke having been made from a straight
> > > gauge spoke blank.
> > >
> > > Fatigue is a process by which a metal is torn apart by repeated loading much lower than that
> > > needed to forcefully break the part. Therefore, it is not rupture strength but rather stress
> > > levels under cyclic loading that cause spokes to fail. That is why stress relieving is highly
> > > important in building durable wheels.
>
>
> "Wayne T" <[email protected]> wrote in message
> news:[email protected]...
> > so, essentially what you are saying is that the fact that the middle of
a
> > double butted spoke is thinner, it allows it to flex and take the stress
> off
> > the ends of the spoke where most spoke tend to break. But wouldn't the
> fact
> > that the middle of a double butted spoke flexes more than a straight
> gauge,
> > cause the middle section to fatique more and, therefore, cause more mid section breakage?
> > >
> > > Jobst Brandt [email protected] Palo Alto CA
> >
> >
>
> Spokes almost never break anywhere but the head. "Midsection breakage" is all but unknown.

Now if I could only remember where my breakage occurred. Its been a while since I've had a
broken spoke.
> --
> Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

[Wayne T]

<[email protected]> wrote in message news:[email protected]...
> "Wayne T" <[email protected]> wrote:
>
> > > > If the straight guage is stronger wouldn't it be more durable than
> > double
> > > > butted under heavy loads?
> > >
> > >
> > > No, because spokes don't break from overload, they break from fatigue. Double butted, or
> > > swaged, spokes fatigue more slowly.
> >
> >
> > I guess it is hard for me to understand how something thinner could
fatigue
> > faster than something thicker.
>
> It is true that thinner metal, given equal stress cycles, will break sooner than thicker metal.
> But in the case of spokes, as A. Muzi and others have pointed out, spokes almost always break at
> the head, where the metal is the same thickness for swaged or for straight gauge spokes.
>
> Fatiguing of the thinner portion of the spoke isn't the problem. The thinner portion of the spoke
> helps to reduce the stress cycle on the head and elbow.

Thanks. That answers my question. Very interesting.

>
> --
> Ted Bennett Portland OR

 

[Jobst Brandt]

Paul Kopit writes:

> Would the manner that the spokes were swaged make any difference? The Wheelsmith spokes taper more
> abruptly than the DT's.

The two spokes are swaged by a different process but the effect is the same as far as stress is
concerned.

You'll notice that the transition is a smooth radius where the taper ends on the reduced diameter.
This is the transition that counts, the other can be a sharp promontory and make no difference. If
you view this as a pipe with a liquid (stress) flowing through it, it will become obvious where flow
lines will concentrate and rush around corners. This is the way FEA displays are qualitatively
displayed. You can see a similar effect on a wind chart.

http://sfports.wr.usgs.gov/wind/streaklines.shtml

Where velocity is high, the vectors are also closer together.

> What is the purpose of making the spoke thicker again at the nipple end?

Threads are relatively sharp cornered features and are a typical area where spokes break. Therefore,
having a bit of greater cross section reduces stress.

Jobst Brandt [email protected] Palo Alto CA

 

[Jobst Brandt]

Sheldon Brown writes:

>>>> Some materials suffer more from stress reversals but steel is interested in the stress change
>>>> and the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are. See
>>>> also:

http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm

>>> In the second of these references, I found:

>>> "In monolithic materials, it has been observed that tensile mean stresses are detrimental and
>>> compressive mean stresses are beneficial to fatigue life in comparison to a base of zero mean
>>> stress."

>>> There has been some controversy on this list about the observed greater durability of quick
>>> release axles vis-a-vis solid axles, and this would seem to support those of us who maintain
>>> that QR axles are less prone to breakage than solid ones, despite having less material.

>> That doesn't apply to axle steel

> Why not?

These monolithic materials are typically ceramics and other non ductile composites.

http://www.grc.nasa.gov/WWW/RT1997/5000/5920janosik.htm
http://www.uni-bayreuth.de/forschungsberichte/94/pen95012231.html

By Poisson's ratio, that characteristic of a material bulging laterally when compressed axially,
makes compression stress into tensile stress in the orthogonal axes. Therefore, if the material is
elastic, its compressive load also causes transverse tension. By this mechanism, compression also
pulls a material apart but not in the axis of loading.

Cork, a marvelous natural material, has a Poisson's ratio of zero and does not extrude out of a
gasket gap when compressed, nor does it become double its length when pressed into a Champaign
bottle as a rubber stopper would with such a reduction in diameter.

http://silver.neep.wisc.edu/~lakes/PoissonIntro.html

Jobst Brandt [email protected] Palo Alto CA

 

[Sheldon Brown]

[email protected] wrote:
> Sheldon Brown writes:
>
>
>>>>>Some materials suffer more from stress reversals but steel is interested in the stress change
>>>>>and the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are. See
>>>>>also:
>>>>
>
> http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
> http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm
>
>
>>>>In the second of these references, I found:
>>>
>
>>>>"In monolithic materials, it has been observed that tensile mean stresses are detrimental and
>>>>compressive mean stresses are beneficial to fatigue life in comparison to a base of zero mean
>>>>stress."
>>>
>
>>>>There has been some controversy on this list about the observed greater durability of quick
>>>>release axles vis-a-vis solid axles, and this would seem to support those of us who maintain
>>>>that QR axles are less prone to breakage than solid ones, despite having less material.
>>>
>
>>>That doesn't apply to axle steel
>>
>
>>Why not?
>
>
> These monolithic materials are typically ceramics and other non ductile composites.
>
> http://www.grc.nasa.gov/WWW/RT1997/5000/5920janosik.htm
> http://www.uni-bayreuth.de/forschungsberichte/94/pen95012231.html
>
> By Poisson's ratio, that characteristic of a material bulging laterally when compressed axially,
> makes compression stress into tensile stress in the orthogonal axes. Therefore, if the material is
> elastic, its compressive load also causes transverse tension. By this mechanism, compression also
> pulls a material apart but not in the axis of loading.

This is interesting in theory, but when axles break, they break perpendicular to the axis.

It seems to me that the issue of ductility isn't germane if the material isn't compressed to the
yield point.

Sheldon "A Mechanic, Not An Engineer" Brown +---------------------------------------------------+
| There was a man with a tongue of wood | Who essayed to sing. | And in truth it was
| lamentable. | But there was one who heard | The clip-clapper of this tongue of wood | And
| knew what the man wished to sing, | And with that the singer was content. | --Stephen Crane |
+---------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Ajames54]

On Wed, 12 Feb 2003 22:07:31 GMT, [email protected] wrote:

>A? James writes:
>

>As I said, their steel is the most ductile and that's what makes it so robust. Swaging the
>midsections is trivial compared to rolling threads and forming heads.
>
>> But since I have no idea what alloys they use or what specs they buy them to I will defer.
>
>So even if you knew the alloys, what would that do to your assessment and comments you might be
>holding back?
>

It isn't so much holding back as simply not wanting to comment on something if I'm not sure
... different steels work harden differently , Since Austenitic steel gets a great deal of
strength from work hardening, doesn't require heat treatment (at least not to make it
harder), has very low magnetic permeability and is generally pretty resistant to Cold Work
Embrittlement I would normally have assumed that Stainless Spokes probably were made from
one of the common Austenitic grades, like 302 or 316 ... Even assuming that they are
Austenitic steel different grades have different properties... higher levels of Nitrogen
would make CWE more likely and higher levels of Nickel would mitigate against it...though
the higher Nickel material would also be much more expensive.

As I said though it is just conjecture on my part (it is also splitting a damn fine hair)...
So even assuming it is something like 302 and delivered to the plant fully annealed there
are so many other factors that it is almost impossible to draw any firm conclusions from a
description...

Give me a few fresh samples, an electron Microscope and someone to run it then I'll venture
an opinion, until then like I say I'm just wondering...

 

[Jobst Brandt]

Sheldon Brown writes:

>>>> That doesn't apply to axle steel

>>> Why not?

>> These monolithic materials are typically ceramics and other non ductile composites.

>> http://www.grc.nasa.gov/WWW/RT1997/5000/5920janosik.htm
>> http://www.uni-bayreuth.de/forschungsberichte/94/pen95012231.html

>> By Poisson's ratio, that characteristic of a material bulging laterally when compressed axially,
>> makes compression stress into tensile stress in the orthogonal axes. Therefore, if the material
>> is elastic, its compressive load also causes transverse tension. By this mechanism, compression
>> also pulls a material apart but not in the axis of loading.

> This is interesting in theory, but when axles break, they break perpendicular to the axis.

> It seems to me that the issue of ductility isn't germane if the material isn't compressed to the
> yield point.

If you consider the material in 3D, this separation of crystallites in any direction upsets the
strength of the material in more than one plane. Stress reversal (compression / tension) has a
significant effect on fatigue life. Some materials more so than others.

http://www.industrialheating.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2832,80-
35,00.html

http://www.mech.uwa.edu.au/DANotes/SSS/shafts/shafts.html

This second site shows a classic stress reversal application, that of a rotation spindle that
experiences a full stress reversal with every revolution.

Jobst Brandt [email protected] Palo Alto CA

 

[Sheldon Brown]

[email protected] wrote:
> Sheldon Brown writes:
>
>
>>>>>That doesn't apply to axle steel
>>>>
>
>>>>Why not?
>>>
>
>>>These monolithic materials are typically ceramics and other non ductile composites.
>>
>
>>>http://www.grc.nasa.gov/WWW/RT1997/5000/5920janosik.htm
>>>http://www.uni-bayreuth.de/forschungsberichte/94/pen95012231.html
>>
>
>>>By Poisson's ratio, that characteristic of a material bulging laterally when compressed axially,
>>>makes compression stress into tensile stress in the orthogonal axes. Therefore, if the material
>>>is elastic, its compressive load also causes transverse tension. By this mechanism, compression
>>>also pulls a material apart but not in the axis of loading.
>>
>
>>This is interesting in theory, but when axles break, they break perpendicular to the axis.
>
>
>>It seems to me that the issue of ductility isn't germane if the material isn't compressed to the
>>yield point.
>
>
> If you consider the material in 3D, this separation of crystallites in any direction upsets the
> strength of the material in more than one plane.

Does this separation occur below the yield point?

> Stress reversal (compression / tension) has a significant effect on fatigue life. Some materials
> more so than others.
>
> http://www.industrialheating.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2832,8035-
> ,00.html

That citation includes the following:

"surface compressive residual stress will improve the fatigue resistance since the applied stress
and residual stress are additive. In contrast, tensile residual stresses are detrimental to fatigue
resistance..."

While I understand they're talking about residual stress, it isn't clear to me that applied
compressive stress would be any less beneficial, as the NASA citation above stated.

> http://www.mech.uwa.edu.au/DANotes/SSS/shafts/shafts.html
>
> This second site shows a classic stress reversal application, that of a rotation spindle that
> experiences a full stress reversal with every revolution.

How is that germane to bicycle axles, which do not revolve? There is no discussion here of an
applied compressive load, only of the compressive components of bending loads.

Sheldon "Still Believes QR Axles Are Less Failure Prone" Brown
+---------------------------------------------------------+
| I don't like spinach, and I'm glad I don't, because | if I liked it I'd eat it, and I just hate
| it. | --Clarence Darrow |
+---------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

[Jobst Brandt]

Sheldon Brown writes:

>> If you consider the material in 3D, this separation of crystallites in any direction upsets the
>> strength of the material in more than one plane.

> Does this separation occur below the yield point?

Yes. Internal friction in a material is the stretching and breaking of bonds. The "harder" the
material the less internal losses and distortions. This gets into the "dynamic" modulus of
elasticity in contrast to the usual modulus of elasticity, but then we've been there a few times.

http://www.tiniusolsen.com/tmech2.html

>> Stress reversal (compression / tension) has a significant effect on fatigue life. Some materials
>> more so than others.

http://www.industrialheating.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2832,80-
35,00.html

> That citation includes the following:

> "surface compressive residual stress will improve the fatigue resistance since the applied stress
> and residual stress are additive. In contrast, tensile residual stresses are detrimental to
> fatigue resistance..."

> While I understand they're talking about residual stress, it isn't clear to me that applied
> compressive stress would be any less beneficial, as the NASA citation above stated.

>> http://www.mech.uwa.edu.au/DANotes/SSS/shafts/shafts.html

>> This second site shows a classic stress reversal application, that of a rotation spindle that
>> experiences a full stress reversal with every revolution.

> How is that germane to bicycle axles, which do not revolve? There is no discussion here of an
> applied compressive load, only of the compressive components of bending loads.

Unloaded, the QR axle is in compression, with chain load and some road shock, depending on how
tightly the QR is stressed, the axle deflects into tension and then back into compression. This is a
stress reversal. The example of the rotating axle only makes the concept clearer. I assumed it "an
exercise for the reader" to see the parallel between that and a rear QR axle on a bicycle.

Jobst Brandt [email protected] Palo Alto CA