On the virtue of traditional wheels when racing Paris-Roubaix

[email protected] wrote:
> On Apr 19, 10:42 am, jim beam <[email protected]> wrote:
>> [email protected] wrote:
>>> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
>>>> [email protected] wrote:
>>>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
>>>>>> Ben C wrote:
>>>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
>>>>>>>> Ben C wrote:
>>>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
>>>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
>>>>>>>>>> an incremental increase in load gets the rim closer to yield strain
>>>>>>>>>> than a wheel without a slack spoke would be.
>>>>>>>>> I don't think that's right. Never mind strain, just consider yield
>>>>>>>>> stress.
>>>>>>>> He is right.
>>>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
>>>>>>>>> by definition the rim yields when the total stress on the rim reaches
>>>>>>>>> its yield stress. The more stress already on it from the spokes the less
>>>>>>>>> additional applied stress you need to bring it to yield.
>>>>>>>> It is less confusing to think of yield strain and consider the
>>>>>>>> stress/strain response of the wheel as a structure with and without
>>>>>>>> Spoke stress on the rim is primarily compression across the cross
>>>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
>>>>>>>> outer surface, tension on the inner.
>>>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
>>>>>>>> compression must be added to the skin compression (outer) caused by a
>>>>>>>> bending load, if you do the math, you find you still come out ahead
>>>>>>> Interesting. Are you saying that the effect of the spoke tension
>>>>>>> mitigating the tension on the inner surface outweighs its negative
>>>>>>> effect on the outer surface?
>>>>>>> Is this because aluminium is stronger in compression than in tension?
>>>>>>> (Is it?).
>>>>>>> I would be interested to see your math.
>>>>>> Very few materials (trying to think of one) are stronger in tension than
>>>>>> compression.
>>>>>> nate
>>>>>> --
>>>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel
>>>>> A fiber composite can be stronger in tension than compression,
>>>> that's the form, not the material itself. like rope.
>>>>> but in
>>>>> continuum materials
>>>> "continuum materials"???
>>> Yes jim, it's a material which may be treated as effectively
>>> continuous rather than a structure of discrete components. You didn't
>>>>> the ratio of tensile to compressive strength is
>>>>> bounded by one for ductile materials (like steel) and approaches zero
>>>>> for brittle materials (like concrete).
>>>> it's not "bounded by", the ratio /is/ close to one for an unflawed
>>>> isotropic ductile material, and /is/ close to zero for a flawed brittle
>>>> material.
>>> "Bounded" means that materials may lie somewhere between unflawed
>>> isotropic ductile and flawed brittle, and that the physics dictate
>>> that the ratio cannot be greater than one for a continuum material.
>>>>> Not that it is at all helpful
>>>>> to think of this problem in terms of pure tension or compression. A
>>>>> rim is not a rope, and if yielding occurs from impact with a
>>>>> cobblestone it will be the result of localized shear strains.
>>>> localized? yes. shear? most unlikely. there may be a shear component
>>>> [hydrostatic], but mainly it's just bending tension and compression.
>>> Metals do not fail in bending, tension, or compression.

>> really??? you'd better let instron know that then!

>
> I really should, because my specimens keep breaking on shear planes
> that aren't orthogonal to the load I'm applying. Maybe I'm doing
> something wrong?

yes, apparently you're unaware of dislocations, their theory and their
methods of propagation!

>
>
>>> Metallic
>>> bonding between atoms is too strong to simply pull them apart in
>>> tension.

>> really????
>>
>>> The metal will fail on a slip plane that is loaded in
>>> shear.

>> ever heard of polycrystalline materials? ever heard of dislocation
>> theory?
>>

>> are you jtaylor?

>

On Mon, 14 Apr 2008 04:17:46 -0700 (PDT), [email protected] wrote:

[snip and hijack]

Dear P,

This thread has drifted off into wheel strength and stiffness, with
excursions into rim collapse, so I'm just tacking this on to your
original post.

Highwheelers used plain and then hollow steel rims, with anywhere from
50 to 100 spokes. On a modern scale, the larger ones would have been
up around 1700C.

These large wheels collapsed far more often than tiny modern wheels.
Here's a typical highwheeler taco from "Collecting and Restoring
http://i27.tinypic.com/99nold.jpg

Luckily, the giant steel rims usually don't mind such contortions and
can often be easily popped back into shape, good as new.

Here's an amusing account of a wheel collapse by a tall fellow who
bought a huge antique highwheeler (an 82-spoke 64-inch Columbia, not
really the largest ever made, but darned close). After a little
practice, he tried to ride it in a parade, crashed, tacoed, and
watched the repair:

"I straightened my cap and grasped the handle-grips. With my foot on
the mounting step, I pushed off."

"Not hard enough."

"The big bicycle rolled forward and slowed. By then I was high in the
air, having demonstrated my incompetence by vaulting upward with
excessive force. Feet sought pedals and found spokes instead. Deprived
of headway, the huge machine ponderously surrendered to gravity,
capsizing like a schooner in a squall."

"The 64-inch wheel, the Largest in the World, locked in a deadly
embrace with foot and fork, suddenly losing its circularity. The
collapse was accompanied by the release of tension in all 82 spokes at
once joined by multitudinous gasp from the crowd."

"Arising from the shambles and oblivious to the surrounding tumult, I
lifted my treasured relic and gaped at the damage. The wheel had taken
the shape of a Pringle potato chip. The spokes hung limp. I felt a
hand on my shoulder. It was one of the New Jersey Wheelmen."

"'I'm all right,' said I, pulling away."

"'We don't care about you,' he hollered above the din."

"Three others joined him and wrested the crippled bicycle from my
hands. The voice over the loudspeaker explained what was happening for
the benefit of the on-lookers--which included me."

"' -- causing the wheel to collapse.' The announcer was continuing his
explanation to the crowd. 'Now, if you watch closely, you will see the
four Wheelmen from New Jersey form a circle and grasp the wheel, then
carefully coordinating their effort . . .'"

"'Are you ready,'" shouted the first Wheelman.

"'On three, then.'"

"Standing back with no small amount of astonishment, I watched the
Wheelmen brace themselves."

"'One, two, three!'"

"'Thwonng!'" snapped the wheel, spokes ringing.

"'...the Wheelmen twist the wheel back to its original condition!
That's how it was done a hundred years ago. Let's give a well-deserved
round of applause for today's demonstration of . . . the
'wheel-snap'!'"

"The four New Jersey Wheelmen stood the big bike upright and took a
bow."

http://www.niquette.com/bicycle-pavilion/ridethg.htm

Cheers,

Carl Fogel

In article
<3a08ca[email protected]>,
[email protected] wrote:
> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
>> [email protected] wrote:
>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
>>>> Ben C wrote:
>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
>>>>>> Ben C wrote:
>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
>>>>>>>> an incremental increase in load gets the rim closer to yield strain
>>>>>>>> than a wheel without a slack spoke would be.
>>>>>>> I don't think that's right. Never mind strain, just consider yield
>>>>>>> stress.
>>>>>> He is right.
>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
>>>>>>> by definition the rim yields when the total stress on the rim reaches
>>>>>>> its yield stress. The more stress already on it from the spokes the less
>>>>>>> additional applied stress you need to bring it to yield.
>>>>>> It is less confusing to think of yield strain and consider the
>>>>>> stress/strain response of the wheel as a structure with and without
>>>>>> Spoke stress on the rim is primarily compression across the cross
>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
>>>>>> outer surface, tension on the inner.
>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
>>>>>> compression must be added to the skin compression (outer) caused by a
>>>>>> bending load, if you do the math, you find you still come out ahead
>>>>> Interesting. Are you saying that the effect of the spoke tension
>>>>> mitigating the tension on the inner surface outweighs its negative
>>>>> effect on the outer surface?
>>>>> Is this because aluminium is stronger in compression than in tension?
>>>>> (Is it?).
>>>>> I would be interested to see your math.
>>>> Very few materials (trying to think of one) are stronger in tension than
>>>> compression.

>>
>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel

>>
>>> A fiber composite can be stronger in tension than compression,

>>
>> that's the form, not the material itself. like rope.
>>
>>> but in
>>> continuum materials

>>
>> "continuum materials"???

>
> Yes jim, it's a material which may be treated as effectively
> continuous rather than a structure of discrete components. You didn't
>
>>
>>> the ratio of tensile to compressive strength is
>>> bounded by one for ductile materials (like steel) and approaches zero
>>> for brittle materials (like concrete).

>>
>> it's not "bounded by", the ratio /is/ close to one for an unflawed
>> isotropic ductile material, and /is/ close to zero for a flawed brittle
>> material.

>
> "Bounded" means that materials may lie somewhere between unflawed
> isotropic ductile and flawed brittle, and that the physics dictate
> that the ratio cannot be greater than one for a continuum material.
>
>>
>>> Not that it is at all helpful
>>> to think of this problem in terms of pure tension or compression. A
>>> rim is not a rope, and if yielding occurs from impact with a
>>> cobblestone it will be the result of localized shear strains.

>>
>> localized? yes. shear? most unlikely. there may be a shear component
>> [hydrostatic], but mainly it's just bending tension and compression.

>
> Metals do not fail in bending, tension, or compression. Metallic
> bonding between atoms is too strong to simply pull them apart in
> tension. The metal will fail on a slip plane that is loaded in

Thank you, sir, for the lesson. I learned something today.

--
Michael Press

On Apr 19, 11:24 am, jim beam <[email protected]> wrote:
> [email protected] wrote:
> > On Apr 19, 10:42 am, jim beam <[email protected]> wrote:
> >> [email protected] wrote:
> >>> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
> >>>> [email protected] wrote:
> >>>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
> >>>>>> Ben C wrote:
> >>>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
> >>>>>>>> Ben C wrote:
> >>>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
> >>>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
> >>>>>>>>>> an incremental increase in load gets the rim closer to yield strain
> >>>>>>>>>> than a wheel without a slack spoke would be.
> >>>>>>>>> I don't think that's right. Never mind strain, just consider yield
> >>>>>>>>> stress.
> >>>>>>>> He is right.
> >>>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
> >>>>>>>>> by definition the rim yields when the total stress on the rim reaches
> >>>>>>>>> its yield stress. The more stress already on it from the spokes the less
> >>>>>>>>> additional applied stress you need to bring it to yield.
> >>>>>>>> It is less confusing to think of yield strain and consider the
> >>>>>>>> stress/strain response of the wheel as a structure with and without
> >>>>>>>> Spoke stress on the rim is primarily compression across the cross
> >>>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
> >>>>>>>> outer surface, tension on the inner.
> >>>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
> >>>>>>>> compression must be added to the skin compression (outer) caused by a
> >>>>>>>> bending load, if you do the math, you find you still come out ahead
> >>>>>>> Interesting. Are you saying that the effect of the spoke tension
> >>>>>>> mitigating the tension on the inner surface outweighs its negative
> >>>>>>> effect on the outer surface?
> >>>>>>> Is this because aluminium is stronger in compression than in tension?
> >>>>>>> (Is it?).
> >>>>>>> I would be interested to see your math.
> >>>>>> Very few materials (trying to think of one) are stronger in tension than
> >>>>>> compression.
> >>>>>> nate
> >>>>>> --
> >>>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel
> >>>>> A fiber composite can be stronger in tension than compression,
> >>>> that's the form, not the material itself. like rope.
> >>>>> but in
> >>>>> continuum materials
> >>>> "continuum materials"???
> >>> Yes jim, it's a material which may be treated as effectively
> >>> continuous rather than a structure of discrete components. You didn't
> >>>>> the ratio of tensile to compressive strength is
> >>>>> bounded by one for ductile materials (like steel) and approaches zero
> >>>>> for brittle materials (like concrete).
> >>>> it's not "bounded by", the ratio /is/ close to one for an unflawed
> >>>> isotropic ductile material, and /is/ close to zero for a flawed brittle
> >>>> material.
> >>> "Bounded" means that materials may lie somewhere between unflawed
> >>> isotropic ductile and flawed brittle, and that the physics dictate
> >>> that the ratio cannot be greater than one for a continuum material.
> >>>>> Not that it is at all helpful
> >>>>> to think of this problem in terms of pure tension or compression. A
> >>>>> rim is not a rope, and if yielding occurs from impact with a
> >>>>> cobblestone it will be the result of localized shear strains.
> >>>> localized? yes. shear? most unlikely. there may be a shear component
> >>>> [hydrostatic], but mainly it's just bending tension and compression.
> >>> Metals do not fail in bending, tension, or compression.
> >> really??? you'd better let instron know that then!

>
> > I really should, because my specimens keep breaking on shear planes
> > that aren't orthogonal to the load I'm applying. Maybe I'm doing
> > something wrong?

>
> yes, apparently you're unaware of dislocations, their theory and their
> methods of propagation!
>

I guess not. Does the same book that explains how dislocations can
move without shear also explain how shear can be hydrostatic? Maybe

>
>
> >>> Metallic
> >>> bonding between atoms is too strong to simply pull them apart in
> >>> tension.
> >> really????

>
> >>> The metal will fail on a slip plane that is loaded in
> >>> shear.
> >> ever heard of polycrystalline materials? ever heard of dislocation
> >> theory?

>
> >> are you jtaylor?

On Apr 19, 11:15 am, jim beam <[email protected]> wrote:
> [email protected] wrote:
> > On Apr 19, 9:56 am, jim beam <[email protected]> wrote:
> >> [email protected] wrote:
> >>> On Apr 18, 10:52 pm, jim beam <[email protected]> wrote:
> >>>> [email protected] wrote:
> >>>>> On Apr 17, 2:41 pm, Ben C <[email protected]> wrote:
> >>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
> >>>>>> [...]
> >>>>>>> There are all kinds of messy things going on when you bring a wheel up
> >>>>>>> to tension. A better example is how much you need to unscrew the
> >>>>>>> nipple to get a spoke on a tensioned wheel to go slack. It's not very
> >>>>>>> much. The wheel may continue to deform past spoke slacking, but it's
> >>>>>>> essentially failed.
> >>>>>> Note however that the strength of the wheel is just the same when the
> >>>>>> spokes are slack as when they are tight, it's just less stiff. If the
> >>>>>> spoke tension is excessively high, it actually reduces the strength of
> >>>>>> the wheel (in that case the rim would yield before the spokes went
> >>>>>> slack).
> >>>>>> The reduced stiffness when the spokes go slack means the rim will deform
> >>>>>> more for a given load and that extra deformation _may_ cause it get out
> >>>>>> of shape and buckle. But spokes can go slack and wheels not fail.
> >>>>> You can't really decouple strength and stiffness that way. It's
> >>>>> exactly because the wheel with the slack spoke is less stiff that an
> >>>>> incremental increase in load gets the rim closer to yield strain than
> >>>>> a wheel without a slack spoke would be.
> >>>> how so? how does the rim yield?
> >>>>> So the strength of the wheel
> >>>>> is not the same. Fatigue failure from overtensioned spokes is a
> >>>>> different issue all together and has been beaten to death elsewhere.
> >>>> spokes don't usually fail from over-tension, they fail from bending
> >>>> fatigue at the elbow if they're too slack.
> >>> We're talking about rims here jim. Try to keep up.
> >> actually, we're talking materials. try to keep up.

>
> >>> We're also
> >>> talking about Roubaix, so the service life requirement is only 250
> >>> km. These wheels can be built up to tensions that would certainly
> >>> result in fatigue failure of the rim if it were to be used for more
> >>> than one day.
> >> what is the point? are you falling for the jobstian misconception of
> >> thinking that increasing tension somehow, mystically, increases strength?

>
> >>>>> Yes, spokes can go slack without catastrophic wheel failure. You can
> >>>>> also knock quite a few holes in an aircraft fuselage without crashing
> >>>>> it.
> >>>> if it's un-pressurized, but not if it is.
> >>> Really?
> >>>http://www.dailymail.co.uk/pages/live/articles/news/worldnews.html?in...
> >> yes, really. pressure vessel rupture. there is a whole science evolved
> >> for its testing and mitigation.

>
> >>>>> Once you're outside of design conditions you're bumping up
> >>>>> against the edge of, "how much farther until it collapses?", and the
> >>>>> real world is far too variable to consider that zone to be safe
> >>>>> operating conditions.
> >>>> so which is stronger in tension - a rope with a load on it, or the same
> >>>> rope without?
> >>> Well, if the rope has a tensile strength of 300 lbs and one of them is
> >>> pre-loaded with 100 lbs, which one is strong enough to hang 210 lbs
> >>> with? You can't just focus on the material strength and ignore the
> >>> boundary conditions.
> >> do you even know what a "boundary condition" is? you use that phrase
> >> liberally, but your context is always incorrect. and you're fudging the
> >> question.

>
> > Same rope under different conditions. Both rigidly fixed on one end.
> > One has a hundred pound weight on the free end. One of them is strong
> > enough for you to hang yourself with. The other one isn't.

>
> so what is the "boundary condition" of using incorrect terminology and
> avoiding the question then? something to do with confusing load with
> strength?

Either I'm right, or you're suggesting that you can keep adding
weights to your rope as long as no single increment is greater than
the tensile strength. I'm not avoiding the question. I am saying
quite clearly that the preloaded rope structure is not as strong as
the non preloaded structure. I do not care what the tensile strength
of any given component is. One of those structures can bear a greater
applied load than the other before failing. That makes it stronger.

[email protected] wrote:
> On Apr 19, 11:24 am, jim beam <[email protected]> wrote:
>> [email protected] wrote:
>>> On Apr 19, 10:42 am, jim beam <[email protected]> wrote:
>>>
>>>> [email protected] wrote:
>>>>> On Apr 19, 9:54 am, jim beam <[email protected]>
>>>>> wrote:
>>>>>> [email protected] wrote:
>>>>>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]>
>>>>>>> wrote:
>>>>>>>> Ben C wrote:
>>>>>>>>> On 2008-04-18, Peter Cole <[email protected]>
>>>>>>>>> wrote:
>>>>>>>>>> Ben C wrote:
>>>>>>>>>>> On 2008-04-17, [email protected]
>>>>>>>>>>> <[email protected]> wrote:
>>>>>>>>>>>> It's exactly because the wheel with the slack
>>>>>>>>>>>> spoke is less stiff that an incremental
>>>>>>>>>>>> increase in load gets the rim closer to yield
>>>>>>>>>>>> strain than a wheel without a slack spoke would
>>>>>>>>>>>> be.
>>>>>>>>>>> I don't think that's right. Never mind strain,
>>>>>>>>>>> just consider yield stress.
>>>>>>>>>> He is right.
>>>>>>>>>>> When the spokes are slack, the structure as a
>>>>>>>>>>> whole is less stiff. But by definition the rim
>>>>>>>>>>> yields when the total stress on the rim reaches
>>>>>>>>>>> its yield stress. The more stress already on it
>>>>>>>>>>> from the spokes the less additional applied
>>>>>>>>>>> stress you need to bring it to yield.
>>>>>>>>>> It is less confusing to think of yield strain and
>>>>>>>>>> consider the stress/strain response of the wheel as
>>>>>>>>>> a structure with and without loaded spokes. Spoke
>>>>>>>>>> stress on the rim is primarily compression across
>>>>>>>>>> the cross section (rim). Bending stress (wheel
>>>>>>>>>> tension on the inner. Since the rim is pre-loaded
>>>>>>>>>> with compression (spoke tension), that compression
>>>>>>>>>> must be added to the skin compression (outer)
>>>>>>>>>> caused by a bending load, if you do the math, you
>>>>>>>>>> loads) with higher spoke tension.
>>>>>>>>> Interesting. Are you saying that the effect of the
>>>>>>>>> spoke tension mitigating the tension on the inner
>>>>>>>>> surface outweighs its negative effect on the outer
>>>>>>>>> surface? Is this because aluminium is stronger in
>>>>>>>>> compression than in tension? (Is it?). I would be
>>>>>>>>> interested to see your math.
>>>>>>>> Very few materials (trying to think of one) are
>>>>>>>> stronger in tension than compression. nate -- replace
>>>>>>>> "roosters" with "cox" to
>>>>>>> A fiber composite can be stronger in tension than
>>>>>>> compression,
>>>>>> that's the form, not the material itself. like rope.
>>>>>>> but in continuum materials
>>>>>> "continuum materials"???
>>>>> Yes jim, it's a material which may be treated as effectively
>>>>> continuous rather than a structure of discrete components.
>>>>>>> the ratio of tensile to compressive strength is bounded
>>>>>>> by one for ductile materials (like steel) and approaches
>>>>>>> zero for brittle materials (like concrete).
>>>>>> it's not "bounded by", the ratio /is/ close to one for an
>>>>>> unflawed isotropic ductile material, and /is/ close to zero
>>>>>> for a flawed brittle material.
>>>>> "Bounded" means that materials may lie somewhere between
>>>>> unflawed isotropic ductile and flawed brittle, and that the
>>>>> physics dictate that the ratio cannot be greater than one for
>>>>> metallurgy school?
>>>>>>> Not that it is at all helpful to think of this problem in
>>>>>>> terms of pure tension or compression. A rim is not a
>>>>>>> rope, and if yielding occurs from impact with a
>>>>>>> cobblestone it will be the result of localized shear
>>>>>>> strains.
>>>>>> localized? yes. shear? most unlikely. there may be a
>>>>>> shear component [hydrostatic], but mainly it's just bending
>>>>>> tension and compression.
>>>>> Metals do not fail in bending, tension, or compression.
>>>> really??? you'd better let instron know that then!
>>> I really should, because my specimens keep breaking on shear
>>> planes that aren't orthogonal to the load I'm applying. Maybe
>>> I'm doing something wrong?

>> yes, apparently you're unaware of dislocations, their theory and
>> their methods of propagation!
>>

>
> I guess not. Does the same book that explains how dislocations can
> move without shear also explain how shear can be hydrostatic?

er, if you resolve uniaxial stress hydrostatically in a bulk sample, you
get a component of shear. hence the cup and cone effect on ductile
tensile test samples. but the core resolves as simple tension, hence
the fracture surface perpendicular to applied stress. and as the size
of the sample reduces, so does the hydrostatic effect, hence the higher
apparent strength of fibers.

so, how does this all relate to "slip planes"? if you're looking at a
single crystal under uniaxial stress, you can resolve single slip plane
orientations, and that is commonly shear. however, dislocations are not
obligated to stick to just one plane. when different planes start to
intersect, that's when you get work hardening, and that's what we see in
bulk materials. bulk materials simply cannot be regarded as having just
shear deformation. [see above.]

no, it's after the chapters on stress/strain fundamentals and things
like mohr's circle and poisson's ratio.

isbn 0-07-016893-8

>
>>
>>>>> Metallic bonding between atoms is too strong to simply pull
>>>>> them apart in tension.
>>>> really????
>>>>> The metal will fail on a slip plane that is loaded in shear.
>>>> ever heard of polycrystalline materials? ever heard of
>>>> dislocation theory?
>>>> are you jtaylor?

>

Michael Press wrote:
> In article
> <3a08ca[email protected]>,
> [email protected] wrote:
>> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
>>> [email protected] wrote:
>>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
>>>>> Ben C wrote:
>>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
>>>>>>> Ben C wrote:
>>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
>>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
>>>>>>>>> an incremental increase in load gets the rim closer to yield strain
>>>>>>>>> than a wheel without a slack spoke would be.
>>>>>>>> I don't think that's right. Never mind strain, just consider yield
>>>>>>>> stress.
>>>>>>> He is right.
>>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
>>>>>>>> by definition the rim yields when the total stress on the rim reaches
>>>>>>>> its yield stress. The more stress already on it from the spokes the less
>>>>>>>> additional applied stress you need to bring it to yield.
>>>>>>> It is less confusing to think of yield strain and consider the
>>>>>>> stress/strain response of the wheel as a structure with and without
>>>>>>> Spoke stress on the rim is primarily compression across the cross
>>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
>>>>>>> outer surface, tension on the inner.
>>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
>>>>>>> compression must be added to the skin compression (outer) caused by a
>>>>>>> bending load, if you do the math, you find you still come out ahead
>>>>>> Interesting. Are you saying that the effect of the spoke tension
>>>>>> mitigating the tension on the inner surface outweighs its negative
>>>>>> effect on the outer surface?
>>>>>> Is this because aluminium is stronger in compression than in tension?
>>>>>> (Is it?).
>>>>>> I would be interested to see your math.
>>>>> Very few materials (trying to think of one) are stronger in tension than
>>>>> compression.
>>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel
>>>> A fiber composite can be stronger in tension than compression,
>>> that's the form, not the material itself. like rope.
>>>
>>>> but in
>>>> continuum materials
>>> "continuum materials"???

>> Yes jim, it's a material which may be treated as effectively
>> continuous rather than a structure of discrete components. You didn't
>>
>>>> the ratio of tensile to compressive strength is
>>>> bounded by one for ductile materials (like steel) and approaches zero
>>>> for brittle materials (like concrete).
>>> it's not "bounded by", the ratio /is/ close to one for an unflawed
>>> isotropic ductile material, and /is/ close to zero for a flawed brittle
>>> material.

>> "Bounded" means that materials may lie somewhere between unflawed
>> isotropic ductile and flawed brittle, and that the physics dictate
>> that the ratio cannot be greater than one for a continuum material.
>>
>>>> Not that it is at all helpful
>>>> to think of this problem in terms of pure tension or compression. A
>>>> rim is not a rope, and if yielding occurs from impact with a
>>>> cobblestone it will be the result of localized shear strains.
>>> localized? yes. shear? most unlikely. there may be a shear component
>>> [hydrostatic], but mainly it's just bending tension and compression.

>> Metals do not fail in bending, tension, or compression. Metallic
>> bonding between atoms is too strong to simply pull them apart in
>> tension. The metal will fail on a slip plane that is loaded in

>
> Thank you, sir, for the lesson. I learned something today.
>

how to be a schmuck vicariously?

[email protected] wrote:
> On Apr 19, 11:15 am, jim beam <[email protected]> wrote:
>> [email protected] wrote:
>>> On Apr 19, 9:56 am, jim beam <[email protected]> wrote:
>>>> [email protected] wrote:
>>>>> On Apr 18, 10:52 pm, jim beam <[email protected]> wrote:
>>>>>> [email protected] wrote:
>>>>>>> On Apr 17, 2:41 pm, Ben C <[email protected]> wrote:
>>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
>>>>>>>> [...]
>>>>>>>>> There are all kinds of messy things going on when you bring a wheel up
>>>>>>>>> to tension. A better example is how much you need to unscrew the
>>>>>>>>> nipple to get a spoke on a tensioned wheel to go slack. It's not very
>>>>>>>>> much. The wheel may continue to deform past spoke slacking, but it's
>>>>>>>>> essentially failed.
>>>>>>>> Note however that the strength of the wheel is just the same when the
>>>>>>>> spokes are slack as when they are tight, it's just less stiff. If the
>>>>>>>> spoke tension is excessively high, it actually reduces the strength of
>>>>>>>> the wheel (in that case the rim would yield before the spokes went
>>>>>>>> slack).
>>>>>>>> The reduced stiffness when the spokes go slack means the rim will deform
>>>>>>>> more for a given load and that extra deformation _may_ cause it get out
>>>>>>>> of shape and buckle. But spokes can go slack and wheels not fail.
>>>>>>> You can't really decouple strength and stiffness that way. It's
>>>>>>> exactly because the wheel with the slack spoke is less stiff that an
>>>>>>> incremental increase in load gets the rim closer to yield strain than
>>>>>>> a wheel without a slack spoke would be.
>>>>>> how so? how does the rim yield?
>>>>>>> So the strength of the wheel
>>>>>>> is not the same. Fatigue failure from overtensioned spokes is a
>>>>>>> different issue all together and has been beaten to death elsewhere.
>>>>>> spokes don't usually fail from over-tension, they fail from bending
>>>>>> fatigue at the elbow if they're too slack.
>>>>> We're talking about rims here jim. Try to keep up.
>>>> actually, we're talking materials. try to keep up.
>>>>> We're also
>>>>> talking about Roubaix, so the service life requirement is only 250
>>>>> km. These wheels can be built up to tensions that would certainly
>>>>> result in fatigue failure of the rim if it were to be used for more
>>>>> than one day.
>>>> what is the point? are you falling for the jobstian misconception of
>>>> thinking that increasing tension somehow, mystically, increases strength?
>>>>>>> Yes, spokes can go slack without catastrophic wheel failure. You can
>>>>>>> also knock quite a few holes in an aircraft fuselage without crashing
>>>>>>> it.
>>>>>> if it's un-pressurized, but not if it is.
>>>>> Really?
>>>>> http://www.dailymail.co.uk/pages/live/articles/news/worldnews.html?in...
>>>> yes, really. pressure vessel rupture. there is a whole science evolved
>>>> for its testing and mitigation.
>>>>>>> Once you're outside of design conditions you're bumping up
>>>>>>> against the edge of, "how much farther until it collapses?", and the
>>>>>>> real world is far too variable to consider that zone to be safe
>>>>>>> operating conditions.
>>>>>> so which is stronger in tension - a rope with a load on it, or the same
>>>>>> rope without?
>>>>> Well, if the rope has a tensile strength of 300 lbs and one of them is
>>>>> pre-loaded with 100 lbs, which one is strong enough to hang 210 lbs
>>>>> with? You can't just focus on the material strength and ignore the
>>>>> boundary conditions.
>>>> do you even know what a "boundary condition" is? you use that phrase
>>>> liberally, but your context is always incorrect. and you're fudging the
>>>> question.
>>> Same rope under different conditions. Both rigidly fixed on one end.
>>> One has a hundred pound weight on the free end. One of them is strong
>>> enough for you to hang yourself with. The other one isn't.

>> so what is the "boundary condition" of using incorrect terminology and
>> avoiding the question then? something to do with confusing load with
>> strength?

>
> Either I'm right, or you're suggesting that you can keep adding
> weights to your rope as long as no single increment is greater than
> the tensile strength.

don't put words in my mouth. read the question properly.

> I'm not avoiding the question. I am saying
> quite clearly that the preloaded rope structure is not as strong as

here's the question one more time: "which is stronger in tension - a
rope with a load on it, or the same rope without?" want to try again?

> I do not care what the tensile strength
> of any given component is.

you should, because when a component yields, the whole structure is
deemed to have failed.

> One of those structures can bear a greater
> applied load than the other before failing. That makes it stronger.

In article <[email protected]>,
jim beam <[email protected]> wrote:

> Michael Press wrote:
> > In article
> > <3a08ca[email protected]>,
> > [email protected] wrote:
> >> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
> >>> [email protected] wrote:
> >>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
> >>>>> Ben C wrote:
> >>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
> >>>>>>> Ben C wrote:
> >>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
> >>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
> >>>>>>>>> an incremental increase in load gets the rim closer to yield strain
> >>>>>>>>> than a wheel without a slack spoke would be.
> >>>>>>>> I don't think that's right. Never mind strain, just consider yield
> >>>>>>>> stress.
> >>>>>>> He is right.
> >>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
> >>>>>>>> by definition the rim yields when the total stress on the rim reaches
> >>>>>>>> its yield stress. The more stress already on it from the spokes the less
> >>>>>>>> additional applied stress you need to bring it to yield.
> >>>>>>> It is less confusing to think of yield strain and consider the
> >>>>>>> stress/strain response of the wheel as a structure with and without
> >>>>>>> Spoke stress on the rim is primarily compression across the cross
> >>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
> >>>>>>> outer surface, tension on the inner.
> >>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
> >>>>>>> compression must be added to the skin compression (outer) caused by a
> >>>>>>> bending load, if you do the math, you find you still come out ahead
> >>>>>> Interesting. Are you saying that the effect of the spoke tension
> >>>>>> mitigating the tension on the inner surface outweighs its negative
> >>>>>> effect on the outer surface?
> >>>>>> Is this because aluminium is stronger in compression than in tension?
> >>>>>> (Is it?).
> >>>>>> I would be interested to see your math.
> >>>>> Very few materials (trying to think of one) are stronger in tension than
> >>>>> compression.
> >>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel
> >>>> A fiber composite can be stronger in tension than compression,
> >>> that's the form, not the material itself. like rope.
> >>>
> >>>> but in
> >>>> continuum materials
> >>> "continuum materials"???
> >> Yes jim, it's a material which may be treated as effectively
> >> continuous rather than a structure of discrete components. You didn't
> >>
> >>>> the ratio of tensile to compressive strength is
> >>>> bounded by one for ductile materials (like steel) and approaches zero
> >>>> for brittle materials (like concrete).
> >>> it's not "bounded by", the ratio /is/ close to one for an unflawed
> >>> isotropic ductile material, and /is/ close to zero for a flawed brittle
> >>> material.
> >> "Bounded" means that materials may lie somewhere between unflawed
> >> isotropic ductile and flawed brittle, and that the physics dictate
> >> that the ratio cannot be greater than one for a continuum material.
> >>
> >>>> Not that it is at all helpful
> >>>> to think of this problem in terms of pure tension or compression. A
> >>>> rim is not a rope, and if yielding occurs from impact with a
> >>>> cobblestone it will be the result of localized shear strains.
> >>> localized? yes. shear? most unlikely. there may be a shear component
> >>> [hydrostatic], but mainly it's just bending tension and compression.
> >> Metals do not fail in bending, tension, or compression. Metallic
> >> bonding between atoms is too strong to simply pull them apart in
> >> tension. The metal will fail on a slip plane that is loaded in

> >
> > Thank you, sir, for the lesson. I learned something today.

> how to be a schmuck vicariously?

I did not expect this. I am twice blessed today.

--
Michael Press

Michael Press wrote:
> In article <[email protected]>,
> jim beam <[email protected]> wrote:
>
>> Michael Press wrote:
>>> In article
>>> <3a08ca[email protected]>,
>>> [email protected] wrote:
>>>> On Apr 19, 9:54 am, jim beam <[email protected]> wrote:
>>>>> [email protected] wrote:
>>>>>> On Apr 19, 7:28 am, Nate Nagel <[email protected]> wrote:
>>>>>>> Ben C wrote:
>>>>>>>> On 2008-04-18, Peter Cole <[email protected]> wrote:
>>>>>>>>> Ben C wrote:
>>>>>>>>>> On 2008-04-17, [email protected] <[email protected]> wrote:
>>>>>>>>>>> It's exactly because the wheel with the slack spoke is less stiff that
>>>>>>>>>>> an incremental increase in load gets the rim closer to yield strain
>>>>>>>>>>> than a wheel without a slack spoke would be.
>>>>>>>>>> I don't think that's right. Never mind strain, just consider yield
>>>>>>>>>> stress.
>>>>>>>>> He is right.
>>>>>>>>>> When the spokes are slack, the structure as a whole is less stiff. But
>>>>>>>>>> by definition the rim yields when the total stress on the rim reaches
>>>>>>>>>> its yield stress. The more stress already on it from the spokes the less
>>>>>>>>>> additional applied stress you need to bring it to yield.
>>>>>>>>> It is less confusing to think of yield strain and consider the
>>>>>>>>> stress/strain response of the wheel as a structure with and without
>>>>>>>>> Spoke stress on the rim is primarily compression across the cross
>>>>>>>>> section (rim). Bending stress (wheel radial load) is compression on the
>>>>>>>>> outer surface, tension on the inner.
>>>>>>>>> Since the rim is pre-loaded with compression (spoke tension), that
>>>>>>>>> compression must be added to the skin compression (outer) caused by a
>>>>>>>>> bending load, if you do the math, you find you still come out ahead
>>>>>>>> Interesting. Are you saying that the effect of the spoke tension
>>>>>>>> mitigating the tension on the inner surface outweighs its negative
>>>>>>>> effect on the outer surface?
>>>>>>>> Is this because aluminium is stronger in compression than in tension?
>>>>>>>> (Is it?).
>>>>>>>> I would be interested to see your math.
>>>>>>> Very few materials (trying to think of one) are stronger in tension than
>>>>>>> compression.
>>>>>>> replace "roosters" with "cox" to reply.http://members.cox.net/njnagel
>>>>>> A fiber composite can be stronger in tension than compression,
>>>>> that's the form, not the material itself. like rope.
>>>>>
>>>>>> but in
>>>>>> continuum materials
>>>>> "continuum materials"???
>>>> Yes jim, it's a material which may be treated as effectively
>>>> continuous rather than a structure of discrete components. You didn't
>>>>
>>>>>> the ratio of tensile to compressive strength is
>>>>>> bounded by one for ductile materials (like steel) and approaches zero
>>>>>> for brittle materials (like concrete).
>>>>> it's not "bounded by", the ratio /is/ close to one for an unflawed
>>>>> isotropic ductile material, and /is/ close to zero for a flawed brittle
>>>>> material.
>>>> "Bounded" means that materials may lie somewhere between unflawed
>>>> isotropic ductile and flawed brittle, and that the physics dictate
>>>> that the ratio cannot be greater than one for a continuum material.
>>>>
>>>>>> Not that it is at all helpful
>>>>>> to think of this problem in terms of pure tension or compression. A
>>>>>> rim is not a rope, and if yielding occurs from impact with a
>>>>>> cobblestone it will be the result of localized shear strains.
>>>>> localized? yes. shear? most unlikely. there may be a shear component
>>>>> [hydrostatic], but mainly it's just bending tension and compression.
>>>> Metals do not fail in bending, tension, or compression. Metallic
>>>> bonding between atoms is too strong to simply pull them apart in
>>>> tension. The metal will fail on a slip plane that is loaded in
>>> Thank you, sir, for the lesson. I learned something today.

>
>> how to be a schmuck vicariously?

>
> I did not expect this.

keep trolling. schmuck.

> I am twice blessed today.

you're not blessed michael, but you're certainly twice something.

On 2008-04-16 23:52:13 +0200, Ron Ruff <[email protected]> said:

> This is it. A shallow aluminum rim will flex first and then dent...

2007 Lars Michalsen switch from his box section equipped bike to a Zipp
404 equipped bike after la carbre but before the last seqtion of real
pave - and crasshed because of the less comlpient wheels. finnished
10th in his last pro race instead of a secure spot on the podium.

--
mvh. Morten Reippuert Knudsen

"Besides, if you can't get a decent kernal panic
or two in a month, what's the point of living?"

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