Re: vacuum de-gas thread continued

Ben C said:

On 2007-09-15, Peter Cole <[email hidden]> wrote:
[...]

Quoted message said:

Vacuum degassing was certainly doable in the 60's for a cost insensitive
application like spokes.

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds 531
frame sort of level) had galvanized spokes. Is it true that stainless
steel has come down in price in the last 40 or 50 years and/or is more
widespread in its use for spokes?

do you /have/ to ask practical questions like that? you'll make him
feel uncomfortable.

Ben C said:

On 2007-09-15, Peter Cole <[email hidden]> wrote:

Quoted message said:

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds 531
frame sort of level) had galvanized spokes. Is it true that stainless
steel has come down in price in the last 40 or 50 years and/or is more
widespread in its use for spokes?

Dear Ben,

Stainless steel spokes are certainly more widespread.

Nowadays, galvanized spokes are considered cheap and inferior.
"Quality" spokes are stainless steel and cost more.

Galvanized spokes are actually a bit stronger than stainless steel
spokes, but the extra strength has no advantage, since typical spoke
tension is 100~150 kgf, well below the 225~250 kgf yield point that
Jobst measured for thinner stainless steel 1.8 mm spokes. (And
inflating the tire can reduce the spoke tension up to 15% on 700c
rims.)

In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
six spokes, three galvanized and three stainless steel (S.S.)::

Union 14 gauge
DT 14 gauge
Robegel Sport 14 gauge

DT S.S. 14 gauge
DT S.S. 15 gauge
Robegel S.S. 15-16 gauge

The DT galvanized 14 gauge has a slightly higher and slightly sharper
stress-strain curve than the DT stainless steel 14 gauge--the
stainless steel was not quite as strong, but was more ductile.

A few years later, Jobst re-tested spokes for the second edition of
1988. He tested only DT and Wheelsmith and only stainless steel
spokes--galvanized had practically vanished.

Jobst noticed an impressive improvement in ductility:

"In contrast to tests performed for the first edition of this book,
these spokes withstood substantial elongation before failure. Some
butted spokes stretched more than six millimeters without breaking, at
which point the test was stopped."

--p. 132, "The Bicycle Wheel," 2nd edition, 1988

So the stainless steel spokes had not only replaced galvanized as the
material for quality spokes, but they had also improved in ductility
over early stainless steel spokes.

A few years after that, Jobst wrote in the third edition of 1993:

"It appears that the better spokes now available would have made the
discovery of many of the concepts of this book more difficult for lack
of failure data. I am grateful in retrospect for the poor durability
of earlier spokes. They operated so near their limits that durability
was significantly altered by the techniques that I have outlined."

--p. 124, "The Bicycle Wheel," 3rd Edition, 1993

In short, spokes apparently improved so much in a decade that the
failure rate plummeted. Jobst's observation is supported by the fact
that riders gradually stopped carrying spare spokes on long rides.

Cheers,

Carl Fogel

jim beam said:

Ben C said:

On 2007-09-15, Peter Cole <[email hidden]> wrote:
[...]

Quoted message said:

Vacuum degassing was certainly doable in the 60's for a cost
insensitive application like spokes.

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds 531
frame sort of level) had galvanized spokes. Is it true that stainless
steel has come down in price in the last 40 or 50 years and/or is more
widespread in its use for spokes?

do you /have/ to ask practical questions like that? you'll make him
feel uncomfortable.

Asking me? I don't care. I just like them because they're prettier.

I'm here for the engineering, not the history.

And the warmth.

Quoted message said:

Ben C said:

On 2007-09-15, Peter Cole <[email hidden]> wrote:

Quoted message said:

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds 531
frame sort of level) had galvanized spokes. Is it true that stainless
steel has come down in price in the last 40 or 50 years and/or is more
widespread in its use for spokes?

Dear Ben,

Stainless steel spokes are certainly more widespread.

Nowadays, galvanized spokes are considered cheap and inferior.
"Quality" spokes are stainless steel and cost more.

Galvanized spokes are actually a bit stronger than stainless steel
spokes, but the extra strength has no advantage, since typical spoke
tension is 100~150 kgf, well below the 225~250 kgf yield point that
Jobst measured for thinner stainless steel 1.8 mm spokes. (And
inflating the tire can reduce the spoke tension up to 15% on 700c
rims.)

In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
six spokes, three galvanized and three stainless steel (S.S.)::

Union 14 gauge
DT 14 gauge
Robegel Sport 14 gauge

DT S.S. 14 gauge
DT S.S. 15 gauge
Robegel S.S. 15-16 gauge

The DT galvanized 14 gauge has a slightly higher and slightly sharper
stress-strain curve than the DT stainless steel 14 gauge--the
stainless steel was not quite as strong, but was more ductile.

A few years later, Jobst re-tested spokes for the second edition of
1988. He tested only DT and Wheelsmith and only stainless steel
spokes--galvanized had practically vanished.

Jobst noticed an impressive improvement in ductility:

"In contrast to tests performed for the first edition of this book,
these spokes withstood substantial elongation before failure. Some
butted spokes stretched more than six millimeters without breaking, at
which point the test was stopped."

--p. 132, "The Bicycle Wheel," 2nd edition, 1988

So the stainless steel spokes had not only replaced galvanized as the
material for quality spokes, but they had also improved in ductility
over early stainless steel spokes.

Thanks for another excellent answer.

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

Ben C? said:

Quoted message said:

Vacuum degassing was certainly doable in the 60's for a cost
insensitive application like spokes.

Quoted message said:

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds
531 frame sort of level) had galvanized spokes. Is it true that
stainless steel has come down in price in the last 40 or 50 years
and/or is more widespread in its use for spokes?

You were riding among the wrong crowd. Stainless spokes were common
on better bicycles in the 1950's when I bought my first Cinelli.

Jobst Brandt

Quoted message said:

Ben C? said:

Quoted message said:

Vacuum degassing was certainly doable in the 60's for a cost
insensitive application like spokes.

Quoted message said:

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds
531 frame sort of level) had galvanized spokes. Is it true that
stainless steel has come down in price in the last 40 or 50 years
and/or is more widespread in its use for spokes?

You were riding among the wrong crowd. Stainless spokes were common
on better bicycles in the 1950's when I bought my first Cinelli.

Bah, you coffee-shop posers with your fancy Italian bikes and shiny
spokes.

Ben C said:

Quoted message said:

Ben C said:

On 2007-09-15, Peter Cole <[email hidden]> wrote:

Quoted message said:

I'm not old enough to remember what bikes were like in the 60's and
70's, but most older bikes I've seen of quite good quality (Reynolds 531
frame sort of level) had galvanized spokes. Is it true that stainless
steel has come down in price in the last 40 or 50 years and/or is more
widespread in its use for spokes?

Dear Ben,

Stainless steel spokes are certainly more widespread.

Nowadays, galvanized spokes are considered cheap and inferior.
"Quality" spokes are stainless steel and cost more.

Galvanized spokes are actually a bit stronger than stainless steel
spokes, but the extra strength has no advantage, since typical spoke
tension is 100~150 kgf, well below the 225~250 kgf yield point that
Jobst measured for thinner stainless steel 1.8 mm spokes. (And
inflating the tire can reduce the spoke tension up to 15% on 700c
rims.)

In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
six spokes, three galvanized and three stainless steel (S.S.)::

Union 14 gauge
DT 14 gauge
Robegel Sport 14 gauge

DT S.S. 14 gauge
DT S.S. 15 gauge
Robegel S.S. 15-16 gauge

The DT galvanized 14 gauge has a slightly higher and slightly sharper
stress-strain curve than the DT stainless steel 14 gauge--the
stainless steel was not quite as strong, but was more ductile.

A few years later, Jobst re-tested spokes for the second edition of
1988. He tested only DT and Wheelsmith and only stainless steel
spokes--galvanized had practically vanished.

Jobst noticed an impressive improvement in ductility:

"In contrast to tests performed for the first edition of this book,
these spokes withstood substantial elongation before failure. Some
butted spokes stretched more than six millimeters without breaking, at
which point the test was stopped."

--p. 132, "The Bicycle Wheel," 2nd edition, 1988

So the stainless steel spokes had not only replaced galvanized as the
material for quality spokes, but they had also improved in ductility
over early stainless steel spokes.

Thanks for another excellent answer.

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

Dear Ben,

I'm still wondering about that.

After considerable fuss and several trips to the local university, I
had hopes of the engineering department doing stress-strain tests on
some new Sapim 14 gauge stainless spokes to see how they stretched in
2007, compared to Jobst's last test in 1988.

Alas, I'm still waiting, months later, which reminds me why I don't
miss working at universities.

I don't know if more ductility means more durable spokes, but the two
do seem to have been noticed at the same time.

A curious point that I forgot is that carbon steel (galvanized) spokes
are actually more fatigue resistant than stainless steel spokes:

"The choice of carbon vs. stainless steel spokes hinges on which
facotr is considered more important: resistance to corrosion or
resistance to fatigue failure. . . . carbon steel has an advantage
over stainless steel in that it is more resistant to the other common
mode of spoke failure, fatigue."

--"Intro. to Engineering Materials: The Bicycle & the Walkman," p.13

Elsewhere, that 1993 textbook by two U. of Pennsylvania engineering
professors has a cycles-to-failure graph for the two steels, showing
that stainless steel spokes failed substantially _sooner_ in their
spoke fatigue testing than carbon steel.

However, that testing involved spinning a straight, unbent spoke
section and pushing it gently sideways as it whirled, which isn't the
same as a bent spoke elbow.

It's possible that more ductile stainless steel somehow produces much
lower residual stresses when bent to an elbow than the more fatigue
resistant carbon steel, which in turn could mean that the textbook
applied the right test to the wrong part of the spoke and got the
wrong answer.

Cheers,

Carl Fogel

In article
<[email hidden]>,

Ben C said:

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

It will extend the time interval between onset of
deterioration in a spoke and failure. A more ductile
metal spoke will yield more extension before fracture.
A compromised spoke will elongate. If the rider notices
the wheel is untrue or that the spoke is loose he will
tighten the spoke. Thus the spoke comes to notice. If
it needs tightening more than once, which is more
likely with a more ductile spoke metal, the rider is
alerted. Probably will wait until the spoke breaks, but
at least the rider knows there is some kind of problem;
and, heck, he may lose the wheel or spokes before the
more ductile spoke fractures.

--
Michael Press

Quoted message said:

Ben C said:

Quoted message said:

On Sep 15, 12:10 pm, Ben C <[email hidden]> wrote:
> On 2007-09-15, Peter Cole <[email hidden]> wrote:

> I'm not old enough to remember what bikes were like in the 60's and
> 70's, but most older bikes I've seen of quite good quality (Reynolds 531
> frame sort of level) had galvanized spokes. Is it true that stainless
> steel has come down in price in the last 40 or 50 years and/or is more
> widespread in its use for spokes?

Dear Ben,

Stainless steel spokes are certainly more widespread.

Nowadays, galvanized spokes are considered cheap and inferior.
"Quality" spokes are stainless steel and cost more.

Galvanized spokes are actually a bit stronger than stainless steel
spokes, but the extra strength has no advantage, since typical spoke
tension is 100~150 kgf, well below the 225~250 kgf yield point that
Jobst measured for thinner stainless steel 1.8 mm spokes. (And
inflating the tire can reduce the spoke tension up to 15% on 700c
rims.)

In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
six spokes, three galvanized and three stainless steel (S.S.)::

Union 14 gauge
DT 14 gauge
Robegel Sport 14 gauge

DT S.S. 14 gauge
DT S.S. 15 gauge
Robegel S.S. 15-16 gauge

The DT galvanized 14 gauge has a slightly higher and slightly sharper
stress-strain curve than the DT stainless steel 14 gauge--the
stainless steel was not quite as strong, but was more ductile.

A few years later, Jobst re-tested spokes for the second edition of
1988. He tested only DT and Wheelsmith and only stainless steel
spokes--galvanized had practically vanished.

Jobst noticed an impressive improvement in ductility:

"In contrast to tests performed for the first edition of this book,
these spokes withstood substantial elongation before failure. Some
butted spokes stretched more than six millimeters without breaking, at
which point the test was stopped."

--p. 132, "The Bicycle Wheel," 2nd edition, 1988

So the stainless steel spokes had not only replaced galvanized as the
material for quality spokes, but they had also improved in ductility
over early stainless steel spokes.

Thanks for another excellent answer.

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

Dear Ben,

I'm still wondering about that.

After considerable fuss and several trips to the local university, I
had hopes of the engineering department doing stress-strain tests on
some new Sapim 14 gauge stainless spokes to see how they stretched in
2007, compared to Jobst's last test in 1988.

Alas, I'm still waiting, months later, which reminds me why I don't
miss working at universities.

I don't know if more ductility means more durable spokes, but the two
do seem to have been noticed at the same time.

A curious point that I forgot is that carbon steel (galvanized) spokes
are actually more fatigue resistant than stainless steel spokes:

"The choice of carbon vs. stainless steel spokes hinges on which
facotr is considered more important: resistance to corrosion or
resistance to fatigue failure. . . . carbon steel has an advantage
over stainless steel in that it is more resistant to the other common
mode of spoke failure, fatigue."

--"Intro. to Engineering Materials: The Bicycle & the Walkman," p.13

Elsewhere, that 1993 textbook by two U. of Pennsylvania engineering
professors has a cycles-to-failure graph for the two steels, showing
that stainless steel spokes failed substantially _sooner_ in their
spoke fatigue testing than carbon steel.

However, that testing involved spinning a straight, unbent spoke
section and pushing it gently sideways as it whirled, which isn't the
same as a bent spoke elbow.

It's possible that more ductile stainless steel somehow produces much
lower residual stresses when bent to an elbow than the more fatigue
resistant carbon steel, which in turn could mean that the textbook
applied the right test to the wrong part of the spoke and got the
wrong answer.

Cheers,

Carl Fogel

A straight section of stainless steel spoke with no residual stresses
will fatigue sooner than a less ductile section of carbon steel spoke.

But it seems to me, as a layman, that the more ductile stainless steel
spoke will be likely to have less residual stress after bending, since
it bends more easily in the first place.

If so, an unstressed straight section of stainless steel spoke will
fatigue sooner than a less ductile carbon steel spoke, as "The Bicycle
& the Walkman" shows, but the case may be reversed at spoke bends,
with the stainless steel spoke having less residual stress--and the
elbow is where most failures occur.

However, that's just a naive expectation, thrown out to see what the
people who study materials say.

Cheers,

Carl Fogel

On 2007-09-16, [email hidden] <[email hidden]> wrote:
[...]

Quoted message said:

A straight section of stainless steel spoke with no residual stresses
will fatigue sooner than a less ductile section of carbon steel spoke.

But it seems to me, as a layman, that the more ductile stainless steel
spoke will be likely to have less residual stress after bending, since
it bends more easily in the first place.

That sounds logical enough. But on the other hand, all steel is supposed
to have about the same modulus of elasticity, so in that sense it's just
as difficult to bend. Ductile means you can bend it further without it
breaking, not necessarily that it's any easier to bend. If the stiffness
is the same, one might think the residual stresses would also be the
same.

Literally ductile means "able to be drawn out [into a wire]". Which
gives me an idea why it might be desirable for spoke materials-- they
are wire. So it might be easier and cheaper to make huge reels of wire
out of the more ductile material.

Quoted message said:

If so, an unstressed straight section of stainless steel spoke will
fatigue sooner than a less ductile carbon steel spoke, as "The Bicycle
& the Walkman" shows, but the case may be reversed at spoke bends,
with the stainless steel spoke having less residual stress--and the
elbow is where most failures occur.

However, that's just a naive expectation, thrown out to see what the
people who study materials say.

My guess is that another factor is corrosion. Galvanizing resists
corrosion but I would think less effectively than stainless steel.

Quoted message said:

Ben C said:

Quoted message said:

On Sep 15, 12:10 pm, Ben C <[email hidden]> wrote:
> On 2007-09-15, Peter Cole <[email hidden]> wrote:
> I'm not old enough to remember what bikes were like in the 60's and
> 70's, but most older bikes I've seen of quite good quality (Reynolds 531
> frame sort of level) had galvanized spokes. Is it true that stainless
> steel has come down in price in the last 40 or 50 years and/or is more
> widespread in its use for spokes?
Dear Ben,

Stainless steel spokes are certainly more widespread.

Nowadays, galvanized spokes are considered cheap and inferior.
"Quality" spokes are stainless steel and cost more.

Galvanized spokes are actually a bit stronger than stainless steel
spokes, but the extra strength has no advantage, since typical spoke
tension is 100~150 kgf, well below the 225~250 kgf yield point that
Jobst measured for thinner stainless steel 1.8 mm spokes. (And
inflating the tire can reduce the spoke tension up to 15% on 700c
rims.)

In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
six spokes, three galvanized and three stainless steel (S.S.)::

Union 14 gauge
DT 14 gauge
Robegel Sport 14 gauge

DT S.S. 14 gauge
DT S.S. 15 gauge
Robegel S.S. 15-16 gauge

The DT galvanized 14 gauge has a slightly higher and slightly sharper
stress-strain curve than the DT stainless steel 14 gauge--the
stainless steel was not quite as strong, but was more ductile.

A few years later, Jobst re-tested spokes for the second edition of
1988. He tested only DT and Wheelsmith and only stainless steel
spokes--galvanized had practically vanished.

Jobst noticed an impressive improvement in ductility:

"In contrast to tests performed for the first edition of this book,
these spokes withstood substantial elongation before failure. Some
butted spokes stretched more than six millimeters without breaking, at
which point the test was stopped."

--p. 132, "The Bicycle Wheel," 2nd edition, 1988

So the stainless steel spokes had not only replaced galvanized as the
material for quality spokes, but they had also improved in ductility
over early stainless steel spokes.

Thanks for another excellent answer.

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

Dear Ben,

I'm still wondering about that.

After considerable fuss and several trips to the local university, I
had hopes of the engineering department doing stress-strain tests on
some new Sapim 14 gauge stainless spokes to see how they stretched in
2007, compared to Jobst's last test in 1988.

Alas, I'm still waiting, months later, which reminds me why I don't
miss working at universities.

I don't know if more ductility means more durable spokes, but the two
do seem to have been noticed at the same time.

A curious point that I forgot is that carbon steel (galvanized) spokes
are actually more fatigue resistant than stainless steel spokes:

"The choice of carbon vs. stainless steel spokes hinges on which
facotr is considered more important: resistance to corrosion or
resistance to fatigue failure. . . . carbon steel has an advantage
over stainless steel in that it is more resistant to the other common
mode of spoke failure, fatigue."

--"Intro. to Engineering Materials: The Bicycle & the Walkman," p.13

Elsewhere, that 1993 textbook by two U. of Pennsylvania engineering
professors has a cycles-to-failure graph for the two steels, showing
that stainless steel spokes failed substantially _sooner_ in their
spoke fatigue testing than carbon steel.

However, that testing involved spinning a straight, unbent spoke
section and pushing it gently sideways as it whirled, which isn't the
same as a bent spoke elbow.

It's possible that more ductile stainless steel somehow produces much
lower residual stresses when bent to an elbow than the more fatigue
resistant carbon steel, which in turn could mean that the textbook
applied the right test to the wrong part of the spoke and got the
wrong answer.

Cheers,

Carl Fogel

The whole story on the material aspect of fatigue is given by the S-N
curve, also known as a Wöhler curve. (See
http://en.wikipedia.org/wiki/Fatigue_%28material%29#The_S-N_curve for an
example). These curves need to be adjusted for the case of spokes, since
they are typically for a (sinusoidal) stress cycle around zero, where
spokes have (significant) a non-zero bias.

It's common experience to have spokes survive 10^7 cycles, with some
(Jobst) reporting 10^8 or so.

S-N curves represent the ideal, with near perfect samples, and must be
derated for realities like defects and corrosion.

The higher fatigue resistance of carbon steel vs stainless, in practical
terms, means that it's theoretically possible to make crappier spokes
and have them last as long. The fact that old carbon spokes failed
earlier seems to only indicate that they were made (much) more poorly.
The S-N curves for those spokes must have departed significantly from
the ideal.

Michael Press said:

In article
<[email hidden]>,

Ben C said:

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

It will extend the time interval between onset of
deterioration in a spoke and failure. A more ductile
metal spoke will yield more extension before fracture.
A compromised spoke will elongate. If the rider notices
the wheel is untrue or that the spoke is loose he will
tighten the spoke. Thus the spoke comes to notice. If
it needs tightening more than once, which is more
likely with a more ductile spoke metal, the rider is
alerted. Probably will wait until the spoke breaks, but
at least the rider knows there is some kind of problem;
and, heck, he may lose the wheel or spokes before the
more ductile spoke fractures.

Since the maximum stress seen by the spoke is when a wheel is unloaded,
and that is well below the point of bulk plastic deformation, I don't
see how ductility enters into the picture.

Ben C said:

On 2007-09-16, [email hidden] <[email hidden]> wrote:
[...]

Quoted message said:

A straight section of stainless steel spoke with no residual stresses
will fatigue sooner than a less ductile section of carbon steel spoke.

But it seems to me, as a layman, that the more ductile stainless steel
spoke will be likely to have less residual stress after bending, since
it bends more easily in the first place.

That sounds logical enough. But on the other hand, all steel is supposed
to have about the same modulus of elasticity, so in that sense it's just
as difficult to bend. Ductile means you can bend it further without it
breaking, not necessarily that it's any easier to bend. If the stiffness
is the same, one might think the residual stresses would also be the
same.

You may be running afoul of nomenclature and definition here (much like
"jim beam" and his confusion over fatigue and endurance limit(s)). The
modulus of elasticity describes how hard it is to made a thing bend below
the point where it will not return. Ductility describes how much it will
stretch (for bending, one side stretches) after that point, and before the
point where it breaks. The force required to produce a certain amount
ductile stretching is not linearly related - if at all- to the force
requried to produce a certain amount of elastic bending.

_ said:

Ben C said:

On 2007-09-16, [email hidden] <[email hidden]> wrote:
[...]

Quoted message said:

A straight section of stainless steel spoke with no residual stresses
will fatigue sooner than a less ductile section of carbon steel spoke.

But it seems to me, as a layman, that the more ductile stainless steel
spoke will be likely to have less residual stress after bending, since
it bends more easily in the first place.

That sounds logical enough. But on the other hand, all steel is supposed
to have about the same modulus of elasticity, so in that sense it's just
as difficult to bend. Ductile means you can bend it further without it
breaking, not necessarily that it's any easier to bend. If the stiffness
is the same, one might think the residual stresses would also be the
same.

You may be running afoul of nomenclature and definition here (much like
"jim beam" and his confusion over fatigue and endurance limit(s)). The
modulus of elasticity describes how hard it is to made a thing bend below
the point where it will not return. Ductility describes how much it will
stretch (for bending, one side stretches) after that point, and before the
point where it breaks. The force required to produce a certain amount
ductile stretching is not linearly related - if at all- to the force
requried to produce a certain amount of elastic bending.

you're both right. mostly. to put it another way, if an alloy reaches
failure at 15% elongation and plasticity commences at 0.5% elongation,
14.5% is a measure of ductility.

Peter Cole said:

Quoted message said:

Ben C said:

On 2007-09-15, [email hidden] <[email hidden]> wrote:
> On Sep 15, 12:10 pm, Ben C <[email hidden]> wrote:
>> On 2007-09-15, Peter Cole <[email hidden]> wrote:
>> I'm not old enough to remember what bikes were like in the 60's and
>> 70's, but most older bikes I've seen of quite good quality
>> (Reynolds 531
>> frame sort of level) had galvanized spokes. Is it true that stainless
>> steel has come down in price in the last 40 or 50 years and/or is more
>> widespread in its use for spokes?
> Dear Ben,
>
> Stainless steel spokes are certainly more widespread.
>
> Nowadays, galvanized spokes are considered cheap and inferior.
> "Quality" spokes are stainless steel and cost more.
>
> Galvanized spokes are actually a bit stronger than stainless steel
> spokes, but the extra strength has no advantage, since typical spoke
> tension is 100~150 kgf, well below the 225~250 kgf yield point that
> Jobst measured for thinner stainless steel 1.8 mm spokes. (And
> inflating the tire can reduce the spoke tension up to 15% on 700c
> rims.)
>
> In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
> six spokes, three galvanized and three stainless steel (S.S.)::
>
> Union 14 gauge
> DT 14 gauge
> Robegel Sport 14 gauge
>
> DT S.S. 14 gauge
> DT S.S. 15 gauge
> Robegel S.S. 15-16 gauge
>
> The DT galvanized 14 gauge has a slightly higher and slightly sharper
> stress-strain curve than the DT stainless steel 14 gauge--the
> stainless steel was not quite as strong, but was more ductile.
>
> A few years later, Jobst re-tested spokes for the second edition of
> 1988. He tested only DT and Wheelsmith and only stainless steel
> spokes--galvanized had practically vanished.
>
> Jobst noticed an impressive improvement in ductility:
>
> "In contrast to tests performed for the first edition of this book,
> these spokes withstood substantial elongation before failure. Some
> butted spokes stretched more than six millimeters without breaking, at
> which point the test was stopped."
>
> --p. 132, "The Bicycle Wheel," 2nd edition, 1988
>
> So the stainless steel spokes had not only replaced galvanized as the
> material for quality spokes, but they had also improved in ductility
> over early stainless steel spokes.
Thanks for another excellent answer.

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

Dear Ben,

I'm still wondering about that.

After considerable fuss and several trips to the local university, I
had hopes of the engineering department doing stress-strain tests on
some new Sapim 14 gauge stainless spokes to see how they stretched in
2007, compared to Jobst's last test in 1988.

Alas, I'm still waiting, months later, which reminds me why I don't
miss working at universities.

I don't know if more ductility means more durable spokes, but the two
do seem to have been noticed at the same time.

A curious point that I forgot is that carbon steel (galvanized) spokes
are actually more fatigue resistant than stainless steel spokes:

"The choice of carbon vs. stainless steel spokes hinges on which
facotr is considered more important: resistance to corrosion or
resistance to fatigue failure. . . . carbon steel has an advantage
over stainless steel in that it is more resistant to the other common
mode of spoke failure, fatigue."

--"Intro. to Engineering Materials: The Bicycle & the Walkman," p.13

Elsewhere, that 1993 textbook by two U. of Pennsylvania engineering
professors has a cycles-to-failure graph for the two steels, showing
that stainless steel spokes failed substantially _sooner_ in their
spoke fatigue testing than carbon steel.

However, that testing involved spinning a straight, unbent spoke
section and pushing it gently sideways as it whirled, which isn't the
same as a bent spoke elbow.

It's possible that more ductile stainless steel somehow produces much
lower residual stresses when bent to an elbow than the more fatigue
resistant carbon steel, which in turn could mean that the textbook
applied the right test to the wrong part of the spoke and got the
wrong answer.

Cheers,

Carl Fogel

The whole story on the material aspect of fatigue is given by the S-N
curve, also known as a W�hler curve. (See
http://en.wikipedia.org/wiki/Fatigue_%28material%29#The_S-N_curve for an
example). These curves need to be adjusted for the case of spokes, since
they are typically for a (sinusoidal) stress cycle around zero, where
spokes have (significant) a non-zero bias.

It's common experience to have spokes survive 10^7 cycles, with some
(Jobst) reporting 10^8 or so.

S-N curves represent the ideal, with near perfect samples, and must be
derated for realities like defects and corrosion.

The higher fatigue resistance of carbon steel vs stainless, in practical
terms, means that it's theoretically possible to make crappier spokes
and have them last as long.

no, if it's a steel whose carbon content is low enough to retain the
dislocation locking mechanism we discussed before, those spokes would
last forever, if stress was below that of their endurance limit.

Quoted message said:

The fact that old carbon spokes failed
earlier seems to only indicate that they were made (much) more poorly.

no, they're made exactly the same way. the difference is the material
quality.

Quoted message said:

The S-N curves for those spokes must have departed significantly from
the ideal.

fudge.

Peter Cole said:

Michael Press said:

In article <[email hidden]>,

Ben C said:

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

It will extend the time interval between onset of
deterioration in a spoke and failure. A more ductile
metal spoke will yield more extension before fracture.
A compromised spoke will elongate. If the rider notices
the wheel is untrue or that the spoke is loose he will
tighten the spoke. Thus the spoke comes to notice. If
it needs tightening more than once, which is more
likely with a more ductile spoke metal, the rider is
alerted. Probably will wait until the spoke breaks, but
at least the rider knows there is some kind of problem;
and, heck, he may lose the wheel or spokes before the
more ductile spoke fractures.

Since the maximum stress seen by the spoke is when a wheel is unloaded,

er, no. maximum stress is on lateral loading.

Quoted message said:

and that is well below the point of bulk plastic deformation, I don't
see how ductility enters into the picture.

Michael Press said:

In article
<[email hidden]>,

Ben C said:

Does the extra ductility have any advantage _per se_ for spokes?

It might be a side-effect of some other improvement and therefore a clue
about the introduction of some new process like vacuum degassing.

It will extend the time interval between onset of
deterioration in a spoke and failure. A more ductile
metal spoke will yield more extension before fracture.
A compromised spoke will elongate. If the rider notices
the wheel is untrue or that the spoke is loose he will
tighten the spoke. Thus the spoke comes to notice. If
it needs tightening more than once, which is more
likely with a more ductile spoke metal, the rider is
alerted. Probably will wait until the spoke breaks, but
at least the rider knows there is some kind of problem;
and, heck, he may lose the wheel or spokes before the
more ductile spoke fractures.

there is a rough correlation between ductility and fatigue resistance,
but it's very imprecise and not typically something you'd use as a
design factor.

since fatigue is the biggest concern for applications that approach
material limits, and at high stress, no material is immune from fatigue,
designers concentrate on delaying onset. this means attention to
design, surface finish, corrosion, stress concentrations, material
quality, etc. even residual stress! this is the approach of the
aerospace industry.

jim beam said:

Peter Cole said:

Quoted message said:

On Sat, 15 Sep 2007 17:10:09 -0500, Ben C <[email hidden]> wrote:

> On 2007-09-15, [email hidden] <[email hidden]> wrote:
>> On Sep 15, 12:10 pm, Ben C <[email hidden]> wrote:
>>> On 2007-09-15, Peter Cole <[email hidden]> wrote:
>>> I'm not old enough to remember what bikes were like in the 60's and
>>> 70's, but most older bikes I've seen of quite good quality
>>> (Reynolds 531
>>> frame sort of level) had galvanized spokes. Is it true that stainless
>>> steel has come down in price in the last 40 or 50 years and/or is
>>> more
>>> widespread in its use for spokes?
>> Dear Ben,
>>
>> Stainless steel spokes are certainly more widespread.
>>
>> Nowadays, galvanized spokes are considered cheap and inferior.
>> "Quality" spokes are stainless steel and cost more.
>>
>> Galvanized spokes are actually a bit stronger than stainless steel
>> spokes, but the extra strength has no advantage, since typical spoke
>> tension is 100~150 kgf, well below the 225~250 kgf yield point that
>> Jobst measured for thinner stainless steel 1.8 mm spokes. (And
>> inflating the tire can reduce the spoke tension up to 15% on 700c
>> rims.)
>>
>> In the 1981-1983 first edition of "The Bicycle Wheel," Jobst tested
>> six spokes, three galvanized and three stainless steel (S.S.)::
>>
>> Union 14 gauge
>> DT 14 gauge
>> Robegel Sport 14 gauge
>>
>> DT S.S. 14 gauge
>> DT S.S. 15 gauge
>> Robegel S.S. 15-16 gauge
>>
>> The DT galvanized 14 gauge has a slightly higher and slightly sharper
>> stress-strain curve than the DT stainless steel 14 gauge--the
>> stainless steel was not quite as strong, but was more ductile.
>>
>> A few years later, Jobst re-tested spokes for the second edition of
>> 1988. He tested only DT and Wheelsmith and only stainless steel
>> spokes--galvanized had practically vanished.
>>
>> Jobst noticed an impressive improvement in ductility:
>>
>> "In contrast to tests performed for the first edition of this book,
>> these spokes withstood substantial elongation before failure. Some
>> butted spokes stretched more than six millimeters without breaking, at
>> which point the test was stopped."
>>
>> --p. 132, "The Bicycle Wheel," 2nd edition, 1988
>>
>> So the stainless steel spokes had not only replaced galvanized as the
>> material for quality spokes, but they had also improved in ductility
>> over early stainless steel spokes.
> Thanks for another excellent answer.
>
> Does the extra ductility have any advantage _per se_ for spokes?
>
> It might be a side-effect of some other improvement and therefore a
> clue
> about the introduction of some new process like vacuum degassing.

Dear Ben,

I'm still wondering about that.

After considerable fuss and several trips to the local university, I
had hopes of the engineering department doing stress-strain tests on
some new Sapim 14 gauge stainless spokes to see how they stretched in
2007, compared to Jobst's last test in 1988.

Alas, I'm still waiting, months later, which reminds me why I don't
miss working at universities.

I don't know if more ductility means more durable spokes, but the two
do seem to have been noticed at the same time.

A curious point that I forgot is that carbon steel (galvanized) spokes
are actually more fatigue resistant than stainless steel spokes:

"The choice of carbon vs. stainless steel spokes hinges on which
facotr is considered more important: resistance to corrosion or
resistance to fatigue failure. . . . carbon steel has an advantage
over stainless steel in that it is more resistant to the other common
mode of spoke failure, fatigue."

--"Intro. to Engineering Materials: The Bicycle & the Walkman," p.13

Elsewhere, that 1993 textbook by two U. of Pennsylvania engineering
professors has a cycles-to-failure graph for the two steels, showing
that stainless steel spokes failed substantially _sooner_ in their
spoke fatigue testing than carbon steel.

However, that testing involved spinning a straight, unbent spoke
section and pushing it gently sideways as it whirled, which isn't the
same as a bent spoke elbow.

It's possible that more ductile stainless steel somehow produces much
lower residual stresses when bent to an elbow than the more fatigue
resistant carbon steel, which in turn could mean that the textbook
applied the right test to the wrong part of the spoke and got the
wrong answer.

Cheers,

Carl Fogel

The whole story on the material aspect of fatigue is given by the S-N
curve, also known as a W�hler curve. (See
http://en.wikipedia.org/wiki/Fatigue_%28material%29#The_S-N_curve for
an example). These curves need to be adjusted for the case of spokes,
since they are typically for a (sinusoidal) stress cycle around zero,
where spokes have (significant) a non-zero bias.

It's common experience to have spokes survive 10^7 cycles, with some
(Jobst) reporting 10^8 or so.

S-N curves represent the ideal, with near perfect samples, and must be
derated for realities like defects and corrosion.

The higher fatigue resistance of carbon steel vs stainless, in
practical terms, means that it's theoretically possible to make
crappier spokes and have them last as long.

no, if it's a steel whose carbon content is low enough to retain the
dislocation locking mechanism we discussed before,

Quoted message said:

those spokes would
last forever, if stress was below that of their endurance limit.

Ditto for stainless.

Quoted message said:

Quoted message said:

The fact that old carbon spokes failed earlier seems to only indicate
that they were made (much) more poorly.

no, they're made exactly the same way. the difference is the material
quality.

Quoted message said:

The S-N curves for those spokes must have departed significantly from
the ideal.

fudge.

Whatever.

jim beam said:

Peter Cole said:

Michael Press said:

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

> Does the extra ductility have any advantage _per se_ for spokes?
>
> It might be a side-effect of some other improvement and therefore a
> clue
> about the introduction of some new process like vacuum degassing.

It will extend the time interval between onset of
deterioration in a spoke and failure. A more ductile
metal spoke will yield more extension before fracture.
A compromised spoke will elongate. If the rider notices
the wheel is untrue or that the spoke is loose he will
tighten the spoke. Thus the spoke comes to notice. If
it needs tightening more than once, which is more
likely with a more ductile spoke metal, the rider is
alerted. Probably will wait until the spoke breaks, but
at least the rider knows there is some kind of problem;
and, heck, he may lose the wheel or spokes before the
more ductile spoke fractures.

Since the maximum stress seen by the spoke is when a wheel is unloaded,

er, no. maximum stress is on lateral loading.

Give me a call when you stretch a spoke.

Quoted message said:

Quoted message said:

and that is well below the point of bulk plastic deformation, I don't
see how ductility enters into the picture.