Stress-relief demonstration suggestions?

Hmmm . . . does squeezing stainless steel spokes render them
immortal?

The idea is that when spokes are bent to form the elbow,
potentially fatal stresses are formed at the bend, stresses
that can be relieved by giving the tensioned spoke a good
squeeze.

Unfortunately, theory and data are controversial.

A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for
millions of wheel revolutions.

(Ten thousand miles is about 53 million inches, which in
turn is about two-thirds of a million spins of a 700c
wheel--and 500 hours at 20 mph. Setting up a test for a
hundred plain and a hundred squeezed spokes would be
daunting.)

Can anyone suggest a practical test that I can use to
convince a pack of skeptical high-school physics students,
one way or the other?

I think that I have the raw material, some widely available
pieces of stainless steel wire that come with three smooth
u-bends from the factory. It's so cheap that I should be
ashamed to steal them in boxes of a hundred, but the
students need to learn the basics of scrounging.

Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?

Carl Fogel

In article ,
says...
Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?

Your first long jump is to assume that paper clips are made of the same
stuff DT et al. use. (not that I would know).

In article ,
says...
Hmmm . . . does squeezing stainless steel spokes render them
immortal?

The idea is that when spokes are bent to form the elbow,
potentially fatal stresses are formed at the bend, stresses
that can be relieved by giving the tensioned spoke a good
squeeze.

Unfortunately, theory and data are controversial.

A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for
millions of wheel revolutions.

(Ten thousand miles is about 53 million inches, which in
turn is about two-thirds of a million spins of a 700c
wheel--and 500 hours at 20 mph. Setting up a test for a
hundred plain and a hundred squeezed spokes would be
daunting.)

Can anyone suggest a practical test that I can use to
convince a pack of skeptical high-school physics students,
one way or the other?

I think that I have the raw material, some widely available
pieces of stainless steel wire that come with three smooth
u-bends from the factory. It's so cheap that I should be
ashamed to steal them in boxes of a hundred, but the
students need to learn the basics of scrounging.

Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?

Carl Fogel

Thinking some more about this...

Most of my fatigued spokes happened in a batch, 11 failures ocurred on
two bikes on a 2500 Km tour in France (3 on my wife's bike and 8 on mine
- all drive side rear and all failed around the spoke bend near the
head). The spokes were not DT, Sapim or Wheelsmith and had been stress
relieved by me. It seemed to me that, compared to a DT spoke, the failed
spokes had a sharper transition to the head, maybe causing an extra
stress concentration. I am certain of a few things, - the french word
for spoke is "rayon" and they are not shaped much like a paper clip.

BTW I replaced all the drive side spokes with DT on returning home, and
around 12000 km, the non-drive side no-names started to fail, so I
replaced them too.

On Fri, 31 Dec 2004 15:57:52 +1100, Bruce Graham
wrote:

In article ,
says...
Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?

Your first long jump is to assume that paper clips are made of the same
stuff DT et al. use. (not that I would know).

Dear Bruce,

Once the thought struck me, my first check was to
google--paper clips are made of stainless steel.

Some months ago, I mentioned that Wheelsmith says that they
use 304 stainless steel, while DT claims to use 18-8
stainless steel--pretty much the same stuff, expressed
differently:

http://groups.google.co.uk/groups?q=...4ax.com&rnum=2
or http://tinyurl.com/4yr6b

In any case, I don't think that anyone has claimed that
bicycle spokes are made of an unusual kind of stainless
steel with unusual stress or fatigue characteristics.
Certainly no one has argued that spoke squeezing works only
on one brand of spoke.

If paper clips are reasonably similar to spokes in material
and manufacturing, then their advantage (apart from being
free) is that they're available in a wide range of much
thinner wires, which presumably would fatigue more easily
and quickly than spokes.

The idea is a test that would eliminate the question of
whether squeezing is seating things (as opposed to relieving
stress) and that would be quick enough to run repeatedly.

The only spoke tests that I know of were performed about 20
years ago, were cut short due to time problems, and involved
no attempts at stress relief. (The fellow who has the spoke
test data offered to send it to me, but then never got
around to it and hasn't replied to my second email--of
course, prettier girls have stood me up with less excuse, so
I'm not heartbroken.)

Carl Fogel

On Fri, 31 Dec 2004 16:33:32 +1100, Bruce Graham
wrote:

In article ,
says...
Hmmm . . . does squeezing stainless steel spokes render them
immortal?

The idea is that when spokes are bent to form the elbow,
potentially fatal stresses are formed at the bend, stresses
that can be relieved by giving the tensioned spoke a good
squeeze.

Unfortunately, theory and data are controversial.

A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for
millions of wheel revolutions.

(Ten thousand miles is about 53 million inches, which in
turn is about two-thirds of a million spins of a 700c
wheel--and 500 hours at 20 mph. Setting up a test for a
hundred plain and a hundred squeezed spokes would be
daunting.)

Can anyone suggest a practical test that I can use to
convince a pack of skeptical high-school physics students,
one way or the other?

I think that I have the raw material, some widely available
pieces of stainless steel wire that come with three smooth
u-bends from the factory. It's so cheap that I should be
ashamed to steal them in boxes of a hundred, but the
students need to learn the basics of scrounging.

Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?

Carl Fogel

Thinking some more about this...

Most of my fatigued spokes happened in a batch, 11 failures ocurred on
two bikes on a 2500 Km tour in France (3 on my wife's bike and 8 on mine
- all drive side rear and all failed around the spoke bend near the
head). The spokes were not DT, Sapim or Wheelsmith and had been stress
relieved by me. It seemed to me that, compared to a DT spoke, the failed
spokes had a sharper transition to the head, maybe causing an extra
stress concentration. I am certain of a few things, - the french word
for spoke is "rayon" and they are not shaped much like a paper clip.

BTW I replaced all the drive side spokes with DT on returning home, and
around 12000 km, the non-drive side no-names started to fail, so I
replaced them too.

Dear Bruce,

You mention some of the points of interest.

The spoke angle and the shape of the head flare may have
changed over the years, possibly for the better.

The materials used and the manufacturing process may have
done the same thing

Even tiny improvements can mount up to much better spokes
over several decades.

And then there's the widespread use of double-butted spokes,
which may reduce spoke failure.

In general, those who believe in spoke squeezing make no
distinction between brands of spokes or whether the spokes
are from 1984 or 2004--the stress relief is what matters,
and it renders spokes immortal.

Those who are skeptical point to various improvements in
what at first seems like brick-simple technology and suggest
that the squeezing affects how the spoke heads fit in the
hub holes.

I waver back and forth, but I'm certain of one thing--the
spokes don't care what either side thinks.

Carl Fogel

Carl Fogel writes:

Hmmm... does squeezing stainless steel spokes render them immortal?

Maybe you should call it "stretching spokes" rather than squeezing,
since stretch is what is being done. This can be accomplished through
various manual and mechanical means. TREK has a method by which the
wheel is stress relieved in two operations, one side at a time.

The idea is that when spokes are bent to form the elbow, potentially
fatal stresses are formed at the bend, stresses that can be relieved
by giving the tensioned spoke a good squeeze.

Unfortunately, theory and data are controversial.

Not at all. As I have explained in detail (something you could find
with your skills in web searching) bending a steel wire always
involves partial spring-back, which in itself proves there are
residual stresses. If it were not the case, the wire would either
return to its original alignment or remain in the position into which
it was bent.

The partial spring-back results from not all depths of the cross
section having been equally deformed, the central "fiber" not having
changed length while the parts on the outside of the bend were
permanently stretched and those on the inside, compressed. In between
these extremes various amounts of plastic length change occurred.

I think that if you review this scenario and observe that there is
partial spring-back, that there must be residual stress.

A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for millions of
wheel revolutions.

Get a coat hanger and start bending.

(Ten thousand miles is about 53 million inches, which in turn is
about two-thirds of a million spins of a 700c wheel--and 500 hours
at 20 mph. Setting up a test for a hundred plain and a hundred
squeezed spokes would be daunting.)

Forget about the miles for a moment and look at the material. As I
mentioned, placing a wire that purposely has been made wavy, in a
tensile testing machine that can tension the wire to its yield stress,
(the stress where the stress strain curve begins to flatten out) will
give a perfectly straight wire when released. This wire has no
stresses or it would spring to some other shape. It has no reason to
take a shape other than straight because all its parts were stretched
to yield to have their collective "memories" erased. This is possible
with ductile spoke wire because it is made to undergo forming.

Can anyone suggest a practical test that I can use to convince a
pack of skeptical high-school physics students, one way or the
other?

If you have a spoke in a tensioned wheel that was bent into its
in-situ shape by bending its elbow form its original obtuse angle to
an acute angle by tensioning, then it will have its outer "fibers" of
the elbow at yield stress and it will remain there because the spoke
is additionally tensioned. By stretching that spoke to nearly twice
its static tension by "stress relieving" over-tension, the outside of
the elbow must yield and when released fall back to a lower stress.

That example is of the elbow, but it is true of the threads as well.
The elbow, however, is more obvious because outbound spokes all get
plastically deformed in the first tensioning of the wheel regardless
of their prior state.

I think that I have the raw material, some widely available pieces
of stainless steel wire that come with three smooth u-bends from the
factory. It's so cheap that I should be ashamed to steal them in
boxes of a hundred, but the students need to learn the basics of
scrounging.

Being practical about this, I think you will see that you can do this
without a materials laboratory.

Any ideas about how to demonstrate over-tensioning stress-relief
using paper-clips?

I like clothes hangers better because they are large enough to clearly
see the results.

http://www.sheldonbrown.com/brandt/s...relieving.html

Jobst Brandt

In article ,
says...
Hmmm . . . does squeezing stainless steel spokes render them
immortal?
The idea is that when spokes are bent to form the elbow,
potentially fatal stresses are formed at the bend, stresses
that can be relieved by giving the tensioned spoke a good
squeeze.
-snip-
Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?


On Fri, 31 Dec 2004 16:33:32 +1100, Bruce Graham
wrote:
Thinking some more about this...
Most of my fatigued spokes happened in a batch, 11 failures ocurred on
two bikes on a 2500 Km tour in France (3 on my wife's bike and 8 on mine
- all drive side rear and all failed around the spoke bend near the
head). The spokes were not DT, Sapim or Wheelsmith and had been stress
relieved by me. It seemed to me that, compared to a DT spoke, the failed
spokes had a sharper transition to the head, maybe causing an extra
stress concentration. I am certain of a few things, - the french word
for spoke is "rayon" and they are not shaped much like a paper clip.

BTW I replaced all the drive side spokes with DT on returning home, and
around 12000 km, the non-drive side no-names started to fail, so I
replaced them too.


In article ,
says...
You mention some of the points of interest.
The spoke angle and the shape of the head flare may have
changed over the years, possibly for the better.
The materials used and the manufacturing process may have
done the same thing
-snip-
And then there's the widespread use of double-butted spokes,
which may reduce spoke failure.
In general, those who believe in spoke squeezing make no
distinction between brands of spokes or whether the spokes
are from 1984 or 2004--the stress relief is what matters,
and it renders spokes immortal.
Those who are skeptical point to various improvements in
what at first seems like brick-simple technology and suggest
that the squeezing affects how the spoke heads fit in the
hub holes.
I waver back and forth, but I'm certain of one thing--the
spokes don't care what either side thinks.

The shape and material of the flange enters into this too.
Simple pierced steel flanges are just hell for spoke
breakage, Phil Wood's flanges being the accepted ideal shape.

Perhaps stressing the spokes as we do has a compound effect
rather than one single mechanism? Relieving stress from
forming, shaping the head/curve to better fit the flange and
also deepening the groove in the flange (resulting in a
broad contact area between flange and spoke rather than
asimple point contact as a steel hub). It may well be that
these effects are insignificantly small _until_ the
momentary high loads we put on the spokes.


--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

wrote:
Carl Fogel writes:


Hmmm... does squeezing stainless steel spokes render them immortal?


Maybe you should call it "stretching spokes" rather than squeezing,
since stretch is what is being done. This can be accomplished through
various manual and mechanical means. TREK has a method by which the
wheel is stress relieved in two operations, one side at a time.


The idea is that when spokes are bent to form the elbow, potentially
fatal stresses are formed at the bend, stresses that can be relieved
by giving the tensioned spoke a good squeeze.


Unfortunately, theory and data are controversial.

translation: "i have no proof & have not attempted to quantify".



Not at all. As I have explained in detail (something you could find
with your skills in web searching) bending a steel wire always
involves partial spring-back, which in itself proves there are
residual stresses.

absolutely fundamentally not.

If it were not the case, the wire would either
return to its original alignment or remain in the position into which
it was bent.

jobst, please please please get it into your head that spring-back is
because of the shape of the deformation graph. residual stress has
nothing to do with it. bending has nothing to do with it - you get
spring-back in linear tension samples too - and the reason, as explained
before, is that you only deform material once you're above the hookes
law part of the graph. but deforming enough for yield does not
magically allow the material to yield to zero and bypass hookes law on
the way. is there any way to explain this to you more simply? as long
as you labor under this fundamental misconception, you're always going
to keep shooting wide of the mark.


The partial spring-back results from not all depths of the cross
section having been equally deformed, the central "fiber" not having
changed length while the parts on the outside of the bend were
permanently stretched and those on the inside, compressed. In between
these extremes various amounts of plastic length change occurred.

you do get differing degrees of deformation, but they are not wholly
responsible for spring-back. see above.


I think that if you review this scenario and observe that there is
partial spring-back, that there must be residual stress.

no, no, no. that's an absolutely fundamental misconception.



A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for millions of
wheel revolutions.


Get a coat hanger and start bending.

you're never going to "see" residual stress just by bending anything.



(Ten thousand miles is about 53 million inches, which in turn is
about two-thirds of a million spins of a 700c wheel--and 500 hours
at 20 mph. Setting up a test for a hundred plain and a hundred
squeezed spokes would be daunting.)


Forget about the miles for a moment and look at the material. As I
mentioned, placing a wire that purposely has been made wavy, in a
tensile testing machine that can tension the wire to its yield stress,
(the stress where the stress strain curve begins to flatten out) will
give a perfectly straight wire when released. This wire has no
stresses or it would spring to some other shape.

rubbish. that wire can have residual stress much as any other. the
questions is the stress orientation & whether it's significant relative
to its application. all you're describing is a material that has
yielded. there's no way you'll ever get a handle on magnitude or
relevance with this kind of hand waving.

It has no reason to
take a shape other than straight because all its parts were stretched
to yield to have their collective "memories" erased. This is possible
with ductile spoke wire because it is made to undergo forming.

fundamental lack of understanding of deformation theory. the effects of
deformation are cumulative in stainless wire. the entire work history
of the material is easily visible under any metallurgical microscope.
you're not erasing anything.



Can anyone suggest a practical test that I can use to convince a
pack of skeptical high-school physics students, one way or the
other?


If you have a spoke in a tensioned wheel that was bent into its
in-situ shape by bending its elbow form its original obtuse angle to
an acute angle by tensioning, then it will have its outer "fibers" of
the elbow at yield stress and it will remain there because the spoke
is additionally tensioned. By stretching that spoke to nearly twice
its static tension by "stress relieving" over-tension, the outside of
the elbow must yield and when released fall back to a lower stress.

assuming you're bending the spoke elbow. if you follow the
manufacturer's instructions you wouldn't do that, and more importantly,
you'd notice that the settled angle of the spoke elbow in the hub hole,
with the "slotting" of the hole that results as the spoke seats itself,
is at about 95 degrees. which is about same as spokes are made with.
that would be a wild coincidence, wouldn't you say? we /are/ assuming
incompetent manufacturers after all...


That example is of the elbow, but it is true of the threads as well.
The elbow, however, is more obvious because outbound spokes all get
plastically deformed in the first tensioning of the wheel regardless
of their prior state.

you're hedging as to exactly which type of residual stress you think
threads have. cast the die jobst, the thread root [the critical part],
do you reckon that's tensile residual or compressive residual?



I think that I have the raw material, some widely available pieces
of stainless steel wire that come with three smooth u-bends from the
factory. It's so cheap that I should be ashamed to steal them in
boxes of a hundred, but the students need to learn the basics of
scrounging.


Being practical about this, I think you will see that you can do this
without a materials laboratory.

not unless you don't understand what you're looking at. to test for the
presence of residual stress, you commonly use a chemical agent that
preferentially attacks material areas with higher [crystal lattice]
energy. to measure magnitude, you commonly use an atomic distance
measuring strategy like x-ray or neutron diffraction. i don't have a
suitable neutron source in my basement. do you?



Any ideas about how to demonstrate over-tensioning stress-relief
using paper-clips?


I like clothes hangers better because they are large enough to clearly
see the results.

all you're seeing is bending. the fact that you've convinced yourself
that you're seeing residual stress simply illustrates just how dangerous
insufficient information or comprehension [not understanding hookes law]
can be.


http://www.sheldonbrown.com/brandt/s...relieving.html

did you read my line-by-line critique of that article? you need to
update it jobst. but don't do it until you've been to the library to
revise your deformation theory please.


Jobst Brandt

On Fri, 31 Dec 2004 00:10:10 -0600, A Muzi
wrote:

In article ,
says...
Hmmm . . . does squeezing stainless steel spokes render them
immortal?
The idea is that when spokes are bent to form the elbow,
potentially fatal stresses are formed at the bend, stresses
that can be relieved by giving the tensioned spoke a good
squeeze.
-snip-
Any ideas about how to demonstrate over-tensioning
stress-relief using paper-clips?


On Fri, 31 Dec 2004 16:33:32 +1100, Bruce Graham
wrote:
Thinking some more about this...
Most of my fatigued spokes happened in a batch, 11 failures ocurred on
two bikes on a 2500 Km tour in France (3 on my wife's bike and 8 on mine
- all drive side rear and all failed around the spoke bend near the
head). The spokes were not DT, Sapim or Wheelsmith and had been stress
relieved by me. It seemed to me that, compared to a DT spoke, the failed
spokes had a sharper transition to the head, maybe causing an extra
stress concentration. I am certain of a few things, - the french word
for spoke is "rayon" and they are not shaped much like a paper clip.

BTW I replaced all the drive side spokes with DT on returning home, and
around 12000 km, the non-drive side no-names started to fail, so I
replaced them too.


In article ,
says...
You mention some of the points of interest.
The spoke angle and the shape of the head flare may have
changed over the years, possibly for the better.
The materials used and the manufacturing process may have
done the same thing
-snip-
And then there's the widespread use of double-butted spokes,
which may reduce spoke failure.
In general, those who believe in spoke squeezing make no
distinction between brands of spokes or whether the spokes
are from 1984 or 2004--the stress relief is what matters,
and it renders spokes immortal.
Those who are skeptical point to various improvements in
what at first seems like brick-simple technology and suggest
that the squeezing affects how the spoke heads fit in the
hub holes.
I waver back and forth, but I'm certain of one thing--the
spokes don't care what either side thinks.

The shape and material of the flange enters into this too.
Simple pierced steel flanges are just hell for spoke
breakage, Phil Wood's flanges being the accepted ideal shape.

Perhaps stressing the spokes as we do has a compound effect
rather than one single mechanism? Relieving stress from
forming, shaping the head/curve to better fit the flange and
also deepening the groove in the flange (resulting in a
broad contact area between flange and spoke rather than
asimple point contact as a steel hub). It may well be that
these effects are insignificantly small _until_ the
momentary high loads we put on the spokes.

Dear Andrew,

Nicely put--not just your point about the hub holes, but
point that everything could contribute.

I take it that your experience with crude flanges versus
better shaped holes (possibly in softer material) suggests
that stress relief alone can't (and shouldn't be expected
to) overcome a hard, badly shaped flange.

Have these simple pierced steel flanges disappeared? Or are
they steel (sorry, couldn't resist it) found on--

Well, on heavy-set bicycles widely available for under $60?

(Mine is sleeping and I don't want to wake it up by tickling
it with a magnet.)

Carl Fogel

On Thu, 30 Dec 2004 23:23:05 -0800, jim beam
wrote:

wrote:
Carl Fogel writes:


Hmmm... does squeezing stainless steel spokes render them immortal?


Maybe you should call it "stretching spokes" rather than squeezing,
since stretch is what is being done. This can be accomplished through
various manual and mechanical means. TREK has a method by which the
wheel is stress relieved in two operations, one side at a time.


The idea is that when spokes are bent to form the elbow, potentially
fatal stresses are formed at the bend, stresses that can be relieved
by giving the tensioned spoke a good squeeze.


Unfortunately, theory and data are controversial.

translation: "i have no proof & have not attempted to quantify".



Not at all. As I have explained in detail (something you could find
with your skills in web searching) bending a steel wire always
involves partial spring-back, which in itself proves there are
residual stresses.

absolutely fundamentally not.

If it were not the case, the wire would either
return to its original alignment or remain in the position into which
it was bent.

jobst, please please please get it into your head that spring-back is
because of the shape of the deformation graph. residual stress has
nothing to do with it. bending has nothing to do with it - you get
spring-back in linear tension samples too - and the reason, as explained
before, is that you only deform material once you're above the hookes
law part of the graph. but deforming enough for yield does not
magically allow the material to yield to zero and bypass hookes law on
the way. is there any way to explain this to you more simply? as long
as you labor under this fundamental misconception, you're always going
to keep shooting wide of the mark.


The partial spring-back results from not all depths of the cross
section having been equally deformed, the central "fiber" not having
changed length while the parts on the outside of the bend were
permanently stretched and those on the inside, compressed. In between
these extremes various amounts of plastic length change occurred.

you do get differing degrees of deformation, but they are not wholly
responsible for spring-back. see above.


I think that if you review this scenario and observe that there is
partial spring-back, that there must be residual stress.

no, no, no. that's an absolutely fundamental misconception.



A test or demonstration would be nice, but testing spokes is
difficult, since even unsqueezed spokes seem to last for millions of
wheel revolutions.


Get a coat hanger and start bending.

you're never going to "see" residual stress just by bending anything.



(Ten thousand miles is about 53 million inches, which in turn is
about two-thirds of a million spins of a 700c wheel--and 500 hours
at 20 mph. Setting up a test for a hundred plain and a hundred
squeezed spokes would be daunting.)


Forget about the miles for a moment and look at the material. As I
mentioned, placing a wire that purposely has been made wavy, in a
tensile testing machine that can tension the wire to its yield stress,
(the stress where the stress strain curve begins to flatten out) will
give a perfectly straight wire when released. This wire has no
stresses or it would spring to some other shape.

rubbish. that wire can have residual stress much as any other. the
questions is the stress orientation & whether it's significant relative
to its application. all you're describing is a material that has
yielded. there's no way you'll ever get a handle on magnitude or
relevance with this kind of hand waving.

It has no reason to
take a shape other than straight because all its parts were stretched
to yield to have their collective "memories" erased. This is possible
with ductile spoke wire because it is made to undergo forming.

fundamental lack of understanding of deformation theory. the effects of
deformation are cumulative in stainless wire. the entire work history
of the material is easily visible under any metallurgical microscope.
you're not erasing anything.



Can anyone suggest a practical test that I can use to convince a
pack of skeptical high-school physics students, one way or the
other?


If you have a spoke in a tensioned wheel that was bent into its
in-situ shape by bending its elbow form its original obtuse angle to
an acute angle by tensioning, then it will have its outer "fibers" of
the elbow at yield stress and it will remain there because the spoke
is additionally tensioned. By stretching that spoke to nearly twice
its static tension by "stress relieving" over-tension, the outside of
the elbow must yield and when released fall back to a lower stress.

assuming you're bending the spoke elbow. if you follow the
manufacturer's instructions you wouldn't do that, and more importantly,
you'd notice that the settled angle of the spoke elbow in the hub hole,
with the "slotting" of the hole that results as the spoke seats itself,
is at about 95 degrees. which is about same as spokes are made with.
that would be a wild coincidence, wouldn't you say? we /are/ assuming
incompetent manufacturers after all...


That example is of the elbow, but it is true of the threads as well.
The elbow, however, is more obvious because outbound spokes all get
plastically deformed in the first tensioning of the wheel regardless
of their prior state.

you're hedging as to exactly which type of residual stress you think
threads have. cast the die jobst, the thread root [the critical part],
do you reckon that's tensile residual or compressive residual?



I think that I have the raw material, some widely available pieces
of stainless steel wire that come with three smooth u-bends from the
factory. It's so cheap that I should be ashamed to steal them in
boxes of a hundred, but the students need to learn the basics of
scrounging.


Being practical about this, I think you will see that you can do this
without a materials laboratory.

not unless you don't understand what you're looking at. to test for the
presence of residual stress, you commonly use a chemical agent that
preferentially attacks material areas with higher [crystal lattice]
energy. to measure magnitude, you commonly use an atomic distance
measuring strategy like x-ray or neutron diffraction. i don't have a
suitable neutron source in my basement. do you?



Any ideas about how to demonstrate over-tensioning stress-relief
using paper-clips?


I like clothes hangers better because they are large enough to clearly
see the results.

all you're seeing is bending. the fact that you've convinced yourself
that you're seeing residual stress simply illustrates just how dangerous
insufficient information or comprehension [not understanding hookes law]
can be.


http://www.sheldonbrown.com/brandt/s...relieving.html

did you read my line-by-line critique of that article? you need to
update it jobst. but don't do it until you've been to the library to
revise your deformation theory please.


Jobst Brandt


Dear Jobst and Jim,

Absolutely!

(How's that for tact?)

Now can either of you suggest a practical way to demonstrate
to a high-school physics class the effect (whatever it is)
of stretching through substantial extra tension a pre-bent
piece of tensioned stainless steel wire, such as a
paper-clip?

That is, can we isolate and magnify the effect so that it
will be clear that both stretched and unstretched pre-bent
stainless steel fatigue at the same rate? Or that one lasts
longer, not necessarily the one that some expect?

I'm not a slave to the paper-clip scheme. Razor blades
occurred to me, since they're much thinner and would
therefore fatigue faster and more easily, but they're not
bent, and they're not under tension.

Music wire has been mentioned in earlier threads, but it's
tricky in that one strand is wrapped around the other.

Possibly some sort of solid guy-wires whose ends are wrapped
around a curve? I'm not sure if those are stainless steel.

Surgical wires?

Orthodontic wiring?

What we're looking for is a simple way to stress a thin
stainless steel wire fast enough that it will break within a
reasonable time. Then we can time things and find out what
the results are of stretching.

Carl Fogel