removing broken spoke nipples

  • Thread starter Bellsouth Ijit 2.0
  • Start date



Lateral load CAN increase spoke tension but seldom does. Typically
when leaning the bicycle while climbing or sprinting, standing, even
with large lean angles, spokes are slackened on the high side while
tension does not increase on the low side because it is these spokes
that are carrying the vertical load and are naturally slackened.

The hazard in this is that as the high side spokes become completely
slack, lateral wheel stiffness is cut in half and can easily cause
collapse... and with fewer spokes even more so. Lateral bending
strength of deep aero rims, that can bridge large spoke-to-spoke
distances for vertical loads, is not significantly higher than
rectangular cross section rims, their width being the same.

This all boils down to that spokes in most loading are acting in
tension and that their tension changes behave like compression
elements until the preload is exceeded. At that point they no longer
contribute to the strength of the wheel.

Jobst Brandt
 
> regarding your questions, jobst cites springback as being evidence
> of residual stress. that is incorrect. if he wants to cite
> anything, he should cite deformation. springback is simply
> elasticity.


With all the misquotes flying around let me restate the point.

Partial spring-back is proof of residual stress. When a cross section
is bent, outer fibers exceed yield first, their elongation being given
by their distance from the neutral axis. No yield occurs at the
neutral axis and between is a zone where yield stress is reached.

As forming force is relaxed, the cross section springs back from this
forming action, the portions that did not reach yield wanting to
return to the original position and those that yielded wanting to stay
at the formed position, leaving the entire cross section in a range of
stress from compression to tension, the neutral axis being only a
theoretical plane that doesn't change length.

That is residual stress from cold forming to which I refer.

Jobst Brandt
 
L

Luns Tee

Guest
In article <[email protected]>,
<[email protected]> wrote:
>> regarding your questions, jobst cites springback as being evidence
>> of residual stress. that is incorrect. if he wants to cite
>> anything, he should cite deformation. springback is simply
>> elasticity.

>
>With all the misquotes flying around let me restate the point.
>
>Partial spring-back is proof of residual stress.


I expect that restating just this (or the arguments that
followed) will do little to stop the misinterpretation.

The proof of residual stress is in spring-back being partial
rather than complete, with complete spring back meaning the material
returns to no stress. The contrast is of partial versus COMPLETE
spring-back, rather than of partial versus NO spring-back.

The former metallurgist seems to believe that any mention of
'partial spring-back' is in contrast there being no spring-back. This
argument makes no sense whatsoever, and is not what's been put forth
aside from his own misinterpretation and subsequent misattribution of
things.

-Luns
 
M

Michael Press

Guest
In article <[email protected]>,
"Andrew Lee" <whatsupandrewathotmaildotcom> wrote:

> jim beam wrote:
> >> "...These peak stresses can be relieved by momentarily increasing
> >> spoke tension (and stress), so that the high stress points of the
> >> spoke yield and plastically deform with a permanent set. When the
> >> stress relief force is relaxed these areas cannot spring back having,
> >> in effect, lost their memory, and drop to the average stress of the
> >> spoke."

> >
> > yet more confused misconception. "cannot spring back" is fundamentally
> > incorrect - it implied that metals yield to zero - they don't. and there
> > is no "memory" in stainless steels. elasticity is not memory.

>
> I pointed the same thing out a few weeks ago, but again, you have really
> poor reading comprehension and logic, and you can't even interpret the most
> basic stress-strain graphs. Maybe that's why are you're an EX-metallurgist?
> Look at your own drawing in photo number 3 here:
>
> http://www.flickr.com/photos/[email protected]/327752060/
>
> See how that yielded metal goes back down along the Hooke's Law line? Where
> does it end up? It doesn't end up at the origin. It's in a parallel track
> because there is plastic deformation. It should be blatantly obvious to a
> materials person that that separation cannot be closed by relaxing the
> stress relief force. Thus, Jobst can accurately say that those high stress
> areas cannot spring back. In the context of that passage, it is clear that
> "spring back" means that the material cannot reach the initial position, not
> that the material does not obey Hooke's Law. I'll bet even non-engineers
> and materials people can interpret what Jobst wrote correctly. What does
> that say about your reading comprehension and understanding of materials?
> Or is it a willful misreading?
>
> Here's my drawing:
>
> http://img215.imageshack.us/img215/1736/img3480wr8.jpg
>
> Do you agree that stress within a spoke is not uniform? In my drawing,
> Point 1 represents the position in the graph of the material at highest
> stress within a spoke, such as the outside of the spoke elbow. Area 4 is
> the average stress of the other regions of the spoke that typically don't
> break from fatigue. Point 1 is more likely to break from fatigue because it
> is at a higher percentage of yield stress than Area 4. If the material at
> Point 1 can be made to relax to a lower stress level, the service life of
> the spoke will improve. It does not matter if 304 stainless has an actual
> endurance limit or not. (Modern stainless spokes have demonstrated
> capability to be considered lifetime spokes, if not infinite life spokes).
>
> During stress relieving, Point 1 is brought to yield. When the spoke is
> relaxed it passes through Point 2, a position of equal stress to Point 1's
> initial stress. It doesn't stop there because it has yielded and the
> dimension of the yielded region is larger in the direction of the stress.
> The material that was initially at Point 1 on the stress-strain graph
> relaxes to approximately Point 3 after stress relief because it can be
> assumed that the bulk of the spoke surrounding the high stress region did
> not yield. During stress relieving, Area 4 also travels up the Hooke's law
> line, "following" Point 1, but since it follows at a lower stress level, it
> doesn't reach yield. Upon relaxation of the stress relief force, Area 4
> returns down the initial Hooke's Law line back to it's initial position (or
> close enough for you nitpickers) because the stress relief force only yields
> a small portion of cross section of the spoke - the spoke does not
> measureably lengthen from the stress relief procedure.
>
> The horizontal distance between Point 1 and Point 2 (marked in red in my
> drawing) is what can't be closed by the relaxing the stress relief force.
> After stress relief, you can reset the origin of yielded return-track
> Hooke's Law back to zero. Thus, formerly high stress region will be mapped
> out somewhere near or within Area 4. Maybe at the top of Area 4, or even a
> bit higher, but in any case, the stress in the region will be below what it
> was at Point 1 before stress relief.
>
> By the way, I have also have a materials background (a B.S. in Materials
> Engineering from way back, though I don't work in the field - but neither do
> you). You occasionally provide some good information regarding materials,
> but more often than not, they are irreverant to the topic, diversions
> really. You get many basic engineering concepts wrong and are so delusional
> that you call others out when you are the one who usually has it wrong. And
> you pick nicks (Jobst helps by making absolutist statements) and miss the
> main points. (Such as brinelling vs. fretting in headsets... so what if you
> can brinell a lousy headset? They generally fail by frettting.)


Thanks for this. Speaking of picking nits, a nit is the egg of
Pediculus humanus capitis, the head louse.
 
D

[email protected]oo.com

Guest
so the last point made, is an end goal of stress relief.:the activity
of stress relieving a bicycle wheel is an activity of which 'stress'
relief in but one component?

can we also conclude: the importance stress relief the activity rises
as spoke tension rises toward the efficient maximal tensions for the
particular wheel.
 
B

Bill Sornson

Guest
Michael Press wrote:

> Speaking of picking nits, a nit is the egg of
> Pediculus humanus capitis, the head louse.


There are many candidates for Head Louse around here.

Bill "jus' sayin'" S.
 
J

jim beam

Guest
Luns Tee wrote:
> In article <[email protected]>,
> <[email protected]> wrote:
>>> regarding your questions, jobst cites springback as being evidence
>>> of residual stress. that is incorrect. if he wants to cite
>>> anything, he should cite deformation. springback is simply
>>> elasticity.

>> With all the misquotes flying around let me restate the point.
>>
>> Partial spring-back is proof of residual stress.

>
> I expect that restating just this (or the arguments that
> followed) will do little to stop the misinterpretation.
>
> The proof of residual stress is in spring-back being partial
> rather than complete, with complete spring back meaning the material
> returns to no stress. The contrast is of partial versus COMPLETE
> spring-back, rather than of partial versus NO spring-back.


jobst is on record as saying that if there were no residual stress,
metal would deform with no springback, like "dragging a brick". no
engineering material has that behavior.

>
> The former metallurgist seems to believe that any mention of
> 'partial spring-back' is in contrast there being no spring-back.


there is no situation where there is "no spring-back". that would mean
hookes law works on pre-deformation extension only, which is untrue.

> This
> argument makes no sense whatsoever, and is not what's been put forth
> aside from his own misinterpretation and subsequent misattribution of
> things.


what's the misinterpretation now?
 
J

jim beam

Guest
[email protected] wrote:
> Lateral load CAN increase spoke tension but seldom does. Typically
> when leaning the bicycle while climbing or sprinting, standing, even
> with large lean angles, spokes are slackened on the high side while
> tension does not increase on the low side because it is these spokes
> that are carrying the vertical load and are naturally slackened.
>
> The hazard in this is that as the high side spokes become completely
> slack, lateral wheel stiffness is cut in half


no, the lateral bracing /offered by spoke support/ is cut in half. the
rim's own stiffness is still significant, so while overall stiffness is
/reduced/, it's not "cut in half".

> and can easily cause
> collapse...


not unless spoke tension is excessive. the only rim i've ever collapsed
was one with excess tension. my "205lbs" rim, *unspoked*, will support
my full body weight, let alone slack spoked.

> and with fewer spokes even more so. Lateral bending
> strength of deep aero rims, that can bridge large spoke-to-spoke
> distances for vertical loads, is not significantly higher than
> rectangular cross section rims, their width being the same.


that's not true either. deeper rims alone are stiffer. measure them.
for built wheels using deep rims, using fewer spokes merely reduces
overall wheel stiffness to that of a higher spoked shallower rim wheel.

>
> This all boils down to that spokes in most loading are acting in
> tension and that their tension changes behave like compression
> elements until the preload is exceeded. At that point they no longer
> contribute to the strength of the wheel.
>
> Jobst Brandt
 
J

jim beam

Guest
[email protected] wrote:
>> regarding your questions, jobst cites springback as being evidence
>> of residual stress. that is incorrect. if he wants to cite
>> anything, he should cite deformation. springback is simply
>> elasticity.

>
> With all the misquotes flying around let me restate the point.
>
> Partial spring-back is proof of residual stress.


ok, that's a much better attempt but still imprecise. [using the word
"partial" is a big step forward though.] /partial/ springback only
indirectly implies residual stress. it directly implies plastic
deformation, and the deformation presumes residual stress.

> When a cross section
> is bent, outer fibers exceed yield first, their elongation being given
> by their distance from the neutral axis. No yield occurs at the
> neutral axis and between is a zone where yield stress is reached.
>
> As forming force is relaxed, the cross section springs back from this
> forming action, the portions that did not reach yield wanting to
> return to the original position and those that yielded wanting to stay
> at the formed position, leaving the entire cross section in a range of
> stress from compression to tension, the neutral axis being only a
> theoretical plane that doesn't change length.


which is all a nice undergrad theoretical diversion. but the reality is
that fatigue doesn't nucleate at the regions with the highest residual
stress - it nucleates at the outer edges which have the least residual
stress. therefore chasing residual stress is a good deal less important
than chasing the factors that /do/ affect nucleation at those points,
namely surface finish and material quality.

>
> That is residual stress from cold forming to which I refer.


and it's still not as much of a problem as you seem to think it is - no
cold worked, cold formed component could be used in any form of dynamic
loading if that were the case. chemicals and residual stress are
another matter.
 
B

Ben C

Guest
On 2007-03-12, [email protected] <[email protected]> wrote:
> so the last point made, is an end goal of stress relief.:the activity
> of stress relieving a bicycle wheel is an activity of which 'stress'
> relief in but one component?


I think so. The other components are letting out the windup ("pinging")
and possibly seating the spokes into the flange, although this second
one is more contentious. The argument is that the spoke will sink into
the soft flange very early in the process, and so by the time you're
stress-relieving, the flange will have already deformed and be providing
a firm support for the spoke.

> can we also conclude: the importance stress relief the activity rises
> as spoke tension rises toward the efficient maximal tensions for the
> particular wheel.


What do you mean by the efficient maximal tension? In theory none of the
spokes ever get tighter in use than they are sitting in the truing
stand. In practice some of them might when you climb hills vigorously
for example.

How much force for stress relief? I don't know. Too little and you'll
presumably only stress relieve those regions very close to yield, but
not some other regions further from yield but still close enough to
reduce fatigue life by a lot. Too much, and I would have thought you'd
risk buckling the rim

Spoke squeezing doesn't raise the tension by as much as you might think,
because the rim itself deforms as you do it. Carl Fogel did some
measurements and explained this many times but Google seems to be
playing up again and I can't find the posts.
 
A

Andrew Lee

Guest
Ben C wrote:
> On 2007-03-12, Andrew Lee <> wrote:
> [...]
>> Here's my drawing:
>>
>> http://img215.imageshack.us/img215/1736/img3480wr8.jpg

> [...]
>> During stress relieving, Point 1 is brought to yield. When the spoke is
>> relaxed it passes through Point 2, a position of equal stress to Point
>> 1's
>> initial stress. It doesn't stop there because it has yielded and the
>> dimension of the yielded region is larger in the direction of the stress.

>
> Is this something like "Poisson's ratio"-- basically when you pull
> things they stretch out long and thin?


Well, my point is that because the region has yielded, it has by definition
permanently deformed and is now longer. That the region has also gotten a
bit skinnier is true, but not relevant to the point that I'm making.

> So to clarify, could it be said that the reason Point 1 ends up
> somewhere around Point 3 is because that part of the spoke has got a
> little bit longer, so ends up held under a little bit less tension?
> That's how it finds its way to a lower point on the stress axis.


Yes.

> But in that case I might expect it to find it somewhere on the line
> between 3 and 2-- under a bit less stress, because it's strained a bit,
> so I think I haven't understood.


Tension in spokes are about the same pre- and post- stress relief, so the
yielded section must be a small fraction of the spoke cross section.

Imagine the high stress region of the spoke prior to stress relief.
According to the stress-strain graph, it is under more strain than the rest
of the spoke. If you could cut that part out of the spoke, and then loosen
the tension in the spoke, it would shorten more than the rest of the spoke.
Put it back into the hole that it came from with the spoke loose. It would
fit in the hole loosely (in the dimension aligned with the spoke anyway).

Now imagine the border of the high stress region (but don't cut it) in the
tensioned but pre-stress relief spoke. It has a certain dimension. After
stress relief it will pretty much remain the same dimension as the initial
pre-stress relieving dimension because outside the border is material that
starts at lower tension and never reaches yield. During stress relief, only
the higher stress material within the border yields, so it is the high
stress part of the spoke that does the conforming to the border dimension,
not the bulk of the spoke outside the border. This border dimension (the
dimension aligned with the spoke) corresponds to the strain at Points 1 and
3.

In reality, you have continuous not step differences in stress within the
spoke, but I think this simplification should hold up OK.

>
>> The material that was initially at Point 1 on the stress-strain graph
>> relaxes to approximately Point 3 after stress relief because it can be
>> assumed that the bulk of the spoke surrounding the high stress region did
>> not yield.

>
> It's this part that I'm not following.


I hope this line of reasoning and visualization helps.
 
A

Andrew Lee

Guest
jim beam wrote:
> Andrew Lee wrote:
>> During stress relieving, Point 1 is brought to yield. When the spoke is
>> relaxed it passes through Point 2, a position of equal stress to Point
>> 1's initial stress. It doesn't stop there because it has yielded and the
>> dimension of the yielded region is larger in the direction of the stress.

>
> no, points 1 & 2 are equal stress.


I didn't say otherwise.

>> The material that was initially at Point 1 on the stress-strain graph
>> relaxes to approximately Point 3 after stress relief because it can be
>> assumed that the bulk of the spoke surrounding the high stress region did
>> not yield. During stress relieving, Area 4 also travels up the Hooke's
>> law line, "following" Point 1, but since it follows at a lower stress
>> level, it doesn't reach yield. Upon relaxation of the stress relief
>> force, Area 4 returns down the initial Hooke's Law line back to it's
>> initial position (or close enough for you nitpickers) because the stress
>> relief force only yields a small portion of cross section of the spoke -
>> the spoke does not measureably lengthen from the stress relief procedure.


> ok, let's be clear about this. for mechanical stress relief to work,
> there are conditions that need to be met, i.e. it's done right after
> initial forming, not after aging. in addition, it results from yielding.
> if there's no yielding, there's no stress relief. yielding requires
> permanent deformation which is therefore measurable.


I'm talking about practical measurement. A small part of the spoke within
the cross section of the elbow yields. This is not something that you would
observe by measuring the length of the entire spoke, which was clearly
stated in my point above. If only you knew how to read... With the proper
tools, I agree it might be possible to measure the small yielded portion.

>> After stress relief, you can reset the origin of yielded return-track
>> Hooke's Law back to zero.

>
> you can set stress back to zero, but not strain - it's yielded.


Of course it it yielded. The strain is non-zero looking back at the
history. I was just resetting the reference point for looking at parts
within the spoke for a forward view. If you came across the spoke and
looked at the part of the spoke that I'm talking about without prior
knowledge of what was done to it, it is just part of the spoke. If you cut
out that tiny section, relaxing the tension, there is no stress or strain on
that piece. It would be silly to call it anything other than zero in
reference to whatever is done to that piece AFTERwards. Do you call the
initial strain on a spoke non-zero because at some point in it's formation
it underwent yielding?

>> Thus, formerly high stress region will be mapped out somewhere near or
>> within Area 4.

>
> area 3, not 4. it's yielded.


I can't catch all the mistakes in a newsgroup posting. I'm should have said
that I'm talking just stress... Point 3 is within the same range of stress
as Area 4.

> with respect andrew, you're showing some confusion on your theory basics.
> it's great to have another materials person onboard, but we need to get
> some clarity here.


I think I covered all your points, at least the ones directed towards me.
I'm not the one confused...
 
J

jim beam

Guest
Andrew Lee wrote:
> jim beam wrote:
>> Andrew Lee wrote:
>>> During stress relieving, Point 1 is brought to yield. When the spoke is
>>> relaxed it passes through Point 2, a position of equal stress to Point
>>> 1's initial stress. It doesn't stop there because it has yielded and the
>>> dimension of the yielded region is larger in the direction of the stress.

>> no, points 1 & 2 are equal stress.

>
> I didn't say otherwise.
>
>>> The material that was initially at Point 1 on the stress-strain graph
>>> relaxes to approximately Point 3 after stress relief because it can be
>>> assumed that the bulk of the spoke surrounding the high stress region did
>>> not yield. During stress relieving, Area 4 also travels up the Hooke's
>>> law line, "following" Point 1, but since it follows at a lower stress
>>> level, it doesn't reach yield. Upon relaxation of the stress relief
>>> force, Area 4 returns down the initial Hooke's Law line back to it's
>>> initial position (or close enough for you nitpickers) because the stress
>>> relief force only yields a small portion of cross section of the spoke -
>>> the spoke does not measureably lengthen from the stress relief procedure.

>
>> ok, let's be clear about this. for mechanical stress relief to work,
>> there are conditions that need to be met, i.e. it's done right after
>> initial forming, not after aging. in addition, it results from yielding.
>> if there's no yielding, there's no stress relief. yielding requires
>> permanent deformation which is therefore measurable.

>
> I'm talking about practical measurement. A small part of the spoke within
> the cross section of the elbow yields.


that sounds like the jobstian dodge - "you can't see it, but trust me,
it's there because it fits my theory".

> This is not something that you would
> observe by measuring the length of the entire spoke, which was clearly
> stated in my point above. If only you knew how to read...


that's a herring or a misunderstanding. i said nothing about yielding
the entire spoke.

> With the proper
> tools, I agree it might be possible to measure the small yielded portion.


which is what should be done if someone is trying to present a theory.

>
>>> After stress relief, you can reset the origin of yielded return-track
>>> Hooke's Law back to zero.

>> you can set stress back to zero, but not strain - it's yielded.

>
> Of course it it yielded. The strain is non-zero looking back at the
> history. I was just resetting the reference point for looking at parts
> within the spoke for a forward view. If you came across the spoke and
> looked at the part of the spoke that I'm talking about without prior
> knowledge of what was done to it, it is just part of the spoke. If you cut
> out that tiny section, relaxing the tension, there is no stress or strain on
> that piece. It would be silly to call it anything other than zero in
> reference to whatever is done to that piece AFTERwards. Do you call the
> initial strain on a spoke non-zero because at some point in it's formation
> it underwent yielding?


i don't think you understood the context. for each separate experiment,
you can of course re-zero, but /within/ a single experiment, you cannot.

>
>>> Thus, formerly high stress region will be mapped out somewhere near or
>>> within Area 4.

>> area 3, not 4. it's yielded.

>
> I can't catch all the mistakes in a newsgroup posting. I'm should have said
> that I'm talking just stress... Point 3 is within the same range of stress
> as Area 4.


well, if you're trying to make a point...

>
>> with respect andrew, you're showing some confusion on your theory basics.
>> it's great to have another materials person onboard, but we need to get
>> some clarity here.

>
> I think I covered all your points, at least the ones directed towards me.
> I'm not the one confused...
>
>


do you care to address the issue of "stress relief" as a function of aging?

i'd also be interested in your thoughts on observed fatigue initiation
points in relation to residual stress locations.
 
P

Peter Cole

Guest
jim beam wrote:
> [email protected] wrote:


>> With all the misquotes flying around let me restate the point.
>>
>> Partial spring-back is proof of residual stress.

>
> ok, that's a much better attempt but still imprecise. [using the word
> "partial" is a big step forward though.]


Really? After all this time (years?), you were laboring under the
misunderstanding that Jobst meant *complete* spring back?


> /partial/ springback only
> indirectly implies residual stress. it directly implies plastic
> deformation, and the deformation presumes residual stress.


No, it reveals the presence of both deformation and elastic stress. It's
the combination of those two things that generates residual stress.

If the piece sprang back fully, there would be no deformation.

If the piece didn't spring back at all, there would be no elastic stress.

Since it sprang back partially, there must be both, hence there must be
residual stress.

I don't know how you can critique stress relief methods if you don't
grasp residual stress.
 
B

Ben C

Guest
On 2007-03-13, Andrew Lee <> wrote:
> Ben C wrote:
>> On 2007-03-12, Andrew Lee <> wrote:
>> [...]
>>> Here's my drawing:
>>>
>>> http://img215.imageshack.us/img215/1736/img3480wr8.jpg

>> [...]
>>> During stress relieving, Point 1 is brought to yield. When the spoke is
>>> relaxed it passes through Point 2, a position of equal stress to Point
>>> 1's
>>> initial stress. It doesn't stop there because it has yielded and the
>>> dimension of the yielded region is larger in the direction of the stress.

>>
>> Is this something like "Poisson's ratio"-- basically when you pull
>> things they stretch out long and thin?

>
> Well, my point is that because the region has yielded, it has by definition
> permanently deformed and is now longer. That the region has also gotten a
> bit skinnier is true, but not relevant to the point that I'm making.
>
>> So to clarify, could it be said that the reason Point 1 ends up
>> somewhere around Point 3 is because that part of the spoke has got a
>> little bit longer, so ends up held under a little bit less tension?
>> That's how it finds its way to a lower point on the stress axis.

>
> Yes.


Point 3 is at the same strain as Point 1, but less stress (because we
had a bit of permanent deformation).

>> But in that case I might expect it to find it somewhere on the line
>> between 3 and 2-- under a bit less stress, because it's strained a bit,
>> so I think I haven't understood.

>
> Tension in spokes are about the same pre- and post- stress relief, so the
> yielded section must be a small fraction of the spoke cross section.
>
> Imagine the high stress region of the spoke prior to stress relief.
> According to the stress-strain graph, it is under more strain than the rest
> of the spoke. If you could cut that part out of the spoke, and then loosen
> the tension in the spoke, it would shorten more than the rest of the spoke.
> Put it back into the hole that it came from with the spoke loose. It would
> fit in the hole loosely (in the dimension aligned with the spoke anyway).
>
> Now imagine the border of the high stress region (but don't cut it) in the
> tensioned but pre-stress relief spoke. It has a certain dimension. After
> stress relief it will pretty much remain the same dimension as the initial
> pre-stress relieving dimension because outside the border is material that
> starts at lower tension and never reaches yield. During stress relief, only
> the higher stress material within the border yields, so it is the high
> stress part of the spoke that does the conforming to the border dimension,
> not the bulk of the spoke outside the border. This border dimension (the
> dimension aligned with the spoke) corresponds to the strain at Points 1 and
> 3.


I think I get the idea. Point 3 is at nearly the same point on the
strain axis as Point 1 because the high-stress region is constrained to
the same dimensions as the surrounding material which didn't yield. But
it's at a lower stress because it did yield.

If we think of the wire as a bundle of fibres, of which the bit that
yielded is one fibre in the middle, that fibre was initially under more
tension than the others, but was extended until it yielded, and then
relaxed again until it took on close to exactly the length it had
before. In some regions perhaps it might even end up held in slight
compression by the surrounding fibres, the detail gets quite complex.
 
J

jim beam

Guest
Peter Cole wrote:
> jim beam wrote:
>> [email protected] wrote:

>
>>> With all the misquotes flying around let me restate the point.
>>>
>>> Partial spring-back is proof of residual stress.

>>
>> ok, that's a much better attempt but still imprecise. [using the word
>> "partial" is a big step forward though.]

>
> Really? After all this time (years?), you were laboring under the
> misunderstanding that Jobst meant *complete* spring back?


eh? i'm commenting because it's the first time jobst's bothered to add
useful context!

>
>
>> /partial/ springback only indirectly implies residual stress. it
>> directly implies plastic deformation, and the deformation presumes
>> residual stress.

>
> No, it reveals the presence of both deformation and elastic stress. It's
> the combination of those two things that generates residual stress.


1. you need to re-read what i've repeated many times before about
elasticity and retain in context with "it directly implies plastic
deformation, and the deformation presumes residual stress."
2. even if we run with the presumption, we /still/ don't have fatigue
nucleating where residual stress would be highest!

>
> If the piece sprang back fully, there would be no deformation.


duh. i said that before.

>
> If the piece didn't spring back at all, there would be no elastic stress.


duh. but this doesn't happen. i said that before too.

>
> Since it sprang back partially, there must be both, hence there must be
> residual stress.


that's the presumption. [repetition]

>
> I don't know how you can critique stress relief methods if you don't
> grasp residual stress.


i don't know how you can critique something you've not read properly.

and you haven't addressed that central omission in this whole "residual
stress" charade - that of fatigue nucleation /not/ occurring in regions
of high residual stress!
 
L

Luns Tee

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

>>
>>>> With all the misquotes flying around let me restate the point.
>>>>
>>>> Partial spring-back is proof of residual stress.
>>>
>>> ok, that's a much better attempt but still imprecise. [using the word
>>> "partial" is a big step forward though.]

>>
>> Really? After all this time (years?), you were laboring under the
>> misunderstanding that Jobst meant *complete* spring back?

>
>eh? i'm commenting because it's the first time jobst's bothered to add
>useful context!


You have a selective memory. If the word 'partial' is a step
forward, then it's a step for you alone, though that said, I'm glad to
see you catching up with reality. It's been there for years, even in
postings that you've yourself responded to, yet up until now, you've
been blind to it and omit it time after time in your own
representations of what's said.


Example from December '06:
in article <[email protected]>, jb quotes JB:

JB> Elasticity is evident in that spokes, when deformed, spring back
JB> partially.
^^^^^^^^^

JB> Partial spring-back shows there is a conflict between different depths
^^^^^^^
JB> of the spoke wire, some in compression, some in tension, trying to
JB> reach a neutral position.




From Jan '05:
in article <[email protected]>, jb quotes JB:

jb>well, here's jobst's own words from earlier in this thread:

"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."
^^^^^^^



Or, going further back to Jun '04:
in article <[email protected]>, jb quotes JB:

JB> For instance,
JB> if you bend a spoke and get only partial spring back, do you agree
^^^^^^^
JB> that this shows residual stress where the outer fibers went beyond
JB> yield while the inner ones that did not and try to return to the
JB> original shape while the outer ones resist. Is that not residual
JB> stress, and if so why do you believe it is not additive to a
JB> subsequent tensile load on the installed spoke?


The correct context has been there FOR YEARS. That said, I am
glad that you at least acknowledge it now.

-Luns
 
J

jim beam

Guest
Luns Tee wrote:
> In article <yK6dnYaLF4hH-mrYn[email protected]>,
> jim beam <[email protected]> wrote:
>> Peter Cole wrote:
>>> jim beam wrote:
>>>> [email protected] wrote:
>>>>> With all the misquotes flying around let me restate the point.
>>>>>
>>>>> Partial spring-back is proof of residual stress.
>>>> ok, that's a much better attempt but still imprecise. [using the word
>>>> "partial" is a big step forward though.]
>>> Really? After all this time (years?), you were laboring under the
>>> misunderstanding that Jobst meant *complete* spring back?

>> eh? i'm commenting because it's the first time jobst's bothered to add
>> useful context!

>
> You have a selective memory. If the word 'partial' is a step
> forward, then it's a step for you alone, though that said, I'm glad to
> see you catching up with reality. It's been there for years, even in
> postings that you've yourself responded to, yet up until now, you've
> been blind to it and omit it time after time in your own
> representations of what's said.
>
>
> Example from December '06:
> in article <[email protected]>, jb quotes JB:
>
> JB> Elasticity is evident in that spokes, when deformed, spring back
> JB> partially.
> ^^^^^^^^^
>
> JB> Partial spring-back shows there is a conflict between different depths
> ^^^^^^^
> JB> of the spoke wire, some in compression, some in tension, trying to
> JB> reach a neutral position.
>
>
>
>
> From Jan '05:
> in article <[email protected]>, jb quotes JB:
>
> jb>well, here's jobst's own words from earlier in this thread:
>
> "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."
> ^^^^^^^
>
>
>
> Or, going further back to Jun '04:
> in article <[email protected]>, jb quotes JB:
>
> JB> For instance,
> JB> if you bend a spoke and get only partial spring back, do you agree
> ^^^^^^^
> JB> that this shows residual stress where the outer fibers went beyond
> JB> yield while the inner ones that did not and try to return to the
> JB> original shape while the outer ones resist. Is that not residual
> JB> stress, and if so why do you believe it is not additive to a
> JB> subsequent tensile load on the installed spoke?
>
>
> The correct context has been there FOR YEARS. That said, I am
> glad that you at least acknowledge it now.
>
> -Luns


but dude, this whole springback thing is "confused" reasoning - that's
why it's necessary to debate it. as stated before, springback is
elasticity. "partial" springback is elasticity plus deformation. it's
the _deformation_ that "implies" residual stress, _not_ the springback.
indeed "springback" shouldn't even be in any such argument as it's
/not/ "evidence" of residual stress. and deformation only is by assumption.
 
P

Peter Cole

Guest
jim beam wrote:
> Peter Cole wrote:
>> jim beam wrote:
>>> [email protected] wrote:

>>
>>>> With all the misquotes flying around let me restate the point.
>>>>
>>>> Partial spring-back is proof of residual stress.
>>>
>>> ok, that's a much better attempt but still imprecise. [using the
>>> word "partial" is a big step forward though.]

>>
>> Really? After all this time (years?), you were laboring under the
>> misunderstanding that Jobst meant *complete* spring back?

>
> eh? i'm commenting because it's the first time jobst's bothered to add
> useful context!


That's BS and you know it.


>>> /partial/ springback only indirectly implies residual stress. it
>>> directly implies plastic deformation, and the deformation presumes
>>> residual stress.

>>
>> No, it reveals the presence of both deformation and elastic stress.
>> It's the combination of those two things that generates residual stress.

>
> 1. you need to re-read what i've repeated many times before about
> elasticity and retain in context with "it directly implies plastic
> deformation, and the deformation presumes residual stress."


What gibberish.


>> Since it sprang back partially, there must be both, hence there must
>> be residual stress.

>
> that's the presumption. [repetition]


No, it's the proof.

This is because we know the deformation is non-uniform across the cross
section because the spoke was bent, and that is a characteristic of
bending deformation.

> and you haven't addressed that central omission in this whole "residual
> stress" charade - that of fatigue nucleation /not/ occurring in regions
> of high residual stress!


I haven't in this thread, because it wasn't the theme, but I have (many
times) in the past. If you don't correct the spoke angle, the static
stress from bending outbound spokes will put the outside skin of the
elbow in tension. If your spokes crack there it means that the static
stress is larger than the residual. The only rational way to get lowest
stress in spokes is to correct the spoke line, then relieve the residual.
 
J

jim beam

Guest
Peter Cole wrote:
> jim beam wrote:
>> Peter Cole wrote:
>>> jim beam wrote:
>>>> [email protected] wrote:
>>>
>>>>> With all the misquotes flying around let me restate the point.
>>>>>
>>>>> Partial spring-back is proof of residual stress.
>>>>
>>>> ok, that's a much better attempt but still imprecise. [using the
>>>> word "partial" is a big step forward though.]
>>>
>>> Really? After all this time (years?), you were laboring under the
>>> misunderstanding that Jobst meant *complete* spring back?

>>
>> eh? i'm commenting because it's the first time jobst's bothered to
>> add useful context!

>
> That's BS and you know it.


really? is that b.s. like presuming to lecture on something you don't
adequately understand, or b.s. you're ******?

>
>
>>>> /partial/ springback only indirectly implies residual stress. it
>>>> directly implies plastic deformation, and the deformation presumes
>>>> residual stress.
>>>
>>> No, it reveals the presence of both deformation and elastic stress.
>>> It's the combination of those two things that generates residual stress.

>>
>> 1. you need to re-read what i've repeated many times before about
>> elasticity and retain in context with "it directly implies plastic
>> deformation, and the deformation presumes residual stress."

>
> What gibberish.
>
>
>>> Since it sprang back partially, there must be both, hence there must
>>> be residual stress.

>>
>> that's the presumption. [repetition]

>
> No, it's the proof.


so where's the x-ray or neutron diffraction? without that, it's
presumption. there's no numbers or profiles on this stuff.

>
> This is because we know the deformation is non-uniform across the cross
> section because the spoke was bent, and that is a characteristic of
> bending deformation.


and that's still presumption that it's a problem! if it were such a big
deal, no cold worked metal would be usable in any form of dynamic loading.

>
>> and you haven't addressed that central omission in this whole
>> "residual stress" charade - that of fatigue nucleation /not/ occurring
>> in regions of high residual stress!

>
> I haven't in this thread, because it wasn't the theme, but I have (many
> times) in the past. If you don't correct the spoke angle, the static
> stress from bending outbound spokes will put the outside skin of the
> elbow in tension.


that's loading tension, not residual stress!!!! unless you don't load,
you'll never remove it!

> If your spokes crack there it means that the static
> stress is larger than the residual. The only rational way to get lowest
> stress in spokes is to correct the spoke line, then relieve the residual.


so worry about applied stress, not residual!!! that's what
manufacturers do.