A Cycling & bikes forum. CycleBanter.com

Go Back   Home » CycleBanter.com forum » rec.bicycles » Techniques
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Residual stress, fatigue and stress relief



 
 
Thread Tools Display Modes
  #21  
Old April 23rd 08, 11:37 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 225
Default Residual stress, fatigue and stress relief

On Apr 23, 4:11 pm, "Leo Lichtman"
wrote:
wrote:

This is because residual compression on one side of the bend is residual tension on the other, (clip)

^^^^^^^^^^^^^^^^
No. You are evidently applying the equations for bending stress, with
symmetry about the neutral axis. If there are tensile stresses present, the
bending stresses add on one side and subtract on the other. Then, if the
higher value (either tensile or compressive) passes the yield point, the
symmetry is gone, and the residual stress could have an effect on fatigue
afterward.


I'm applying the equations for static equilibrium. If some part of
your spoke is under residual compression, the material around that
zone must be in tension to keep it there.
Ads
  #22  
Old April 23rd 08, 11:44 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 225
Default Residual stress, fatigue and stress relief

On Apr 23, 4:20 pm, Peter Cole wrote:
wrote:
This is because residual compression on one side of the bend is
residual tension on the other, and trying to produce just the right
amount of residual stress in a spoke by hand is like aligning
microscope lenses with a framing hammer. It works great as long as
you never look into the eye piece.


It doesn't matter for the overload method of stress relief. That's what
makes it such a useful technique.


So the magnitude doesn't matter? Proof loading of things like gun
barrels is done to a fairly precise stress level. To think that
without doing any calculations on spoke yielding and cracking or using
any instrumentation in application other than your bare hands will
achieve this level of precision is absurd. I'm willing to believe
that residual stresses may improve fatigue life under the right proof
loading conditions, but I will not accept that the average wheel
builder (myself included) has taken the time to figure out exactly
what those conditions are and ensured that they're being followed.
  #23  
Old April 23rd 08, 11:48 PM posted to rec.bicycles.tech
Michael Press
external usenet poster
 
Posts: 9,202
Default Residual stress, fatigue and stress relief

In article ,
daveornee wrote:

Peter Cole Wrote:
Ben C wrote:

The controversy here is not that brief overload relieves stress or

that
stress relief improves fatigue life.


Not true.

It's the claim that this is known
to be _the significant beneficial effect_ of spoke-squeezing, the

Mavic
method, and other "stabilization" practices that people do when
wheel-building.


Not true. The specific claim (originally by Jobst) is that spoke
squeezing causes stress relief by the exact mechanism described in the
sources I cited. "Stabilization" is your word -- and a meaningless
one,
too. Stress relief is a specific term. That there are residual
stresses
in spokes is not a matter of faith. Overloading in the direction of
the
working load will either diminish undesirable residual stresses or
create desirable residual stresses or both. That is the whole point.
It
needs no other qualifications.

"Stabilizing" is a term used Barnett Bicycle Institute in thier wheel
building classes. It is not meaningless. Stabilizing makes sure the
spokes are embeded and residual windup removed.


Thereby putting the wheel out of true.
Spoke wind up is never present when
attention is paid while turning the
nipples. Turn until the nipple turns
with respect to the spoke, then back
the spoke wrench until the spoke is
not wound up.


The process also
temporarily overloads spokes in the direction of the working load....


No it does not. All strain is elastic when the
spoke wrench turns the nipple.

likely better than the spoke squeezing method. I can see and
immediately measure the results of the process. I know that if a wheel
isn't stabilized it will detension as it is ridden...


No it won't. Nipples unwind when the spoke tension is insufficient
to the job of carrying the cyclic load at the contact patch.

sometimes to the
point where nipples will back-off and the wheel will have spokes that
are totally slack.


Oil the threads and spoke bed. Use a sufficient number
of spokes to carry the load.

--
Michael Press
  #24  
Old April 24th 08, 12:05 AM posted to rec.bicycles.tech
daveornee[_185_]
external usenet poster
 
Posts: 1
Default Residual stress, fatigue and stress relief


Michael Press Wrote:
In article ,
daveornee wrote:

Peter Cole Wrote:
Ben C wrote:

The controversy here is not that brief overload relieves stress

or
that
stress relief improves fatigue life.

Not true.

It's the claim that this is known
to be _the significant beneficial effect_ of spoke-squeezing,

the
Mavic
method, and other "stabilization" practices that people do when
wheel-building.

Not true. The specific claim (originally by Jobst) is that spoke
squeezing causes stress relief by the exact mechanism described in

the
sources I cited. "Stabilization" is your word -- and a meaningless
one,
too. Stress relief is a specific term. That there are residual
stresses
in spokes is not a matter of faith. Overloading in the direction

of
the
working load will either diminish undesirable residual stresses or
create desirable residual stresses or both. That is the whole

point.
It
needs no other qualifications.

"Stabilizing" is a term used Barnett Bicycle Institute in thier

wheel
building classes. It is not meaningless. Stabilizing makes sure

the
spokes are embeded and residual windup removed.


Thereby putting the wheel out of true.
Spoke wind up is never present when
attention is paid while turning the
nipples. Turn until the nipple turns
with respect to the spoke, then back
the spoke wrench until the spoke is
not wound up.


The process also
temporarily overloads spokes in the direction of the working

load....

No it does not. All strain is elastic when the
spoke wrench turns the nipple.

likely better than the spoke squeezing method. I can see and
immediately measure the results of the process. I know that if a

wheel
isn't stabilized it will detension as it is ridden...


No it won't. Nipples unwind when the spoke tension is insufficient
to the job of carrying the cyclic load at the contact patch.

sometimes to the
point where nipples will back-off and the wheel will have spokes

that
are totally slack.


Oil the threads and spoke bed. Use a sufficient number
of spokes to carry the load.

--
Michael Press

I build my way and it always works. I properly lubricate the threads
and I make sure there isn't windup as I tighten nipples.
If the wheel goes out of true while stabilizing it isn't likely to stay
true when riding.
I use the proper numbers of spokes for the intended loads in my
builds.
I don't uderstand what you mean:
"No it does not. All strain is elastic when the spoke wrench turns the
nipple."
Pick apart as you want!


--
daveornee

  #26  
Old April 24th 08, 04:25 AM posted to rec.bicycles.tech
jim beam
external usenet poster
 
Posts: 5,758
Default Residual stress, fatigue and stress relief

daveornee wrote:
Peter Cole Wrote:
Ben C wrote:

The controversy here is not that brief overload relieves stress or

that
stress relief improves fatigue life.

Not true.

It's the claim that this is known
to be _the significant beneficial effect_ of spoke-squeezing, the

Mavic
method, and other "stabilization" practices that people do when
wheel-building.

Not true. The specific claim (originally by Jobst) is that spoke
squeezing causes stress relief by the exact mechanism described in the
sources I cited. "Stabilization" is your word -- and a meaningless
one,
too. Stress relief is a specific term. That there are residual
stresses
in spokes is not a matter of faith. Overloading in the direction of
the
working load will either diminish undesirable residual stresses or
create desirable residual stresses or both. That is the whole point.
It
needs no other qualifications.

"Stabilizing" is a term used Barnett Bicycle Institute in thier wheel
building classes. It is not meaningless. Stabilizing makes sure the
spokes are embeded and residual windup removed. The process also
temporarily overloads spokes in the direction of the working load....
likely better than the spoke squeezing method. I can see and
immediately measure the results of the process. I know that if a wheel
isn't stabilized it will detension as it is ridden... sometimes to the
point where nipples will back-off and the wheel will have spokes that
are totally slack.




indeed. and it's easy to test this observation at home - it's not like
this is inaccessible rocket surgery.
  #27  
Old April 24th 08, 04:26 AM posted to rec.bicycles.tech
jim beam
external usenet poster
 
Posts: 5,758
Default Residual stress, fatigue and stress relief

Peter Cole wrote:
Ben C wrote:

I think jim's point is that no-one has shown that spoke fatigue starts
on the inside of the bend significantly (or at all) more often than it
starts on the outside.


"jim beam" doesn't correct his spoke lines. He will have a moment under
normal load. That will likely be larger than any residual stress
contribution.

The evidence we would expect to see for residual stress being a factor
just isn't there.

Having said that many people (who aren't jim beam) don't scrutinize the
broken spoke carefully through a magnifying glass, but just chuck it in
the trash, so we wouldn't know.


People like Jobst & I are at a disadvantage from a "forensics" angle --
we don't break spokes, so have no samples to analyze. "jim beam" seems
to have plenty.


so how freakin' hard is it to go to a bike shop and get them to save a
bunch of broken spokes for you??????????? neither you nor jobst can
manage this? how about find a magnifier and bother to look at the
fatigue patterns?????


Follow his faith-based analysis if you want.


try observing fact - it makes life a lot easier than trying to swallow
misinterpreted garbage from a pair of lazy presumptive bull****ting
amateurs!!!
  #28  
Old April 24th 08, 04:29 AM posted to rec.bicycles.tech
jim beam
external usenet poster
 
Posts: 5,758
Default Residual stress, fatigue and stress relief

Peter Cole wrote:
Ben C wrote:

I don't remember Jobst mentioning anything about this mechanism of
notches resulting in compressive residual stress but never mind.


Never mind, yourself. If threads aren't notches, I don't know what are.
Jobst claimed that his technique of stress relief would improve failure
rates at the threads, too. The published material I cited supports this
claim.


er, actually, the residual stress at the root of cold rolled threads is
compressive, not tensile. you *don't* want to "relieve" that.

and your cite is for the phenomenon of residual stress and mechanical
stress relief. nobody contests that it exists. what's being contested,
and the point you /still/ don't seem to be able to grasp, is that
OBSERVATION OF THE FACTS contradicts the supposition that it plays any
material role in spoke fatigue. supposition, not matter how hotly
defended, is simply not fact, and no amount of repetition by either you
or jobst can make it so.
  #29  
Old April 24th 08, 04:37 AM posted to rec.bicycles.tech
jim beam
external usenet poster
 
Posts: 5,758
Default Residual stress, fatigue and stress relief

Ben C wrote:
On 2008-04-23, Peter Cole wrote:
Ben C wrote:

I think jim's point is that no-one has shown that spoke fatigue starts
on the inside of the bend significantly (or at all) more often than it
starts on the outside.

"jim beam" doesn't correct his spoke lines. He will have a moment under
normal load. That will likely be larger than any residual stress
contribution.


The presence of moment under normal load is my preferred likely
candidate for what causes most spoke failures.

And in fact part of what Jobst calls "residual stress" is I believe
just a convoluted description of moment under load.


no, he's completely unclear on either concept.



He says that when you put the bend in the elbow of an outbound spoke the
bend can't spring back because the flange is in the way but is held
there by spoke tension. He calls that "residual stress", which is
confusing, but that's what he calls it.


it's not confusing, it's just plain wrong. see above.



For that to be possible there must be quite a bit of moment, since spoke
tension is not high enough to hold a bend in an elbow that is close to
flush with the flange. Overloading reduces that tension by bending the
elbow and/or deforming the hub and reducing the moment. Jobst says
instead overloading deforms the fibres or something and relieves the
"residual stress". But it is actually basically the same thing (although
I think Jobst denies the hub can possibly deform at this point).

That is my conclusion from all the discussions I have read about this on
RBT. Residual stress deserves mention as a possible mechanism that may
also be involved, but no more than that.


why bother to muddy the water with something not observed to be the
case? if we want to discuss irrelevancies, let's discuss stress
corrosion cracking and hydrogen embrittlement as well!



Beam is right: straight-pull spokes are a better design. On the other
hand with aluminium hubs and quality steel spokes breakages are rare
these days so it's not really as big a problem as a casual reader of RBT
might take it for.

The evidence we would expect to see for residual stress being a factor
just isn't there.

Having said that many people (who aren't jim beam) don't scrutinize the
broken spoke carefully through a magnifying glass, but just chuck it in
the trash, so we wouldn't know.

People like Jobst & I are at a disadvantage from a "forensics" angle --
we don't break spokes, so have no samples to analyze.


I thought Jobst did used to break them before he started
stress-relieving.


and he failed to correlate his use of the new breed of spoke, made of
fatigue resistant vacuum degassed stainless steel, with prolonged life,
instead attributing it to the process he "invented" [copied] instead.
that kind of, er, "oversight" might be good for selling books to those
with insufficient scientific or engineering background, but it's just
plain insulting to those who do.



"jim beam" seems to have plenty. Follow his faith-based analysis if
you want.


I know you don't really want to be a troll. Fight the urge.

  #30  
Old April 24th 08, 04:59 AM posted to rec.bicycles.tech
jim beam
external usenet poster
 
Posts: 5,758
Default Residual stress, fatigue and stress relief

Peter Cole wrote:
Ben C wrote:

The controversy here is not that brief overload relieves stress or that
stress relief improves fatigue life.


Not true.

It's the claim that this is known
to be _the significant beneficial effect_ of spoke-squeezing, the Mavic
method, and other "stabilization" practices that people do when
wheel-building.


Not true. The specific claim (originally by Jobst) is that spoke
squeezing causes stress relief by the exact mechanism described in the
sources I cited. "Stabilization" is your word -- and a meaningless one,
too. Stress relief is a specific term. That there are residual stresses
in spokes is not a matter of faith. Overloading in the direction of the
working load will either diminish undesirable residual stresses or
create desirable residual stresses or both. That is the whole point. It
needs no other qualifications.


jobstian "stress relief" theory is presumptive nonsense that has no
correlation with observed fact. it's as well grounded as his assumption
that fatigue can be eliminated from spokes made of stainless steel, a
material with no fatigue endurance limit.

absent sufficient knowledge and absent proper application of scientific
method, you're just perpetuating jobstian mistakes - and looking foolish
to boot.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Your best solution to relieving residual stress! liverliver Techniques 2 December 28th 07 06:48 PM
yet another residual stress redux jim beam Techniques 0 March 17th 07 10:41 PM
Spoke stress relief test [email protected] Techniques 32 December 27th 06 07:21 PM
Stress-relief demonstration suggestions? [email protected] Techniques 73 January 8th 05 03:09 AM
RR: Stress relief Mike Kennedy Mountain Biking 3 October 5th 04 06:59 PM


All times are GMT +1. The time now is 10:25 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 CycleBanter.com.
The comments are property of their posters.