Interesting tech info.

Discussion in 'Cycling Equipment' started by Jim Beam, Mar 20, 2003.

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  1. Jim Beam

    Jim Beam Guest

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  2. Jobst Brandt

    Jobst Brandt Guest

    Jim Beam writes:

    > There is a good summary of spoke technology at the bottom of this page!

    http://www.chickencycles.co.uk/products/spokes/index.html

    That's excellent. By the way, the torsional stiffness of oval spokes is practically that of a round
    spoke of the minor diameter. That's shocking for that 2.3-0.9mm oval spoke that is torsionally ten
    times weaker than a 1.6mm dia spoke as in 15-16ga spoke. Torsional stiffness goes as the 4th power
    of the minor diameter.

    Jobst Brandt [email protected] Palo Alto CA
     
  3. jim beam <[email protected]> wrote:
    > There is a good summary of spoke technology at the bottom of this page!

    > http://www.chickencycles.co.uk/products/spokes/index.html

    One comment, they quote the fatigue life of various spokes, for most models in the range of 900,000
    - 1.5 million cycles. That sounds like a lot but 1 million cycles is actually only 2000 km of
    riding! I am sure that they are quoting a test where the spoke is allowed to go completely slack so
    it is cycled through higher stresses than usual in a well built wheel. Which underscores the
    importance of building wheels to high tension.
     
  4. [email protected] wrote:
    > Jim Beam writes:
    >
    >
    >>There is a good summary of spoke technology at the bottom of this page!
    >
    >
    > http://www.chickencycles.co.uk/products/spokes/index.html
    >
    > That's excellent.

    I agree, it is a very good description of how spokes (and wheels) actually work. It looks a major
    spoke manufacturer has finally caught on to the excellent work Mr. Brandt has been doing the past
    few decades!

    If I can pick nits, the description of how metal fatigue works is a common layman's
    mis-interpretation:

    "As a part of a spoke is bent beyond its elastic limit, the material will work-harden. If this
    continues it will become more brittle and weaker; a microscopic crack can then easily form."

    (As most readers here probably know, metal fatigue can occur below the elastic limit, and does not
    cause work-hardening or embrittlement).

    However, they do get the main points right, and the small error cited above detracts little from the
    overall description of spoke function.

    Mark McMaster [email protected]
     
  5. Jobst Brandt

    Jobst Brandt Guest

    Benjamin Weiner <[email protected]> writes:

    >> There is a good summary of spoke technology at the bottom of this page!

    http://www.chickencycles.co.uk/products/spokes/index.html

    > One comment, they quote the fatigue life of various spokes, for most models in the range of
    > 900,000 - 1.5 million cycles. That sounds like a lot but 1 million cycles is actually only 2000 km
    > of riding! I am sure that they are quoting a test where the spoke is allowed to go completely
    > slack so it is cycled through higher stresses than usual in a well built wheel. Which underscores
    > the importance of building wheels to high tension.

    I think they got that from the Sapim web site where similar guestimates seem to abound on fatigue.
    In fact, I can't make any sense of the graphs shown there:

    http://www.sapim.be/

    Click on the "Race Proven", then "why SAPIM quality", then "Sapim Fatigue chart". The chart is
    pure imagination and wrong. I wrote to them but I doubt that they understand anything about metal
    fatigue. It is sad how the bicycle industry is run mostly by people with no technical education
    or practice.

    As I have often mentioned, spokes that do not fail in three or four thousand kilometers will most
    likely never fail without being damaged by external intervention. My wheels have about 200 million
    stress cycles and I don't anticipate any failures nor have I had any in many years except ones cased
    by the chain dropping into the spokes to cause a nick where a couple spokes failed in that time.

    Jobst Brandt [email protected] Palo Alto CA
     
  6. "Mark McMaster" <[email protected]> wrote in message news:[email protected]...
    >
    > If I can pick nits, the description of how metal fatigue works is a common layman's
    > mis-interpretation:
    >
    > "As a part of a spoke is bent beyond its elastic limit, the material will work-harden. If this
    > continues it will become more brittle and weaker; a microscopic crack can then easily form."
    >
    > (As most readers here probably know, metal fatigue can occur below the elastic limit, and does not
    > cause work-hardening or embrittlement).
    >
    I do not think that this is the most appropriate forum in which to debate the details of fatigue,
    but seeing you brought it up....... I would not have made the statement in the Sapim article, but I
    certainly would not make your statement either. I know of no instance of fatigue crack propagation
    in metals that occurred without plastic deformation at the crack tip and that means that some part
    of the metal has been strained beyond the elastic
    limit. The plastic zone may be very small, but without it fatigue cracks in structural metals do
    not propagate.

    John Retchford
     
  7. Wow.

    Perhaps you want to write to Boeing while you're about it and let them know that fatigue is dead.
    Boeing must have some audacious cojones to dare to try telling their customers that their product
    has a limited number of flying hours and take-offs.

    Obviously a cynical ploy to sell more planes.

    And by that argument, a manufacturer like Sapim, you know, one with real life production experience
    over nearly 80 years and millions of dollars in research and the company that other small-bit
    non-expert players like Mavic send their product to for fatigue testing, is, as you say, merely
    blowing smoke.

    WFT are you thinking?

    Your big ego does not a materials expert make. Go ahead, pour out your usual spite and condemnation.
    You're still not a materials expert Jobst. And no amount of bluster can mask that fact.

    Ford.

    [email protected] wrote:
    >
    > Click on the "Race Proven", then "why SAPIM quality", then "Sapim Fatigue chart". The chart is
    > pure imagination and wrong. I wrote to them but I doubt that they understand anything about metal
    > fatigue. It is sad how the bicycle industry is run mostly by people with no technical education or
    > practice.
     
  8. Ajames54™

    Ajames54™ Guest

    On Fri, 21 Mar 2003 05:34:20 GMT, [email protected] wrote:

    >Benjamin Weiner <[email protected]> writes:
    >
    >>> There is a good summary of spoke technology at the bottom of this page!
    >
    >http://www.chickencycles.co.uk/products/spokes/index.html
    >
    >> One comment, they quote the fatigue life of various spokes, for most models in the range of
    >> 900,000 - 1.5 million cycles. That sounds like a lot but 1 million cycles is actually only 2000
    >> km of riding! I am sure that they are quoting a test where the spoke is allowed to go completely
    >> slack so it is cycled through higher stresses than usual in a well built wheel. Which underscores
    >> the importance of building wheels to high tension.
    >
    >I think they got that from the Sapim web site where similar guestimates seem to abound on fatigue.
    >In fact, I can't make any sense of the graphs shown there:
    >
    >http://www.sapim.be/
    >
    SNIP
    >
    >Jobst Brandt [email protected] Palo Alto CA

    It would be really interesting to know their methodology... I only looked quickly but I can't even
    see if they tested to failure or if it is some sort of acceptance test. As it is I agree it is
    pretty much a joke...

    It would be much the same as ratings a piece of audio equipment and saying it goes up to eleven...

    I'll be generous though and simply assume that when the Web designers said "we want a graph of
    fatigue life ..." the marketing department got the memo not engineering.
     
  9. Spam Hater

    Spam Hater Guest

    ford exploder wrote:

    > Wow.
    >
    > Perhaps you want to write to Boeing while you're about it and let them know that fatigue is dead.
    > Boeing must have some audacious cojones to dare to try telling their customers that their product
    > has a limited number of flying hours and take-offs.
    >
    > Obviously a cynical ploy to sell more planes.
    >
    > And by that argument, a manufacturer like Sapim, you know, one with real life production
    > experience over nearly 80 years and millions of dollars in research and the company that other
    > small-bit non-expert players like Mavic send their product to for fatigue testing, is, as you say,
    > merely blowing smoke.
    >
    > WFT are you thinking?
    >
    > Your big ego does not a materials expert make. Go ahead, pour out your usual spite and
    > condemnation. You're still not a materials expert Jobst. And no amount of bluster can mask
    > that fact.
    >
    >
    > Ford.
    >
    >
    >
    >
    > [email protected] wrote:
    >>
    >> Click on the "Race Proven", then "why SAPIM quality", then "Sapim Fatigue chart". The chart is
    >> pure imagination and wrong. I wrote to them but I doubt that they understand anything about metal
    >> fatigue. It is sad how the bicycle industry is run mostly by people with no technical education
    >> or practice.
    >>

    Wow... your email address says it all... I would trust what Jobst says over your rantings any day.
    And Jobst is not the first person to psoit that the bicyckle industry is run by people with no
    business in the business. Check out Cannondale's 'decision' to market motorcycles...

    Joe

    --

    I don't herd cats anymore. All you end up with are scratches and a bunch of pissed off cats.
     
  10. Jobst Brandt

    Jobst Brandt Guest

    John Retchford writes:

    >> If I can pick nits, the description of how metal fatigue works is a common layman's
    >> mis-interpretation:

    >> "As a part of a spoke is bent beyond its elastic limit, the material will work-harden. If this
    >> continues it will become more brittle and weaker; a microscopic crack can then easily form."

    >> (As most readers here probably know, metal fatigue can occur below the elastic limit, and does
    >> not cause work-hardening or embrittlement).

    > I do not think that this is the most appropriate forum in which to debate the details of fatigue,
    > but seeing you brought it up... I would not have made the statement in the Sapim article, but I
    > certainly would not make your statement either.

    I think Mark's comments are appropriate and accurate in the context.

    > I know of no instance of fatigue crack propagation in metals that occurred without plastic
    > deformation at the crack tip and that means that some part of the metal has been strained beyond
    > the elastic
    > limit. The plastic zone may be very small, but without it fatigue cracks in structural metals do
    > not propagate.

    I think metallurgical terms, need be defined before making such claims. On a microscopic scale,
    occurrence of yield is what leads to fatigue failures, but in the context of ultimate strength and
    yield of a specimen such as a spoke, stress refers to the load divided by the cross sectional area,
    rather than internal yield stresses caused by in-homogeneities in the metal. In the case of high
    quality spokes these locations are small enough that spokes fail primarily due to residual high
    surfaces macroscopic stresses from manufacture and installation that act in the way you describe.

    Notches and surface blemishes shown on the Chicken web site are another matter entirely because they
    are both stress concentrations and they contain residual stress from plastic deformation. These are
    not caused by bending spokes into place but rather from sharp objects. Ductility of top grade spokes
    is discussed and shown graphically in "the Bicycle Wheel" if there is any doubt about spoke failures
    from such effects.

    http://www.avocet.com/wheelbook/wheelbook.html

    Jobst Brandt [email protected] Palo Alto CA
     
  11. Mike Zaharis

    Mike Zaharis Guest

    ford exploder <[email protected]> wrote in message
    news:<[email protected]>...
    > Wow.
    >
    > Perhaps you want to write to Boeing while you're about it and let them know that fatigue is dead.
    > Boeing must have some audacious cojones to dare to try telling their customers that their product
    > has a limited number of flying hours and take-offs.
    >
    > Obviously a cynical ploy to sell more planes.
    >
    > And by that argument, a manufacturer like Sapim, you know, one with real life production
    > experience over nearly 80 years and millions of dollars in research and the company that other
    > small-bit non-expert players like Mavic send their product to for fatigue testing, is, as you say,
    > merely blowing smoke.
    >
    > WFT are you thinking?
    >
    > Your big ego does not a materials expert make. Go ahead, pour out your usual spite and
    > condemnation. You're still not a materials expert Jobst. And no amount of bluster can mask
    > that fact.
    >
    >
    > Ford.
    >
    >

    Not like Jobst needs my defense, but here goes anyway:

    Well, Boeing mostly makes airplanes in Aluminum, which does not have a cyclic fatigue limit. What
    that means is that there is no stress level below which aluminum will not undergo fatigue failure,
    if given enough cycles. To avoid terminally overbuilding an airplane, Boeing picks a number of
    cycles that would accommodate a reasonable aircraft lifecycle, then designs the airplane to be
    strong enough at the end of its design life to be able to (hopefully) withstand any stress that it
    would encounter, with a sufficient safety margin. Aluminum bicycle designers, in theory, should also
    do this, but my guess is that most don't the calculations to ensure that their bikes have an
    acceptable life, or at least assume a very short design life.

    Steel, on the other hand, does have a specific fatigue limit. There is a certain cyclic stress level
    below which steel won't fail, no matter how many cycles. One generally designs in steel such that a
    component that would be cyclically stressed would not be cyclically stressed above this limit.

    So, what Jobst is saying does not necessarily represent an attempt to tell Boeing they don't know
    what they're doing.

    See the following site:

    http://oregonstate.edu/instruct/engr322/engr322KJF/flashcards/chp8/fat2/fat2.html
     
  12. [email protected] (Mike Zaharis) wrote in message
    news:<[email protected]>...
    > ford exploder <[email protected]> wrote in message
    > news:<[email protected]>...
    > > Wow.
    > >
    > > Perhaps you want to write to Boeing while you're about it and let them know that fatigue is
    > > dead. Boeing must have some audacious cojones to dare to try telling their customers that their
    > > product has a limited number of flying hours and take-offs.
    > >
    > > Obviously a cynical ploy to sell more planes.
    > >
    > > And by that argument, a manufacturer like Sapim, you know, one with real life production
    > > experience over nearly 80 years and millions of dollars in research and the company that other
    > > small-bit non-expert players like Mavic send their product to for fatigue testing, is, as you
    > > say, merely blowing smoke.
    > >
    > > WFT are you thinking?
    We should probably let Jobst alone. He spends a lot of time helping here. Nothing more important to
    do I guess.
    > >
    > > Your big ego does not a materials expert make. Go ahead, pour out your usual spite and
    > > condemnation. You're still not a materials expert Jobst. And no amount of bluster can mask
    > > that fact.
    > >
    > >
    > > Ford.
    > >
    > >
    >
    > Not like Jobst needs my defense, but here goes anyway:
    >
    > Well, Boeing mostly makes airplanes in Aluminum, which does not have a cyclic fatigue limit. What
    > that means is that there is no stress level below which aluminum will not undergo fatigue failure,
    > if given enough cycles. To avoid terminally overbuilding an airplane, Boeing picks a number of
    > cycles that would accommodate a reasonable aircraft lifecycle, then designs the airplane to be
    > strong enough at the end of its design life to be able to (hopefully) withstand any stress that it
    > would encounter, with a sufficient safety margin. Aluminum bicycle designers, in theory, should
    > also do this, but my guess is that most don't the calculations to ensure that their bikes have an
    > acceptable life, or at least assume a very short design life.
    >
    > Steel, on the other hand, does have a specific fatigue limit. There is a certain cyclic stress
    > level below which steel won't fail, no matter how many cycles. One generally designs in steel
    > such that a component that would be cyclically stressed would not be cyclically stressed above
    > this limit.
    >
    > So, what Jobst is saying does not necessarily represent an attempt to tell Boeing they don't know
    > what they're doing.
    >
    > See the following site:
    >
    > http://oregonstate.edu/instruct/engr322/engr322KJF/flashcards/chp8/fat2/fat2.html
     
  13. Phil Holman

    Phil Holman Guest

    "ford exploder" <[email protected]> wrote in message
    news:[email protected]...
    > Wow.
    >
    > Perhaps you want to write to Boeing while you're about it and let them know that fatigue is dead.
    > Boeing must have some audacious cojones to dare to try telling their customers that their product
    > has a limited number of flying hours and take-offs.
    >
    > Obviously a cynical ploy to sell more planes.

    Early steel prototypes had a hard time taking off. At the Boeing field, we have some of the fastest
    ground carts in the world. Safety is the main concern but operational performance, economics and
    producibility are also major considerations despite the additional engineering and maintenance
    required. Inspection intervals of primary structure increase after one lifetime and usually makes it
    economically burdensome to continue flying. Phil Holman
     
  14. <[email protected]> wrote in message news:[email protected]...
    > John Retchford writes:
    >
    Mark McMaster:> >> If I can pick nits, the description of how metal fatigue works is a
    > >> common layman's mis-interpretation:
    >
    > >> "As a part of a spoke is bent beyond its elastic limit, the material will work-harden. If this
    > >> continues it will become more brittle and weaker; a microscopic crack can then easily form."
    >
    > >> (As most readers here probably know, metal fatigue can occur below the elastic limit, and does
    > >> not cause work-hardening or embrittlement).
    >
    Me:> > I do not think that this is the most appropriate forum in which to
    > > debate the details of fatigue, but seeing you brought it up... I would not have made the
    > > statement in the Sapim article, but I certainly would not make your statement either.
    >
    Jobst Brandt:> I think Mark's comments are appropriate and accurate in the context.
    >
    In the context of fatigue cracking, which is the only one introduced by Mark, I point out below that
    his remark is somewhat misleading. He says he is picking nits. I am just suggesting we pick the
    right nits.

    Mf:> > I know of no instance of fatigue crack propagation in metals that
    > > occurred without plastic deformation at the crack tip and that means that some part of the metal
    > > has been strained beyond the elastic
    > > limit. The plastic zone may be very small, but without it fatigue cracks in structural metals
    > > do not propagate.
    >
    Jobst Brandt:> I think metallurgical terms, need be defined before making such
    > claims.

    Sorry. Which terms gave you difficulty?

    Jobst Brandt:> On a microscopic scale, occurrence of yield is what leads to
    > fatigue failures,

    This is the point I make above. I am glad you agree with me.

    Jobst Brandt continues:> but in the context of ultimate strength and yield of
    > a specimen such as a spoke, stress refers to the load divided by the cross sectional area, rather
    > than internal yield stresses caused by in-homogeneities in the metal. In the case of high quality
    > spokes these locations are small enough that spokes fail primarily due to residual high surfaces
    > macroscopic stresses from manufacture and installation that act in the way you describe.
    >
    I agree that the scale of the stress being considered (that is the area by which we divide the force
    acting) needs to match the process being described. This is why I focussed on the microscopic scale.
    Fatigue cracking involves only a relatively small number of atoms at a time. If we want to look at
    things like ultimate strength (you introduced this) we need to consider the whole cross section
    unless we want to consider the mechanism of the phenomonon. I am sure you are correct in pointing
    out the importance of surface residual stress in influencing the fatigue life of spokes.

    John Retchford
     
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